Citation
Nitrification inhibitor effects on potato yields and soil inorganic nitrogen

Material Information

Title:
Nitrification inhibitor effects on potato yields and soil inorganic nitrogen
Creator:
Martin, Harris Warthman, 1954-
Publication Date:
Language:
English
Physical Description:
xxiii, 308 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Biomass ( jstor )
Crops ( jstor )
Fertilizer application ( jstor )
Fertilizers ( jstor )
Leaching ( jstor )
Nitrogen ( jstor )
Soil interactions ( jstor )
Soil science ( jstor )
Soils ( jstor )
Tubers ( jstor )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1990.
Bibliography:
Includes bibliographical references (leaves 280-306).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Harris Warthman Martin.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Resource Identifier:
001603301 ( ALEPH )
AHM7551 ( NOTIS )
23245362 ( OCLC )

Downloads

This item has the following downloads:


Full Text










NITRIFICATION INHIBITOR EFFECTS ON POTATO
YIELDS AND SOIL INORGANIC NITROGEN












By

HARRIS WARTHMAN MARTIN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA 1-tS 1r iR Lunii L,


1990













I dedicate this work to my children Rachel and Stan,

who have often played quietly so that daddy could work on

his dissertation.













ACKNOWLEDGMENTS

I want to express my appreciation and gratitude to

Dr. D.A. Graetz, chairman of my committee, for his guidance,

understanding and friendship, all of which were necessary

for this research.

I also thank the members of my committee, Drs. J.G.

Fiskell, D.R. Hensel, S.J. Locascio, D.L. Myhre, and J.B.

Sartain, for their patience and tolerance. I extend my

appreciation to other faculty members for their assistance.

These include Drs. V. Carlisle, M.A. Collins, N. Commerford,

J.G. Dorsey, D.H. Hubbell, B.L. McNeal, F. Martin, and T.L.

Yuan.

Without the help of all the following people, this

research could not have been completed. I am greatly in

debt to all of them. They are, in alphabetical order, Lisa

Ames, Tracy Beaudreau, Candy Cantlin, Jose Escameil,

Victoria Feldman, Peter Krottje, Dawn Lucas, Gail Luparello,

Kevin Moorehead, Abdul Rahim Mohamad, Ruth Neal, John

Purcel, Nathan Rembert, Ed Rope, Jorge Santos, B.K. Singh,

Irma L. Smith, Lyda Toy Stock, and the secretaries in the

Soil Science Department, the staff of the NERDC, IFAS

Computer Network, and CIRCA, the staff and field hands at


iii







the IFAS farms at the Gainesville Horticulture Unit, and the

Hastings and Live Oak ARECs.

I would like to acknowledge the financial assistance

of the State of Florida and the SKW Trostberg company of

West Germany.
















TABLE OF CONTENTS


Page


ACKNOWLEDGMENTS .

LIST OF TABLES .

LIST OF FIGURES. .

ABSTRACT . .

CHAPTERS

1. INTRODUCTION .


2. REVIEW OF LITERATURE .

Nitrification Inhibitors .
Crop Response to Inhibitors .
Nitrogen Nutrition of Potato and
Other Plants .
Conclusions. .


. iii

. vii

. xvii

. xxii


* 3
S. 30

. 37
. 44


3. MATERIALS AND METHODS. .

Nitrogen and Amendments Applied to
Potato .
Urea and DCD Applied to a Fallow
Quartzipsamment. .


4. TUBER YIELD, PLANT N CONTENT, AND BIOMASS.

Tuber Yield ..
Proportion of Marketable Tuber Yield
That Was Grade A .
Proportion of Total Tuber Yield That
Was Marketable .
Tuber Specific Gravity .
Tuber N Concentration .
Plant Shoot Biomass at Harvest .
Total Biomass at Harvest .
Plant Shoot N Concentration at Harvest
N Uptake by Plant Shoots at Harvest. .
N Uptake by Tubers .


. .


. .

* .

. .
. .
. .
. .
. .
* .
. .
. .








Total N Uptake by Plant Shoots and
Tubers 99
Leaf N Concentration at Tuber Initiation 102
Leaf N Concentration at Flowering. ... .108
Leaf N Concentration at Tuber Maturation 115

5. EXTRACTABLE SOIL N AND DCD SOILS PLANTED
TO POTATO. .. 121

Soil Inorganic N ... 121
Extractable Soil DCD ... 149
Rainfall . 156

6. UREA AND DCD APPLIED TO A FALLOW
QUARTZIPSAMMENT. .. .160

Soil NH4 -N 160
Soil NO- -N 170
Total Soil Inorganic N 179
NO3--N/(NO3--N + NH4-N) Ratio .. 186
Soil DCD .. 193

7. DISCUSSION ... .203

Plant Yield/N Content and Soil N and DCD 203
Urea and DCD Applied to a Fallow
Quartzipsamment .. 233

8. CONCLUSIONS. .. .241

Plant Yield/N Content and Soil N and DCD 241
Urea and DCD Applied to a Fallow
Quartzipsamment .. 243
General Conclusions. .. .244
Recommendations For Future Research. 245

APPENDICES

A. SOIL CHARACTERIZATION. .. .249

B. SAMPLE ANALYSIS OF VARIANCE TABLE. .. .251

C. INORGANIC N CONCENTRATIONS IN SOILS PLANTED
TO POTATO AS AFFECTED BY SELECTED
TREATMENTS .. 252

D. ANALYSIS OF VARIANCE OF INORGANIC N IN
SOILS PLANTED TO POTATO. .. .267

REFERENCES . ... .280

BIOGRAPHICAL SKETCH. .. .307













LIST OF TABLES


Table Page

3-1. Classification of the soils used. ... 47

3-2. Selected soil properties at harvest 48

3-3. Timing of soil and leaf sampling in
potato fields. ... 52

4-1. Effects of N rate and amendment on market-
able tuber yield .. 58

4-2. Effects of N rate and amendment on total
tuber yield. ... 60

4-3. Interaction (DCD Q X NR **) of DCD and N
rate effects on tuber yield (Hastings,
1983). ... 63

4-4. Interaction (Nty R X NR L *) of nitra-
pyrin and N rate effects on tuber
yield (Gainesville, 1984). .. 64

4-5. Interaction (IBDU v Ih X NR L *) of IBDU v
inhibitors, and N rate effects on tuber
yield (Hastings, 1984) ... 66

4-6. Effects of N rate and amendment on the
proportion of marketable yield that
was grade A. .. 67

4-7. Interaction (DCD L X NR L *) of DCD and N
rate effects on the proportion of
marketable yield that was grade A
(Hastings, 1985) ... 68

4-8. Interaction (IBDU v Ih X NR L *) of IBDU v
inhibitors, and N rate effects on the
proportion of marketable yield that was
grade A (Hastings, 1985) 68

4-9. Effects of N rate and amendment on the
proportion of total yield that was
marketable .. 71


vii








4-10. Interaction (DCD v nitrapyrin X NR Q *) of
DCD v nitrapyrin, and N rate effects
on the proportion of total yield that
was marketable (Gainesville, 1984) 72

4-11. Interaction (IBDU v Ih X NR *) of IBDU v
inhibitors, and N rate effects on the
proportion of total yield that was
marketable (Hastings, 1983). 72

4-12. Effects of N rate and amendment on tuber
specific gravity ... 73

4-13. Interaction (DCD Q X NR *) of DCD and N
rate effects on tuber specific
gravity (Hastings, 1983) ... 75

4-14. Interaction (DCD v nitrapyrin X NR *) of
DCD v nitrapyrin, and N rate effects
on tuber specific gravity (Hastings,
1983). . 75

4-15. Effects of N rate and amendment on tuber
N concentration in 1983 and 1984 77

4-16. Interaction (DCD Q X NR *) of DCD and N
rate effects on tuber N concentration
(Hastings, 1983) .. 78

4-17. Interaction (DCD L X NR L *) of DCD and N
rate effects on tuber N concentration
(Gainesville, 1984). ... 78

4-18. Interaction (Nty R X NR *) of nitrapyrin
and N rate effects on tuber N
concentration (Hastings, 1983) .... 80

4-19. Interaction (DCD v nitrapyrin X NR L x)
of DCD v nitrapyrin, and N rate
effects on tuber N concentration
(Hastings, 1984) ... .80

4-20. Effects of N rate and amendment on plant
shoot biomass at harvest in 1983 and
1984 . 82

4-21. Interaction (Nty R X NR L *) of nitrapyrin
and N rate effects on plant shoot
biomass at harvest (Gainesville,
1984). ... 83


viii







4-22. Effects of N rate and amendment on total
biomass at harvest in 1983 and 1984. 84

4-23. Interaction (DCD Q X NR **) of DCD and N
rate effects on total biomass at
harvest (Hastings, 1983) ... 86

4-24. Interaction (Nty R X NR L *) of nitra-
pyrin rate and N rate effects on
total biomass at harvest (Gaines-
ville, 1984) 86

4-25. Effects of N rate and amendment on
plant shoot N concentration at
harvest in 1983 and 1984 ... 88

4-26. Interaction (DCD Q X NR L x) of DCD and
N rate effects on plant N concern
tration at harvest (Hastings, 1984). 89

4-27. Interaction (Nty R X NR L *) of
nitrapyrin and N rate effects on
plant shoot N concentration at
harvest (Hastings, 1984). ... .. 89

4-28. Interaction (IBDU v Ih X NR L **) of
IBDU v inhibitors, and N rate effects
on plant shoot N concentration at
harvest (Hastings, 1984) ... 91

4-29. Effects of N rate and amendment on N
uptake by plant shoots at harvest in
1983 and 1984. ... 92

4-30. Interaction (Nty R X NR L *) of nitra-
pyrin and N rate effects on N uptake
by plant shoots at harvest (Gaines-
ville, 1984) .. 93

4-31. Interaction (DCD v nitrapyrin X NR x) of
DCD v nitrapyrin, and N rate effects
on N uptake by plant shoots at harvest
(Gainesville, 1983). ... 93

4-32. Effects of N rate and amendment on N
uptake by tubers in 1983 and 1984. 95

4-33. Interaction (DCD Q X NR **) of DCD and N
rate effects on N uptake by tubers
(Hastings, 1983) ... ...... 96








4-34. Interaction (Nty R X NR L *) of nitrapyrin
and N rate effects on N uptake by
tubers (Gainesville, 1984) ... 96

4-35. Interaction (DCD v nitrapyrin X NR x) of
DCD v nitrapyrin, and N rate effects
on N uptake by tubers (Hastings,
1983). .. .. 98

4-36. Interaction (DCD v nitrapyrin X NR L x) of
DCD v nitrapyrin, and N rate effects on
N uptake by tubers (Hastings, 1984). 98

4-37. Effects of N rate and amendment on total N
uptake by plant shoots and tubers at
harvest in 1983 and 1984 .. 100

4-38. Interaction (DCD Q X NR **) of DCD and N
rate effects on total N uptake by plant
shoots and tubers at harvest (Hastings,
1983). ... 101

4-39. Interaction (Nty R X NR Q **) of nitra-
pyrin and N rate effects on total N
uptake by plant shoots and tubers at
harvest (Gainesville, 1984). ... 101

4-40. Effects of N rate and amendment on leaf
N concentration at tuber initiation. 103

4-41. Interaction (Nty R X NR *) of nitrapyrin
rate and N rate effects on leaf N
concentration at tuber initiation (48
dap) (Gainesville, 1984) ... .106

4-42. Interaction (DCD v nitrapyrin X NR Q *)
of DCD v nitrapyrin, and N rate effects
on leaf N concentration at tuber initi-
ation (51 dap) (Hastings, 1985). ... .106

4-43. Interaction (IBDU v Ih X NR L ***) of
IBDU v inhibitors, and N rate effects
on leaf N concentration at tuber
initiation (55 dap) (Hastings, 1984) 107

4-44. Effects of N rate and amendment on leaf
N concentration at flowering .. .109








4-45. Interaction (DCD Q X NR L *) of DCD and N
rate effects on leaf N concentration
at flowering (81 dap) (Hastings,
1984). . 111

4-46. Interaction (Nty R X NR Q *) of nitra-
pyrin and N rate effects on leaf N
concentration at flowering (81 dap)
(Hastings, 1984) .. 111

4-47. Interaction (DCD v nitrapyrin X NR Q **)
of DCD v nitrapyrin, and N rate effects
on leaf N concentration at flowering
(81 dap) (Hastings, 1984). .. .113

4-48. Interaction (IBDU v Ih X NR *) of IBDU v
inhibitors, and N rate effects on
leaf N concentration at flowering
(66 dap) (Gainesville, 1983) .. .113

4-49. Interaction (IBDU v Ih X NR Q *) of IBDU
v inhibitors, and N rate effects on
leaf N concentration at flowering
(81 dap) (Hastings, 1984). .. .114

4-50. Interaction (IBDU v IH X NR L *) of IBDU
v inhibitors, and N rate effects on
leaf N concentration at flowering
(73 dap) (Hastings, 1985). .. .114

4-51. Effects of N rate and amendment on leaf
N concentration at tuber maturation
in 1983 and 1984 ... 116

4-52. Interaction (DCD L X NR L *) of DCD and
N rate effects on leaf N concentration
at tuber maturation (98 dap)
(Hastings, 1984) .. 118

4-53. Interaction (Nty R X NR Q ***) of nitra-
pyrin rate and N rate effects on leaf
N concentration at tuber maturation
(94 dap) (Gainesville, 1984) .. .118

4-54. Interaction (DCD v nitrapyrin X NR Q *)
of DCD v nitrapyrin, and N rate effects
on leaf N concentration at tuber
maturation (94 dap) (Gainesville,
1984). . 120








5-1. Effects of N rate and amendment on soil
inorganic N concentration at the
planting + one week stage of potato
(Hastings) ... 123

5-2. Interactions (DCD Q X NR L **) of DCD rate
and N rate effects on soil inorganic
N concentration 6 days after fertilizer
application (Hastings, 1984) .. .124

5-3. Interaction (Nty R X NR Q x) of nitra-
pyrin rate and N rate effects on soil
inorganic N concentration 6 days
after fertilizer application
(Hastings, 1984) ... .124

5-4. Effects of N rate and amendment on soil
inorganic N at the pre-emergence stage
of potato. ... 126

5-5. Interactions (DCD Q X NR Q *, DCD L X
NR Q x, and DCD Q X NR L *) of DCD
and N rate effects on soil inorganic
N concentration at the pre-emergence
stage of potato (1984) ... 127

5-6. Interactions (Nty R X NR and Nty R X
NR L **) of nitrapyrin and N rate
effects on soil inorganic N concentra-
tion at the pre-emergence stage of
potato ... 127

5-7. Interaction (DCD v Nty X NR L x) of
DCD v nitrapyrin and N rate effects
on soil inorganic N concentration 13
days after fertilizer application
(Gainesville, 1984). ... 129

5-8. Interaction (IBDU v Ih X NR L **) of
IBDU v inhibitors, and N rate effects
on soil inorganic N concentration at
the pre-emergence stage of potato
(1984) . 131

5-9. Effects of N rate and amendment on soil
inorganic N concentration at the
vegetative stage of potato ... 132


xii








5-10. Interactions (DCD L X NR Q and DCD Q X
NR Q *) of DCD and N rate effects on
soil inorganic N concentration 31 days
after fertilizer application
(Gainesville, 1984). ... 134

5-11. Interaction (Nty R X NR Q ***) of nitra-
pyrin and N rate effects on soil
inorganic N concentration 31 days
after fertilizer application (Gaines-
ville, 1984) 134

5-12. Interaction (IBDU v Ih X NR L *) of
IBDU v inhibitors, and N rate effects
on soil inorganic N concentration 31
days after fertilizer application
(Gainesville, 1984). ... ..136

5-13. Effects of nitrogen rate and amendment
on soil inorganic N concentration at
the tuber initiation stage ... 138

5-14. Interactions (Nty R X NR L **) of nytra-
pyrin and N rate effects on soil
inorganic N concentration 45 days
after fertilizer application (Gaines-
ville, 1984) 139

5-15. Interaction (DCD v nitrapyrin X NR Q **)
of DCD v nitrapyrin, and N rate effects
on soil inorganic N concentration 45
days after fertilizer application
(Gainesville, 1984). ... 139

5-16. Interaction (DCD v nitrapyrin X NR L *
and X NR Q *) of DCD v nitrapyrin, and
N rate effects on soil inorganic N
concentration 46 days after fertil-
izer application (Hastings, 1984). 140

5-17. Effects of nitrogen rate and amendment on
soil inorganic N concentration at the
tuber bulking stage. ... 142

5-18. Interaction (DCD L X NR L *) of DCD and N
rate effects on soil inorganic N con-
centration 69 days after fertilizer
application (Gainesville, 1984). 144


xiii









5-19. Interaction (Nty R X NR L x) of nitrapyrin
and N rate effects on soil inorganic N
concentration 69 days after fertilizer
application (Gainesville, 1984). 144

5-20. Interactions (IBDU v Ih X NR **, IBDU v
Ih X NR L **, and X NR Q **) of
IBDU v inhibitors, and N rate effects
on soil inorganic N concentration at
the tuber bulking stage. ... 145

5-21. Interaction (IBDU v Ih X NR L *) of
IBDU v inhibitors, and N rate effects
on soil inorganic N concentration 74 days
after fertilizer application (Hastings,
1984). ... 145

5-22. Effects of N rate and amendment on soil
inorganic N concentration at potato
harvest. ... 147

5-23. Interaction (DCD L X NR L *) of DCD and N
rate effects on soil inorganic N con-
centration 103 days after fertilizer
application (Hastings, 1984) 148

5-24. Interaction (Nty R X NR L **) of nitra-
pyrin and N rate effects on soil
inorganic N concentration 108 days
after fertilizer application (Gaines-
ville, 1984) ... 148

5-25. Interaction (IBDU v Ih X NR x) of IBDU v
inhibitors, and N rate effects on
soil inorganic N concentration 98
days after fertilizer application
(Gainesville, 1983). ... 150

5-26. Effects of N and DCD rates on soil DCD
concentration (Gainesville). 157

5-27. Effects of N and DCD rates on soil DCD
concentration (Hastings) ... .158

6-1. Effects of DCD rate on soil NH4-N concen-
tration at five depths over six
sampling dates in a Quartzipsamment
at Live Oak. ... 162


xiv









6-2. Effects of DCD Rate on soil NO3--N concen-
tration at five depths over six
sampling dates in a Quartzipsamment
at Live Oak. 172

6-3. Effects of DCD rate on soil inorganic N
(NH4-N + N03--N) at five depths over
six sampling dates in a Quartzipsamment
at Live Oak. .. 182

6-4. Effects of DCD rate on soil NO3--N/
(N03--N + NH4-N) ratio at five depths
over six sampling dates in a Quartz-
ipsamment at Live Oak. ... 191

6-5. Effects of DCD rate on DCD at five depths
over six sampling dates in a typic
Quartzipsamment at Live Oak. ... 195

7-1. Summary of positive N rate effects on
potato plant parameters. ... 207

B-1. Analysis of variance table for plant
response parameters in the studies
with potato. ... 251

D-1. Analysis of variance of nitrogen and
amendment rate effects on soil NH4-N
concentration (Gainesville, 1983). 268

D-2. Analysis of variance of nitrogen and
amendment rate effects on soil NO3-N
concentration (Gainesville, 1983). 269

D-3. Analysis of variance of nitrogen and
amendment rate effects on soil
NO3--N/(NO3-N + NH4-N) ratio
(Gainesville, 1983). .. 270

D-4. Analysis of variance nitrogen and
amendment rate effects on soil NH,4-N
concentration (Gainesville, 1984). 271

D-5. Analysis of variance of nitrogen and
amendment rate effects on soil N3--N
concentration (Gainesville, 1984). 272

D-6. Analysis of variance of nitrogen and
amendment rate effects on soil NO3-N/
(N03O-N + NH4-N) ratio (Gainesville,
1984). ... 273








D-7. Analysis of variance of nitrogen and
amendment rate effects on soil NH4-N
and N03--N concentration (Hastings,
1983). .. 274

D-8. Analysis of variance of nitrogen and
amendment rate effects on soil NO'-N/
(NO'-N + NH4 -N) ratio (Hastings,
1983). ... 275

D-9. Analysis of variance of nitrogen and
amendment rate effects on soil NH4-N
concentration (Hastings, 1984) .... .276

D-10. Analysis of variance of nitrogen and
amendment rate effects on soil N03-N
concentration (Hastings, 1984) .... .277

D-11. Analysis of variance of nitrogen and
amendment rate effects on soil N03-N/
(N03 -N + NH4-N) ratio (Hastings,
1984). . 278

D-12. Analysis of variance of nitrogen and
amendment rate effects on total soil
inorganic N means for all sampling
dates. .. .... 279


xvi













LIST OF FIGURES


Figure Page

2-1. The structure of nitropyrin, or 2-chloro-
6-(trichloromethyl)-pyridine
(N-Serve) 5

2-2. Tautomers of DCD 7

5-1. Effects of DCD rate on soil DCD concentra-
tion (Gainesville, 1983) ...... 151

5-2. Effects of DCD rate on soil DCD concentra-
tion (Gainesville, 1984) ...... 152

5-3. Effects of DCD rate on soil DCD concentra-
tion (Hastings, 1983) ... 154

5-4. Effects of DCD rate on soil DCD concentra-
tion (Hastings, 1984) ... 155

6-1. Effects of DCD rate on soil NH4-N concen-
tration with depth 14 days after
application of 200 kg N ha'1 to a
fallow Quartzipsamment at Live Oak 161

6-2. Effects of DCD rate on soil NH4+-N concen-
tration with depth 31 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak. 163

6-3. Effects of DCD rate on soil NH4-N concen-
tration with depth 46 days after
application of 200 kg N ha-' to a
fallow Quartzipsamment at Live Oak 164

6-4. Effects of DCD rate on soil NH4-N concen-
tration with depth 60 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak 165

6-5. Effects of DCD rate on soil NH4-N concen-
tration with depth 81 days after
application of 200 kg N ha'1 to a
fallow Quartzipsamment at Live Oak 167


xvii








6-6. Effects of DCD rate on soil NH4-N concen-
tration with depth 116 days after
application of 200 kg N ha-I to a
fallow Quartzipsamment at Live Oak 168

6-7. Effects of DCD rate on soil NH4-N in the
1.22 m profile of a fallow Quartz-
ipsamment at Live Oak ... 169

6-8. Effects of DCD rate on soil N03O-N concen-
tration with depth 14 days after
application of 200 kg N ha'' to a
fallow Quartzipsamment at Live Oak 171

6-9. Effects of DCD rate on soil NO'-N concen-
tration with depth 31 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak 173

6-10. Effects of DCD rate on soil N03--N concen-
tration with depth 46 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak .. 175

6-11. Effects of DCD rate on soil N03--N concen-
tration with depth 60 days after
application of 200 kg N ha'1 to a
fallow Quartzipsamment at Live Oak 176

6-12. Effects of DCD rate on soil NO'-N concen-
tration with depth 81 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak 177

6-13. Effects of DCD rate on soil NO--N concen-
tration with depth 116 days after
application of 200 kg N ha-1 to a
fallow Quartzipsamment at Live Oak 178

6-14. Effects of DCD rate on soil N03--N in the
1.22 m profile of a fallow Quartz-
ipsamment at Live Oak .. 180

6-15. Effects of DCD rate on soil inorganic
N (NH4-N + N03-N) concentration
with depth 14 days after application
of 200 kg N ha-1 to a fallow Quartz-
ipsamment at Live Oak .. .. 181


xviii








6-16. Effects of DCD rate on soil inorganic
N (NH4-N + N03--N) concentration
with depth 31 days after application
of 200 kg N ha-1 to a fallow Quartz-
ipsamment at Live Oak .. .. 183

6-17. Effects of DCD rate on soil inorganic
N (NH4-N + N03--N) concentration
with depth 46 days after application
of 200 kg N Ha-' to a fallow Quartz-
ipsamment at Live Oak .. .. 184

6-18. Effects of DCD rate on soil inorganic
N (NH44-N + NO--N) concentration
with depth 60 days after application
of 200 kg N ha-I to a fallow Quartz-
ipsamment at Live Oak ... 185

6-19. Effects of DCD rate on soil inorganic
N (NH4+-N + N03--N) concentration
with depth 81 days after application
of 200 kg N hal to a fallow Quartz-
ipsamment at Live Oak ... 187

6-20. Effects of DCD rate on soil inorganic
N (NH4-N + N03--N) concentration
with depth 116 days after application
of 200 kg N ha-1 to a fallow Quartz-
ipsamment at Live Oak. ... 188

6-21. Effects of DCD rate on soil inorganic
N (NH4-N + NO3--N) in the sampled
profile of a fallow Quartzipsamment
at Live Oak. 189

6-22. Effects of DCD rate on soil nitrification
ratio, i.e., (N03--N x 100/(NH4-N +
NH3--N) in the 1.22 m profile of a
fallow Quartzipsamment at Live Oak 192

6-23. Effects of DCD rate on soil DCD concen-
tration with depth 14 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak. .. .. 194

6-24. Effects of DCD rate on soil DCD concen-
tration with depth 31 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak .... 196


xix








6-25. Effects of DCD rate on soil DCD concen-
tration with depth 46 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak. .. ... 197

6-26. Effects of DCD rate on soil DCD concen-
tration with depth 60 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak. ... .. 198

6-27. Effects of DCD rate on soil DCD concen-
tration with depth 81 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak. .. ... 199

6-28. Effects of DCD rate on soil DCD concen-
tration with depth 116 days after
DCD application to a fallow Quartz-
ipsamment at Live Oak .. .. 200

6-29. Effects of DCD rate on total DCD in the
1.22 m profile of a fallow Quartz-
ipsamment at Live Oak ... 201

C-1. Effects of N rate on soil inorganic N
concentration (Gainesville, 1983) 253

C-2. Effects of N rate on soil NHf4 and N03-
concentrations (Gainesville, 1983) 254

C-3. Effects of N rate on soil NH4 and N03O
concentrations (Gainesville, 1984) 255

C-4. Effects of N rate on soil NH4+ and N03-
concentrations (Hastings, 1984) 256

C-5. Effects of DCD rate on soil inorganic N
concentration (Gainesville, 1983) 257

C-6. Effects of DCD rate on soil NH,* and N03-
concentrations (Gainesville, 1983) 258

C-7. Effects of DCD rate on soil inorganic N
concentration (Gainesville, 1984) 259

C-8. Effects of DCD rate on soil NH4 and N03-
concentrations (Gainesville, 1984) 260

C-9. Effects of DCD rate on soil inorganic N
concentration (Hastings, 1983) 261








C-10. Effects of DCD rate on soil inorganic N
concentration (Hastings, 1984) 262

C-11. Effects of DCD rate on soil NH4 and N03,
concentrations (Hastings, 1984) 263

C-12. Contrast of IBDU and inhibitor effects on
soil inorganic N concentration (Gaines-
ville, 1983) 264

C-13. Contrast of IBDU and inhibitor effects on
soil inorganic N concentration (Gaines-
ville, 1984) .. 265

C-14. Contrast of IBDU and inhibitor effects on
soil inorganic N concentration (Hastings,
1984) ... 266


xxi











Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of
the Requirements for the Degree of Doctor of Philosophy


NITRIFICATION INHIBITOR EFFECTS ON POTATO
YIELDS AND SOIL INORGANIC NITROGEN

By

Harris Warthman Martin

August 1990

Chairman: D. A. Graetz
Major Department: Soil Science

Rapid loss of applied N from soils may result after

nitrification of NH4-N to N03--N. Nitrification inhibitors

should reduce N losses from leaching and denitrification,

thus increasing N utilization by crops. The effects of

nitrification inhibitors on soil inorganic N (SIN) concen-

trations, plant N uptake, and crop yield were evaluated.

Dicyandiamide (DCD) and 2-chloro-6-(trichloromethyl)-

pyridine (nitrapyrin) nitrification inhibitors were evalu-

ated on potato (Solanum tuberosum L. cv. Atlantic). Treat-

ments were combinations of N at 67, 134, and 202 kg ha-l;

DCD at 0, 5.6, and 11.2 kg ha'1; nitrapyrin at 0.56 and 1.12

kg ha-1; and isobutylidene diurea (IBDU) applied as one-

third of the N. Studies were conducted on an Arenic

Ochraqualf, a Grossarenic Paleudult, and a Grossarenic

Paleaquult.

Tuber yields were increased 17% by use of nitrifi-

cation inhibitors in one of five tests. At this location


xxii







severe leaching had occurred. Nitrification inhibitors

increased leaf N concentrations at flowering in three of

four tests. Tuber yields were higher with DCD than with

nitrapyrin in three of five tests. Tuber yields increased

with an increase in N from 67 to 134 kg ha-1 in three of

three tests. In one test where severe leaching had

occurred, tuber yields increased with an increase in N to

202 kg ha'-. Nitrification was inhibited by nitrification

inhibitors in all of four tests, and increased SIN concen-

trations in one. SIN concentrations in mid- and late-season

were higher with one-third N as IBDU-N, than with nitrifi-

cation inhibitors.

In a second study, DCD was applied to a fallow Typic

Quartzipsamment at 0, 20, 40, and 60 kg ha'1 with urea at

200 kg N ha-1. Dicyandiamide inhibited nitrification for 81

days. However, SIN concentrations were reduced with DCD.

Residence half times of DCD in the 0 to 1.2 m depth were 61

to 66 days with 20 to 60 kg DCD ha1.

Use of nitrification inhibitors increased crop yields

only under conditions where SIN concentrations were

increased, N rates were 134 kg ha-' or less, and leaching

was severe. Inhibition of nitrification did not lead to

increases in SIN concentrations in most experiments.

Increases in potato yields with nitrification inhibitors did

not occur in most experiments as SIN concentrations were not

increased.


xxiii













CHAPTER 1
INTRODUCTION


Nitrate is subject to greater leaching and denitrif-

ication losses from soil than NH4*. Nitrification, the

natural transformation of NH4* to NO3- by certain soil

bacteria, promotes losses of N by denitrification and

leaching out of the crop root zone. As a result, crops make

inefficient use of fertilizer N. In addition, leaching of

NO03 poses an environmental hazard.

It has been commonly assumed that inhibiting nitrif-

ication should reduce N losses from leaching and denitrif-

ication, increase N utilization by crops, and provide more

even N nourishment of crops over longer periods of time than

would otherwise be possible. If this is true, control of

nitrification should lead to increased efficiency of N use

with corresponding improvements in crop growth, yield, and

quality. Dicyandiamide (DCD) and 2-chloro-6-(trichloro-

methyl)-pyridine (nitrapyrin) are two of a number of syn-

thetic nitrification inhibitors that have been tested and

made available commercially.

The objectives of this study were (1) to assess the

effects of DCD and nitrapyrin on potato (Solanum tuberosum

L. cv. Atlantic) tuber yield, crop quality (tuber specific







2

gravity and tuber grade proportions), plant biomass, plant N

concentration, and N uptake in Northeast Florida; (2) to

assess the effectiveness of DCD and nitrapyrin as inhibitors

of nitrification in sandy coastal plain soils of Northeast

Florida, as measured by their effects on extractable soil

inorganic NH4+-N, N03--N, and the total of these; (3) to

compare the effects of DCD to those of nitrapyrin, and to

compare the effects of the two inhibitors with those of

isobutylidene diurea (IBDU), a slow release N source; (4) to

determine the extent to which N rate, inhibitors, and IBDU

effects on plant response parameters can be attributed to

the effects of these treatments on total soil inorganic N

concentrations; (5) to study DCD's nitrification inhibiting

effect and the fate of DCD in the soil, by measuring the

effects of DCD on soil inorganic N concentrations and move-

ment, and DCD movement and loss in a fallow, deep sandy

soil; and (6) to contribute to an understanding of why

nitrification inhibitors often do not increase crop yield.














CHAPTER 2
LITERATURE REVIEW


Nitrification Inhibitors

Introduction

Numerous compounds have been proposed for regulating

nitrification in soils, including organic and inorganic

compounds, pesticides, chelating agents, and plant products.

A number of these are manufactured and patented in the USA,

Japan (Ranney, 1978), and Europe. Of the number of inhibi-

tors mentioned in the literature over a period of 20 years

(Ranney, 1978), only nitrapyrin, DCD, and to a lesser extent

2-amino-4-chloro methyl pyrimidine (AM) have been tested

thoroughly (Slangen and Kerkhoff, 1984). The inhibitors of

nitrification are effective if they retard one or more steps

in the following chain of microbial reactions:


Nitrosomonas
NH --------------> hydroxylamine -->

nitroxyl? --> nitrohydroxylamine --> [1]

Nitrobacter
NO- -------------> N03O (Hauck, 1972).


The ideal nitrification inhibitor should inhibit

Nitrosomonas, not Nitrobacter, since such inhibition would

result in accumulation of NO,.2 It should also be nontoxic









to other soil organisms, fish, mammals, and crops and be

safe in the environment. It should be able to move with the

fertilizer or fertilizer solution, that is, be effective

throughout the fertilizer reaction zone. Rapid movement

through soils because of high vapor pressure or little

movement because of low vapor pressure or strong sorption

could lead to poor performance. The ideal nitrification

inhibitor should be sufficiently persistent in its action so

that nitrification is inhibited for an adequate period of

time, usually from several weeks to months. The chemical

should be a low cost additive to fertilizer (Hauck, 1972;

Turner and MacGregor, 1978; Sampei, 1972).


Chemical Properties of the Inhibitors

Nitrapyrin. Nitrapyrin was first introduced in 1962

by C.A.I. Goring of the Dow Chemical Company (Goring, 1962a,

1962b). This product stimulated the interest of quite a few

researchers in several countries, resulting in many studies

and published papers. As of 1981, nitrapyrin was used on >1

million hectares of agricultural land annually in the USA

(Ashworth and Rodgers, 1981). Nitrapyrin is the principal

nitrification inhibitor used commercially in North America,

though 5-ethoxy-3-trichloromethyl-1,2,4-thiadizole (terra-

zole) is also used widely (Hergert and Wiese, 1980).

Nitrapyrin is a white crystalline solid with a molecu-

lar weight of 230.9 atomic units and a melting point of 62

to 630C (Goring, 1962a, 1962b). It is soluble in liquid NH3









but insoluble in water; thus it has to be dry-mixed with

solid fertilizers or applied directly, preferably as a

solution or emulsion (Turner et al., 1962). It has the

following structure (Figure 2-1):








Cl- CC

N



Figure 2-1. The structure of nitrapyrin, or 2-chloro-
6-(trichloromethyl)-pyridine (N-Serve).


Nitrapyrin is marketed as "N-Serve 24 nitrogen stabilizer"

(a.i. 240 g L-1) and "N-Serve 24E nitrogen stabilizer" (a.i.

240 g L-1) with an emulsifier (Slangen and Kerkhoff, 1984).

Dicyandiamide. The ability of DCD to inhibit nitrifi-

cation has been observed by Brioux (1910), Nommik (1958,

1959), Reddy (1964a, 1964b), Rathstack (1978), Vilsmeier and

Amberger (1978), Guster (1981), Kick and Poletschny (1981),

Ashworth and Rodgers (1981), and others. The advantages of

DCD over nitrapyrin for a given application, are due primar-

ily to its different physical properties and its N content.

While nitrapyrin has a low water solubility, high vapor

pressure, high corrosiveness, and leaves a residue of

chloropicolinic acid, DCD is a solid at room temperature and









can be processed as powder, granules, or pellets. It has a

relatively high solubility in water, contains 16% N, and

breaks down to NHf4 and CO2, leaving no synthetic organic

residues. Part of its cost can be justified by its N con-

tent (Amberger, 1981a; Kick and Poletschny, 1981; SKW,

1973). Because of these characteristics, DCD can be used as

an additive to liquid, organic, or mineral fertilizers,

surface coated on to, or incorporated into solid fertilizers

containing NH4/ or urea, or applied alone to the soil

(Amberger, 1984; Solansky, 1981; SKW, 1973). It requires no

special equipment for its application. A brief review and

discussion of agronomic properties of DCD and of the manu-

facture of DCD-containing fertilizers was published by

Rieder and Michaud (1980). According to Ashworth and

Rodgers (1981) 20% of the cost of DCD application is

offset by the fertilizer value of the N contained in DCD.

The commercially marketed DCD products, Didin and

Alzodin, were developed by SUddeutsche Kalkstickstoffwerke

Trostberg Akteingessellschaft, Trostberg, West Germany

(hereafter referred to as SKW) in close cooperation with the

Institute fur Pflanzenernahrung der TU Munchen at

Weihenstephan in West Germany (Amberger, 1981a). Compounds

containing urea (Didin) or (NH4)2SO4 (Alzodin) are available

in granulated and coated form from SKW (SKW 1979a, 1979b),

and Chisso Corp. of Japan (Chisso Corp., 1981; Slangen and

Kerkhoff, 1984).









Dicyandiamide, abbreviated as DCD, is the most common

name for this compound. It is also referred to as cyano-

guanidine. The empirical formula is C2N4H4. Dicyandiamide

has a molecular weight of 84.04 atomic units (AERO, 1964;

May, 1979; Weast, 1979). DCD has been thought by most

workers to exist as a tautomer with the following structure

(Figure 2-2):



HN H2N
\\ H
C-N-C-N <-----> C=N-C-N
/ /
H2N H2N

Tautomer #1 Tautomer #2



Figure 2-2. Tautomers of DCD.


It is generally insoluble in nonpolar solvents and

soluble in polar solvents (May, 1979) such as water, (SKW,

1973; Weast, 1979) and liquid anhydrous NH3 (72 g DCD 100 g-1

NH3 at -330C) (SKW, 1973; Reitter, 1975; Ashworth and

Rodgers, 1981). Its solubility in water is temperature

dependent, i.e., 33, 52, and 121 g L-1 at 20, 30, and 500C,

respectively (SKW, 1973). It is amphoteric and has an acid

dissociation constant (Ka) at 250C of 6 X 1015.

Dicyandiamide may exist as an impurity in the now

archaic fertilizer CaCN2 (calcium cyanamide, lime nitrogen,

or calcium carbamonitrile) (Harger, 1920; Vilsmeier and

Amberger, 1978). At one time CaCN2 was a commonly used N









fertilizer in Europe and Japan (May, 1979). Dicyandiamide

often appeared as a decomposition product of CaCN2 (Murata,

1939). It makes up approximately 10% of the N in CaCN2

(Amberger, 1981b).


Mechanism of Nitrification Inhibition

General. Nitrification inhibitors affect certain

chemosynthetic autotrophic soil bacteria in the Nitrobacter-

iaceae family by retarding either their growth or their

functions. Inhibition of nitrification activity can be

caused by interfering with respiration and cytochrome oxi-

dase function, by chelating essential metal ions, by produc-

tion of acid in the microenvironment, and by liberation of

toxic compounds such as mercaptans, sulfoxides, and sulfones

(Hauck, 1972).

Lees (1946) observed that chemicals such as Na

diethyldithiocarbamate and salicylaldoxime which inhibit

copper enzymes, inhibit oxidation of NH4* by Nitrosomonas.

Quastel (1965) observed that thiourea and allylthiourea

inhibit nitrification as well, possibly by combining with

metallic cations, such as Cu24, needed for this process in

soil.

It has been proposed that the affinity of the N atom

in the structure R-NH-C= for the Cu containing NH4 oxidiz-

ing enzyme is primarily involved in inhibition of nitrifica-

tion (Quastel and Scholefield, 1951). Such a structure

occurs in tautomer structure No. 1 of DCD (Figure 2-2). A









closely related structure, with which the former may

resonate, i.e. R=N-C=, is contained within the structure of

nitrapyrin (Figure 2-1). The other tautomer (No. 2) of DCD

contains another related structure, R-N=C-. Both nitrapyrin

and DCD inhibit the cytochrome oxidase involved in NH3

oxidation by Nitrosomonas (Hauck, 1980).

Nitrapyrin. Nitrapyrin inhibits nitrification by

inhibiting Nitrosomonas (Goring, 1962a) and has very little

effect on Nitrobacter, (Shattuck and Alexander, 1963).

Zacherl and Amberger (1984) reported that nitrapyrin was

bactericidal rather than bacteriostatic. Shattuck and

Alexander (1963) observed that nitrapyrin had no effect on

several heterotrophic bacteria and fungi; thus it can be

used to distinguish autotrophic from heterotrophic nitri-

fying organisms.

From their work with pure cultures of Nitrosomonas and

Nitrobacter, and others to which nitrapyrin was added,

MUller and Hickisch (1979) concluded that the decrease in

the number of microorganisms is small and cannot be the only

explanation for the inhibition of the nitrification process

over a relatively long period. Hooper and Terry (1973)

concluded that the effect of nitrapyrin was irreversible

because they found that NO2--N or NO3--N accumulation did not

recommence in cell-free extracts after treatments with

nitrapyrin had finished.









Goring (1962a) studied the effect of reinfestation

(reinoculation) by nitrifying bacteria contained in small

amounts of fresh soil, on the control of nitrification by

nitrapyrin. Nitrification proceeded more rapidly in rein-

fested than in uninfested soil. He presumed that nitrapyrin

destroys the majority of the nitrifying organisms and is

then decomposed to nonlethal concentrations. The rate of

recovery of nitrification thus depended on the recovery of

the surviving nitrifying organisms and was, therefore,

enhanced by repeated reinfestation.

Rodgers et al. (1980) found that recovery of nitrify-

ing bacteria took approximately 40 days after a 1 mg L-1

addition of nitrapyrin to aqueous suspensions of different

soils to which 200 mg NH4*-N L' was added. Even after

prolonged incubation with nitrapyrin, no evidence was

obtained for the development of nitrapyrin resistant nitri-

fying organisms. Research with different strains of Nitro-

somonas (Belser and Schmidt, 1981; Laskowski and Bidlack,

1977) showed substantial differences in sensitivity among

strains, to nitrapyrin.

Dicyandiamide. Dicyandiamide inhibits nitrification

by interfering with the metabolism of Nitrosomonas (Verona

and Gherarducci, 1980; Amberger, 1981a), specifically by

inhibiting the oxidative phosphorylation (Amberger, 1984) of

the Cu containing cytochrome oxidase enzyme which oxidizes

NH4 (Hauck, 1980). Amberger (1981b) proposed that there is







11

a temporary decoupling of respiration and energy transfer in

Nitrosomonas due to a reaction of the C-N group of DCD with

sulfhydrile groups and heavy metals of cytochrome oxidase.

He based this proposal on the results of his earlier work

(Amberger, 1978) with cyanamide and related products.

Dicyandiamide is a bacteriostat, not a bactericide

(Zacherl and Amberger, 1984). The microbial effects of DCD

are selective for Nitrosomonas, with no effect on the fungi,

cellulose-decomposing bacteria, ammonifying and denitrifying

bacteria, Azotobacter (Verona and Gherarducci, 1980), or

Rhizobium sp. (Neglia and Verona, 1976) that were tested.

Verona and Gherarducci (1980) found that several days

after application of DCD, the numbers of Nitrosomonas in

soil eventually decreased. After the DCD had decomposed,

the original numbers of Nitrosomonas reappeared in the soil.

Solansky (1981) commented that this reduction of numbers

must represent a decrease in the bacteria's rate of multi-

plication as a result of their starvation due to a lack of

metabolic substrate.


Inhibitor Concentration Effects and Longevity

Nitrapyrin. Reports of the duration of nitrapyrin's

nitrification inhibiting effect have been various: 15 days

for complete inhibition and 49 days for partial inhibition

(Hendrickson et al., 1978), 59 days (Westermann et al.,

1981), 91 to 100 days (McCormick et al., 1983), 112 days









(Terry et al., 1981), 148 days (Liu et al., 1984), and 280

days (Janssen, 1969).

Goring (1962a) found that the minimum active concen-

trations of nitrapyrin for a six-week incubation period in

87 soils (with 200 mg kg-1 NH4-N) were principally in the

0.2 to 2.0 mg kg-' range, but a few were as high as 20 mg

kg'1 and several were as low as 0.05 mg kg-1. A number of

workers have found that under laboratory and field condi-

tions, nitrapyrin inhibited nitrification of NH4+ and amide

fertilizers at rates varying from 0.2 to 2.0% of applied N

(Goring, 1962a, 1962b; McBeath, 1962; Turner et al., 1962;

Gasser and Penny, 1964; Nielson and Cunningham, 1964; Sabey,

1968).

McCormick et al. (1984) recommended that nitrapyrin

should be applied at a rate of 0.8 to 0.9 kg ha'- with a

banded fertilizer application to give effective control of

nitrification. Goring and Scott (1976) reported that the

rates of nitrapyrin application advised by Dow Chemical

Company were 4.5 to 6.75 L ha-1 of N-Serve 24 or 24E for

potatoes before or after planting. These recommended rates

were based on fertilizer application in bands or rows

(Goring and Scott, 1976).

Dicyandiamide. Bazilevich (1968) grew corn in potted

soil and found that 35 days after DCD application, the

inhibiting effect of DCD on the rhizosphere microflora was

still observed, while after 50 days the number of









microorganisms increased but remained less than control

populations; after 85 days populations were the same as the

control.

Bazilevich and Kabanova (1973) found that 6.8 kg DCD

ha'1 inhibited nitrification of applied (NH4)2SO4-N for 1 to

1.5 months. Smirnov (1978) observed that 10 to 15% of the

amount of applied N as DCD-N was needed to inhibit the

nitrification of fertilizer derived and native NH4*-N for a

period of 1.5 to 2 months.

Amberger and Guster (1978) found that DCD at 5 to 10%

of the applied N was sufficient to inhibit nitrification in

a pot culture with sandy loam (pH 6.1) over at least 6

weeks. Without any inhibitor, Amberger and Vilsmeier

(1979c) found that 50% of total N and 100% of NH4,-N,

applied to soil in the laboratory as liquid manure was

nitrified within 20 to 40 days at temperatures of 8 to 200C.

Addition of DCD at a rate of 10 mg DCD kg'1 of liquid manure

resulted in intensive inhibition of nitrification for 20 to

60 days depending on environmental conditions such as

leaching rainfall and soil temperature. Increased DCD rates

lengthened these times. Reddy (1964a), in incubation

studies with DCD and (NH4)2SO4 in Georgia coastal plain

soils, found that with Cecil sandy loam (Paleudult) and

Lakeland sand (Quartzipsamment), 25 mg kg'1 DCD inhibited

nitrification for up to 90 days. Some inhibition was still









occurring after 150 days in the Lakeland soil (Reddy,

1964a).

In a laboratory incubation study with a Mulat sand

(Typic Ochraquult) from the Horticulture Unit near

Gainesville, Florida, Mohamad (1985) found that the duration

of DCD effectiveness was directly related to DCD concen-

tration in the soil. With 5 and 10 mg DCD kg-1 soil, 100 mg

of added NH4*-N kg"- soil was subject to considerable nitri-

fication within two weeks. With 25 mg DCD kg-1 soil, how-

ever, significant nitrification did not occur for eight

weeks and some inhibition of nitrification continued for at

least twelve weeks. He found that the effectiveness of DCD

added to soil at the rate of 10 mg kg-1 was not affected by

NH.4-N concentrations in the soil within the range of 0 to

120 mg NH4*-N kg-1 soil.

In a field study with the same Ochraquult, Mohamad

(1985) found that the duration of inhibition varied from

year to year and varied with N rate and DCD rate. In one

year with 22.4 kg ha-1 DCD and 202 kg ha-1 urea-N, DCD

increased soil NH4-N concentration for eight weeks. With

11.2 kg ha'- DCD, however, NH4-N concentrations were only

increased for four weeks. With these DCD and N rates,

NOR--N concentration in the soil was reduced for four weeks.

In a second year, 11.2 kg ha-1 DCD had little effect on soil

NH4/-N or N03--N concentrations while 22.4 kg ha' DCD









increased soil NH4-N concentration for six weeks and

decreased soil NO;--N concentration for four weeks.

Vilsmeier and Amberger (1978) found that DCD as 10% of

applied N in (NH4)2SO4 and urea strongly inhibited nitrifica-

tion for an average of 60 days. Randal and Malzer (1981)

found that DCD inhibited nitrification of NH4/ from (NH4)2S04

and urea for a maximum of 9 weeks. In the laboratory,

Rathstack (1978) added urea and large concentrations of DCD

to soil under environmentally controlled conditions. He

found that as DCD-N (as a percent of applied N) increased

from 10 to 20 to 30%, nitrification inhibition continued for

26, 32, and 45 days respectively. In a field study,

Touchton (1981b), however, found that 5% DCD-N as a percent-

age of total N was as effective in inhibiting nitrification

as 10 and 15% rates.

These and other reports indicate that DCD is effective

at inhibiting nitrification for a minimum of 20 days, more

often for 40 to 60 days, and occasionally for as long as 90

days. These values are sometimes but not always a function

of DCD concentration in the soil or N fertilizer. The

duration of inhibiting effects and the effective concentra-

tion vary with soil type and environmental conditions.

Since effective inhibition is likely to taper off gradually,

it is not possible to determine exactly the duration of

effectiveness.









Inhibitor Losses

Volatilization of nitrapyrin. Nitrapyrin has a rela-

tively low vapor pressure of 0.373 N m-2 (at 230C) (Goring,

1962b). This is the reason that application of nitrapyrin

in spots or bands, instead of broadcasting, is preferred

(Turner et al., 1962). According to Hendrickson et al.

(1978), nitrapyrin is more likely to be lost to volatiliza-

tion when sidedressed, even though covered with soil, than

when applied at planting. Nitrapyrin volatilizes rapidly

when unincorporated into the soil, resulting in losses of up

to 80% (Briggs, 1975) and thus is much more effective as a

nitrification inhibitor when incorporated (Briggs, 1975;

Gasser and Penny, 1964). This volatility results in gaseous

diffusion of nitrapyrin through air-filled pores in the soil

(Goring, 1962b) and can be aggravated by wind at the soil

surface (McCall and Swann, 1978). Higher soil temperatures

accelerate the rate of diffusion of nitrapyrin in soils

(Hendrickson et al., 1978).

Because of its volatility, low water solubility, and

sorption by soil organic matter, nitrapyrin has very little

tendency to leach downward in the soil (Mullison and Norris,

1979). When NH4-N fertilizer is applied to soil with

nitrapyrin, much of the NH4*-N can leach down below the zone

of soil containing nitrapyrin, thus rendering the inhibitor

ineffective (Hendrickson et al, 1978; Rudert and Locascio,

1979b).









Decomposition hydrolysiss) of nitrapyrin. The prin-

cipal decomposition residue of nitrapyrin in plants and

soils is 6-chloro-picolinic acid, formed by hydrolysis of

the trichloromethyl group (Briggs, 1975; Herlihy and Quirke,

1975; Hendrickson and Keeney, 1979; Redemann et al., 1964,

1965). Hydrolysis of nitrapyrin is enhanced in moisture

saturated soils (Hendrickson and Keeney, 1979; Laskowski et

al., 1974). As soil temperature increases, the rate of

nitrapyrin hydrolysis increases exponentially (Redemann et

al., 1964; Hendrickson and Keeney, 1979). Hendrickson and

Keeney (1979) found that the rate of nitrapyrin hydrolysis

was not affected by pH in the 2.7 to 11.9 range. Touchton

et al. (1979b) found, on the other hand, that the rate of

nitrapyrin disappearance increased with increasing soil pH

in 2 of 3 soils tested.

Redemann et al. (1964) found that the amount of

applied nitrapyrin remaining in the soil was an exponential

function of time and observed a half life (residence half

time) for nitrapyrin in four soils, from 4 to 22 days at

20*C. Herlihy and Quirke (1975) observed nitrapyrin half

lives ranging from 9 to 16 days at 20C and from 43 to 77

days at 100C.

Decomposition of DCD. That DCD which is retained in

the soil eventually breaks down into NH4/-N and NO3--N and

carbon compounds, presumably by the action of soil microor-

ganisms (Rathstack, 1978). Rieder and Michaud (1980)









reported that rapid mineralization of DCD-N to NH4+-N and

N03--N in three soils began after 28 days and was complete

after approximately 70 days. Garita (1981) applied DCD to

soil in a banana plantation in Costa Rica. When the DCD was

in an (NH4)2SO4 formulation (Alzodin), none was detectable in

soil extracts after 46 days. When it was applied in a urea

formulation (Didin), none was detectable after 59 days.

Graetz et al. (1981) applied DCD to soil under sweet corn

(Zea mays L. var. saccharata (Sturt.) Bailey.) in Northeast

Florida and found detectable DCD in soil extracts 77 days

after application. Kappan (1907) concluded that DCD decom-

posed more slowly in infertile soils than in fertile soils.

In an incubation study, Vilsmeier (1980) was able to

identify the breakdown products of DCD in soil. The

sequence of reactions was shown to be



DCD ---> guanylurea ---> guanidine ---> NH4 [2]



As temperature increased, the rate of breakdown increased,

particularly for the DCD to guanylurea step. At very high

temperatures (70*C), guanidine accumulated.

Whereas the rate of decomposition of DCD in soil

depends on temperature and quantity of DCD applied, soil

moisture content has been said to play only a minor part

(Vilsmeier, 1980, 1981; Amberger and Vilsmeier, 1979a,

1979b). Murata (1939) observed that DCD was ammonified








19

under waterlogged conditions. A low value for Po2 (Eh less

than 250 my at pH 7) and the presence of FeO or actively

decomposing organic matter was favorable for DCD decomposi-

tion (Murata, 1939). Bazilevich (1968) found that DCD was

decomposed much faster in plant-bearing than in fallow or

untilled soil. Thus, he concluded that plant root exudates

were used as nutrients or carbon sources by the micro-

organisms which break down DCD, with DCD acting as an N

source for these microorganisms. Reddy and Datta (1965)

observed that the nitrification inhibiting effect of DCD was

partially counteracted by the addition of organic matter.

In the presence of added organic matter, decomposition of

DCD was more rapid. They attributed this rate effect to the

high exchange capacity and absorbing power of the organic

matter. Reddy (1964a) claimed that DCD decomposed faster in

a sandy loam soil with a relatively high organic matter

content than in a coarse textured sandy soil with a low

organic matter content.

Leaching of DCD. If leaching of N03'-N is a reason

for using nitrification inhibitors, then leaching of the

inhibitors should also be of much interest. The volatility

of nitrapyrin can cause NH,4-N to move below the zone of

maximum nitrapyrin concentration in the soil (Rudert and

Locascio, 1979b). DCD, on the other hand, does not

volatilize but is subject to leaching (Amberger and Guster,

1979; Bock et al., 1981; Sampei and Fukushima, 1973). If it









leaches more rapidly than NH4+-N, then its effectiveness

will be compromised (Bock et al., 1981).

Amberger and Guster (1979) observed that as much as

15% of the DCD applied with liquid cattle manure to potted

soil in the greenhouse was leached by 56 mm of simulated

percolation. More DCD was leached from fallow potted soil

than when growing plants were present.

Bock et al. (1981) studied the movement of DCD and

various sources of fertilizer N through soil columns. While

NH4+ is held against leaching to some extent by the cation

exchange capacity, even in sandy soils, the tautomers of DCD

carry little charge; thus DCD can separate from the NH4+

when the two are applied together. Under conditions of mass

flow, this separation was observed by Bock et al. (1981).

This did not occur with urea, however, since DCD and urea

moved with the soil solution at about the same rate. This

is not surprising since urea also is uncharged.

Retention of DCD in six soils (belonging to several

soil orders) studied by Bock et al. (1981) generally

increased with increasing soil organic matter content and

cation exchange capacity (CEC). DCD is only weakly sorbed

by soil organic matter (Vilsmeier, 1979), but even weak

sorption could be significant. Bock et al. (1981) observed

no relationship between soil pH or presence of free calcium

carbonate and DCD retention. They found that a simulated 5










cm rainfall moved most of a surface applied DCD solution

below the 5 cm depth in all the soils studied.


Effects of Inhibitors on Other N Transformations

Volatilization of NH,. Rodgers (1983) reported that

the use of DCD increased the amount of NH3 lost by volatil-

ization 20 to 60% compared to soil amended with urea only.

He concluded that the beneficial effects of DCD may be

counteracted by increased loss of NH3 by volatilization.

Apparently no other research has been reported on the

effects of nitrification inhibitors on NH3 volatilization.

Volatilization of NH3 may have been the reason for

some of Graetz et al.'s (1981) field results with vege-

tables. They found that with plastic mulched tomato

(Lycopersicon esculentum Mill.) fruit yield was increased

with addition of DCD to NH4NO3 and to urea. With unmulched

bell peppers (Capsicum frutescens var. grossum (L.) Bailey),

DCD increased fruit yield when NH4NO3 was used but decreased

yield when urea was used.

N mineralization. Kreitinger et al. (1985) found that

nitrapyrin stimulated N mineralization rates by 77% in soil

suspensions not receiving NH4-N and by 40% in NH4 -N sup-

plemented suspensions. The reason for this anomalous obser-

vation was not apparent. The fixation of CO2 was not

increased by the addition of NH4-N to suspensions of

leached soil. However, nitrapyrin inhibited CO2 fixation in

both NH4+-amended and unamended suspensions.








22

In a field study with 15N, Norman et al. (1989) found

that DCD increased mineralization of organic N in rice paddy

soil and increased plant uptake of native soil N as opposed

to fertilizer N. In a field lysimeter study with 15N

applied to corn (Zea mays L.), Walters and Malzer (1990b)

obtained similar results with nitrapyrin. In a laboratory

incubation study, however, Mohamad (1985) found that DCD did

not affect mineralization of soil organic N in a sandy

Florida Ochraquult.

Denitrification. Nitrification inhibitors indirectly

inhibit denitrification because of their inhibition of

nitrification (Mitsui et al., 1964). Evidence for this

indirect inhibition has been provided for flooded soils

(Prasad and Lakhdive, 1969; Rajale and Prasad, 1970; Sampei

and Fukushima, 1973) and for nonflooded soils (Nishihara,

1962; Smirnov et al., 1977; Liu et al., 1984; Cribbs and

Mills, 1979; McElhannon and Mills, 1981; Kostov, 1977;

Vilsmeier, 1981). Others have observed that inhibitors such

as DCD did not affect denitrification (Mitsui et al., 1962;

Simpson et al., 1985). Since nitrification is inhibited,

less NO3- (the substrate for denitrification) is formed from

NH4 (Meyer, 1981; Vilsmeier, 1981). This indirect effect

on denitrification is of practical importance, especially

where crops such as rice (Oriza sativa L.) are grown in

flooded soils.







23

N immobilization. Hauck (1972) observed that nitrifi-

cation can result in a reduction of N immobilization and NH3

fixation. It follows, therefore, that inhibition of nitri-

fication could increase N immobilization and fixation. When

Chancy and Kamprath (1982) applied nitrapyrin to corn, they

observed that nitrapyrin resulted in more of the total

inorganic N in the 0 to 15 cm depth being in the NHf4 form.

However, this did not significantly increase the total

inorganic N concentration at any depth. They could not

explain this discrepancy; they did not consider the pos-

sibility of increased immobilization.

Terry et al. (1981) reported no effect of nitrapyrin

on immobilization of NH4t-N added with synthetic sewage

sludge to a silt loam (Aeric Ochraqualf) soil. In a

laboratory study under controlled conditions, Mohamad (1985)

did not observe any effect of DCD on fertilizer N immobil-

ization. In another laboratory study, however, Osiname et

al. (1983) did observe an increase in immobilization of

fertilizer N with nitrification inhibitors.

Until recently, most of the research investigating the

effects of nitrification inhibitors on the immobilization of

fertilizer N has been done by Smirnov's group in the Soviet

Union. Smirnov et al. (1968) amended 15N labeled (NH4)2SO4

and urea with DCD and found that although N losses were

markedly lowered by DCD application, more of the fertilizer

N was immobilized in organic forms in the soil as a result









of DCD application. Smirnov (1968) applied "N labeled

NH4-N fertilizers amended with DCD, to barley and oats. He

found that DCD application increased utilization of fertil-

izer N by the crops somewhat, almost halved losses of N, and

increased transformation of fertilizer N into organic N.

Smirnov et al. (1972a, 1972b) found that DCD application

increased the immobilization of fertilizer N under corn, but

not under oats (Avena sativa L). In another study, Smirnov

et al. (1973) applied DCD as 0.5% of the fertilizer weight

with (NH4)2SO4 and urea at the rate of 120 mg N kg'1 soil.

They found that N losses were reduced by 23 to 25% with

(NH4)2SO4 and by 12 to 14% with urea, while immobilization of

fertilizer N was increased by DCD application.

Juma and Paul (1983) found that the nitrification

inhibitor 4-amino-1,2,4-triazole (ATC) increased the recov-

ery in Canadian topsoil of 1N supplied as labelled urea or

aqueous NH3, by 41 to 57% on the average, without increasing

"5N uptake (37%) by wheat. Soil treated with ATC contained

nearly twice as much 15N in the biomass as untreated soil.

Ashworth et al. (1984) found that similar increases in non-

extractable soil 15N were measured after incubating soils

from Alberta, Canada, in the laboratory with labeled

(NH4)2SO4 and the inhibitor etridiazol. Norman et al. (1989)

found that DCD increased immobilization of fertilizer N

applied to paddy soil in Arkansas. Walters and Malzer

(1990a, 1990b) found that in the first year of their study,









nitrapyrin increased immobilization of incorporated urea-N

and decreased plant recovery of fertilizer derived N (FDN)

in a Typic Hapludoll in Minnesota. This led to an increase

the following year in mineralization, plant uptake, and

leaching of residual FDN.


N Leaching and Inhibitor Effects

Potato production in many regions of the world is

concentrated in areas of sandy soils where irrigation is

common (Bundy et al., 1986). Irrigation of the potato crop

is considered essential on such sands and lighter soils

(Curwen et al., 1982). Potato grown on these soils is

relatively shallow-rooted (Lesczynski and Tanner, 1986) and

requires frequent irrigation (Curwen and Massie, 1984) and

high N fertilizer rates (Kelling et al., 1984) to maximize

tuber yield and quality. In studies with Russet Burbank

potato on a loamy sand, more than 90% of the root length was

in the upper 30 cm of the soil profile (Lesczynski and

Tanner, 1976; Tanner et al., 1982); thus fertilizer N

leached below 30 cm is not likely to be recovered by the

crop (Bundy et al., 1986).

In such an environment, the potential for loss of

fertilizer N by means of leaching of NO;--N is high (Bundy

et al., 1986). Some of these soils have such low CEC and

water holding capacities that appreciable leaching of NH4+-N

can occur as well. The tendency of NH4-N to leach would be

accentuated if fertilizer N persists in the NH4 form for an







26

extended period of time, or if the concentrations of soluble

salts in the soil are high (Hendrickson et al., 1978).

It is not unusual for potato growers to apply water

frequently and in amounts in excess of actual evapotranspir-

ational losses. This practice can be wasteful and in some

cases reduce tuber yields by leaching fertilizer N beyond

the root zone, and by creating anaerobic conditions in

poorly drained soils (Wolfe et al., 1983).

Nonuniform water infiltration under potato plant

canopies can promote N leaching losses and decreased crop

recovery of fertilizer N (Lesczynski and Tanner, 1976;

Saffinga et al., 1976; 1977; Tanner et al., 1982). In sandy

Entisols of central Wisconsin, only 2.5 cm of applied water

resulted in a 15 to 20 cm downward movement of added N03'-N

(Endelman et al., 1974). In Long Island, NY, rates of N

fertilizer in excess of potato crop requirements resulted in

NO3-N enrichment of the groundwater (Meisinger, 1976).

It can be difficult to accurately determine N03--N

movement in field soils. The presence of water flow chan-

nels in the soil can result in rapid movement of applied N

fertilizer not only to regions below the rooting zone, but

below the zone of biodegradation as well. As a result, much

of the downward moving NO3'-N tends to avoid contact with

installed sampling devices such as porous cup extractors

(Simpson and Cunningham, 1982). Peak water and leachate

flow periods may be missed entirely because of this









channelization (Rourke, 1985). This makes accurate

measurements of movement of inorganic N difficult in a soil

planted to potato (Simpson and Cunningham, 1982).

Under overhead irrigation, soil N03--N and other

soluble salts move downward and decrease in concentration as

the crop growing season progresses. Elkashif et al. (1983)

observed this to be the case in Northeast Florida at the

University of Florida Horticulture Unit at Gainesville,

Florida. At the Agricultural Research and Education Center

(AREC) at Hastings, Florida, potato was grown with subsur-

face irrigation and they observed that soil soluble salts

increased as the season progressed, due to low rainfall and

upward movement of soluble salts as water evaporated during

dry periods. These reports indicate that potato fields

present special challenges for the accurate measurement of N

leaching.

Nitrification inhibitors have been shown to reduce

losses of N accompanying nitrification vis. leaching and

denitrification under situations where these losses are high

(Sahrawat et al., 1977), thus reducing N03'-N pollution of

ground and surface waters (Huber et al., 1969; Norris,

1972). Touchton et al. (1979a) reported that nitrapyrin

prevented N03--N from accumulating below the 15 cm depth in

a somewhat poorly drained Typic Hapludoll in Illinois. In

percolation studies, Nishihara and Tsuneyoshi (1968) found







28

that the amount of N in the percolate (leachate) was greatly

reduced by amendment of urea with nitrapyrin.

Soubies et al. (1962) applied DCD in the fall at a

rate of 5.5 to 24% of fertilizer N, which reduced leaching

losses of N over the winter by as much as 67%. Kiangsi

(1976) found that DCD and other inhibitors prevented more

than 20% of the N losses caused by leaching of soil NO3--N.

Scheffer et al. (1984) found that DCD reduced leaching of

mineral fertilizer N applied to sandy soils by an average of

28%. When DCD was applied with liquid manure, however,

leaching was reduced with fall application but not with

spring application. Kuntze and Scheffer (1981) found that

DCD reduced N03--N leaching into subsoil drainage water by

20%. Kick and Poletschny (1981) found that during the

German winter, DCD resulted in reduction of N leaching by 67

to 80%.

Timmons (1984) found that nitrapyrin reduced NO'3-N

leaching losses by 30 to 51 kg ha-1 in a column study.

Using 15N and field lysimeters planted to corn on a sandy

loam (Typic Hapludoll) in Minnesota for three years, he

found that the average quantity of N03--N leached was 12 kg

ha-' (7%) less when urea was applied with nitrapyrin than

when urea was applied alone. His results were very

inconsistent because of variability in amounts of leaching

rainfall, plant uptake of fertilizer N, and other factors.









In a similar three year study with lysimeters on the

same soil, Walters and Malzer (1990a, 1990b) found that the

maximum rate of N03--N leaching loss was delayed 25 to 50

days when nitrapyrin was applied with 180 kg ha-1 urea-N.

Although nitrapyrin reduced soil water percolation, the

quantity of N leached was not reduced over the three year

period. They found that the effects of nitrapyrin on N03--N

leaching were confounded by the long term effects of

nitrapyrin on N immobilization and mineralization. This

paper was the first to describe the long term effects of a

nitrification inhibitor on most relevant portions of the

soil N cycle. An important factors that was not measured,

however, was inhibitor effects on volatilization of NH3. In

the first year, nitrapyrin resulted in a decrease in NO3--N

leaching due to an increase in immobilization of fertilizer

N. In subsequent years, this immobilized (residual) fertil-

izer N was mineralized, increasing leaching of N03--N.

Plant N uptake and N rate influenced this set of

relationships. While plant recovery of FDN in the year of

application was decreased by nitrapyrin, greater uptake of

residual FDN in subsequent years tended to equalize the

total amount of FDN recovered in plant material by the third

year of their study. In the previously unfertilized soil

which was used in their study, they found that N leaching

losses increased in each successive year. This reflected

mineralization and leaching of residual immobilized N from







30

the previous year's application. They observed that a two-

fold increase in N application rate resulted in a 3.4-fold

increase in N leached over three years. The relative dif-

ference in N leaching levels with two N rates increased with

each succeeding year. In part this was because less of net

fertilizer N remained immobilized after one year with a 180

kg ha-' N rate than with a 90 kg ha-1 N rate (Walters and

Malzer, 1990a, 1990b).

These reports indicate that in the field, inhibitors

can sometimes reduce NO3--N leaching, at least temporarily,

by as much as 70 to 80% but more often by 5 to 30%. The

only long-term well-controlled field experiments reported in

the literature showed an average reduction in leaching of

NO3--N, of only 7% in one case (Timmons, 1984) and no

reduction at all in another (Walters and Malzer, 1990b).


Crop Response to Inhibitors

According to Hauck (1972), decreased N losses and

increased crop yields resulting from the use of nitrifica-

tion inhibitors are readily demonstrated in laboratory and

greenhouse experiments. It is far less easy to demonstrate

the value of nitrification inhibitors in field soils since

field experiments usually are more insensitive than labora-

tory and greenhouse tests, and small differences in effi-

ciency of N use are difficult to measure accurately. Also,

in a single season, beneficial effects of controlling

nitrification may not be obvious. For example, rapid







31

nitrification may not precede conditions conducive to N03O-N

loss by denitrification or leaching. Therefore as discussed

by Hauck (1972), reports appear in the literature that

nitrification was inhibited by a chemical in the laboratory

but that this inhibition was not reflected in increased

yield or N uptake or that anomalous results were obtained

(Ashworth et al., 1980, 1984; Colliver, 1980; Maddux et al.,

1985; Meisinger et al., 1980; Touchton, 1981; Welch, 1979).

A substantial amount of literature exists reporting on

the effects of nitrapyrin and DCD on the crop yields, yield

components, and N contents of corn, wheat (Triticum aestivum

L.), rice (Oryza sativa L.), potato, pasture and fodder

grasses, spinach (Spinacia oleracea L.), and to a lesser

extent, on sorghum (Sorghum vulgare Pers.), rye (Secale

cereale L.), oat, barley (Hordeum vulgare L.), cotton

(Gossypium hirsutum L.), sugar beet (Beta vulgaris L.

(Mangels)), turf grasses, and various vegetables. A number

of greenhouse studies have indicated that DCD can increase

yield and/or N uptake by some crops. The effects of DCD on

crop yields in field studies have been mixed. Dicyandiamide

appears to have given better results in Europe than in the

USA. The majority of the work reported on nitrapyrin has

been conducted in the USA with lesser amounts in the

Commonwealth countries and the European community. The most

extensive research with DCD has been conducted in West









Germany, the USSR, and the USA, and to a lesser extent in

Japan, India, The Netherlands, France, England, and Poland.

In a number of field studies that were conducted for

two or more years, the effects of nitrification inhibitors

on crops varied considerably from year to year with seed

cotton (Reeves et al., 1988), winter barley (Guster, 1981),

and other crops, especially when the inhibitor was applied

in the summer (Guster, 1981). The effectiveness of inhibi-

tors such as DCD has also varied from one soil to another in

the same year (Nishihara, 1962).

In the USA, some researchers observed no corn yield

increase when nitrapyrin was applied (Touchton et al., 1979;

Boswell, 1977, Robertson et al., 1982). In other cases,

yield increases occurred only at low N rates (Touchton et

al., 1979a; McCormick et al., 1984, Walters and Malzer,

1990a), only with fall N application (Touchton et al.,

1979a; McCormick et al., 1984), or only when temperatures

were low and rainfall was excessive during the early growth

period (Touchton and Boswell, 1980). In some cases, nitra-

pyrin has resulted in decreased corn yields (Robertson et

al., 1982; Touchton et al., 1979a; Walters and Malzer,

1990a). Other workers have observed more favorable results

(Tsai et al., 1978; Malzer et al., 1979).

Summarizing the studies on nitrapyrin application to

corn in Kansas (Dept. of Agron., Kansas State U., 1976,

1977, 1978), those irrigated corn sites where yield









increases due to nitrapyrin occurred, were on sandy soil.

Smirnov (1978) observed that in the USSR, crop yield

increases resulting from DCD application, occurred most

often in the humid regions of the country and under irri-

gation. Of all the crops tested in the USSR, increased

yields due to DCD application were most common with cotton

and rice (Smirnov, 1978).

In the USA, researchers observed corn yield decreases

(Reddy, 1964b) or no increase when DCD was applied (Graetz

et al., 1981; Randal and Malzer, 1981). When DCD applica-

tion did not increase crop yields, this has been attributed

to the lack of substantial leaching rainfall (Graetz et al.,

1981; Touchton, 1981; Robertson et al., 1982; Mohamad,

1985).

Yield was not increased by nitrapyrin application to

tomato (Jaworski and Morton, 1967), sweet corn (Zea mavs

var. sacharata Bailey) (Rudert and Locascio, 1979a), radish

(Raphanus sativus L.) (Sander and Barker, 1978), kale

(Brassica oleracea L. var. acephala D.C. (Borecole)) (Spratt

and Gasser, 1970), cabbage (Brassica oleracea convar.

capitata (L.)) (Gysi and Stroll, 1980), Chinese cabbage

(Brassica pekinensis (Lour.) Rupr.) (Roorda van Eysinga and

Meijs, 1980), mustard (Brassica campestris L.) (Jung and

Dressel, 1978), endive (Cichorium endivia L.) (Roorda van

Eysinga and Meijs, 1981), and lettuce (Lactuca sativa L.)

(Moore, 1973). In other cases, nitrapyrin increased sweet









corn (Swezey and Turner, 1962) and tomato (Lycopersicon

esculentum Mill.) yields (Graetz et al., 1981). In one

study, nitrapyrin only increased lettuce yields when

irrigation was frequent (Welch et al., 1979).

In several studies, DCD has had no effect on the

yields of sweet corn (Mohamad, 1985), lettuce (Roorda van

Eysinga et al., 1980d), endive (Cichorium Endivia L.)

(Roorda van Eysinga and Meijs, 1981), Chinese cabbage

(Roorda van Eysinga and Meijs, 1980), or onion (Allium cepa

L.) (Rotini and Guerrucci, 1961).

As with other crops, potato yield responses to nitra-

pyrin have varied. In some cases nitrapyrin application has

decreased potato yields even though it was effective in

inhibiting nitrification (Hendrickson et al., 1978; Vendrell

et al., 1981). In other cases it has had no effect (Potter

et al., 1971; Roberts, 1979). In yet others, it has in-

creased yields (Roberts, 1979). The effects of nitrapyrin

on potato tuber quality factors have likewise been sometimes

negative (Hendrickson et al., 1978) and sometimes positive

(Potter et al., 1971). In some cases nitrapyrin has been

found to reduce incidence of potato scab (Streptomyces

scabies) (Huber and Watson, 1970; Potter et al., 1971).

Lack of potato yield response to nitrification inhibi-

tor application was observed by Schmitt (1938), Amberger

(1981b), and Munzert (1984). Potato yield increases, mostly

in Europe, were observed by Schmitt (1937), Rieder (1981),







35

Wolkowski et al. (1986), and Munzert (1984). In some cases,

these increases only occurred at low N rates (Smirnov et

al., 1976a).

In Germany, Munzert (1984) found that when potato

yields were increased by DCD application, more oversized

tubers were produced. Wolkowski et al. (1986) commented

that early research by others had shown that use of nitrifi-

cation inhibitors on potatoes with completely NH4-N

sources, while sometimes resulting in improved N efficiency,

also resulted in decreases in tuber grade and yield. They

attributed this to the potato's aversion to exclusive NH4-N

nutrition. In their own study, they found that DCD

increased yield and fertilizer N use efficiency but in some

cases depressed tuber grade.

Why nitrification inhibitors often do not increase

crop yields. Several studies have found that nitrification

inhibitors increased crop yields much more, or only, at the

lowest of several N rates (Huber et al., 1981; Liu et al.,

1984; Touchton, 1981; Bazilevich and Kabanova, 1973;

Krischenko et al., 1972; Makarov and Gerashchenko, 1976;

Frye et al., 1981; Malzer et al., 1979; McCormick et al.,

1984; Amberger, 1981b; Smirnov et al., 1972a, 1973, 1976a,

1976b). Ashworth (1986) considered the tendency of nitrifi-

cation inhibitors to increase immobilization of applied N as

a possible explanation for the inconsistent and sometimes









slightly negative effects of inhibitors on crop yield

(Ashworth et al., 1980, 1984; Meisinger et al., 1980).

McCormick et al. (1984) concluded that when nitrifica-

tion is inhibited but no yield responses occur, either

(1) the soil already contains high concentrations of plant

available N and the addition of N fertilizer does not

increase yield, (2) little or no N losses occur following

fertilizer application, or (3) N rates used are far in

excess of those required for maximum yield.

Blackmer (1986) presented a hypothesis that does much

to explain why crop yields are often not increased by nitri-

fication inhibitors, as well as split N fertilizer applica-

tions, urease inhibitors, and slow release N sources. He

proposed that the lack of response to inhibitors, etc.,

could be the result of several causes including (1) signif-

icant losses of N did not occur in the absence of the

treatment; (2) the treatment was not effective at preventing

losses; (3) N availability was not a factor limiting crop

growth, even after significant losses occurred; (4) unex-

pected effects of the treatments masked the intended

effects; and (5) the experimental method lacked sufficient

sensitivity to detect significant yield responses that

occurred.

Treatments conserving fertilizer N should be expected

to cause statistically significant increases in crop yields

only when a favorable interaction among the following









conditions is attained: (1) experimental methods provide a

high degree of precision, (2) the treatment saves a sub-

stantial portion of the fertilizer N applied, (3) fertilizer

N is applied at relatively low rates, and (4) studies are

conducted on soils having small amounts of soil derived

available N (Blackmer, 1986).

Effective nitrification inhibitors sometimes result in

excess NH4-N availability or N03'-N deficiency in NH4-N

sensitive or N03'-N requiring species. These two problems

can occur together and can be hard to separate. Imbalances

of NH4/N03- in the nutrition of the crop may induce or be

accentuated by K deficiency (Barker et al., 1967) and/or Cl

toxicity. Inhibition of nitrification may in such cases

lead to yield depressions with crops that are not able to

assimilate relatively high amounts of NH4-N (Dibb and

Welch, 1976; Kapusta and Varsa, 1972). In some cases an

increase in the NH4+/N03- ratio can cause a redistribution of

N inside the plant, sometimes resulting in changes in crop

protein content, but not necessarily in crop yield (El Wali

et al., 1979; Sommer and Rossig, 1978; Touchton et al.,

1979a; Warren et al., 1980).


Nitrogen Nutrition of Potato and Other Plants


General

The quantity and form of N available to the potato

crop have substantial effects on the internal physiology of









the plant, tuber initiation, vine growth, tuber yield and

specific gravity, proportion of cull tubers, leaf N concen-

trations, disease susceptibility, N leaching, and N fertil-

izer use efficiency. Nitrogen has been reported to play a

major role in the production and maintenance of optimum

plant canopy for continuous tuber bulking through long

growing seasons (Bremner and Taha, 1966; Bremner and Radley,

1966; Moorby, 1978). When N fertilizer rates are high to

excessive, the proportion of the total tuber crop made up by

culls, especially misshapen or oversized culls, has been

found to increase (Bundy et al., 1986; Chamberland and

Scott, 1968; Murphy and Goven, 1975; Terman et al., 1951;

Westermann and Kleinkopf, 1985).


Nitrogen Source

It has been recognized for quite some time (Maze,

1900; Muntz, 1893) that most plants may utilize either NH4*

or N03- salts as N sources. Different plant species, how-

ever, differ in their uptake and assimilation of NH4-N and

NO'3-N (Barker and Mills, 1980). The uptake and use of

NH4-N v N03--N by plants are related not only to the form of

N but also to the associated ion, the concentration of other

nutrients present, and plant factors such as age and nitrate

reductase activity (Hauck, 1972). Hewitt et al. (1976) and

Street and Sheat (1958) concluded that N03--N is usually

superior to NH4-N for plant growth, but the two sources may







39
vary with species, environmental conditions, soil conditions

such as pH, and other factors.

According to Nightingale (1948), NH4-N nutrition dif-

fers from NOa'-N nutrition in three main ways; (a) the

demand for 02 to the roots is increased with NH4+-N nutri-

tion, (b) competition for absorption of cations other than

NH4' may be detrimental to growth if the supply of other

cations is low, and (c) there may be indirect effects asso-

ciated with shifts in pH of the medium, such as the avail-

ability of Mo and P at low pH resulting from use of NH4-N,

and of heavy metals such as Mn and Fe at high pH values.

Some Solanaceous crops, e.g. tobacco (Nicotiana

tabaccum L.) (McCants et al., 1959), tomato (Morris and

Giddens, 1963; Pill and Lambeth, 1977; Wilcox et al., 1977),

and potato (Volk and Gammon, 1952, 1954; Hendrickson et al.,

1978) are known to grow better when a high NO3-/NH4 ratio is

available to them. The literature does not indicate, how-

ever, that this preference can be assumed for all crop

species in the Solanaceae family. Contradictory results

have been obtained for several crop species including

tobacco (Gous et al., 1971; Elliott, 1970; Rhoads, 1972),

and non-Solanaceae species such as ryegrass (Poletschny and

Sommer, 1976), and cotton (Reeves et al., 1988).

In field studies using 15NH4NO3 and NH415NO0, Roberts and

Cheng (1984) found that when supplied with both N forms to-

gether, potato preferentially took up NOa--N over NH4/-N.









Davis et al. (1986b) found that potato plant age did not

alter the response of plant growth to NH4+-N as opposed to

NOa-N.

The research that has examined the N form preference

of potato, shows that when NH4-N is abundant, and NO'3-N is

absent, the plant often does not do well. Under highly

controlled conditions, when NH4+ is the only N form avail-

able to the plant, growth is unthrifty and stunted (Chen and

Li, 1978; Davis et al., 1986b; Loescher, 1981; Polizotto et

al., 1975), with reduced tuber weights (Davis, 1983; Davis

et al., 1986b). Other reported effects of high NH4+-N

include nutritional imbalances such as a greater requirement

for K (Barker et al., 1967), reduced uptake of Ca and Mg,

increased uptake of P (Davis et al., 1986b; Polizotto et

al., 1975), reduced water uptake (Polizotto et al., 1975;

Quebedeaux and Ozbun, 1973), altered metabolism such as

decreased starch synthesis (Matsumoto et al., 1969), and

reduced tuber quality (Middleton et al., 1975; Painter and

Augustin, 1976; Hendrickson et al., 1978; Volk and Gammon,

1954).

Another symptom of excess NH4-N and insufficient

NO'-N nutrition, is small and weak looking plants, with

chlorotic, tightly-rolled leaves (Davis et al., 1986b).

This phenomenon is generally referred to as nutritional leaf

roll (Volk and Gammon, 1952; 1954). In Florida, nutritional

leaf roll is most severe on the very sandy and/or strongly







41

acidic soils, on relatively newly cleared lands, or reculti-

vated land that has been in meadow for several years (Volk

and Gammon, 1952; 1954). Volk and Gammon (1954) found that

on highly acid soils, nutritional leaf roll was severe where

the amount of soil N03--N available to the plant was low,

but it did not develop where N03--N was high, regardless of

NH4+-N concentrations in the soil. What they observed,

therefore, was not an NH4+-N toxicity, but a N03--N defi-

ciency.

Ammonium nitrate fertilizer resulted in higher potato

yields than did NH4,-N sources lacking in N03--N in studies

in Maine (Terman et al., 1951), north Florida (Volk and

Gammon, 1954), and Germany (Meisinger et al., 1978). In

other cases, NH4-N sources resulted in greater potato

yields than N03--N or mixed sources in Wisconsin (Bundy et

al., 1986) and eastern Washington (Davis et al., 1986a,

1986b). In such cases, the favorable response to NH4+-N, in

contrast to N03--N, is usually attributed to substantial

leaching of N03--N, as a result of heavy irrigation or rain-

fall (Davis et al., 1986a). In yet other field studies with

potato, no significant differences in yield were found

between NH4+-N and N03--N sources in Maine (Brown et al.,

1930), eastern Washington (Davis et al., 1986a), New Bruns-

wick (MacLean 1983), and Michigan (Vitosh, 1971).

The conflicting results of these efforts to evaluate N

fertilizer sources for potato production has in part been









due to the wide variety of cultural practices, soils, and

climatic conditions in these studies (Bundy et al., 1986;

Meisenger et al., 1978). Sanderson and White (1987) found

that cultivars showed differential performance in response

to N sources and rates, though Meisinger et al. (1978) and

Rowberry and Johnston (1980) found no such cultivar differ-

ence. This contradiction was attributed to differences in

the lengths of growing season from one region to another.

In some studies, interactions between N rate effects, and

differences in effects due to N source, have occurred

(Giroux, 1982; Sanderson and White, 1987), while in other

studies (Giroux, 1982; Rowberry and Johnston, 1980), no such

interaction occurred.

Slow release N fertilizers such as IBDU and sulfur

coated urea (SCU) have been compared to NH4NO3 as N sources

for potato in North Florida. The NH4NO3 fertilizer out-

yielded the slow release N sources by 25 to 27%. Appar-

ently, the slow release N sources did not release N

sufficiently to meet the crop's requirements, and rainfall

was light, limiting NO'3-N leaching losses (Elkashif et al.,

1983). Since these slow release N sources break down first

to NH4-N, releasing N03--N only after nitrification com-

mences, it is possible that these plants also suffered from

a N03--N deficiency.









Nitrogen Recovery

Leaching, denitrification, NH3 volatilization, and

other types of N losses result in N-use efficiency by crop

plants as low as 20% and rarely higher than 80% of added

plus native soil N (Amberger, 1981b; Blue and Graetz, 1977;

Nelson et al., 1977; Prasad et al., 1971; Smirnov, 1968;

1978; Volk, 1956). Other causes of incomplete recovery of N

from soil-plant systems include fertilizer-derived injury to

plant roots or foliage and plant preference for NH4'-N or

NO3--N. Meteorological conditions, management practices,

and soil characteristics affect all of these factors (Hauck

and Koshino, 1971). One factor that is often overlooked, is

the immobilization of fertilizer N by heterotrophic soil

microorganisms (Ashworth, 1986).

Asfary et al. (1983) found that apparent potato crop

recovery of fertilizer N ranged from 50 to 71% without

irrigation, and from 73 to 79% with irrigation. Bundy et

al. (1986) found that although N concentration in the tubers

was not affected by N source, the proportion of supplemental

N recovered in tubers differed significantly among N

sources. The order of increasing recoveries was (NH4)2SO4 >

urea = NH4NO3 > Ca(N03)2. They also found that the propor-

tion of added N recovered in the tubers decreased as applied

N rates were increased.









Conclusions

The chemistry of DCD and nitrapyrin are fairly well

understood. There is a reasonable understanding of the

mechanism by which they inhibit nitrification, though more

research should be done in this area. The longevity of

inhibition and concentration effects of the inhibitors are

quite variable, depending on environmental and soil condi-

tions. The loss mechanisms for nitrapyrin volatilizationn

and hydrolysis) are fairly well understood, while those of

DCD (leaching and decomposition) need further study. There

is a need for more long term (three or more years) research

on the effects of inhibitors on soil N transformations other

than nitrification, soil N leaching and water quality, and

total soil inorganic N.

Crop response to inhibitors in the greenhouse has been

fairly predictable but field trials are another matter.

More often than not, crop yields are not increased by nitri-

fication inhibitors. The conditions under which favorable

responses occur are subject to several interacting factors,

making favorable responses almost impossible to predict.

These interacting factors include N rate, leaching rainfall,

soil drainage, immobilization and mineralization of fertil-

izer N, temperature, and time of fertilizer application.

Some reasons for this have been proposed by Hauck (1972),

McCormick et al. (1984), Blackmer (1986), and Ashworth

(1986), Norman et al. (1989), and Walters and Malzer (1990a,







45

1990b). Chancy and Kamprath (1982) were the first research-

ers to clearly document that nitrification inhibitors inhib-

ited nitrification while not increasing total inorganic N

concentration in the soil. Other researchers reporting the

effects of nitrification inhibitors on total soil inorganic

N have done so indirectly or without statistical analysis.












CHAPTER 3
MATERIALS AND METHODS


Nitrogen and Amendments Applied to Potato

Experimental design. Potato (Solanum tuberosum L. cv.

Atlantic) was grown in 1983, 1984, and 1985 at the AREC at

Hastings in St. Johns County, and in 1983 and 1984, at the

Horticulture Unit, at Gainesville, in Alachua County. The

soil at the AREC Hastings (Table 3-1) was an Elzey fine sand

(sandy, siliceous, hyperthermic Arenic Ochraqualf) (USDA,

1983). The soil at the Horticulture Unit was a Millhopper

sand (loamy, siliceous, hyperthermic Grossarenic Paleudult)

in 1983, and a Plummer fine sand (loamy, siliceous, thermic

Grossarenic Paleaquult) in 1984 (USDA, 1985). Selected soil

characteristics at harvest are shown in Table 3-2.

The experiment was a randomized complete block fac-

torial design within each year and location, with four

blocks. The factors were N rate and amendment. In 1983,

there were two N rates, 134 and 202 kg N ha-1. In 1984 and

1985, a third N rate, 67 kg ha-' was added. In 1983 and

1984, ammonium nitrate was the N source. In 1985, N was

applied as 75% NH4+-N and 25% NO;--N, supplied from a mixture

of (NH4),SO, and NH4NO3. At each N rate, two rates of DCD,

5.6 and 11.2 kg ha-1, were compared to a control (no












Table 3-1. Classification of the soils used.


Location Soil Series Taxonomic Name


Gainesville 1983




Gainesville 1984




Hastings 1983




Hastings 1984




Hastings 1985




Live Oak 1985


Millhopper sand




Plummer fine sand




Elzey fine sand




Elzey fine sand




Elzey fine sand




Lakeland fine sand


Loamy, siliceous
hyperthermic
Grossarenic
Paleudult

Loamy, siliceous
hyperthermic
Grossarenic
Paleaquult

Sandy, siliceous
hyperthermic
Arenic
Ochraqualf

Sandy, siliceous
hyperthermic
Arenic
Ochraqualf

Sandy, siliceous
hyperthermic
Arenic
Ochraqualf

Thermic, coated
Typic
Quartzipsamment













Table 3-2. Selected soil properties at harvest.


Organic
pH CEC Sand Silt Clay C N


Location & Year

Gainesville 1983
Millhopper sand

Gainesville 1984
Plummer fine sand

Hastings 1983
Elzey fine sand

Hastings 1984
Elzey fine sand

Hastings 1985
Elzey fine sand


cmol
kg-1 dag kg--

Soils Planted to Potatot

4.9 8.11 84.5 11.4 4.4 2.1 0.129


5.6 3.07 90.7


4.5 3$ 94.1


5.2 2.70 94.7


4.8 3.36 94.1


4.9 4.4


4.2 1.7


0.9 4.4


4.3 1.6


0.8 0.045


1.2 0.068


1.0 0.056


1.0 0.062


Depth (cm)

0-15

15-30

30-61

61-91

91-122


5.3

5.2

4.8

4.6

4.5


4.04

3.30

2.06

1.04

0.90


92.3

91.9

92.2

92.7

92.9


Fallow Soil

6.0 1.7

5.6 2.5

5.4 2.4

4.8 2.5

4.5 2.6


tSampled to a depth of 30-33 cm.
*Estimated from data of USDA (1983).


1.2

1.0

0.6

0.3

0.2


0.055

0.036

0.021

0.010

0.008









amendment) and to two rates of nitrapyrin at 0.56 and 1.12

kg ha-1. These two nitrification inhibitors were compared

to a slow release N form, IBDU as one-third of the total N

applied. For statistical purposes, these six treatments (a

control, two DCD rates, two nitrapyrin rates, and one IBDU

rate) were considered six rates of the factor amendment.

Dicyandiamide (obtained from SKW Trostberg A.G.)

powder was ground to pass a 2 mm sieve and coated onto

NH4NO3 using vegetable oil as an adherent (German Patent

Specification No. 2 531 962, cited in Rieder and Michaud,

1980). Liquid nitrapyrin was poured onto the fertilizer

mixtures and mixed just prior to fertilizer application.

In all three years, 12 kg ha-1 P as triple super-

phosphate, 186 kg ha'1 K as K2SO,, 34 kg ha-1 Mg as MgO and 56

kg ha-1 of TM300 micronutrient mix were applied pre-plant.

The TM300 contained 2.40% B, 2.40% Cu, 14.4% Fe, 6.00% Mn,

0.06% Mo, and 5.60% Zn by weight. In 1985, K was applied in

two equal applications. Fertilizers were applied in two

bands 5 cm deep and 5 cm on each side of the potato seed

pieces.

At Hastings, four row plots were used. Each row was

1.02 x 4.5 m. At Gainesville, one row plots were used.

Each row was 1.02 x 12.2 m. Potato seed pieces were planted

in bedded rows 25 to 31 cm high, about 51 cm wide at the

base and 15 to 21 cm wide at the top. The seed pieces were







50

cut and coated with the fungicide cis-N-trichloromethylthio-

4-cyclohexene-1,2-dicarboximide captain ) and planted 20 cm

apart in the row.

Standard cultural practices for Northeast Florida

potato production were followed. The soil nematicide D-D (a

mixture of dichloropropene and dichloropropane) was applied

to the soil at a rate of 31 L ha-1 2 to 6 weeks prior to

planting. The herbicide 4-amino-6-(l,l-dimethylethyl)-3-

(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin), at 0.28

kg ha-' of active ingredient, was applied 11 to 20 days

after planting (dap) at Gainesville. At Hastings, a

combination of metribuzin and N-(l-ethylpropyl)-3,4-

dimethyl-2,6-dinitro-benzenamine (pendimethalin) was used.

Vine killer was not used prior to harvest at either

location. The insecticide 2-methyl-2(methylthio)-

propionaldehyde-O(methylcarbamoyl)oxime (aldicarb) was used

at planting at Hastings. All plots were cultivated per-

iodically to control weeds and reverse bed erosion. At

Gainesville, overhead sprinkler irrigation and surface ditch

drainage were used. At Hastings, subsoil, i.e., seepage or

water furrow irrigation-drainage was used.

Plant sampling. Tubers were harvested at maturity,

graded according to U.S. Grade Standards and weighed. The

grades were PK (pickouts) rotten and green tubers, G&NG

(grader and harvester damaged), B (3.8 to 4.8 cm), Al (4.8

to 6.35 cm), A2 (6.35 to 7.6 cm), and A3 (7.6 to 9.5 cm) in







51

diameter. Subsamples were taken of harvested grade A tubers

for the measurement of specific gravity, tuber dry weight,

and tuber N concentration.

Whole plant samples were taken to measure above ground

(shoot) phytomass and total shoot N concentration just

before harvest in 1983 and 1984. Whole leaf samples, i.e.,

blade plus petiole, were taken periodically during the

growing season in all three years (Table 3-3) and were

analyzed for total N concentration (Bremner, 1965). Leaf N

concentration at tuber initiation (43 to 55 dap) was mea-

sured in all five location-year combinations (growth stages

according to Kleinkopf et al., 1981). Leaf N concentration

at flowering (66 to 81 dap), which corresponds to the tuber

bulking stage, was measured at all locations and in all

years except in 1983 at Hastings. Leaf N concentration at

the tuber maturation stage was measured in samples taken

just before harvest (93 to 98 dap) in 1983 and 1984.

Soil sampling. Composite soil samples were taken to a

depth of 33 cm in each field in 1983 and 1984 for the pur-

pose of soil characterization. Soil was sampled with a 4.8

cm i.d. tube at two to four week intervals (Table 3-3) in

the beds down to the tillage pan at a depth of 33 cm for

determination of extractable soil inorganic N. Samples were

taken from the soil both adjacent to and away from the fer-

tilizer bands and all such samples from each plot were com-

posited. At Hastings, 12 cores were taken from each plot.










Timing of soil and leaf sampling in potato fields.


Days after Planting

Gainesville Hastings

Potato Growth Stage 1983 1984 1983 1984 1985


Soil Sampling

Near planting 5 6 -
Emergence 16 13 18 -
Vegetative 35 31 31 32 -
Tuber initiation 45 46 -
Tuber bulking 59 69 61 74 -
At harvest 98 108 103 -

Leaf Sampling

Early (tuber initiation) 43 48 54 55 51
Flowering (tuber bulking) 66 74 81 73
Late (tuber maturation) 93 94 95 98 -


Table 3-3.









At Gainesville, 9 cores were taken per plot. The samples

were placed in polyethylene bags, cooled during transport to

the lab, and frozen until extraction and analysis.

Analytical procedures. Leaf, shoot, and tuber N

concentrations were determined using a semimicro-Kjeldahl

block digestion and distillation procedure (Nelson and

Sommers, 1972). Tuber specific gravity (SG) was measured by

comparing tuber fresh weights in air and submerged in water.

The formula used was



(TUWA TRWA)
SG =
(TUWA TRWA) (TUWW TRWW)


where

TUWA = tuber weight in air
TRWA = tare weight in air
TUWW = tuber weight in water
TRWW = tare weight in water.



Tuber subsamples were cut, dried and ground for determin-

ation of dry weight and analyzed for N concentration.

Soil pH was determined using a 2:1 water:soil ratio.

Soil organic carbon was quantified using a modified

Walkley-Black procedure (Allison, 1965). Total soil N was

determined using a semimicro-Kjeldahl block digestion and

distillation procedure (Nelson and Sommers, 1972). Cation

exchange capacity was measured by Na'/NIH4 exchange using a

leaching technique with the salts being buffered to pH 7









(Schollenberger and Simon, 1945). Particle size distribu-

tion was determined by the pipette method (Day, 1965).

Soil inorganic N (ammonium and nitrate plus nitrite)

was extracted for one hour with 1 M KC1 containing 15 mg L-1

of phenyl mercuric acetate as a bactericide (Bremner, 1965).

This extract was distilled into boric acid indicator for

determination of NH4-N and N03--N concentrations. Soil DCD

concentrations were determined using a modification of

Vilsmeier's (1979, 1982) method. The naphthol reagent was

filtered through a 0.45 pm filter rather than being centri-

fuged. Because the naphthol reagent is unstable, a new

batch was made up each day. Because of this instability the

same blank solution could not be used for all the samples

and standards in a set. Therefore, a separate blank was

used for each group of six samples or standards. The blanks

used for the standards were 0.01 M CaCl2. The blanks used

for the soil extract samples were extracts of soil from

plots which received 0 kg ha-1 DCD and the same N rate as

the sampled soil.

Statistical procedures. Statistical analyses of

potato yield and other plant data, and soil inorganic N data

were carried out with Statistical Analysis System (SAS), a

computer system for data analysis (SAS Institute Inc.,

1982a, 1982b, 1983, 1985a, 1985b; Freund and Littel, 1981;

Helwig, 1983). Analysis of variance was carried out with

the PROC GLM procedure and orthogonal single degree of







55

freedom contrasts. The control treatment was considered the

lowest of three DCD treatment rates. Five orthogonal con-

trasts were used for the inhibitor and IBDU treatments.

These were: DCD rate linear, DCD rate quadratic, nitrapyrin

rate (0.56 v 1.12 kg ha-1 nitrapyrin), DCD v nitrapyrin (5.6

and 11.2 kg ha-1 DCD v 0.56 and 1.12 kg ha-1 nitrapyrin), and

IBDU v inhibitors. In 1984 and 1985, the effects of the

three N rates were analyzed with linear and quadratic con-

trasts. Where the effects of N rate and amendment inter-

acted, the data were subsetted so that the effects of each

factor (N rate and amendment) could be analyzed at each rate

of the other factor. As a result of crop damage, there were

two missing cells at Gainesville, in 1983. Thus the plant

response means for this experiment are least square means

computed by the LSMEANS statement in SAS.


Urea and DCD Applied to a Fallow Quartzipsamment

Experimental design. A study was conducted at the

AREC at Live Oak in Suwannee County on a Lakeland fine sand

(thermic, coated Typic Quartzipsamment) to evaluate the

effectiveness of DCD as a nitrification inhibitor and to

determine the effects of DCD application on concentrations

of DCD, NH4-N, and NO3--N in the soil profile over time.

Selected soil properties are shown in Table 3-2. A ran-

domized complete block design with four blocks was used.

Dicyandiamide was applied at rates of 0, 20, 40, and 60 kg

ha-. Nitrogen as urea was broadcast and incorporated at









the rate of 200 kg N ha-1 to all plots on March 29, 1985.

The urea and DCD were thoroughly mixed together by spraying

the urea with 0.5% water and 0.5% vegetable oil with an air

sprayer, adding the DCD and mixing until uniform. The plots

were 3.65 x 7.5 m. The plots remained fallow during the

study and were kept free of weeds by cultivation.

Soil sampling and analysis. The fallow soil was

sampled at approximately two week intervals starting 14 days

after fertilizer application. Four cores were taken from

each plot and all four cores for each depth were mixed

together on each sampling date. The depths sampled were 0

to 15 cm, 15 to 30 cm, 30 to 61 cm, 61 to 91 cm, and 91 to

122 cm. The soil samples were analyzed for inorganic NH4'-N

and NO3--N concentrations by KC1 extraction and distillation

(Bremner, 1965). Soil DCD concentrations were measured by

the modification of the method of Vilsmeier (1979, 1982)

mentioned above.

Statistical procedures. Analysis of variance was

carried out with the PROC GLM procedure and orthogonal

single degree of freedom contrasts (DCD rate linear,

quadratic and cubic).













CHAPTER 4
TUBER YIELD, PLANT N CONTENT, AND BIOMASS


Tuber Yield

N rate effects. Marketable (grades A and B) and total

tuber yield increased with increases in N rate in four of

five year-location combinations. In 1983 at Hastings,

marketable tuber yield increased from 18.6 to 21.7 t ha-1

with an increase in N rate from 134 to 202 kg ha-1 (Table

4-1). In 1983 at Gainesville, marketable yield was not

influenced by N rate. In 1984, an increase in N rate from

67 to 134 kg ha-1 resulted in an increase in marketable

tuber yield from 24.8 to 29.0 t ha-1 at Gainesville, and

from 16.7 to 21.1 t ha-1 at Hastings. A further increase in

N rate from 134 to 202 kg ha-1, did not influence marketable

tuber yield at either location in 1984. In 1985 at

Hastings, marketable tuber yield increased from 29.9 to 33.8

t ha'1 with an increase in N rate from 67 to 134 kg ha-1. A

further increase in N rate to 202 kg ha-1 had no effect.

Nitrogen rate and all other treatment effects on total tuber

yield (Table 4-2) were similar to affects on marketable

tuber yield in all three years and at both locations.

Amendment effects. In 1983 at Hastings, DCD rate

interacted with N rate effects on marketable tuber yield










Table 4-1.


Effects of N rate and amendment on marketable
tuber yield.


Gainesville

Treatment 1983 1984


t/ha

N Rate (kc/ha)
67 -t 24.8
134 26.7(23)* 29.0
202 27.4(22) 29.0
NS L**
Qx

Amendment
Control 28.8(8) 29.7
5.6 kg/ha DCD 25.7(8) 28.0
11.2 kg/ha DCD 26.5(7) 28.9
0.56 kg/ha Ntys 26.7(8) 26.0
1.12 kg/ha Nty 26.4(8) 25.7
IBDU (1/3 of N) 28.5(6) 27.3

Significance
DCD Linear NS NS
DCD Quadratic NS NS
Nty Rate NS NS
DCD v Nty NS *
IBDU v Ih' NS NS

Interactions NS Nty R X NR L*


Nonsignificant (NS) or significant at the 0.10 (x), 0.05
(*), 0.01 (**), or 0.001 (***) probability levels,
respectively.

tRate not included in 1983.
*Gainesville 1983 means are least square means. Number of
observations are in parentheses.
SNty = nitrapyrin.
*Ih = inhibitors.












Table 4-1--Extended.


Hastings

1983 1984 1985


/4- I


18.6
21.7
L***


Li


ia.


16.7
21.1
23.7
L***
Qx


20.6
21.5
21.2
19.3
19.7
20.9


18.3
21.0
21.4
18.0
21.5
20.7


29.9
33.8
34.5
L***
Q*


33.3
33.4
33.4
31.2
32.1
32.9


IBDU v Ih X NR L *


r


DCD Q X NR **










Table 4-2.


Effects of N rate and amendment on total tuber
yield.


Gainesville

Treatment 1983 1984


t/ha

N Rate (kq/hal
67 -t 25.7
134 27.9(23)* 30.2
202 29.0(22) 30.1
NS L**
Q*

Amendment
Control 29.8(8) 30.6
5.6 kg/ha DCD 27.4(8) 29.1
11.2 kg/ha DCD 27.7(7) 29.8
0.56 kg/ha Ntys 28.1(8) 27.3
1.12 kg/ha Nty 27.7(8) 26.8
IBDU (1/3 of N) 30.1(6) 28.5

Significance
DCD Linear NS NS
DCD Quadratic NS NS
Nty Rate NS NS
DCD v Nty NS x
IBDU v Ih# NS NS

Interactions NS Nty R X NR L *


Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*),
0.01 (**), or 0.001 (***) probability levels, respectively.

*Rate not included in 1983.
*Gainesville 1983 means are least square means. Number of
observations are in parentheses.
SNty = nitrapyrin.
#Ih = inhibitors.











Table 4-2--Extended.


Hastings

1983 1984 1985


LIJ


18.7
21.8
L**


zIa


17.9
22.6
25.5
L***
Qx


21.9
23.0
22.7
20.8
21.2
22.3


18.3
21.1
21.5
18.1
21.6
20.8


32.8
36.9
36.8
L***
Q**


35.8
36.1
36.2
34.4
34.8
35.7


**


IBDU v Ih X NR L *


DCD Q X NR **







62

(Table 4-3). With 134 kg ha-1 N, marketable yield increased

from 14.6 to 21.7 t ha-1 with an increase in DCD rate from 0

to 5.6 kg ha'-. A further increase in DCD to 11.2 kg ha'I

had no effect on marketable yield. With 202 kg ha'- N, DCD

rate had no effect on marketable yield. Dicyandiamide rate

had no effect on marketable or total tuber yield in 1983 or

1984 at Gainesville, or in 1984 or 1985 at Hastings.

In 1983 at Hastings, marketable tuber yield increased

from 18.0 to 21.5 t ha-1 with an increase in nitrapyrin rate

from 0.56 to 1.12 kg ha'1 (Table 4-1). In 1984 at Gaines-

ville, nitrapyrin rate interacted with N rate effects on

tuber yield (Table 4-4). With 67 kg ha-1 N, marketable

yield increased from 21.3 to 26.6 t ha-1 with an increase in

nitrapyrin rate from 0.56 to 1.12 kg ha-1. With 134 and 202

kg ha-1 N, tuber yield was not affected by nitrapyrin rate.

In 1983 at Gainesville and Hastings, tuber yield means

were similar with DCD and nitrapyrin (Table 4-1). In 1984

at both locations, and in 1985 at Hastings, tuber yield

means were higher with DCD than with nitrapyrin. In 1984 at

Gainesville, marketable yield means were 28.4 t ha-1 with

DCD and 25.8 t ha-1 with nitrapyrin. In 1984 at Hastings,

marketable yield means were 21.4 t ha-1 with DCD and 19.5 t

ha-1 with nitrapyrin. In 1985 at Hastings, marketable yield

means were 33.4 t ha-' with DCD and 31.6 t ha-1 with

nitrapyrin.










Table 4-3.


Interaction (DCD Q X NR **) of DCD and N rate
effects on tuber yield (Hastings, 1983).


DCD Rate (kq/ha)

N Rate 0 5.6 11.2


kg/ha Marketable Yield (t/ha)

134 14.6 21.7 19.2 L**Q**
202 21.9 20.2 23.5 NS
NS x

Total Yield (t/ha)

134 14.7 21.8 19.3 L**Q**
202 21.9 20.3 23.6 NS
NS x



Nonsignificant (NS) or significant at the 0.1 (x), 0.05
(*), or 0.01 (**) probability levels, respectively.










Table 4-4.


Interaction (Nty R X NR L *) of nitrapyrin and
N rate effects on tuber yield (Gainesville,
1984).


Nitrapyrin Rate (kg/ha)

N Rate 0.56 1.12


kg/ha Marketable Yield (t/ha)

67 21.3 26.6 x
134 29.0 26.2 NS
202 27.7 24.4 NS
L*Q* NS

Total Yield (t/ha)

67 22.0 27.6 x
134 30.1 27.0 NS
202 29.6 25.7 NS
L*Qx NS


Nonsignificant (NS) or significant at the 0.1 (x), or 0.05
(*)probability levels, respectively.







65

Marketable and total yields in 1984 at Hastings, were

influenced by an interaction between the IBDU v inhibitor

contrast, and N rate (Table 4-5). With 67 kg ha-1 N, mar-

ketable yield means were higher with IBDU (18.3 t ha-1) than

with inhibitors (16.3 t ha-1). With 134 and 202 kg ha-1 N,

tuber yield means were similar with IBDU and inhibitors.


Proportion of Marketable Tuber Yield That
Was Grade A

N rate effects. The proportion of marketable yield

that was grade A (Table 4-6), increased with increasing N

rate in all year-location combinations except in 1983 at

Gainesville. In 1984 at Gainesville, the proportion of

marketable yield that was grade A increased from 80.4 to

84.2% with an increase in N rate from 67 to 134 kg ha-1. A

further increase in N to 202 kg ha-1 had no effect.

In 1983 at Hastings, the proportion of marketable

yield that was grade A increased from 74.6 to 77.6% with an

increase in N rate from 67 to 134 kg ha-1. In 1984 at

Hastings, the proportion of marketable yield that was grade

A increased from 84.6 to 88.5% with an increase in N rate

from 67 to 134 kg ha-1. A further increase in N to 202 kg

ha-1 had no affect. In 1985 at Hastings, N and DCD rate

interacted in their effects on the proportion of marketable

yield that was grade A (Table 4-7). With 0 DCD, N rate had

no effect. With 5.6 and 11.2 kg ha'1 DCD, the proportion of

marketable yield that was grade A increased with an increase











Table 4-5.


Interaction (IBDU v Ih X NR L *) of IBDU v
inhibitors, and N rate effects on tuber yield
(Hastings, 1984).


N Rate IBDU Inhibitors


kg/ha Marketable Yield (t/ha)

67 18.3 16.3 x
134 21.7 20.9 NS
202 22.9 24.1 NS
L*** L***

Total Yield (t/ha)

67 19.5 17.5 *
134 23.0 22.5 NS
202 24.4 25.9 NS
L*** L***


Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*),
or 0.001 (***) probability levels, respectively.









03




48



0






4,
a)

(1



4-4
0

0
0




0










a)






0
(A


O






4-4


4(-
441

C i7


S(4 ) 1 4



'ognr c h





D mCD 0






0 k0 Go
I *





















4- 00 r-4
I *
(c( 'l
0101z;


.1>M--
(U U



a) s-I Ol 0.X & r-4
4) 10. .o .
CAo r-i cD r-i


C 4 t t0 r

rtU Or H -


.omo
f y '0


U) U) ul En M
0 a3z 0 0
aES a


M rm tv) r. co co

r- r- r1 r- r r-


















00 O0 0%O 00 0%
C4 r-.4 C4 r- C4
0%o a% c( (1 cIS
0 m m C-101 0
mammes OIQ


U) 03 03 0C
z xzzz


*ro

H (
1


0 (0 4-1 Z
- (a >
a) aO 0 >

Ql Ql >1 Q Q
U U 4P U M
M QZQ
QQZQH c-


4
0-I





QH
u
Q 3


a 2 2a z a







o a* a ao a


0
o
o








-4
0
C*
0
.'



in


o


0



0

a)
4t.
o
o



















0 4
-)





*4










0.0
c *













.,4








ON
N( a




0 m
z 0n
Z'-
tnSa

fii-<





*

zr CI


(o
a)







a

fn.4
(00



to










E)
4J









0




to
4(U
0
'-4 (0












0 >


1) c


at .


a) ..

c *




'a H










Table 4-7.


Interaction (DCD L X NR L *) of DCD and N rate
effects on the proportion of marketable yield
that was grade A (Hastings, 1985).


DCD Rate (kg/ha)
N Rate 0 5.6 11.2


kg/ha %

67 90.5 88.4 88.6 NS
134 92.9 92.1 92.5 NS
202 92.7 93.4 94.7 NS
NS L** L***

Nonsignificant (NS) or significant at the 0.05 (*),
0.01 (**), or 0.001 (***) probability levels, respectively.


Table 4-8. Interaction (IBDU v Ih X NR L *) of IBDU v
inhibitors, and N rate effects on the proportion
of marketable yield that was grade A (Hastings,
1985).


N Rate IBDU Inhibitors


kg/ha %

67 91.3 88.6 *
134 92.6 91.9 NS
202 92.5 93.3 NS
NS L**
Qx


Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*),
or 0.01 (**) probability levels, respectively.







69
in N rate from 67 to 202 kg ha-1. With 5.6 kg ha-1 DCD, the

proportion of marketable yield that was grade A increased

from 88.4 to 93.4% with an increase in N rate. With 11.2 kg

ha-1 DCD, the proportion of marketable yield that was grade

A increased from 88.6 to 94.7% with an increase in N rate.

Amendment effects. In 1983 at Hastings, the

proportion of marketable yield that was grade A increased

from 73.3 to 79.3% with an increase in DCD rate from 0 to

11.2 kg ha-1. The proportion of marketable yield that was

grade A increased from 73.7 to 78.8% with an increase in

nitrapyrin rate from 0.56 to 1.12 kg ha-1 in 1983 at

Hastings.

In 1984 at Gainesville, the proportion of marketable

yield that was grade A was higher with DCD (83.9%) than with

nitrapyrin (81.4%) (Table 4-6). In 1984 at Hastings, the

proportion of marketable yield that was grade A was higher

with IBDU treatments (88.8%) than with inhibitors (87.1%).

In 1985 at Hastings, the IBDU v inhibitor contrast inter-

acted with N rate (Table 4-8). With 67 kg ha-1 N, the

proportion of marketable yield that was grade A was higher

with IBDU (91.3%) than with inhibitors (88.6%). With 134

and 202 kg ha-1 N, the proportion of marketable yield that

was grade A was similar with IBDU and inhibitors.









Proportion of Total Tuber Yield That
Was Marketable

N rate effects. In 1985 at Hastings, the proportion

of total yield that was marketable (Table 4-9), was similar

with N rates of 67 and 134 kg ha-1 but was increased from

91.5 to 93.6% with an increase in N rate from 134 to 202 kg

ha- .

Amendment effects. In 1984 at Gainesville, the DCD v

nitrapyrin contrast interacted with N rate (Table 4-10).

With 202 kg ha-1 N, the proportion of total yield that was

marketable was higher with DCD (97.0%) than with nitrapyrin

(93.9%). With 67 and 134 kg ha-1 N, the proportion of total

yield that was marketable was similar with the two inhib-

itors. In 1983 at Hastings, IBDU v inhibitors interacted

with N rate (Table 4-11). With 202 kg ha-1 N, the propor-

tion of total yield that was marketable was higher with

inhibitors (99.7%) than with IBDU (99.1%). With 134 kg ha-1

N, the proportion of total yield that was marketable was

similar with the two types of amendments.


Tuber Specific Gravity

N rate effects. Tuber specific gravity increased from

1.0841 to 1.0854 as N rate increased from 134 to 202 kg ha-1

in 1983 at Hastings (Table 4-12). In 1984 at Hastings,

tuber specific gravity increased from 1.0769 to 1.0796 as N

rate increased from 67 to 202 kg ha-1. In 1985 at Hastings,

tuber specific gravity increased from 1.0775 to 1.0791 with














io







*a
4J
(0

4J

4-4



0


0
o








0
-I1


0)






4cJ
0)
0













.P
0)









0





440
0 -I
0E





a
4- (












4-
4-1 1


r-q Lrlin w x
,; 4 4



crr m C4



mmmc/u
CA cn W















a r coa


















)n On co













M C
C4 C4

I *
















r- mO CD
!C< t
!DluV


14 01 01 01 01 01




N uo- W r-r

all (A (i t M M











































00 0Co %O CO cn










uc a a
r ,-- pt--







'0 4 1 ( C4 0 v-

0 Ln- cD io ^

UE r ow-4
of U o-1


u
*4
Na P

:a CO 4 HZ
' Nd <

d 0 td >3
0) 0) QH

UU4JU
uu +J u
Q Q %QH 1


EO U) CO O CMW
MU)ul M)M
z z z z z








tntlmvl







ZZZmmZ









V3VJVIg














Vll1Ca3V


0
0
o
O

0







o
*
0























41
O
O
C

























4
*4
















o
0
O
r-4

*

a)
4>






CO
-,' 0)
.-H





ON
C w
'a








0 d








0 H


-4













0

O
4-)






























c,
oa
O










0)


























0 4 4
I .
0)












cn
4)



.- U)

*-I1 0)


Z *.-IU)











o1*
(0P~










Table 4-10.


Interaction (DCD v nitrapyrin X NR Q *) of DCD
v nitrapyrin, and N rate effects on the propor-
tion of total yield that was marketable
(Gainesville, 1984).


N Rate DCD Nitrapyrin


kg/ha %

67 96.8 95.4 NS
134 94.8 96.4 NS
202 97.0 93.9 *
Q* NS


Nonsignificant (NS) or significant at the 0.05 (*)
probability level.






Table 4-11. Interaction (IBDU v Ih X NR *) of IBDU v inhib-
itors, and N rate effects on the proportion of
total yield that was marketable (Hastings,
1983).


N Rate IBDU Inhibitors


kg/ha %_

134 99.8 99.6 NS

202 99.1 99.7 *

NS NS


Nonsignificant (NS) or significant at the 0.05 (*)
probability level.












000
r- ON O0




N- t -1




000 -ON

















00
I *





C41 W-4














oo0
.0
-4 00





+
m (




9 rn
+*00
I *. U2
v-i r4


tD O(A CN N r- OCl
00 r- w OD C7 00


.-0 .M r-4 r-I v-I o-t






0000000






















CA n Oo uI W C01






0O00000











r4 00 C-4 C) CD
000000
V -4
000000












coooooo





w %000








u r-l H
C C lC Q
k rocuH
ErO## r
O0n0-lorQ
#**** n


a a a *









ZZaa a







-Ic z z
U2U2Ef C


a a a 0













mm mm a
COW CO CO


r a
H1 0

0)a $ >4C H

*'-4 0 M 0i
AOl w0 > $4
Q 0 >40 Q 4J
U U 4J U M 3
S0
004U0IS C
Q3ZQn 8i


0
0
O







.)
0
O0









a >



x z
O >
Q Q
U U
QmQ


.Ic

-l

0
0
0

0
0






















C*





.4-
4-)
r-4




0










r.
0


IA








0
*

















ai







M-4
0





r-4












* -,4,


0.0


a
0p
0a)

OW
c

Zr4

4JQ)


CO 4


Ocn
n(ok


0t
C
mi







to
*0










4 (
. 00)




o >4

04 '
w-I 0 H
-Q) .4 .Q




(go .a M


r-I C4






74

an increase in N rate from 67 to 134 kg ha-', then decreased

to 1.0784 with a further increase in N rate to 202 kg ha-'.

Tuber specific gravity was not influenced by N rate in 1983

or 1984 at Gainesville.

Amendment effects. In 1983 at Hastings, DCD rate

interacted with N rate effects on tuber specific gravity

(Table 4-13). With 202 kg ha-' N, tuber specific gravity

decreased from 1.0862 to 1.0818 with an increase in DCD rate

from 0 to 5.6 kg ha-1. With a further increase in DCD to

11.2 kg ha-1, tuber specific gravity increased to 1.0856.

With 134 kg ha-1 N, DCD rate had no effect on tuber specific

gravity. In 1985 at Hastings, tuber specific gravity

decreased from 1.0786 to 1.0762 with an increase in DCD rate

from 0 to 11.2 kg ha-1 (Table 4-12).

In 1983 at Gainesville, tuber specific gravity

decreased from 1.0932 to 1.0880 with an increase in

nitrapyrin rate from 0.56 to 1.12 kg ha-1 (Table 4-12).

Tuber specific gravity was not influenced by nitrapyrin rate

in 1983, 1984, or 1985 at Hastings, or in 1984 at Gaines-

ville.

In 1984 at Gainesville and Hastings, and in 1985 at

Hastings, tuber specific gravity was higher with the nitra-

pyrin treatments than with the DCD treatments (Table 4-12).

In 1984 at Gainesville, tuber specific gravity was 1.0760

with nitrapyrin and 1.0730 with DCD. In 1984 at Hastings,

tuber specific gravity was 1.0792 with nitrapyrin and 1.0777











Table 4-13. Interaction (DCD Q X NR *) of DCD and N rate
effects on tuber specific gravity (Hastings,
1983).


DCD Rate (kg/ha)

N Rate 0 5.6 11.2


kg/ha

134 1.0828 1.0845 1.0846 NS

202 1.0862 1.0818 1.0856 Q*

x NS NS


Nonsignificant (NS) or significant at the 0.1 (x),
(*) probability levels, respectively.


or 0.05


Table 4-14. Interaction (DCD v nitrapyrin X NR *) of DCD v
nitrapyrin, and N rate effects on tuber
specific gravity (Hastings, 1983).


N Rate DCD Nitrapyrin


kg/ha

134 1.0845 1.0841 NS
202 1.0837 1.0870 *
NS **


Nonsignificant (NS) or significant at the 0.05 (*), or 0.01
(**) probability levels, respectively.









with DCD. In 1985 at Hastings, tuber specific gravity was

1.0792 with nitrapyrin and 1.0770 with DCD.

In 1983 at Hastings, the DCD v nitrapyrin contrast

interacted with the N rate effect on tuber specific gravity

(Table 4-14). With 202 kg ha-1 N, tuber specific gravity

was higher with nitrapyrin (1.0870) than with DCD (1.0837).

With 134 kg ha-' N, tuber specific gravity was similar with

the two inhibitors.


Tuber N Concentration

N rate effects. Tuber N concentration means increased

with increases in N rate in all five year-location combin-

ations (Table 4-15). In 1983 at both locations, tuber N

concentration increased from 0.98% with 134 kg ha'1 N, to

1.07-1.08% with 202 kg ha'1 N. In 1984, with an increase in

N rate from 67 to 202 kg ha-1, tuber N concentration in-

creased from 1.23 to 1.62% at Gainesville, and from 1.12 to

1.33% at Hastings. In 1985 at Hastings, tuber N concentra-

tion was not measured.

Amendment effects. In 1983 at Hastings, DCD rate

interacted with N rate effects on tuber N concentration

(Table 4-16). With 134 kg ha-1 N, tuber N concentration

increased from 0.92 to 1.02% with an increase in DCD rate

from 0 to 5.6 kg ha-1 and did not increase further with an

increase in DCD to 11.2 kg ha-1. With 202 kg ha-1 N, tuber N

concentration was not affected by an increase in DCD rate
























-%4V-4-C4 C4-"C4-













O( W00 o- 0 N

0 -4 -4 0 -4 4-
mOoomo
*


O 0 m 000n i-n




oo r r oo co n
* o o o o -
o 1 ;W- i -*


QQ 4
0 (a0 0





rU -4M H -

So tn v-4 o r-i
C-) cj -I


CW z W z
22222Z;


*


x >4
OPS

QM 4
z *t zl Uz Q
r Z *n 2 2Q


x















) (D CO) CD


0
.9.
41
$4 (

() 4 ..
>r 1 -

00u >

QQ>QQ ~


,l,-i rl














CO !- 4
O, 0 -H
I .
0 >- i-l


,-4
0
O
0
O
C4


0





,-4




*C



o



A;




,-4

0

()

4.

. I
C





S-4
C*)

-'4 --

O4 >
r. *1
Cp
e4 ()

$.4 (
0$.


mH m
CO



drl
to





u >4


- -r4
Ol (A

0 0
0 1
Z 4


.,4

a)




0
.4




ul
o
0

0
4











a

V.e
CA
4













to
-4

(U)

( i


ea)
i-o




. a)
rl ( *D






1o e
r-.9.4


+1*




4- O 0 4'
CI .4
o. A




Full Text
xml version 1.0 encoding UTF-8
REPORT xmlns http:www.fcla.edudlsmddaitss xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.fcla.edudlsmddaitssdaitssReport.xsd
INGEST IEID E1GZXPAON_TMA4JP INGEST_TIME 2017-07-13T22:01:44Z PACKAGE AA00003752_00001
AGREEMENT_INFO ACCOUNT UF PROJECT UFDC
FILES



PAGE 1

NITRIFICATION INHIBITOR EFFECTS ON POTATO YIELDS AND SOIL INORGANIC NITROGEN By HARRIS WARTHMAN MARTIN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1990 l.Wfil'RSJ H

PAGE 2

I dedicate this work to my children Rachel and Stan, who have often played quietly so that daddy could work on his dissertation.

PAGE 3

ACKNOWLEDGMENTS I want to express my appreciation and gratitude to Dr. D.A. Graetz, chairman of my committee, for his guidance, understanding and friendship, all of which were necessary for this research. I also thank the members of my committee, Drs. J.G. Fiskell, D.R. Hensel, S.J. Locascio, D.L. Myhre, and J.B. Sartain, for their patience and tolerance. I extend my appreciation to other faculty members for their assistance. These include Drs. V. Carlisle, M.A. Collins, N. Commerford, J.G. Dorsey, D.H. Hubbell, B.L. McNeal, F. Martin, and T.L. Yuan. Without the help of all the following people, this research could not have been completed. I am greatly in debt to all of them. They are, in alphabetical order, Lisa Ames, Tracy Beaudreau, Candy Cantlin, Jose Escameil, Victoria Feldman, Peter Krottje, Dawn Lucas, Gail Luparello, Kevin Moorehead, Abdul Rahim Mohamad, Ruth Neal, John Purcel, Nathan Rembert, Ed Rope, Jorge Santos, B.K. Singh, Irma L. Smith, Lyda Toy Stock, and the secretaries in the Soil Science Department, the staff of the NERDC, IFAS Computer Network, and CIRCA, the staff and field hands at iii

PAGE 4

the IFAS farms at the Gainesville Horticulture Unit, and the Hastings and Live Oak ARECs. I would like to acknowledge the financial assistance of the State of Florida and the SKW Trostberg company of West Germany. i v

PAGE 5

TABLE OF CONTENTS Page ACKNOWLEDGMENTS. LIST OF TABLES .. LIST OF FIGURES .. ABSTRACT iii . . . . vii xvii . xxii CHAPTERS 1. 2. 3. INTRODUCTION REVIEW OF LITERATURE 1 3 Nitrification Inhibitors 3 Crop Response to Inhibitors ........ 30 Nitrogen Nutrition of Potato and Other Plants ........... 37 Conclusions. . . ......... 44 MATERIALS AND METHODS . Nitrogen and Amendments Applied to Potato . . . . . . Urea and DCD Applied to a Fallow Quartzipsamment ....... 46 46 55 4. TUBER YIELD, PLANT N CONTENT, AND BIOMASS ... 57 Tuber Yield ............... 57 Proportion of Marketable Tuber Yield That Was Grade A ..... ..... 65 Proportion of Total Tuber Yield That Was Marketable ............ 70 Tuber Specific Gravity. . . .. 70 Tuber N Concentration. . . ... 76 Plant Shoot Biomass at Harvest .... 81 Total Biomass at Harvest. . . .. 81 Plant Shoot N Concentration at Harvest .. 87 N Uptake by Plant Shoots at Harvest. 90 N Uptake by Tubers . . . . . 94 V

PAGE 6

Total N Uptake by Plant Shoots and Tubers . . . . . . . . 9 9 Leaf N Concentration at Tuber Initiation. 102 Leaf N Concentration at Flowering ..... 108 Leaf N Concentration at Tuber Maturation. 115 5. EXTRACTABLE SOIL N AND DCD SOILS PLANTED 6. 7. 8. TO POTATO. . . . . . . 121 Soil Inorganic N. Extractable Soil DCD Rainfall .... . . . . . 121 . . . . . 14 9 . . . . . 15 6 UREA AND DCD APPLIED TO A FALLOW QUARTZIPSAMMENT ...... 160 Soil NH 4 -N . . . . . . . Soil NO 3 -N . . . . . . . 160 170 179 186 . . 19 3 Total Soil Inorganic N ........ N0 3 --N/ (N0 3 --N + NH/-N) Ratio Soil DCD . . . . . . DISCUSSION . 2 0 3 Plant Yield/N Content and Soil N and DCD. 203 Urea and DCD Applied to a Fallow Quartzipsamment. ........ 233 CONCLUSIONS ....... . 241 Plant Yield/N Content and Soil N and DCD. 241 Urea and DCD Applied to a Fallow Quartzipsamment ...... General Conclusions ...... Recommendations For Future Research. 243 . 244 245 APPENDICES A. B. c. SOIL CHARACTERIZATION ....... SAMPLE ANALYSIS OF VARIANCE TABLE .. INORGANIC N CONCENTRATIONS IN SOILS PLANTED TO POTATO AS AFFECTED BY SELECTED 249 . 251 TREATMENTS .............. 252 D. ANALYSIS OF VARIANCE OF INORGANIC NIN SOILS PLANTED TO POTATO ..... . 267 . 280 REFERENCES BIOGRAPHICAL SKETCH .. . . . . 3 0 7 vi

PAGE 7

Table 3-1. 3-2. 3-3. 4-1. 4-2. 4-3. 4-4. 4-5. 4-6. 4-7. 4-8. 4-9. LIST OF TABLES Classification of the soils used .. Selected soil properties at harvest. Timing of soil and leaf sampling in potato fields ....... Effects of N rate and amendment on marketable tuber yield . . . . . Effects of N rate and amendment on total tuber yield. . . . . Interaction (DCD Q X NR **) of DCD and N rate effects on tuber yield (Hastings, 1983) ............... Interaction (Nty RX NR L *) of nitra pyrin and N rate effects on tuber yield (Gainesville, 1984) .... Interaction (IBDU V Ih X NR L *) of IBDU V inhibitors, and N rate effects on tuber yield (Hastings, 1984) ...... Effects of N rate and amendment on the proportion of marketable yield that was grade A. . . .. Interaction (DCD L X NR L *) of DCD and N rate effects on the proportion of marketable yield that was grade A . (Hastings, 1985) ........... Interaction (IBDU V Ih X NR L *) of IBDU V inhibitors, and N rate effects on the proportion of marketable yield that was grade A (Hastings, 1985) ..... Effects of N rate and amendment on the proportion of total yield that was marketable ............ vii Page 47 48 52 58 60 63 64 66 67 68 68 71

PAGE 8

4-10. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on the proportion of total yield that was marketable (Gainesville, 1984) . 72 4-11. Interaction (IBDU V Ih X NR *) of inhibitors, and N rate effects proportion of total yield that marketable (Hastings, 1983) .. IBDU v on the was 4-12. Effects of N rate and amendment on tuber 72 specific gravity . . . . 73 4-13. Interaction (DCD Q X NR *) of DCD and N rate effects on tuber specific gravity (Hastings, 1983) . . . . 75 4-14. Interaction (DCD v nitrapyrin X NR *) of DCD v nitrapyrin, and N rate effects on tuber specific gravity (Hastings, 1983). . . . . . . 75 4-15. Effects of N rate and amendment on tuber N concentration in 1983 and 1984 . . 77 4-16. Interaction (DCD Q X NR *) of DCD and N rate effects on tuber N concentration (Hastings, 1983) . . . . . . 78 4-17. Interaction (DCD L X NR L *) of DCD and N rate effects on tuber N concentration (Gainesville, 1984). . . . . . 78 4-18. Interaction (Nty RX NR *) of nitrapyrin and N rate effects on tuber N concentration (Hastings, 1983) . 80 4-19. Interaction (DCD v nitrapyrin X NR L x) of DCD v nitrapyrin, and N rate effects on tuber N concentration (Hastings, 1984) . . . . . 80 4-20. Effects of N rate and amendment on plant shoot biomass at harvest in 1983 and 1984 . . . . . . . . . 82 4-21. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on plant shoot biomass at harvest (Gainesville, 1984) .................. 83 viii

PAGE 9

4-22. Effects of N rate and amendment on total biomass at harvest in 1983 and 1984. . 84 4-23. Interaction (DCD Q X NR **) of DCD and N rate effects on total biomass at harvest (Hastings, 1983) . . . . 86 4-24. Interaction (Nty RX NR L *) of nitra pyrin rate and N rate effects on total biomass at harvest (Gainesville, 1984) .......... 4-25. Effects of N rate and amendment on plant shoot N concentration at 86 harvest in 1983 and 1984 . 88 4-26. Interaction (DCD Q X NR L x) of DCD and N rate effects on plant N concen tration at harvest (Hastings, 1984). 89 4-27. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on plant shoot N concentration at harvest (Hastings, 1984) ... 4-28. Interaction (IBDU v Ih X NR L **) of IBDU v inhibitors, and N rate effects on plant shoot N concentration at 89 harvest (Hastings, 1984) . . . 91 4-29. Effects of N rate and amendment on N uptake by plant shoots at harvest in 1983 and 1984. . . . . . 92 4-30. Interaction (Nty RX NR L *) of nitra pyrin and N rate effects on N uptake by plant shoots at harvest (Gainesville, 1984) . . . . . . . 93 4-31. Interaction (DCD v nitrapyrin X NR x) of 4-32. DCD v nitrapyrin, and N rate e f fects on N uptake by plant shoots at harvest (Gainesville, 1983). . . . . . 93 Effects of N rate and amendment on N uptake by tubers in 1983 and 1984. 95 4-33. Interaction (DCD Q X NR **) of DCD and N rate effects on N uptake by tubers (Hastings, 1983) . . . . . . 96 i x

PAGE 10

4-34. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on N uptake by tubers (Gainesville, 1984) . . . 96 4-35. Interaction (DCD v nitrapyrin X NR x) of DCD v nitrapyrin, and N rate effects on N uptake by tubers (Hastings, 1983). . . . . . . . 98 4-36. Interaction (DCD v nitrapyrin X NR L x) of DCD v nitrapyrin, and N rate effects on N uptake by tubers (Hastings, 1984). 98 4-37. Effects of N rate and amendment on total N uptake by plant shoots and tubers at harvest in 1983 and 1984 ........ 100 4-38. Interaction (DCD Q X NR **) of DCD and N rate effects on total N uptake by plant shoots and tubers at harvest (Hastings, 1983). . . . . . . . 101 4-39. Interaction (Nty RX NR Q **) of nitra pyrin and N rate effects on total N uptake by plant shoots and tubers at harvest (Gainesville, 19 84) . . 101 4-40. Effects of N rate and amendment on leaf N concentration at tuber initiation. 103 4-41. Interaction (Nty RX NR *) of nitrapyrin rate and N rate effects on leaf N concentration at tuber initiation (48 dap) (Gainesville, 1984) . . . 106 4-42. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on leaf N concentration at tuber initiation (51 dap) (Hastings, 1985) ..... 106 4-43. Interaction (IBDU v Ih X NR L ***) of IBDU v inhibitors, and N rate effects on leaf N concentration at tuber i nitiation (55 dap) (Hastings, 1984) 107 4-44. Effects of N rate and amendment on leaf N concentration at flowering. . 109 X

PAGE 11

4-45. Interaction (DCD Q X NR L *) of DCD and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 1984). . . . . . . . 111 4-46. Interaction (Nty RX NR Q *) of nitra pyrin and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 1984) . . . . . 111 4-47. Interaction (DCD v nitrapyrin of DCD v nitrapyrin, and N on leaf N concentration at (81 dap) (Hastings, 1984). X NR Q **) rate effects flowering 4-48. Interaction (IBDU v Ih X NR *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering 113 (66 dap) (Gainesville, 1983) ...... 113 4-49. Interaction (IBDU v Ih X NR Q *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 1984). . 114 4-50. Interaction (IBDU v IH X NR L *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering (73 dap) (Hastings, 1985). . . 114 4-51. Effects of N rate and amendment on leaf N concentration at tuber maturation in 1983 and 1984 . . . 116 4-52. Interaction (DCD L X NR L *) of DCD and N rate effects on leaf N concentration at tuber maturation (98 dap) (Hastings, 1984) ............ 118 4-53. Interaction (Nty RX NR Q ***) of nitra pyrin rate and N rate effects on leaf N concentration at tuber maturation (94 dap) (Gainesville, 1984) . . . 118 4-54. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on leaf N concentration at tuber maturation (94 dap) (Gainesville, 1984) . . . . . . . . . 120 xi

PAGE 12

5-1. 5-2. 5-3. 5-4. 5-5. Effects of N rate and amendment on soil inorganic N concentration at the planting+ one week stage of potato (Hastings) ......... Interactions (DCD Q X NR L **) of DCD rate and N rate effects on soil inorganic N concentration 6 days after fertilizer application (Hastings, 1984) ..... Interaction (Nty RX NR Q x) of nitra pyrin rate and N rate effects on soil inorganic N concentration 6 days after fertilizer application (Hastings, 1984) ..... Effects of N rate and amendment on soil inorganic Nat the pre-emergence stage of potato. . . . . . Interactions (DCD Q X NR Q *, DCD L X NR Q x, and DCD Q X NR L *) of DCD and N rate effects on soil inorganic N concentration at the pre-emergence stage of potato (1984) ...... 5-6. Interactions (Nty RX NR and Nty RX NR L **) of nitrapyrin and N rate effects on soil inorganic N concentra tion at the pre-emergence stage of 123 124 124 126 127 potato. . . . . . . . 127 5-7. 5-8. 5-9. Interaction (DCD V Nty X NR L x) of DCD v nitrapyrin and N rate effects on soil inorganic N concentration 13 days after fertilizer application (Gainesville, 1984) .... Interaction (IBDU v Ih X NR L **) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration at the pre-emergence stage of potato ( 1984) . . . . . . . Effects of N rate and amendment on soil inorganic N concentration at the vegetative stage of potato ..... xii 129 131 132

PAGE 13

5-10. Interactions (DCD L X NR Q and DCD Q X NR Q *) of DCD and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 1984) ........... 134 5-11. Interaction (Nty RX NR Q ***) of nitra pyrin and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 19 84) . . . . . . . 134 5-12. Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 1984). . . . . 136 5-13. Effects of nitrogen rate and amendment on soil inorganic N concentration at the tuber initiation stage ....... 138 5-14. Interactions (Nty RX NR L **) of nytra pyrin and N rate effects on soil inorganic N concentration 45 days after fertilizer application (Gainesville, 19 84) . . . . . . . 139 5-15. Interaction (DCD v nitrapyrin X NR Q **) of DCD v nitrapyrin, and N rate effects on soil inorganic N concentration 45 days after fertilizer application (Gainesville, 1984). . . . . 139 5-16. Interaction (DCD v nitrapyrin X NR L and X NR Q *) of DCD v nitrapyrin, and N rate effects on soil inorganic N concentration 46 days after fertilizer application (Hastings, 1984). . 140 5-17. Effects of nitrogen rate and amendment on soil inorganic N concentration at the tuber bulking stage. . . 142 5-18. Interaction (DCD L X NR L *) of DCD and N rate effects on soil inorganic N con centration 69 days after fertilizer application (Gainesville, 1984) ..... 144 xiii

PAGE 14

5-19. Interaction (Nty RX NR L x) of nitrapyrin and N rate effects on soil inorganic N concentration 69 days after fertilizer application (Gainesville, 1984). . 144 5-20. Interactions (IBDU v Ih X NR **, IBDU v Ih X NR L **, and X NR Q **) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration at the tuber bulking stage ......... 145 5-21. Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration 74 days after fertilizer application (Hastings, 1984) . . . . . . . . 145 5-22. Effects of N rate and amendment on soil inorganic N concentration at potato harvest. . . . . . 14 7 5-23. Interaction (DCD L X NR L *) of DCD and N rate effects on soil inorganic N con centration 103 days after fertilizer application (Hastings, 1984) . . 148 5-24. Interaction (Nty RX NR L **) of nitra pyrin and N rate effects on soil inorganic N concentration 108 days after fertilizer application (Gainesville, 1984) .............. 148 5-25. Interaction (IBDU v Ih X NR x) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration 98 days after fertilizer application (Gainesville, 1983). . . . . 150 5-26. Effects of N and DCD rates on soil DCD concentration (Gainesville). . . 157 5-27. Effects of N and DCD rates on soil DCD concentration (Hastings) . . . 158 6-1. Effects of DCD rate on soil NH/-N concen tration at five depths over six sampling dates in a Quartzipsamrnent at Live Oak. . . . . . . 162 xiv

PAGE 15

6-2. 6-3. 6-4. 6-5. 7-1. B-1. D-1. D-2. D-3. D-4. D-5. D-6. Effects of DCD Rate on soil N0 3 --N concen tration at five depths over six sampling dates in a Quartzipsamment at Live Oak. . . . . . . 172 Effects of DCD rate on soil inorganic N (NH/-N + N0 3 --N) at five depths over six sampling dates in a Quartzipsamment at Live Oak ............... 182 Effects of DCD rate on soil N0 3 --N/ (N0 3 --N + NH/-N) ratio at five depths over six sampling dates in a Quartzipsamment at Live Oak. . . . 191 Effects of DCD rate on DCD at five depths over six sampling dates in a typic Quartzipsamrnent at Live Oak ....... 195 Summary of positive N rate effects on potato plant parameters ..... Analysis of variance table for plant response parameters in the studies with potato ........... Analysis of variance of nitrogen and amendment rate effects on soil NH/-N 207 251 concentration (Gainesville, 1983). 268 Analysis of variance of nitrogen and amendment rate effects on soil N0 3 --N concentration (Gainesville, 1983). 269 Analysis of variance of nitrogen and amendment rate effects on soil N0 3 --N/ (N0 3 --N + NH/-N) ratio (Gainesville, 1983) ........... 270 Analysis of variance nitrogen and amendment rate effects on soil NH/-N concentration (Gainesville, 1984). 271 Analysis of variance of nitrogen and amendment rate effects on soil N0 3 --N concentration (Gainesville, 1984). 272 Analysis of variance of nitrogen and amendment rate effects on soil N0 3 --N/ (N0 3 --N + NH/-N) ratio (Gainesville, 1984). . . .......... 273 xv

PAGE 16

D-7. D-8. Analysis of variance of nitrogen and amendment rate effects on soil NH/-N and NO 3 -N concentration (Hastings, 1983). . . . . . . . 274 Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N/ (NO 3 --N + NH/-N) ratio (Hastings, 1983) . . . . . . . . . 275 D-9. Analysis of variance of nitrogen and amendment rate effects on soil NH/-N concentration (Hastings, 1984) . 276 D-10. Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N concentration (Hastings, 1984) . 277 D-11. Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N/ (NO 3 --N + NH/-N) ratio (Hastings, 1984). . . . . . . . 278 D-12. Analysis of variance of nitrogen and amendment rate effects on total soil inorganic N means for all sampling dates................ 279 xvi

PAGE 17

Figure 2-1. 2-2. 5-1. 5-2. 5-3. 5-4. 6-1. 6-2. 6-3. 6-4. 6-5. LIST OF FIGURES The structure of nitropyrin, or 2-chloro6-(trichloromethyl)-pyridine (N-Serve) . . . . . . Tautomers of DCD Effects of DCD rate on soil DCD concentration (Gainesville, 1983) ...... Effects of DCD rate on soil DCD concentration (Gainesville, 1984) ...... Effects of DCD rate on soil DCD concentration (Hastings, 1983) . . . Effects of DCD rate on soil DCD concentration (Hastings, 1984) . . . Effects of DCD rate on soil NH/-N concen tration with depth 14 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak Effects of DCD rate on soil NH/-N concen tration with depth 31 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. Effects of DCD rate on soil NH/-N concen tration with depth 46 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak Effects of DCD rate on soil NH/-N concen tration with depth 60 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak Effects of DCD rate on soil NH/-N concen tration with depth 81 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak xvii . Page 5 7 151 152 154 155 161 163 164 165 167

PAGE 18

6-6. Effects of DCD rate on soil NH/-N concen tration with depth 116 days after application of 200 kg N ha1 to a fallow Quartzipsanunent at Live Oak 168 6-7. Effects of DCD rate on soil NH/-N in the 1.22 m profile of a fallow Quartzipsanunent at Live Oak. . . . . 169 6-8. Effects of DCD rate on soil N0 3 --N concen tration with depth 14 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak 171 6-9. Effects of DCD rate on soil NO 3 --N concen tration with depth 31 days after application of 200 kg N ha1 to a fallow Quartzipsanunent at Live Oak 173 6-10. Effects of DCD rate on soil NO 3 --N concen tration with depth 46 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak . 175 6-11. Effects of DCD rate on soil NO 3 --N concen tration with depth 60 days after application of 200 kg N ha1 to a fallow Quartzipsanunent at Live Oak 176 6-12. Effects of DCD rate on soil N0 3 --N concen tration with depth 81 days after application of 200 kg N ha 1 to a fallow Quartzipsanunent at Live Oak 177 6-13. Effects of DCD rate on soil NO 3 --N concen tration with depth 116 days after application of 200 kg N ha 1 to a fallow Quartzipsanunent at Live Oak 178 6-14. Effects of DCD rate on soil NO 3 --N in the 1.22 m profile of a fallow Quartzipsanunent at Live Oak. . . . . 180 6-15. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concentration with depth 14 days after application of 200 kg N ha 1 to a fallow Quartzipsamment at Live Oak. . . . . 181 xviii

PAGE 19

6-16. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concentration with depth 31 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. . . . . 183 6-17. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concentration with depth 46 days after application of 200 kg N Ha1 to a fallow Quartzipsamment at Live Oak. . . . . 184 6-18. Effects of DCD rate on soil inorganic N ( NH/-N + NO 3 -N) concentration with depth 60 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. . . . . 185 6-19. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concentration with depth 81 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. . . . . 187 6-20. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concentration with depth 116 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. . . . . 188 6-21. Effects of DCD rate on soil inorganic N (NH/-N + N0 3 --N) in the sampled profile of a fallow Quartzipsamment at Live Oak. . . . . . 189 6-22. Effects of DCD rate on soil nitrification ratio, i.e., (NO3--N X 100/(NH/-N + NH 3 --N) in the 1.22 m profile of a fallow Quartzipsamment at Live Oak 192 6-23. Effects of DCD rate on soil DCD concen tration with depth 14 days after DCD application to a fallow Quartzipsamment at Live Oak. . . . . 194 6-24. Effects of DCD rate on soil DCD concen tration with depth 31 days after DCD application to a fallow Quartzipsamment at Live Oak. . . . 196 xix

PAGE 20

6-25. Effects of DCD rate on soil DCD concentration with depth 46 days after DCD application to a fallow Quartzipsamment at Live Oak. . . . 6-26. Effects of DCD rate on soil DCD concentration with depth 60 days after DCD application to a fallow Quartzipsamment at Live Oak. . . . 6-27. Effects of DCD rate on soil DCD concentration with depth 81 days after DCD application to a fallow Quartzipsamment at Live Oak. . . . 6-28. Effects of DCD rate on soil DCD concen tration with depth 116 days after DCD application to a fallow Quartz. 197 . 198 . 199 ipsamment at Live Oak. . 200 6-29. Effects of DCD rate on total DCD in the 1.22 m profile of a fallow Quartzipsamment at Live Oak. . . . 201 C-1. Effects of N rate on soil inorganic N concentration (Gainesville, 1983) . 253 C-2. Effects of N rate on soil NH+ 4 and N0 3 concentrations (Gainesville, 1983) 254 C-3. Effects of N rate on soil NH 4 + and N0 3 concentrations (Gainesville, 1984) 255 C-4. Effects of N rate on soil NH 4 + and N0 3 concentrations (Hastings, 1984) . . 256 C-5. Effects of DCD rate on soil inorganic N concentration (Gainesville, 1983) 257 C-6. Effects of DCD rate on soil NH/ and N0 3 concentrations (Gainesville, 1983) 258 C-7. Effects of DCD rate on soil inorganic N concentration (Gainesville, 1984) 259 C-8. Effects of DCD rate on soil NH/ and N0 3 concentrations (Gainesville, 1984) 260 C-9. Effects of DCD rate on soil inorganic N concentration (Hastings, 1983) . . 261 xx

PAGE 21

C-10. Effects of DCD rate on soil inorganic N concentration (Hastings, 1984) 262 C-11. Effects of DCD rate on soil NH/ and N0 3 concentrations (Hastings, 1984) 263 C-12. Contrast of IBDU and inhibitor effects on soil inorganic N concentration (Gaines ville, 1983) . . . . . . 264 C-13. Contrast of IBDU and inhibitor effects on soil inorganic N concentration (Gaines ville, 1984) . . . . . . 265 C-14. Contrast of IBDU and inhibitor effects on soil inorganic N concentration (Hastings, 1984) . . . . . . . . 266 xxi

PAGE 22

Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy NITRIFICATION INHIBITOR EFFECTS ON POTATO YIELDS AND SOIL INORGANIC NITROGEN By Harris Warthrnan Martin August 1990 Chairman: D. A. Graetz Major Department: Soil Science Rapid loss of applied N from soils may result after nitrification of NH/-N to NO 3 --N. Nitrification inhibitors should reduce N losses from leaching and denitrification, thus increasing N utilization by crops. The effects of nitrification inhibitors on soil inorganic N (SIN) concen trations, plant N uptake, and crop yield were evaluated. Dicyandiamide (DCD) and 2-chloro-6-(trichloromethyl) pyridine (nitrapyrin) nitrification inhibitors were evalu ated on potato (Solanurn tuberosurn L. cv. Atlantic). Treat ments were combinations of Nat 67, 134, and 202 kg ha 1 ; DCD at 0, 5.6, and 11.2 kg ha 1 ; nitrapyrin at 0.56 and 1.12 kg ha 1 ; and isobutylidene diurea ( I BDU) applied as one third of the N. Studies were conducted on an Arenic Ochraqualf, a Grossarenic Paleudult, and a Grossarenic Paleaquult. Tuber yields were increased 1 7% by use of nitrifi cation inhibitors in one of f ive tests. At this location xx i i

PAGE 23

severe leaching had occurred. Nitrification inhibitors increased leaf N concentrations at flowering in three of four tests. Tuber yields were higher with DCD than with nitrapyrin in three of five tests. Tuber yields increased with an increase in N from 67 to 134 kg ha1 in three of three tests. In one test where severe leaching had occurred, tuber yields increased with an increase in N to 202 kg ha1 Nitrification was inhibited by nitrification inhibitors in all of four tests, and increased SIN concen trations in one. SIN concentrations in midand late-season were higher with one-third N as IBDU-N, than with nitrifi cation inhibitors. In a second study, DCD was applied to a fallow Typic Quartzipsamment at 0, 20, 40, and 60 kg ha1 with urea at 200 kg N ha1 Dicyandiamide inhibited nitrification for 81 days. However, SIN concentrations were reduced with DCD Residence half times of DCD in the Oto 1.2 m depth were 61 to 66 days with 20 to 60 kg DCD ha1 Use of nitrification inhibitors increased crop yields only under conditions where SIN concentrations were increased, N rates were 134 kg ha1 or less, and leaching was severe. Inhibition of nitrification did not lead to increases in SIN concentrations in most experiments. Increases in potato yields with nitrification inhibitors did not occur in most experiments as SIN concentrations were not increased. xxiii

PAGE 24

CHAPTER 1 INTRODUCTION Nitrate is subject to greater leaching and denitrif ication losses from soil than NH/. Nitrification, the natural transformation of NH/ to NO 3 by certain soil bacteria, promotes losses of N by denitrification and leaching out of the crop root zone. As a result, crops make inefficient use of fertilizer N. In addition, leaching of N0 3 poses an environmental hazard. It has been commonly assumed that inhibiting nitrif ication should reduce N losses from leaching and denitrif ication, increase N utilization by crops, and provide more even N nourishment of crops over longer periods of time than would otherwise be possible. If this is true, control of nitrification should lead to increased efficiency of Nuse with corresponding improvements in crop growth, yield, and quality. Dicyandiarnide (DCD) and 2-chloro-6-(trichloro methyl)-pyridine (nitrapyrin) are two of a number of syn thetic nitrification inhibitors that have been tested and made available commercially. The objectives of this study were (1) to assess the effects of DCD and nitrapyrin on potato (Solanurn tuberosurn L. cv. Atlantic) tuber yield, crop quality (tuber specific 1

PAGE 25

2 gravity and tuber grade proportions), plant biomass, plant N concentration, and N uptake in Northeast Florida; (2) to assess the effectiveness of DCD and nitrapyrin as inhibitors of nitrification in sandy coastal plain soils of Northeast Florida, as measured by their effects on extractable soil inorganic NH/-N, N0 3 --N, and the total of these; (3) to compare the effects of DCD to those of nitrapyrin, and to compare the effects of the two inhibitors with those of isobutylidene diurea (IBDU), a slow release N source; (4) to determine the extent to which N rate, inhibitors, and IBDU effects on plant response parameters can be attributed to the effects of these treatments on total soil inorganic N concentrations; (5) to study DCD's nitrification inhibiting effect and the fate of DCD in the soil, by measuring the effects of DCD on soil inorganic N concentrations and move ment, and DCD movement and loss in a fallow, deep sandy soil; and (6) to contribute to an understanding of why nitrification inhibitors often do not increase crop yield.

PAGE 26

CHAPTER 2 LITERATURE REVIEW Nitrification Inhibitors Introduction Numerous compounds have been proposed for regulating nitrification in soils, including organic and inorganic compounds, pesticides, chelating agents, and plant products. A number of these are manufactured and patented in the USA, Japan (Ranney, 1978), and Europe. Of the number of inhibi tors mentioned in the literature over a period of 20 years (Ranney, 1978), only nitrapyrin, DCD, and to a lesser extent 2-arnino-4-chloro methyl pyrimidine (AM) have been tested thoroughly (Slangen and Kerkhoff, 1984). The inhibitors of nitrification are effective if they retard one or more steps in the following chain of microbial reactions: Nitrosomonas NH/--------------> hydroxylarnine --> nitroxyl? --> nitrohydroxylarnine --> Nitrobacter N0 2 -------------> N0 3 ( Hauck, 19 7 2) [l] The ideal nitrification inhibitor should inhibit Nitrosomonas, not Nitrobacter, since such inhibition would result in accumulation of No 2 -. It should also be nontoxic 3

PAGE 27

4 to other soil organisms, fish, mammals, and crops and be safe in the environment. It should be able to move with the fertilizer or fertilizer solution, that is, be effective throughout the fertilizer reaction zone. Rapid movement through soils because of high vapor pressure or little movement because of low vapor pressure or strong sorption could lead to poor performance. The ideal nitrification inhibitor should be sufficiently persistent in its action so that nitrification is inhibited for an adequate period of time, usually from several weeks to months. The chemical should be a low cost additive to fertilizer (Hauck, 1972; Turner and MacGregor, 1978; Sampei, 1972). Chemical Properties of the Inhibitors Nitrapyrin. Nitrapyrin was first introduced in 1962 by C.A.I. Goring of the Dow Chemical Company (Goring, 1962a, 1962b). This product stimulated the interest of quite a few researchers in several countries, resulting in many studies and published papers. As of 1981, nitrapyrin was used on >l million hectares of agricultural land annually in the USA (Ashworth and Rodgers, 1981). Nitrapyrin is the principal nitrification inhibitor used commercially in North America, though 5-ethoxy-3-trichloromethyl-1,2,4-thiadizole (terra zole) is also used widely (Hergert and Wiese, 1980). Nitrapyrin is a white crystalline solid with a molecu lar weight of 230.9 atomic units and a melting point of 62 to 63C (Goring, 1962a, 1962b). It is soluble in liquid NH 3

PAGE 28

but insoluble in water; thus it has to be dry-mixed with solid fertilizers or applied directly, preferably as a solution or emulsion (Turner et al., 1962). It has the following structure (Figure 2-1): Cl 5 Figure 2-1. The structure of nitrapyrin, or 2-chloro6-(trichloromethyl)-pyridine (N-Serve). Nitrapyrin is marketed as "N-Serve 24 nitrogen stabilizer" (a.i. 240 g L1 ) and "N-Serve 24E nitrogen stabilizer" (a.i. 240 g L1 ) with an emulsifier (Slangen and Kerkhoff, 1984). Dicyandiamide. The ability of DCD to inhibit nitrifi cation has been observed by Brioux (1910), Nommik (1958, 1959), Reddy (1964a, 1964b), Rathstack (1978), Vilsmeier and Amberger (1978), Guster (1981), Kick and Poletschny (1981), Ashworth and Rodgers (1981), and others. The advantages of DCD over nitrapyrin for a given application, are due primar ily to its different physical properties and its N content. While nitrapyrin has a low water solubility, high vapor pressure, high corrosiveness, and leaves a residue of chloropicolinic acid, DCD is a solid at room temperature and

PAGE 29

6 can be processed as powder, granules, or pellets. It has a relatively high solubility in water, contains 16% N, and breaks down to NH/ and CO 2 leaving no synthetic organic residues. Part of its cost can be justified by its N con tent (Arnberger, 1981a; Kick and Poletschny, 1981; SKW, 1973). Because of these characteristics, DCD can be used as an additive to liquid, organic, or mineral fertilizers, surface coated on to, or incorporated into solid fertilizers containing NH/ or urea, or applied alone to the soil (Arnberger, 1984; Solansky, 1981; SKW, 1973). It requires no special equipment for its application. A brief review and discussion of agronomic properties of DCD and of the manu facture of DCD-containing fertilizers was published by Rieder and Michaud (1980). According to Ashworth and Rodgers (1981) 20% of the cost of DCD application is offset by the fertilizer value of the N contained in DCD. The commercially marketed DCD products, Didin and Alzodin, were developed by Suddeutsche Kalkstickstoffwerke Trostberg Akteingessellschaft, Trostberg, West Germany (hereafter referred to as SKW) in close cooperation with the Institut fur Pflanzenernahrung der TU Munchen at Weihenstephan in West Germany (Arnberger, 1981a). Compounds containing urea (Didin) or (NH 4 ) 2 SO 4 (Alzodin) are available in granulated and coated form from SKW (SKW 1979a, 1979b), and Chisso Corp. of Japan (Chisso Corp., 1981; Slangen and Kerkhoff, 1984).

PAGE 30

Dicyandiamide, abbreviated as DCD, is the most common name for this compound. It is also referred to as cyano guanidine. The empirical formula is C 2 N 4 H 4 Dicyandiamide has a molecular weight of 84.04 atomic units (AERO, 1964; May, 1979; Weast, 1979). DCD has been thought by most workers to exist as a tautomer with the following structure (Figure 2-2): HN \ H C-N-CN I <-----> Tautomer #1 Tautomer #2 Figure 2-2. Tautomers of DCD. 7 It is generally insoluble in nonpolar solvents and soluble in polar solvents (May, 1979) such as water, (SKW, 1973; Weast, 1979) and liquid anhydrous NH 3 (72 g DCD 100 g1 NH 3 at -33C) (SKW, 1973; Reitter, 1975; Ashworth and Rodgers, 1981). Its solubility in water is temperature dependent, i.e., 33, 52, and 121 g L 1 at 20, 30, and 50C, respectively (SKW, 1973). It is amphoteric and has an acid dissociation constant (Ka) at 25C of 6 X 10 15 Dicyandiamide may exist as an impurity in the now archaic fertilizer CaCN 2 (calcium cyanamide, lime nitrogen, or calcium carbamonitrile) (Harger, 1920; Vilsmeier and Amberger, 1978). At one time CaCN 2 was a commonly used N

PAGE 31

fertilizer in Europe and Japan (May, 1979). Dicyandiamide often appeared as a decomposition product of CaCN 2 (Murata, 1939). It makes up approximately 10% of the Nin CaCN 2 (Amberger, 1981b). Mechanism of Nitrification Inhibition 8 General. Nitrification inhibitors affect certain chemosynthetic autotrophic soil bacteria in the Nitrobacter iaceae family by retarding either their growth or their functions. Inhibition of nitrification activity can be caused by interfering with respiration and cytochrome oxi dase function, by chelating essential metal ions, by produc tion of acid in the microenvironrnent, and by liberation of toxic compounds such as mercaptans, sulfoxides, and sulfones (Hauck, 1972). Lees (1946) observed that chemicals such as Na diethyldithiocarbarnate and salicylaldoxime which inhibit copper enzymes, inhibit oxidation of NH / by Nitrosomonas. Quastel (1965) observed that thiourea and allylthiourea inhibit nitrification as well, possibly by combining with metallic cations, such as cu 2 +, needed for this process in soil. It has been proposed that the affinity of the N atom in the structure R-NH-C= for the Cu containing NH / oxidiz ing enzyme is primarily involved in inhibition of nitrifi ca tion (Quastel and Scholefield, 1951). Such a struc t u re occurs in tautomer structure No. 1 of DCD (Figure 2 2 ) A

PAGE 32

9 closely related structure, with which the former may resonate, i.e. R=N-C=, is contained within the structure of nitrapyrin (Figure 2-1). The other tautomer (No. 2) of DCD contains another related structure, R-N=C-. Both nitrapyrin and DCD inhibit the cytochrome oxidase involved in NH 3 oxidation by Nitrosomonas (Hauck, 1980). Nitrapyrin Nitrapyrin inhibits nitrification by inhibiting Nitrosomonas (Goring, 1962a) and has very little effect on Nitrobacter, (Shattuck and Alexander, 1963). Zacherl and Arnberger (1984) reported that nitrapyrin was bactericidal rather than bacteriostatic. Shattuck and Alexander (1963) observed that nitrapyrin had no effect on several heterotrophic bacteria and fungi; thus it can be used to distinguish autotrophic from heterotrophic nitri fying organisms. From their work with pure cultures of Nitrosomonas and Nitrobacter, and others to which nitrapyrin was added, Muller and Hickisch (1979) concluded that the decrease in the number of microorganisms is small and cannot be the only explanation for the inhibition of the nitrification process over a relatively long period. Hooper and Terry (1973) concluded that the effect of nitrapyrin was irreversible because they found that NO 2 --N or NO 3 --N accumulation did not recommence in cellf ree extracts a f ter treatments with nitrapyrin had finished.

PAGE 33

10 Goring (1962a) studied the effect of reinfestation (reinoculation) by nitrifying bacteria contained in small amounts of fresh soil, on the control of nitrification by nitrapyrin. Nitrification proceeded more rapidly in rein fested than in uninfested soil. He presumed that nitrapyrin destroys the majority of the nitrifying organisms and is then decomposed to nonlethal concentrations. The rate of recovery of nitrification thus depended on the recovery of the surviving nitrifying organisms and was, therefore, enhanced by repeated reinfestation. Rodgers et al. (1980) found that recovery of nitrify ing bacteria took approximately 40 days after a 1 mg L1 addition of nitrapyrin to aqueous suspensions of different soils to which 200 mg NH/-N L1 was added. Even after prolonged incubation with nitrapyrin, no evidence was obtained for the development of nitrapyrin resistant nitri fying organisms. Research with different strains of Nitro somonas (Belser and Schmidt, 1981; Laskowski and Bidlack, 1977) showed substantial differences in sensitivity among strains, to nitrapyrin. Dicyandiamide. Dicyandiamide inhibits nitrification by interfering with the metabolism of Nitrosomonas (Verona and Gherarducci, 1980; Amberger, 1981a), specifically by inhibiting the oxidative phosphorylation (Amberger, 1984) of the Cu containing cytochrome oxidase enzyme which oxidizes NH/ (Hauck, 1980). Amberger (1981b) proposed that there is

PAGE 34

11 a temporary decoupling of respiration and energy transfer in Nitrosomonas due to a reaction of the C=N group of DCD with sulfhydrile groups and heavy metals of cytochrome oxidase. He based this proposal on the results of his earlier work (Amberger, 1978) with cyanamide and related products. Dicyandiamide is a bacteriostat, not a bactericide (Zacherl and Amberger, 1984). The microbial effects of DCD are selective for Nitrosomonas, with no effect on the fungi, cellulose-decomposing bacteria, ammonifying and denitrifying bacteria, Azotobacter (Verona and Gherarducci, 1980), or Rhizobium sp. (Neglia and Verona, 1976) that were tested. Verona and Gherarducci (1980) found that several days after application of DCD, the numbers of Nitrosomonas in soil eventually decreased. After the DCD had decomposed, the original numbers of Nitrosomonas reappeared in the soil. Solansky (1981) commented that this reduction of numbers must represent a decrease in the bacteria's rate of multi plication as a result of their starvation due to a lack of metabolic substrate. Inhibitor Concentration Effects and Longevity Nitrapyrin. Reports of the duration of nitrapyrin's nitrification inhibiting effect have been various: 15 days for complete inhibition and 49 days for partial inhibition (Hendrickson et al., 1978), 59 days (Westermann et al., 1981), 91 to 100 days (McCormick et al., 1983), 112 days

PAGE 35

12 (Terry et al., 1981), 148 days (Liu et al., 1984), and 280 days (Janssen, 1969). Goring (1962a) found that the minimum active concen trations of nitrapyrin for a six-week incubation period in 87 soils (with 200 mg kg1 NH/-N) were principally in the O. 2 to 2. O mg kg1 range, but a few were as high as 2 0 mg kg1 and several were as low as O. 05 mg kg1 A number of workers have found that under laboratory and field condi tions, nitrapyrin inhibited nitrification of NH/ and amide fertilizers at rates varying from 0.2 to 2.0% of applied N (Goring, 1962a, 1962b; McBeath, 1962; Turner et al., 1962; Gasser and Penny, 1964; Nielson and Cunningham, 1964; Sabey, 1968). McCormick et al. (1984) recommended that nitrapyrin should be applied at a rate of O. 8 to O. 9 kg ha 1 with a banded fertilizer application to give effective control of nitrification. Goring and Scott (1976) reported that the rates of nitrapyrin application advised by Dow Chemical Company were 4. 5 to 6. 75 L ha 1 of N-Serve 24 or 24E for potatoes before or after planting. These recommended rates were based on fertilizer application in bands or rows (Goring and Scott, 1976). Dicyandiamide. Bazilevich (1968) grew corn in potted soil and found that 35 days after DCD application, the inhibiting effect of DCD on the rhizosphere microflora was still observed, while after 50 days the number of

PAGE 36

13 microorganisms increased but remained less than control populations; after 85 days populations were the same as the control. Bazilevich and Kabanova (1973) found that 6.8 kg DCD ha1 inhibited nitrification of applied (NH 4 ) 2 SO 4 -N for 1 to 1.5 months. Smirnov (1978) observed that 10 to 15% of the amount of applied N as DCD-N was needed to inhibit the nitrification of fertilizer derived and native NH/-N for a period of 1.5 to 2 months. Amberger and Guster (1978) found that DCD at 5 to 10% of the applied N was sufficient to inhibit nitrification in a pot culture with sandy loam (pH 6.1) over at least 6 weeks. Without any inhibitor, Amberger and Vilsmeier (1979c) found that 50% of total N and 100% of NH/-N, applied to soil in the laboratory as liquid manure was nitrified within 20 to 40 days at temperatures of 8 to 20C. Addition of DCD at a rate of 10 mg DCD kg 1 of liquid manure resulted in intensive inhibition of nitrification for 20 to 60 days depending on environmental conditions such as leaching rainfall and soil temperature. Increased DCD rates lengthened these times. Reddy (1964a), in incubation studies with DCD and (NH 4 ) 2 SO 4 in Georgia coastal plain soils, found that with Cecil sandy loam (Paleudult) and Lakeland sand (Quartzipsarnment), 25 mg kg 1 DCD inhibited nitrification for up to 90 days. Some inhibition was still

PAGE 37

occurring after 150 days in the Lakeland soil (Reddy, 1964a). 14 In a laboratory incubation study with a Mulat sand (Typic Ochraquult) from the Horticulture Unit near Gainesville, Florida, Mohamad (1985) found that the duration of DCD effectiveness was directly related to DCD concen tration in the soil. With 5 and 10 mg DCD kg1 soil, 100 mg of added NH/-N kg1 soil was subject to considerable nitri fication within two weeks. With 25 mg DCD kg1 soil, how ever, significant nitrification did not occur for eight weeks and some inhibition of nitrification continued for at least twelve weeks. He found that the effectiveness of DCD added to soil at the rate of 10 mg kg1 was not affected by NH/-N concentrations in the soil within the range of Oto 120 mg NH/-N kg1 soil. In a field study with the same Ochraquult, Mohamad (1985) found that the duration of inhibition varied from year to year and varied with N rate and DCD rate. In one year with 22.4 kg ha1 DCD and 202 kg ha 1 urea-N, DCD increased soil NH/-N concentration for eight weeks. With 11.2 kg ha1 DCD, however, NH/-N concentrations were only increased for four weeks. With these DCD and N rates, NO 3 --N concentration in the soil was reduced for four weeks. In a second year, 11.2 kg ha 1 DCD had little effect on soil NH/-N or NO 3 --N concentrations while 22. 4 kg ha 1 DCD

PAGE 38

increased soil NH/-N concentration for six weeks and decreased soil NO 3 --N concentration for four weeks. 15 Vilsmeier and Amberger (1978) found that DCD as 10% of applied Nin (NH 4 ) 2 SO 4 and urea strongly inhibited nitrifica tion for an average of 60 days. Randal and Malzer (1981) found that DCD inhibited nitrification of NH/ from (NH 4 ) 2 SO 4 and urea for a maximum of 9 weeks. In the laboratory, Rathstack (1978) added urea and large concentrations of DCD to soil under env i ronmentally controlled conditions. He found that as DCD-N (as a percent of applied N) increased from 10 to 20 to 30%, nitrification inhibition continued for 26, 32, and 45 days respectively. In a field study, Touchton (1981b), however, found that 5% DCD-N as a percent age of total N was as effective in inhibiting nitrification as 10 and 15% rates. These and other reports indicate that DCD is effective at inhibiting nitrification for a minimum of 20 days, more often for 40 to 60 days, and occasionally for as long as 90 days. These values are sometimes but not always a function of DCD concentration in the soil or N fertilizer. The duration of inhibiting effects and the effective concentra tion vary with soil type and environmental conditions. Since effective inhibition is likely to taper off gradually, it is not possible to determine exactly the duration of effectiveness.

PAGE 39

16 Inhibitor Losses Volatilization of nitrapyrin. Nitrapyrin has a rela tively low vapor pressure of 0.373 N m2 (at 23C) (Goring, 1962b). This is the reason that application of nitrapyrin in spots or bands, instead of broadcasting, is preferred (Turner et al., 1962). According to Hendrickson et al. (1978), nitrapyrin is more likely to be lost to volatiliza tion when sidedressed, even though covered with soil, than when applied at planting. Nitrapyrin volatilizes rapidly when unincorporated into the soil, resulting in losses of up to 80% (Briggs, 1975) and thus is much more effective as a nitrification inhibitor when incorporated (Briggs, 1975; Gasser and Penny, 1964). This volatility results in gaseous diffusion of nitrapyrin through air-filled pores in the soil (Goring, 1962b) and can be aggravated by wind at the soil surface (McCall and Swann, 1978). Higher soil temperatures accelerate the rate of diffusion of nitrapyrin in soils (Hendrickson et al., 1978). Because of its volatility, low water solubility, and sorption by soil organic matter, nitrapyrin has very little tendency to leach downward in the soil (Mullison and Norris, 1979). When NH/-N fertilizer is applied to soil with nitrapyrin, much of the NH/-N can leach down below the zone of soil containing nitrapyrin, thus rendering the inhibitor ineffective (Hendrickson et al, 1978; Rudert and Locascio, 1979b).

PAGE 40

17 Decomposition (hydrolysis) of nitrapyrin. The prin cipal decomposition residue of nitrapyrin in plants and soils is 6-chloro-picolinic acid, formed by hydrolysis of the trichloromethyl group (Briggs, 1975; Herlihy and Quirke, 1975; Hendrickson and Keeney, 1979; Redemann et al., 1964, 1965). Hydrolysis of nitrapyrin is enhanced in moisture saturated soils (Hendrickson and Keeney, 1979; Laskowski et al., 1974). As soil temperature increases, the rate of nitrapyrin hydrolysis increases exponentially (Redemann et al., 1964; Hendrickson and Keeney, 1979). Hendrickson and Keeney (1979) found that the rate of nitrapyrin hydrolysis was not affected by pH in the 2.7 to 11.9 range. Touchton et al. (1979b) found, on the other hand, that the rate of nitrapyrin disappearance increased with increasing soil pH in 2 of 3 soils tested. Redemann et al. (1964) found that the amount of applied nitrapyrin remaining in the soil was an exponential function of ti.me and observed a half life (residence half ti.me) for nitrapyrin in four soils, from 4 to 22 days at 20C. Herlihy and Quirke (1975) observed nitrapyrin half lives ranging from 9 to 16 days at 20C and from 43 to 77 days at 10c. Decomposition of DCD. That DCD which is retained in the soil eventually breaks down into NH/-N and N0 3 --N and carbon compounds, presumably by the action of soil microor ganisms (Rathstack, 1978). Rieder and Michaud (1980)

PAGE 41

18 reported that rapid mineralization of DCD-N to NH/-N and NO 3 --N in three soils began after 28 days and was complete after approximately 70 days. Garita (1981) applied DCD to soil in a banana plantation in Costa Rica. When the DCD was in an (NH 4 ) 2 SO 4 formulation (Alzodin), none was detectable in soil extracts after 46 days. When it was applied in a urea formulation (Didin), none was detectable after 59 days. Graetz et al. (1981) applied DCD to soil under sweet corn (Zea mays L. var. saccharata (Sturt.) Bailey.) in Northeast Florida and found detectable DCD in soil extracts 77 days after application. Kappan (1907) concluded that DCD decom posed more slowly in infertile soils than in fertile soils. In an incubation study, Vilsmeier (1980) was able to identify the breakdown products of DCD in soil. The sequence of reactions was shown to be DCD ---> guanylurea ---> guanidine ---> NH/ [ 2 ] As temperature increased, the rate of breakdown increased, particularly for the DCD to guanylurea step. At very high temperatures (70C), guanidine accumulated. Whereas the rate of decomposition of DCD in soil depends on temperature and quantity o f DCD applied, soil moisture content has been said to play only a minor part (Vilsmeier, 1980, 1981; Amberger and Vilsmeier, 1979 a, 1979b). Murata (1939) observed that DCD was ammon if i e d

PAGE 42

19 under waterlogged conditions. A low value for P 02 (Eh less than 250 mv at pH 7) and the presence of FeO or actively decomposing organic matter was favorable for DCD decomposi tion (Murata, 1939). Bazilevich (1968) found that DCD was decomposed much faster in plant-bearing than in fallow or untilled soil. Thus, he concluded that plant root exudates were used as nutrients or carbon sources by the micro organisms which break down DCD, with DCD acting as an N source for these microorganisms. Reddy and Datta (1965) observed that the nitrification inhibiting effect of DCD was partially counteracted by the addition of organic matter. In the presence of added organic matter, decomposition of DCD was more rapid. They attributed this rate effect to the high exchange capacity and absorbing power of the organic matter. Reddy (1964a) claimed that DCD decomposed faster in a sandy loam soil with a relatively high organic matter content than in a coarse textured sandy soil with a low organic matter content. Leaching of DCD. If leaching of N0 3 -N is a reason for using nitrification inhibitors, then leaching of the inhibitors should also be of much interest. The volatility of nitrapyrin can cause NH/-N to move below the zone of maximum nitrapyrin concentration in the soil (Rudert and Locascio, 1979b). DCD, on the other hand, does not volatilize but is subject to leaching (Arnberger and Guster, 1979; Bock et al., 1981; Sampei and Fukushima, 1973). If it

PAGE 43

leaches more rapidly than NH/-N, then its effectiveness will be compromised (Bock et al., 1981). 20 Amberger and Guster (1979) observed that as much as 15% of the DCD applied with liquid cattle manure to potted soil in the greenhouse was leached by 56 mm of simulated percolation. More DCD was leached from fallow potted soil than when growing plants were present. Bock et al. (1981) studied the movement of DCD and various sources of fertilizer N through soil columns. While NH/ is held against leaching to some extent by the cation exchange capacity, even in sandy soils, the tautomers of DCD carry little charge; thus DCD can separate from the NH/ when the two are applied together. Under conditions of mass flow, this separation was observed by Bock et al. (1981). This did not occur with urea, however, since DCD and urea moved with the soil solution at about the same rate. This is not surprising since urea also is uncharged. Retention of DCD in six soils (belonging to several soil orders) studied by Bock et al. (1981) generally increased with increasing soil organic matter content and cation exchange capacity (CEC). DCD is only weakly sorbed by soil organic matter (Vilsmeier, 1979), but even weak sorption could be significant. Bock et al. (1981) observed no relationship between soil pH or presence of free calcium carbonate and DCD retention. They found that a simulat e d 5

PAGE 44

cm rainfall moved most of a surface applied DCD solution below the 5 cm depth in all the soils studied. Effects of Inhibitors on Other N Transformations 21 Volatilization of NH 3 Rodgers (1983) reported that the use of DCD increased the amount of NH 3 lost by volatil ization 20 to 60% compared to soil amended with urea only. He concluded that the beneficial effects of DCD may be counteracted by increased loss of NH 3 by volatilization. Apparently no other research has been reported on the effects of nitrification inhibitors on NH 3 volatilization. Volatilization of NH 3 may have been the reason for some of Graetz et al.'s (1981) field results with vege tables. They found that with plastic mulched tomato {Lycopersicon esculentum Mill.) fruit yield was increased with addition of DCD to NH 4 NO 3 and to urea. With unmulched bell peppers (Capsicum frutescens var. grossum (L.) Bailey), DCD increased fruit yield when NH 4 NO 3 was used but decreased yield when urea was used. N mineralization. Kreitinger et al. (1985) found that nitrapyrin stimulated N mineralization rates by 77% in soil suspensions not receiving NH/-N and by 40% in NH/-N sup plemented suspensions. The reason for this anomalous obser vation was not apparent. The fixation of CO 2 was not increased by t he addition of NH/-N to suspensions of leached soil. However, nitrapyrin inhibited CO 2 fixation in both NH/-amended and unamended suspensions.

PAGE 45

22 In a field study with 15 N, Norman et al. (1989) found that DCD increased mineralization of organic Nin rice paddy soil and increased plant uptake of native soil N as opposed to fertilizer N. In a field lysimeter study with 1 5 N applied to corn (Zea mays L.), Walters and Malzer (1990b) obtained similar results with nitrapyrin. In a laboratory incubation study, however, Mohamad (1985) found that DCD did not affect mineralization of soil organic Nin a sandy Florida Ochraquult. Denitrification. Nitrification inhibitors indirectly inhibit denitrification because of their inhibition of nitrification (Mitsui et al., 1964). Evidence for this indirect inhibition has been provided for flooded soils (Prasad and Lakhdive, 1969; Rajale and Prasad, 1970; Sampei and Fukushima, 1973) and for nonflooded soils (Nishihara, 1962; Smirnov et al., 1977; Liu et al., 1984; Cribbs and Mills, 1979; McElhannon and Mills, 1981; Kostov, 1977; Vilsmeier, 1981). Others have observed that inhibitors such as DCD did not affect denitrification (Mitsui et al., 1962; Simpson et al., 1985). Since nitrification is inhibited, less NO 3 (the substrate for denitrification) is formed from NH/ (Meyer, 1981; Vilsmeier, 1981). This indirect effect on denitrification is of practical importance, especially where crops such as rice (Oriza sativa L.) are grown in flooded soils.

PAGE 46

23 N immobilization. Hauck (1972) observed that nitrifi cation can result in a reduction of N immobilization and NH 3 fixation. It follows, therefore, that inhibition of nitri fication could increase N immobilization and fixation. When Chancy and Kamprath (1982) applied nitrapyrin to corn, they observed that nitrapyrin resulted in more of the total inorganic Nin the Oto 15 cm depth being in the NH/ form. However, this did not significantly increase the total inorganic N concentration at any depth. They could not explain this discrepancy; they did not consider the pos sibility of increased immobilization. Terry et al. (1981) reported no effect of nitrapyrin on immobilization of NH/-N added with synthetic sewage sludge to a silt loam (Aerie Ochraqualf) soil. In a laboratory study under controlled conditions, Mohamad (1985) did not observe any effect of DCD on fertilizer N immobil ization. I n another laboratory study, however, Osiname et al. (1983) did observe an increase in immobilization of fertilizer N with nitrification inhibitors. Until recently, most of the research investigating the effects of nitr i fication inhibitors on the immobilization of fertilizer N has been done by Smirnov's group in the Soviet Union. Smirnov et al. (1968) amended 15 N labeled (NH 4 ) 2 SO 4 and urea with DCD and found that although N losses were markedly lowered by DCD application, more of the fertilizer N was immobilized in organic forms in the soil as a result

PAGE 47

24 of DCD application. Smirnov (1968) applied 15 N labeled NH/-N fertilizers amended with DCD, to barley and oats. He found that DCD application increased utilization of fertil izer N by the crops somewhat, almost halved losses of N, and increased transformation of fertilizer N into organic N. Smirnov et al. (1972a, 1972b) found that DCD application increased the immobilization of fertilizer N under corn, but not under oats (Avena sativa L). In another study, Smirnov et al. (1973) applied DCD as 0.5% of the fertilizer weight with (NH 4 ) 2 SO 4 and urea at the rate of 120 mg N kg1 soil. They found that N losses were reduced by 23 to 25% with (NH 4 ) 2 SO 4 and by 12 to 14% with urea, while immobilization of fertilizer N was increased by DCD application. Juma and Paul (1983) found that the nitrification inhibitor 4-amino-1,2,4-triazole (ATC) increased the recov ery in Canadian topsoil of 15 N supplied as labelled urea or aqueous NH 3 by 41 to 57% on the average, without increasing 15 N uptake (37%) by wheat. Soil treated with ATC contained nearly twice as much 15 N in the biomass as untreated soil. Ashworth et al. (1984) found that similar increases in non extractable soil 15 N were measured after incubating soils from Alberta, Canada, in the laboratory with labeled (NH 4 ) 2 SO 4 and the inhibitor etridiazol. Norman et al. (1989) found that DCD increased immobilization of fertilizer N applied to paddy soil in Arkansas. Walters and Malzer (1990a, 1990b) found that in the first year of their study,

PAGE 48

25 nitrapyrin increased immobilization of incorporated urea-N and decreased plant recovery of fertilizer derived N (FON) in a Typic Hapludoll in Minnesota. This led to an increase the following year in mineralization, plant uptake, and leaching of residual FON. N Leaching and Inhibitor Effects Potato production in many regions of the world is concentrated in areas of sandy soils where irrigation is common (Bundy et al., 1986). Irrigation of the potato crop is considered essential on such sands and lighter soils (Curwen et al., 1982). Potato grown on these soils is relatively shallow-rooted (Lesczynski and Tanner, 1986) and requires frequent irrigation (Curwen and Massie, 1984) and high N fertilizer rates (Kelling et al., 1984) to maximize tuber yield and quality. In studies with Russet Burbank potato on a loamy sand, more than 90% of the root length was in the upper 30 cm of the soil profile (Lesczynski and Tanner, 1976; Tanner et al., 1982); thus fertilizer N leached below 30 cm is not likely to be recovered by the crop (Bundy et al., 1986). In such an environment, the potential for loss of fertilizer N by means of leaching of N0 3 -N is high (Bundy et al., 1986). Some of these soils have such low CEC and water holding capacities that appreciable leaching of NH/-N can occur as well. The tendency of NH/-N to leach would be accentuated if fertilizer N persists in the NH/ form for an

PAGE 49

26 extended period of time, or if the concentrations of soluble salts in the soil are high (Hendrickson et al., 1978). It is not unusual for potato growers to apply water frequently and in amounts in excess of actual evapotranspir ational losses. This practice can be wasteful and in some cases reduce tuber yields by leaching fertilizer N beyond the root zone, and by creating anaerobic conditions in poorly drained soils (Wolfe et al., 1983). Nonuniform water infiltration under potato plant canopies can promote N leaching losses and decreased crop recovery of fertilizer N (Lesczynski and Tanner, 1976; Saffinga et al., 1976; 1977; Tanner et al., 1982). In sandy Entisols of central Wisconsin, only 2.5 cm of applied water resulted in a 15 to 20 cm downward movement of added N0 3 --N (Endelman et al., 1974). In Long Island, NY, rates of N fertilizer in excess of potato crop requirements resulted in N0 3 --N enrichment of the groundwater (Meisinger, 1976). It can be difficult to accurately determine N0 3 -N movement in field soils. The presence of water flow chan nels in the soil can result in rapid movement of applied N fertilizer not only to regions below the rooting zone, but below the zone of biodegradation as well. As a result, much of the downward moving N0 3 --N tends to avoid contact with installed sampling devices such as porous cup extractors (Simpson and Cunningham, 1982). Peak water and leachate flow periods may be missed entirely because of this

PAGE 50

27 channelization (Rourke, 1985). This makes accurate measurements of movement of inorganic N difficult in a soil planted to potato (Simpson and Cunningham, 1982). Under overhead irrigation, soil N0 3 --N and other soluble salts move downward and decrease in concentration as the crop growing season progresses. Elkashif et al. (1983) observed this to be the case in Northeast Florida at the University of Florida Horticulture Unit at Gainesville, Florida. At the Agricultural Research and Education Center (AREC) at Hastings, Florida, potato was grown with subsur face irrigation and they observed that soil soluble salts increased as the season progressed, due to low rainfall and upward movement of soluble salts as water evaporated during dry periods. These reports indicate that potato fields present special challenges for the accurate measurement of N leaching. Nitrification inhibitors have been shown to reduce losses of N accompanying nitrification vis. leaching and denitrification under situations where these losses are high (Sahrawat et al., 1977), thus reducing N0 3 --N pollution of ground and surface waters (Huber et al., 1969; Norris, 1972). Touchton et al. (1979a) reported that nitrapyrin prevented N0 3 -N from accumulating below the 15 cm depth in a somewhat poorly drained Typic Hapludoll in Illinois. In percolation studies, Nishihara and Tsuneyoshi (1968) found

PAGE 51

28 that the amount of Nin the percolate (leachate) was greatly reduced by amendment of urea with nitrapyrin. Soubies et al. (1962) applied DCD in the fall at a rate of 5.5 to 24% of fertilizer N, which reduced leaching losses of N over the winter by as much as 67%. Kiangsi (1976) found that DCD and other inhibitors prevented more than 20% of the N losses caused by leaching of soil N0 3 --N. Scheffer et al. (1984) found that DCD reduced leaching of mineral fertilizer N applied to sandy soils by an average of 28%. When DCD was applied with liquid manure, however, leaching was reduced with fall application but not with spring application. Kuntze and Scheffer (1981) found that DCD reduced N0 3 --N leaching into subsoil drainage water by 20%. Kick and Poletschny (1981) found that during the German winter, DCD resulted in reduction of N leaching by 67 to 80%. Timmons (1984) found that nitrapyrin reduced N0 3 -N leaching losses by 30 to 51 kg ha1 in a column study. Using 1 5 N and field lysimeters planted to corn on a sandy loam (Typic Hapludoll) in Minnesota for three years, he found that the average quantity of N0 3 -N leached was 12 kg ha1 (7%) less when urea was applied with nitrapyrin than when urea was applied alone. His results were very inconsistent because of variability in amounts of leaching rainfall, plant uptake of fertilizer N, and other fact ors

PAGE 52

29 In a similar three year study with lysimeters on the same soil, Walters and Malzer (1990a, 1990b) found that the maximum rate of NO 3 --N leaching loss was delayed 25 to 50 days when nitrapyrin was applied with 180 kg ha1 urea-N. Although nitrapyrin reduced soil water percolation, the quantity of N leached was not reduced over the three year period. They found that the effects of nitrapyrin on NO 3 --N leaching were confounded by the long term effects of nitrapyrin on N immobilization and mineralization. This paper was the first to describe the long term effects of a nitrification inhibitor on most relevant portions of the soil N cycle. An important factors that was not measured, however, was inhibitor effects on volatilization of NH 3 In the first year, nitrapyrin resulted in a decrease in NO 3 --N leaching due to an increase in immobilization of fertilizer N. In subsequent years, this immobilized (residual) fertil izer N was mineralized, increasing leaching of NO 3 --N. Plant N uptake and N rate influenced this set of relationships. While plant recovery of FDN in the year of application was decreased by nitrapyrin, greater uptake of residual FDN in subsequent years tended to equalize the total amount of FDN recovered in plant material by the third year of their study. In the previously unfertilized soil which was used in their study, they found that N leaching losses increased in each successive year. This reflected mineralization and leaching of residual immobilized N from

PAGE 53

30 the previous year's application. They observed that a two fold increase in N application rate resulted in a 3.4-fold increase in N leached over three years The relative dif ference in N leaching levels with two N rates increased with each succeeding year. In part this was because less of net fertilizer N remained immobilized after one year with a 180 kg ha1 N rate than with a 90 kg ha1 N rate (Walters and Malzer, 1990a, 1990b). These reports indicate that in the field, inhibitors can sometimes reduce NO 3 --N leaching, at least temporarily, by as much as 70 to 80% but more often by 5 to 30%. The only long-term well-controlled field experiments reported in the literature showed an average reduction in leaching of N0 3 --N, of only 7% in one case (Timmons, 1984) and no reduction at all in another (Walters and Malzer, 1990b). Crop Response to Inhibitors According to Hauck (1972), decreased N losses and increased crop yields resulting from the use of nitrifica tion inhibitors are readily demonstrated in laboratory and greenhouse experiments. It is far less easy to demonstrate the value of nitrification inhibitors in f i eld soils since field experiments usually are more insensitive than labora tory and greenhouse tests, and small d i fferences i n eff ciency of Nuse are difficult to measure accurately. Also in a single season, bene f icial effects of cont r o lling nitrification may not be obvious. For e xam p l e rapid

PAGE 54

31 nitrification may not precede conditions conducive to NO 3 --N loss by denitrification or leaching. Therefore as discussed by Hauck (1972), reports appear in the literature that nitrification was inhibited by a chemical in the laboratory but that this inhibition was not reflected in increased yield or N uptake or that anomalous results were obtained (Ashworth et al., 1980, 1984; Colliver, 1980; Maddux et al., 1985; Meisinger et al., 1980; Touchton, 1981; Welch, 1979). A substantial amount of literature exists reporting on the effects of nitrapyrin and DCD on the crop yields, yield components, and N contents of corn, wheat (Triticum aestivum L.), rice (Oryza sativa L.), potato, pasture and fodder grasses, spinach (Spinacia oleracea L.), and to a lesser extent, on sorghum (Sorghum vulgare Pers.), rye (Secale cereale L.), oat, barley (Hordeum vulgare L.), cotton (Gossypium hirsutum L.), sugar beet (Beta vulgaris L. (Mangels)), turf grasses, and various vegetables. A number of greenhouse studies have indicated that DCD can increase yield and/or N uptake by some crops. The effects of DCD on crop yields in field studies have been mixed. Dicyandiamide appears to have given better results in Europe than in the USA. The majority of the work reported on nitrapyrin has been conducted in the USA with lesser amounts in the Commonwealth countries and the European community. The most extensive research with DCD has been conducted in West

PAGE 55

32 Germany, the USSR, and the USA, and to a lesser extent in Japan, India, The Netherlands, France, England, and Poland. In a number of field studies that were conducted for two or more years, the effects of nitrification inhibitors on crops varied considerably from year to year with seed cotton (Reeves et al., 1988), winter barley (Guster, 1981), and other crops, especially when the inhibitor was applied in the summer (Guster, 1981). The effectiveness of inhibi tors such as DCD has also varied from one soil to another in the same year (Nishihara, 1962). In the USA, some researchers observed no corn yield increase when nitrapyrin was applied (Touchton et al., 1979; Boswell, 1977, Robertson et al., 1982). In other cases, yield increases occurred only at low N rates (Touchton et al., 1979a; McCormick et al., 1984, Walters and Malzer, 1990a), only with fall N application (Touchton et al., 1979a; McCormick et al., 1984), or only when temperatures were low and rainfall was excessive during the early growth period (Touchton and Boswell, 1980). In some cases, nitra pyrin has resulted in decreased corn yields (Robertson et al., 1982; Touchton et al., 1979a; Walters and Malzer, 1990a). Other workers have observed more favorable results (Tsai et al., 1978; Malzer et al., 1979). Summarizing the studies on nitrapyrin application to corn in Kansas (Dept. of Agron., Kansas State U., 1976, 1977, 1978), those irrigated corn sites where yield

PAGE 56

33 increases due to nitrapyrin occurred, were on sandy soil. Smirnov {1978) observed that in the USSR, crop yield increases resulting from DCD application, occurred most often in the humid regions of the country and under irri gation. Of all the crops tested in the USSR, increased yields due to DCD application were most common with cotton and rice {Smirnov, 1978). In the USA, researchers observed corn yield decreases {Reddy, 1964b) or no increase when DCD was applied (Graetz et al., 1981; Randal and Malzer, 1981). When DCD applica tion did not increase crop yields, this has been attributed to the lack of substantial leaching rainfall (Graetz et al., 1981; Touchton, 1981; Robertson et al., 1982; Mohamad, 1985). Yield was not increased by nitrapyrin application to tomato {Jaworski and Morton, 1967), sweet corn {Zea mays var. sacharata Bailey) {Rudert and Locascio, 1979a), radish (Raphanus sativus L.) {Sander and Barker, 1978), kale {Brassica oleracea L. var. acephala D.C. {Borecole)) (Spratt and Gasser, 1970), cabbage (Brassica oleracea convar. capitata (L.)) (Gysi and Stroll, 1980), Chinese cabbage {Brassica pekinensis (Lour.) Rupr.) {Roorda van Eysinga and Meijs, 1980), mustard {Brassica campestris L.) {Jung and Dressel, 1978), endive (Cichorium endivia L.) (Roorda van Eysinga and Meijs, 1981), and lettuce {Lactuca sativa L.) (Moore, 1973). In other cases, nitrapyrin increased sweet

PAGE 57

corn (Swezey and Turner, 1962) and tomato (Lycopersicon esculentum Mill.) yields (Graetz et al., 1981). In one study, nitrapyrin only increased lettuce yields when irrigation was frequent (Welch et al., 1979). 34 In several studies, DCD has had no effect on the yields of sweet corn (Mohamad, 1985), lettuce (Roorda van Eysinga et al., 1980d), endive (Cichorium Endivia L.) (Roorda van Eysinga and Meijs, 1981), Chinese cabbage (Roorda van Eysinga and Meijs, 1980), or onion (Allium cepa L.) (Rotini and Guerrucci, 1961). As with other crops, potato yield responses to nitra pyrin have varied. In some cases nitrapyrin application has decreased potato yields even though it was effective in inhibiting nitrification (Hendrickson et al., 1978; Vendrell et al., 1981). In other cases it has had no effect (Potter et al., 1971; Roberts, 1979). In yet others, it has in creased yields (Roberts, 1979). The effects of nitrapyrin on potato tuber quality factors have likewise been sometimes negative (Hendrickson et al., 1978) and sometimes positive (Potter et al., 1971). In some cases nitrapyrin has been found to reduce incidence of potato scab (Streptomyces scabies) (Huber and Watson, 1970; Potter et al., 1971). Lack of potato yield response to nitrification inhibi tor application was observed by Schmitt (1938), Amberger (1981b), and Munzert (1984). Potato yield increases, mostly in Europe, were observed by Schmitt (1937), Rieder (1981),

PAGE 58

35 Wolkowski et al. (1986), and Munzert (1984). In some cases, these increases only occurred at low N rates (Smirnov et al., 1976a). In Germany, Munzert (1984) found that when potato yields were increased by DCD application, more oversized tubers were produced. Wolkowski et al. (1986) commented that early research by others had shown that use of nitrifi cation inhibitors on potatoes with completely NH/-N sources, while sometimes resulting in improved N efficiency, also resulted in decreases in tuber grade and yield. They attributed this to the potato's aversion to exclusive NH/-N nutrition. In their own study, they found that DCD increased yield and fertilizer Nuse efficiency but in some cases depressed tuber grade. Why nitrification inhibitors often do not increase crop yields. Several studies have found that nitrification inhibitors increased crop yields much more, or only, at the lowest of several N rates (Huber et al., 1981; Liu et al., 1984; Touchton, 1981; Bazilevich and Kabanova, 1973; Krischenko et al., 1972; Makarov and Gerashchenko, 1976; Frye et al., 1981; Malzer et al., 1979; McCormick et al., 1984; Amberger, 1981b; Smirnov et al., 1972a, 1973, 1976a, 1976b). Ashworth (1986) considered the tendency of nitrifi cation inhibitors to increase immobilization of applied N as a possible explanation for the inconsistent and sometimes

PAGE 59

slightly negative effects of inhibitors on crop yield (Ashworth e t al., 1980, 1984; Meisinger et al., 1980). 36 McCormick et al. (1984) concluded that when nitrifica tion is inhibited but no yield responses occur, either (1) the soil already contains high concentrations of plant available N and the addition of N fertilizer does not increase yield, (2) little or no N losses occur following fertilizer application, or (3) N rates used are far in excess of those required for maximum yield. Blackmer (1986) presented a hypothesis that does much to explain why crop yields are often not increased by nitri fication inhibitors, as well as split N fertilizer applica tions, urease inhibitors, and slow release N sources. He proposed that the lack of response to inhibitors, etc., could be the result of several causes including (1) signif icant losses of N did not occur in the absence of the treatment; (2) the treatment was not effective at preventing losses; (3) N availability was not a factor limiting crop growth, even after significant losses occurred; (4) unex pected effects of the treatments masked the intended effects; and (5) the experimental method lacked sufficient sensitivity to detect significant yield responses that occurred. Treatments conserving fertilizer N should be expected to cause statistically significant increases in crop yi elds only when a favorable interaction among the following

PAGE 60

37 conditions is attained: (1) experimental methods provide a high degree of precision, (2) the treatment saves a sub stantial portion of the fertilizer N applied, (3) fertilizer N is applied at relatively low rates, and (4) studies are conducted on soils having small amounts of soil derived available N (Blaclaner, 1986). Effective nitrification inhibitors sometimes result in excess NH/-N availability or NO 3 --N deficiency in NH/-N sensitive or NO 3 --N requiring species. These two problems can occur together and can be hard to separate. Imbalances of NH//NO 3 in the nutrition of the crop may induce or be accentuated by K deficiency (Barker et al., 1967) and/or Cl toxicity. Inhibition of nitrification may in such cases lead to yield depressions with crops that are not able to assimilate relatively high amounts of NH/-N (Dibb and Welch, 1976; Kapusta and Varsa, 1972). In some cases an increase in the NH//NO 3 ratio can cause a redistribution of N inside the plant, sometimes resulting in changes in crop protein content, but not necessarily in crop yield (El Wali et al., 1979; Sommer and Rossig, 1978; Touchton et al., 1979a; Warren et al., 1980). Nitrogen Nutrition of Potato and Other Plants General The quantity and form of N available to the potato crop have substantia l effects on the i nternal physiology of

PAGE 61

38 the plant, tuber initiation, vine growth, tuber yield and specific gravity, proportion of cull tubers, leaf N concen trations, disease susceptibility, N leaching, and N fertil izer use efficiency. Nitrogen has been reported to play a major role in the production and maintenance of optimum plant canopy for continuous tuber bulking through long growing seasons (Bremner and Taha, 1966; Bremner and Radley, 1966; Moorby, 1978). When N fertilizer rates are high to excessive, the proportion of the total tuber crop made up by culls, especially misshapen or oversized culls, has been found to increase (Bundy et al., 1986; Chamberland and Scott, 1968; Murphy and Goven, 1975; Terman et al., 1951; Westermann and Kleinkopf, 1985). Nitrogen Source It has been recognized for quite some ti.me (Maze, 1900; Muntz, 1893) that most plants may utilize either NH/ or NO 3 salts as N sources. Different plant species, how ever, differ in their uptake and assimilation of NH/-N and NO 3 --N (Barker and Mills, 1980). The uptake and use of NH/-N v NO 3 -N by plants are related not only to the form of N but also to the associated ion, the concentration of other nutrients present, and plant factors such as age and nitrate reductase activity (Hauck, 1972). Hewitt et al. (1976) and Street and Sheat (1958) concluded that NO 3 --N is usually superior to NH/-N for plant growth, but the two sources may

PAGE 62

39 vary with species, environmental conditions, soil conditions such as pH, and other factors. According to Nightingale (1948), NH/-N nutrition dif fers from NO 3 --N nutrition in three main ways; (a) the demand for 0 2 to the roots is increased with NH/-N nutri tion, (b) competition for absorption of cations other than NH/ may be detrimental to growth if the supply of other cations is low, and (c) there may be indirect effects asso ciated with shifts in pH of the medium, such as the avail ability of Mo and Pat low pH resulting from use of NH/-N, and of heavy metals such as Mn and Fe at high pH values. Some Solanaceous crops, e.g. tobacco (Nicotiana tabaccum L.) (Mccants et al., 1959), tomato (Morris and Giddens, 1963; Pill and Lambeth, 1977; Wilcox et al., 1977), and potato (Volk and Gammon, 1952, 1954; Hendrickson et al., 1978) are known to grow better when a high NO 3 -/NH/ ratio is available to them. The literature does not indicate, how ever, that this preference can be assumed for all crop species in the Solanaceae family. Contradictory results have been obtained for several crop species including tobacco (Gaus et al., 1971; Elliott, 1970; Rhoads, 1972), and non-Solanaceae species such as ryegrass (Poletschny and Sommer, 1976), and cotton (Reeves et al., 1988). In field studies using 15 NH 4 NO 3 and NH/ 5 NO 31 Roberts and Cheng (1984) found that when supplied with both N forms to gether, potato preferentially took up NO 3 --N over NH/-N.

PAGE 63

Davis et al. (1986b) found that potato plant age did not alter the response of plant growth to NH/-N as opposed to N0 3 --N. 40 The research that has examined the N form preference of potato, shows that when NH/-N is abundant, and NO 3 --N is absent, the plant often does not do well. Under highly controlled conditions, when NH/ is the only N form avail able to the plant, growth is unthrifty and stunted (Chen and Li, 1978; Davis et al., 1986b; Loescher, 1981; Polizotto et al., 1975), with reduced tuber weights (Davis, 1983; Davis et al., 1986b). Other reported effects of high NH/-N include nutritional imbalances such as a greater requirement for K (Barker et al., 1967), reduced uptake of Ca and Mg, increased uptake of P (Davis et al., 1986b; Polizotto et al., 1975), reduced water uptake (Polizotto et al., 1975; Quebedeaux and Ozbun, 1973), altered metabolism such as decreased starch synthesis (Matsumoto et al., 1969), and reduced tuber quality (Middleton et al., 1975; Painter and Augustin, 1976; Hendrickson et al., 1978; Volk and Gammon, 1954). Another symptom of excess NH/-N and insufficient NO 3 --N nutrition, is small and weak looking plants, with chlorotic, tightly-rolled leaves (Davis et al., 1986b). This phenomenon is generally referred to as nutritional leaf roll (Volk and Gammon, 1952; 1954). In Florida, nutritional leaf roll is most severe on the very sandy and/or strongly

PAGE 64

41 acidic soils, on relatively newly cleared lands, or reculti vated land that has been in meadow for several years (Volk and Gammon, 1952; 1954). Volk and Gammon (1954) found that on highly acid soils nutritional leaf roll was severe where the amount of soil NO 3 --N available to the plant was low, but it did not develop where NO 3 --N was high, regardless of NH/-N concentrations in the soil. What they observed, therefore, was not an NH/-N toxicity, but a N0 3 --N defi ciency. Ammonium nitrate fertilizer resulted in higher potato yields than did NH/-N sources lacking in N0 3 --N in studies in Maine (Terman et al., 1951), north Florida (Volk and Gammon, 1954), and Germany (Meisinger et al., 1978). In other cases, NH/-N sources resulted in greater potato yields than N0 3 --N or mixed sources in Wisconsin (Bundy et al., 1986) and eastern Washington (Davis et al., 1986a, 1986b). In such cases, the favorable response to NH/-N, in contrast to N0 3 -N, is usually attributed to substantial leaching of N0 3 --N, as a result of heavy irrigation or rain fall (Davis et al., 1 986a). In yet other field studies with potato, no significant differences in yield were found between NH/-N and NO 3 -N sources i n Maine (Brown et al., 1 930), eastern Washington (Davis et al., 1986a), New Bruns wick (MacLean 1983), and M i chigan (V i tosh, 1971) The conflicting results of thes e e fforts to evaluate N fertil i zer sources f or potato production has in part been

PAGE 65

42 due to the wide variety of cultural practices, soils, and climatic conditions in these studies (Bundy et al., 1986; Meisenger et al., 1978). Sanderson and White (1987) found that cultivars showed differential performance in response to N sources and rates, though Meisinger et al. (1978) and Rowberry and Johnston (1980) found no such cultivar differ ence. This contradiction was attributed to differences in the lengths of growing season from one region to another. In some studies, interactions between N rate effects, and differences in effects due to N source, have occurred (Giroux, 1982; Sanderson and White, 1987), while in other studies (Giroux, 1982; Rowberry and Johnston, 1980), no such interaction occurred. Slow release N fertilizers such as IBDU and sulfur coated urea (SCU) have been compared to NH 4 NO 3 as N sources for potato in North Florida. The NH 4 N0 3 fertilizer out yielded the slow release N sources by 25 to 27%. Appar ently, the slow release N sources did not release N sufficiently to meet the crop's requirements, and rainfall was light, limiting N0 3 --N leaching losses (Elkashif et al., 1983). Since these slow release N sources break down first to NH/-N, releasing NO 3 -N only after nitrification com mences, it is possible that these plants also suffered from a NO 3 -N deficiency.

PAGE 66

43 Nitrogen Recovery Leaching, denitrification, NH 3 volatilization, and other types of N losses result in N-use efficiency by crop plants as low as 20% and rarely higher than 80% of added plus native soil N (Amberger, 1981b; Blue and Graetz, 1977; Nelson et al., 1977; Prasad et al., 1971; Smirnov, 1968; 1978; Volk, 1956). Other causes of incomplete recovery of N from soil-plant systems include fertilizer-derived injury to plant roots or foliage and plant preference for NH/-N or NO 3 --N. Meteorological conditions, management practices, and soil characteristics affect all of these factors (Hauck and Koshino, 1971). One factor that is often overlooked, is the immobilization of fertilizer N by heterotrophic soil microorganisms (Ashworth, 1986). Asfary et al. (1983) found that apparent potato crop recovery of fertilizer N ranged from 50 to 71% without irrigation, and from 73 to 79% with irrigation. Bundy et al. (1986) found that although N concentration in the tubers was not affected by N source, the proportion of supplemental N recovered in tubers differed significantly among N sources. The order of increasing recoveries was (NH 4 ) 2 SO 4 > urea= NH 4 NO 3 > Ca(NO 3 ) 2 They also found that the propor tion of added N recovered in the tubers decreased as applied N rates were increased.

PAGE 67

44 Conclusions The chemistry of DCD and nitrapyrin are fairly well understood. There is a reasonable understanding of the mechanism by which they inhibit nitrification, though more research should be done in this area. The longevity of inhibition and concentration effects of the inhibitors are quite variable, depending on environmental and soil condi tions. The loss mechanisms for nitrapyrin (volatilization and hydrolysis) are fairly well understood, while those of DCD (leaching and decomposition) need further study. There is a need for more long term (three or more years) research on the effects of inhibitors on soil N transformations other than nitrification, soil N leaching and water quality, and total soil inorganic N. Crop response to inhibitors in the greenhouse has been fairly predictable but field trials are another matter. More often than not, crop yields are not increased by nitri fication inhibitors. The conditions under which favorable responses occur are subject to several interacting factors, making favorable responses almost impossible to predict. These interacting factors include N rate, leaching rainfall, soil drainage, immobilization and mineralization of fertil izer N, temperature, and time of fertilizer application. Some reasons for this have been proposed by Hauck (1972), McCormick et al. (1984), Blackmer (1986), and Ashworth (1986), Norman et al. (1989), and Walters and Malzer (1990a,

PAGE 68

45 1990b). Chancy and Kamprath (1982) were the first research ers to clearly document that nitrification inhibitors inhib ited nitrification while not increasing total inorganic N concentration in the soil. Other researchers reporting the effects of nitrification inhibitors on total soil inorganic N have done so indirectly or without statistical analysis.

PAGE 69

CHAPTER 3 MATERIALS AND METHODS Nitrogen and Amendments Applied to Potato Experimental design. Potato (Solanum tuberosum L. cv. Atlantic) was grown in 1983, 1984, and 1985 at the AREC at Hastings in St. Johns County, and in 1983 and 1984, at the Horticulture Unit, at Gainesville, in Alachua County. The soil at the AREC Hastings (Table 3-1) was an Elzey fine sand (sandy, siliceous, hypertherrnic Arenic Ochraqualf) (USDA, 1983). The soil at the Horticulture Unit was a Millhopper sand (loamy, siliceous, hypertherrnic Grossarenic Paleudult) in 1983, and a Plummer fine sand (loamy, siliceous, thermic Grossarenic Paleaquult) in 1984 (USDA, 1985). Selected soil characteristics at harvest are shown in Table 3-2. The experiment was a randomized complete block fac torial design within each year and location, with four blocks. The factors were N rate and amendment. In 1983, there were two N rates, 134 and 202 kg N ha1 In 1984 and 1985, a third N rate, 67 kg ha 1 was added. In 1983 and 1984, ammonium nitrate was the N source. In 1985, N was applied as 75% NH/-N and 25% NO 3 -N, supplied from a mixture of (NH 4 ) 2 SO 4 and NH 4 NO 3 At each N rate, two rates of DCD, 5.6 and 11.2 kg ha1 were compared to a control (no 46

PAGE 70

47 Table 3-1. Classification of the soils used. Location Soil Series Gainesville 1983 Millhopper sand Gainesville 1984 Plummer fine sand Hastings 1983 Elzey fine sand Hastings 1984 Elzey fine sand Hastings 1985 Elzey fine sand Live Oak 1985 Lakeland fine sand Taxonomic Name Loamy, siliceous hyperthermic Grossarenic Paleudult Loamy, siliceous hyperthermic Grossarenic Paleaquult Sandy, siliceous hyperthermic Arenic Ochraqualf Sandy, siliceous hyperthermic Arenic Ochraqualf Sandy, siliceous hyperthermic Arenic Ochraqualf Thermic, coated Typic Quartzipsamment

PAGE 71

48 Table 3-2. Selected soil properties at harvest. Organic pH CEC Sand Silt Clay C N cmol kg-1 ag kg1 Location & Year Soils Planted to Potatot Gainesville 1983 4.9 8.11 84.5 11.4 4.4 2. 1 0.129 Millhopper sand Gainesville 1984 5.6 3.07 90.7 4.9 4.4 0.8 0.045 Plummer fine sand Hastings 1983 4.5 3; 94.1 4.2 1.7 1.2 0.068 Elzey fine sand Hastings 1984 5.2 2.70 94.7 0.9 4.4 1.0 0.056 Elzey fine sand Hastings 1985 4.8 3.36 94.1 4.3 1.6 1.0 0.062 Elzey fine sand Depth ( cm) Fallow Soil 0-15 5.3 4.04 92.3 6.0 1.7 1.2 0.055 15-30 5.2 3.30 91.9 5.6 2.5 1.0 0.036 30-61 4.8 2.06 92.2 5.4 2.4 0.6 0.021 61-91 4.6 1.04 92.7 4.8 2.5 0.3 0.010 91-122 4.5 0.90 92.9 4.5 2.6 0.2 0.008 tsampled to a depth of 30-33 cm. *Estimated from data of USDA (1983).

PAGE 72

49 amendment) and to two rates of nitrapyrin at 0.56 and 1.12 kg ha1 These two nitrification inhibitors were compared to a slow release N form, IBDU as one-third of the total N applied. For statistical purposes, these six treatments (a control, two DCD rates, two nitrapyrin rates, and one IBDU rate) were considered six rates of the factor amendment. Dicyandiamide (obtained from SKW Trostberg A.G.) powder was ground to pass a 2 mm sieve and coated onto NH 4 NO 3 using vegetable oil as an adherent (German Patent Specification No. 2 531 962, cited in Rieder and Michaud, 1980). Liquid nitrapyrin was poured onto the fertilizer mixtures and mixed just prior to fertilizer application. In all three years, 12 kg ha1 Pas triple super phosphate, 186 kg ha 1 K as K 2 SO 41 34 kg ha 1 Mg as MgO and 56 kg ha1 of TM300 micronutrient mix were applied pre-plant. The TM300 contained 2.40% B, 2.40% Cu, 14.4% Fe, 6.00% Mn, 0.06% Mo, and 5.60% Zn by weight. In 1985, K was applied in two equal applications. Fertilizers were applied in two bands 5 cm deep and 5 cm on each side of the potato seed pieces. At Hastings, f our row plots were used. Each row was 1.02 x 4.5 m. At Gainesville, one row plots were used. Each row was 1.02 x 12.2 m. Potato seed pieces were planted in bedded rows 25 to 31 cm high, about 51 cm wide at the base and 15 to 21 cm wide at the top. The seed pieces were

PAGE 73

50 cut and coated with the fungicide cis-N-trichloromethylthio4-cyclohexene-1,2-dicarboxirnide (captan) and planted 20 cm apart in the row. Standard cultural practices for Northeast Florida potato production were followed. The soil nematicide D-D (a mixture of dichloropropene and dichloropropane) was applied to the soil at a rate of 31 L ha1 2 to 6 weeks prior to planting. The herbicide 4-amino-6-(1,1-dirnethylethyl)-3(methylthio)-1,2,4-triazin-5(4H)-one (metribuzin), at 0.28 kg ha1 of active ingredient, was applied 11 to 20 days after planting (dap) at Gainesville. At Hastings, a combination of metribuzin and N-(1-ethylpropyl)-3,4dirnethyl-2,6-dinitro-benzenamine (pendirnethalin) was used. Vine killer was not used prior to harvest at either location. The insecticide 2-methyl-2(methylthio) propionaldehyde-O(methylcarbamoyl)oxirne (aldicarb) was used at planting at Hastings. All plots were cultivated per iodically to control weeds and reverse bed erosion. At Gainesville, overhead sprinkler irrigation and surface ditch drainage were used. At Hastings, subsoil, i.e., seepage or water furrow irrigation-drainage was used. Plant sampling. Tubers were harvested at maturity, graded according to U.S. Grade Standards and weighed. The grades were PK (pickouts) rotten and green tubers, G&NG (grader and harvester damaged), B (3.8 to 4.8 cm), Al (4.8 to 6.35 cm), A2 (6.35 to 7.6 cm), and A3 (7.6 to 9.5 cm) in

PAGE 74

51 diameter. Subsamples were taken of harvested grade A tubers for the measurement of specific gravity, tuber dry weight, and tuber N concentration. Whole plant samples were taken to measure above ground (shoot) phytomass and total shoot N concentration just before harvest in 1983 and 1984. Whole leaf samples, i.e., blade plus petiole, were taken periodically during the growing season in all three years (Table 3-3) and were analyzed for total N concentration (Bremner, 1965). Leaf N concentration at tuber initiation (43 to 55 dap) was mea sured in all five location-year combinations (growth stages according to Kleinkopf et al., 1981). Leaf N concentration at flowering (66 to 81 dap), which corresponds to the tuber bulking stage, was measured at all locations and in all years except in 1983 at Hastings. Leaf N concentration at the tuber maturation stage was measured in samples taken just before harvest (93 to 98 dap) in 1983 and 1984. Soil sampling Composite soil samples were taken to a depth of 33 cm in each field in 1983 and 1984 for the pur pose of soil characterization. Soil was sampled with a 4.8 cm i.d. tube at two to four week intervals (Table 3-3) in the beds down to the tillage pan at a depth of 33 cm for determination of extractable soil inorganic N. Samples were taken from the soil both adjacent to and away from the fer tilizer bands and all such samples from each plot were com posited. At Hastings, 12 cores were taken from each plot.

PAGE 75

52 Table 3-3. Ti.ming of soil and leaf sampling in potato fields. Potato Growth Stage Near planting Emergence Vegetative Tuber initiation Tuber bulking At harvest Early (tuber initiation) Flowering (tuber bulking) Late (tuber maturation) Days after Planting Gainesville Hastings 1983 16 35 59 98 43 66 93 1984 1983 Soil Sampling 13 31 45 69 108 5 31 61 Leaf Sampling 48 74 94 54 95 1984 6 18 32 46 74 103 55 81 98 1985 51 73

PAGE 76

53 At Gainesville, 9 cores were taken per plot. The samples were placed in polyethylene bags, cooled during transport to the lab, and frozen until extraction and analysis. Analytical procedures. Leaf, shoot, and tuber N concentrations were determined using a semimicro-Kjeldahl block digestion and distillation procedure (Nelson and Sommers, 1972). Tuber specific gravity (SG) was measured by comparing tuber fresh weights in air and submerged in water. The formula used was (TUWA TRWA) SG = (TUWA TRWA) (TUWW TRWW) where TUWA = tuber weight in air TRWA = tare weight in air TUWW = tuber weight in water TRWW = tare weight in water. Tuber subsamples were cut, dried and ground for determin ation of dry weight and analyzed for N concentration. Soil pH was determined using a 2:1 water:soil ratio. Soil organic carbon was quantified using a modified Walkley-Black procedure (Allison, 1965). Total soil N was determined using a semimicro-Kjeldahl block digestion and distillation procedure (Nelson and Sommers, 1972). Cation exchange capacity was measured by Na + /NH/ exchange using a leaching technique with the salts being buffered to pH 7

PAGE 77

(Schollenberger and Simon, 1945). Particle size distribu tion was determined by the pipette method (Day, 1965). 54 Soil inorganic N (ammonium and nitrate plus nitrite) was extracted for one hour with 1 M KCl containing 15 mg L1 of phenyl mercuric acetate as a bactericide (Bremner, 1965). This extract was distilled into boric acid indicator for determination of NH/-N and NO 3 --N concentrations. Soil DCD concentrations were determined using a modification of Vilsmeier's (1979, 1982) method. The naphthol reagent was filtered through a 0.45 m filter rather than being centri fuged. Because the naphthol reagent is unstable, a new batch was made up each day. Because of this instability the same blank solution could not be used for all the samples and standards in a set. Therefore, a separate blank was used for each group of six samples or standards. The blanks used for the standards were 0.01 M CaC1 2 The blanks used for the soil extract samples were extracts of soil from plots which received O kg ha1 DCD and the same N rate as the sampled soil. Statistical procedures. Statistical analyses of potato yield and other plant data, and soil inorganic N data were carried out with Statistical Analysis System (SAS), a computer system for data analysis (SAS Institute Inc., 1982a, 1982b, 1983, 1985a, 1985b; Freund and Littel, 1981; Helwig, 1983). Analysis of variance was carried out with the PROC GLM procedure and orthogonal single degree of

PAGE 78

55 freedom contrasts. The control treatment was considered the lowest of three DCD treatment rates. Five orthogonal con trasts were used for the inhibitor and IBDU treatments. These were: DCD rate linear, DCD rate quadratic, nitrapyrin rate (0.56 v 1.12 kg ha1 nitrapyrin), DCD v nitrapyrin (5.6 and 11. 2 kg ha1 DCD v O. 56 and 1.12 kg ha1 nitrapyrin), and IBDU v inhibitors. In 1984 and 1985, the effects of the three N rates were analyzed with linear and quadratic con trasts. Where the effects of N rate and amendment inter acted, the data were subsetted so that the effects of each factor (N rate and amendment) could be analyzed at each rate of the other factor. As a result of crop damage, there were two missing cells at Gainesville, in 1983. Thus the plant response means for this experiment are least square means computed by the LSMEANS statement in SAS. Urea and DCD Applied to a Fallow Quartzipsamment Experimental design. A study was conducted at the AREC at Live Oak in Suwannee County on a Lakeland fine sand (thermic, coated Typic Quartzipsamment) to evaluate the effectiveness of DCD as a nitrification inhibitor and to determine the effects of DCD application on concentrations of DCD, NH/-N, and N0 3 -N in the soil profile over time. Selected soil properties are shown in Table 3-2. A ran domized complete block design with four blocks was used. Dicyandiamide was applied at rates of 0, 20, 40, and 60 kg ha 1 Nitrogen as urea was broadcast and incorporated at

PAGE 79

56 the rate of 200 kg N ha1 to all plots on March 29, 1985. The urea and DCD were thoroughly mixed together by spraying the urea with 0.5% water and 0.5% vegetable oil with an air sprayer, adding the DCD and mixing until uniform. The plots were 3.65 x 7.5 m. The plots remained fallow during the study and were kept free of weeds by cultivation. Soil sampling and analysis. The fallow soil was sampled at approximately two week intervals starting 14 days after fertilizer application. Four cores were taken from each plot and all four cores for each depth were mixed together on each sampling date. The depths sampled were 0 to 15 cm, 15 to 30 cm, 30 to 61 cm, 61 to 91 cm, and 91 to 122 cm. The soil samples were analyzed for inorganic NH/-N and N0 3 --N concentrations by KCl extraction and distillation (Bremner, 1965). Soil DCD concentrations were measured by the modification of the method of Vilsmeier (1979, 1982) mentioned above. Statistical procedures. Analysis of variance was carried out with the PROC GLM procedure and orthogonal single degree of freedom contrasts (DCD rate linear, quadratic and cubic).

PAGE 80

CHAPTER 4 TUBER YIELD, PLANT N CONTENT, AND BIOMASS Tuber Yield N rate effects. Marketable (grades A and B) and total tuber yield increased with increases in N rate in four of five year-location combinations. In 1983 at Hastings, marketable tuber yield increased from 18.6 to 21.7 t ha1 with an increase in N rate from 134 to 202 kg ha1 (Table 4-1). In 1983 at Gainesville, marketable yield was not influenced by N rate. In 1984, an increase in N rate from 67 to 134 kg ha 1 resulted in an increase in marketable tuber yield from 24.8 to 29.0 t ha1 at Gainesville, and from 16.7 to 21.1 t ha 1 at Hastings. A further increase in N rate from 134 to 202 kg ha1 did not influence marketable tuber yield at either location in 1984. In 1985 at Hastings, marketable tuber yield increased from 29.9 to 33.8 t ha1 with an increase in N rate from 67 to 134 kg ha1 A further increase in N rate to 202 kg ha1 had no effect. Nitrogen rate and all other treatment effects on total tuber yield (Table 4-2) were similar to affects on marketable tuber yield in all three years and at both locations. Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on marketable tuber yield 57

PAGE 81

58 Table 4-1. Effects of N rate and amendment on marketable tuber yield. Treatment N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Ntys 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih# Interactions 1983 _t 26.7(23)* 27.4(22) NS 28.8(8) 25.7(8) 26.5(7) 26.7(8) 26.4(8) 28.5(6) NS NS NS NS NS NS Gainesville 1984 t/ha 24.8 29.0 29.0 L** Qx 29.7 28.0 28.9 26.0 25.7 27.3 NS NS NS NS Nty RX NR L* Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 'Ih = inhibitors.

PAGE 82

59 Table 4-1--Extended. Hastings 1983 1984 1985 t/ha 16.7 29.9 18.6 21.1 33.8 21.7 23.7 34.5 L*** L*** L*** Qx Q* 18.3 20.6 33.3 21.0 21. 5 33.4 21.4 21.2 33.4 18.0 19.3 31.2 21.5 19.7 32.1 20.7 20.9 32.9 NS NS NS NS NS NS NS NS ** NS NS NS DCD Q X NR ** IBDU v Ih X NR L NS

PAGE 83

60 Table 4-2. Effects of N rate and amendment on total tuber yield. Treatment N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Nty 5 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih* Interactions Gainesville 1983 1984 --------t/ha-------_t 27.9(23)* 29.0(22) NS 29.8(8) 27.4(8) 27.7(7) 28.1(8) 27.7(8) 30.1(6) NS NS NS NS NS NS 25.7 30.2 30.1 L** Q* 30.6 29.1 29.8 27.3 26.8 28.5 NS NS NS X NS Nty RX NR L Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. *Rate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. *Ih = inhibitors.

PAGE 84

61 Table 4-2--Extended. Hastings 1983 1984 1985 t/ha 17.9 32.8 18.7 22.6 36.9 21.8 25.5 36.8 L** L*** L*** Qx Q** 18.3 21.9 35.8 21.1 23.0 36.1 21.5 22.7 36.2 18.1 20.8 34.4 21.6 21.2 34.8 20.8 22.3 35.7 NS NS NS NS NS NS NS NS ** NS NS NS DCD Q X NR ** IBDU v Ih X NR L NS

PAGE 85

62 (Table 4-3). With 134 kg ha1 N, marketable yield increased from 14. 6 to 21. 7 t ha1 with an increase in DCD rate from 0 to 5. 6 kg ha1 A further increase in DCD to 11. 2 kg ha1 had no effect on marketable yield. With 202 kg ha1 N, DCD rate had no effect on marketable yield. Dicyandiarnide rate had no effect on marketable or total tuber yield in 1983 or 1984 at Gainesville, or in 1984 or 1985 at Hastings. In 1983 at Hastings, marketable tuber yield increased from 18.0 to 21.5 t ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha 1 (Table 4-1). In 1984 at Gaines ville, nitrapyrin rate interacted with N rate effects on tuber yield (Table 4-4). With 67 kg ha1 N, marketable yield increased from 21. 3 to 26. 6 t ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 134 and 202 kg ha1 N, tuber yield was not affected by nitrapyrin rate. In 1983 at Gainesville and Hastings, tuber yield means were similar with DCD and nitrapyrin (Table 4-1). In 1984 at both locations, and in 1985 at Hastings, tuber yield means were higher with DCD than with nitrapyrin. In 1984 at Gainesville, marketable yield means were 28. 4 t ha1 with DCD and 25.8 t ha1 with nitrapyrin. In 1984 at Hastings, marketable yield means were 21. 4 t ha 1 with DCD and 19. 5 t ha 1 with nitrapyrin. In 1985 at Hastings, marketable yield means were 33.4 t ha 1 with DCD and 31.6 t ha 1 with nitrapyrin.

PAGE 86

63 Table 4-3. Interaction ( DCD Q X NR **) of DCD and N rate effects on tuber yield (Hastings, 1983). DCD Rate (kg/ha) N Rate 0 5.6 11.2 kg/ha Marketable Yield (t/ha) 134 14.6 21.7 19.2 L**Q** 202 21.9 20.2 23.5 NS NS X Total Yield (t/ha) 134 14.7 21.8 19.3 L**Q** 202 21.9 20.3 23.6 NS NS X Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 87

Table 4-4. N Rate kg/ha 67 134 202 67 134 202 64 Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on tuber yield (Gainesville, 19 84) Nitrapyrin Rate (kg/ha) 0.56 1.12 Marketable Yield (t/ha) 21.3 29.0 27.7 L*Q* 22.0 30.1 29.6 L*Qx Total Yield (t/ha) 26.6 X 26.2 NS 24.4 NS NS 27.6 X 27.0 NS 25.7 NS NS Nonsignificant (NS) or significant at the 0.1 (x), or 0.05 (*)probability levels, respectively.

PAGE 88

65 Marketable and total yields in 1984 at Hastings, were influenced by an interaction between the IBDU v inhibitor contrast, and N rate (Table 4-5). With 67 kg ha1 N, mar ketable yield means were higher with IBDU (18.3 t ha1 ) than with inhibitors (16.3 t ha1 ). With 134 and 202 kg ha1 N, tuber yield means were similar with IBDU and inhibitors. Proportion of Marketable Tuber Yield That Was Grade A N rate effects. The proportion of marketable yield that was grade A (Table 4-6), increased with increasing N rate in all year-location combinations except in 1983 at Gainesville. In 1984 at Gainesville, the proportion of marketable yield that was grade A increased from 80.4 to 84.2% with an increase in N rate from 67 to 134 kg ha1 A further increase in N to 202 kg ha1 had no effect. In 1983 at Hastings, the proportion of marketable yield that was grade A increased from 74.6 to 77.6% with an increase in N rate from 67 to 134 kg ha1 In 1984 at Hastings, the proportion of marketable yield that was grade A increased from 84.6 to 88.5% with an increase in N rate from 67 to 134 kg ha 1 A further increase in N to 202 kg ha1 had no affect. In 1985 at Hastings, N and DCD rate interacted in their effects on the proportion of marketable yield that was grade A (Table 4-7). With 0 DCD, N rate had no effect. With 5.6 and 11.2 kg ha1 DCD, the proportion of marketable yield that was grade A increased with an increase

PAGE 89

Table 4-5. N Rate kg/ha 67 134 202 67 134 202 Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on tuber yield (Hastings, 1984). IBDU Inhibitors Marketable Yield (t/ha) 18.3 21.7 22.9 L*** 16.3 X 20.9 NS 24.1 NS L*** Total Yield (t/ha) 19.5 23.0 24.4 L*** 17.5 22.5 NS 25.9 NS L*** 66 Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.001 (***) probability levels, respectively.

PAGE 90

Table 4-6. Effects of N rate and amendment on the proportion of marketable yield that was grade A. Gainesville Hastings Treatment 1983 1984 1983 1984 1985 -------------%---------------N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Nty 5 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v 1h 11 _t 91.8(23)* 92.1(22) NS 92.5(8) 91.0(8) 92.6(7) 91.7(8) 90.9(8) 92.9(6) NS X NS NS NS 80.4 84.2 84.6 L** Qx 85.3 83.5 84.3 82.2 80.5 82.7 NS NS NS NS 74.6 77.6 73.3 76.7 79.3 73.7 78.8 74.8 NS NS NS 84.6 88.5 89.4 L*** Q* 87.6 87.3 87.9 86.1 87.2 88.8 NS NS NS NS 89.4 92.2 93 1 L*** Q* 92.0 91. 3 91.9 91. 2 90.8 92.1 NS NS NS NS NS Interactions NS NS NS NS DCD L X NR L IBDU v Ih X NR L Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 'Ih = inhibitors. -..J

PAGE 91

Table 4-7. N Rate kg/ha 67 134 202 68 Interaction (DCD L X NR L *) of DCD and N rate effects on the proportion of marketable yield that was grade A (Hastings, 1985). DCD Rate (kg/ha) 0 5.6 11.2 ----------%----------90.5 92.9 92.7 NS 88.4 92.1 93.4 L** 88.6 NS 92.5 NS 94.7 NS L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 4-8. Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on the proportion of marketable yield that was grade A (Hastings, 1985) N Rate kg/ha 67 134 202 IBDU Inhibitors ---------%--------91.3 92.6 92.5 NS Qx 88.6 91. 9 NS 93.3 NS L** Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 92

69 in N rate from 67 to 202 kg ha1 With 5.6 kg ha1 DCD, the proportion of marketable yield that was grade A increased from 88.4 to 93.4% with an increase in N rate. With 11.2 kg ha1 DCD, the proportion of marketable yield that was grade A increased from 88.6 to 94.7% with an increase in N rate. Amendment effects. In 1983 at Hastings, the proportion of marketable yield that was grade A increased from 73.3 to 79.3% with an increase in DCD rate from Oto 11.2 kg ha1 The proportion of marketable yield that was grade A increased from 73.7 to 78.8% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 in 1983 at Hastings. In 1984 at Gainesville, the proportion of marketable yield that was grade A was higher with DCD (83.9%) than with nitrapyrin ( 81.4%) (Table 4-6). In 1984 at Hastings, the proportion of marketable yield that was grade A was higher with IBDU treatments (88.8%) than with inhibitors (87.1%). I n 1985 at Hastings, the IBDU v inhibitor contrast inter acted with N rate (Table 4-8). With 67 kg ha 1 N, the proportion of marketable yield that was grade A was higher with IBDU (91.3%) than with inhibitors (88.6%). With 134 and 202 kg ha1 N, the proportion of marketable yield that was grade A was similar with IBDU and inhibitors.

PAGE 93

Proportion of Total Tuber Yield That Was Marketable 70 N rate effects. In 1985 at Hastings, the proportion of total yield that was marketable (Table 4-9), was similar with N rates of 67 and 134 kg ha1 but was increased from 91.5 to 93.6% with an increase in N rate from 134 to 202 kg Amendment effects. In 1984 at Gainesville, the DCD v nitrapyrin contrast interacted with N rate (Table 4-10). With 202 kg ha1 N, the proportion of total yield that was marketable was higher with DCD (97.0%) than with nitrapyrin (93.9%). With 67 and 134 kg ha1 N, the proportion of total yield that was marketable was similar with the two inhib itors. In 1983 at Hastings, IBDU v inhibitors interacted with N rate (Table 4-11). With 202 kg ha1 N, the propor tion of total yield that was marketable was higher with inhibitors (99.7%) than with IBDU (99.1%). With 134 kg ha1 N, the proportion of total yield that was marketable was similar with the two types of amendments. Tuber Specific Gravity N rate effects. Tuber specific gravity increased from 1.0841 to 1.0854 as N rate increased from 134 to 202 kg ha 1 in 1983 at Hastings (Table 4-12). In 1984 at Hastings, tuber specific gravity increased from 1.0769 to 1.0796 as N rate increased from 67 to 202 kg ha1 In 1985 at Hastings, tuber specific gravity increased from 1.0775 to 1.0791 with

PAGE 94

Table 4-9. Effects of N rate and amendment on the proportion of total yield that was marketable. Gainesville Hastings Treatment 1983 1984 1983 1984 1985 % N Rate (kgLha) 67 _t 96.0 93.4 91.1 134 95.6(23)* 95.7 99.6 93.3 91. 5 202 94.6(22) 95.8 99.6 93.2 93.6 NS NS NS NS L*** Qx Amendment Control 96.5(8) 96.8 99.8 94.2 93.0 5.6 kg/ha DCD 93.8(8) 95.8 99.6 93.4 92.5 11.2 kg/ha DCD 95.6(7) 96.6 99.6 93.1 91. 9 0.56 kg/ha Ntys 94.8(8) 94.6 99.5 92.6 91.0 1.12 kg/ha Nty 95.1(8) 96.0 99.6 92.7 92.0 IBDU (1/3 of N) 94.8(6) 95.3 99.5 93.7 92.0 Significance DCD Linear NS NS NS NS NS DCD Quadratic NS NS NS NS NS Nty Rate NS NS NS NS NS DCD v Nty NS NS NS NS NS IBDU v 1h 11 NS NS NS NS NS Interactions NS DCD v Nty X NR Q IBDU v Ih X NR NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. sNty = nitrapyrin. 1 Ih = inhibitors. -..J .....

PAGE 95

72 Table 4-10. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on the propor tion of total yield that was marketable (Gainesville, 1984). N Rate kg/ha 67 134 202 DCD Nitrapyrin --------%---------96.8 94.8 97.0 Q* 95.4 NS 96.4 NS 93.9 NS Nonsignificant (NS) or significant at the 0.05 (*) probability level. Table 4-11. Interaction (IBDU v Ih X NR *) of IBDU v inhib itors, and N rate effects on the proportion of total yield that was marketable (Hastings, 1983). N Rate kg/ha 134 202 IBDU Inhibitors -------% -------99.8 99.1 NS 99.6 NS 99.7 NS Nonsignificant (NS) or significant at the 0.05 (*) probability level.

PAGE 96

, Table 4-12. Effects of N rate and amendment on tuber specific gravity. Treatment N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Ntys 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih 1 Interactions Gainesville 1983 _t 1.0892(23)* 1.0909(22) NS 1.0882(8) 1.0892(8) 1.0908(7) 1.0932(8) 1.0880(8) 1.0910(6) NS NS X NS NS NS 1984 1.0754 1.0732 1.0741 NS 1.0742 1.0723 1.0738 1.0754 1.0766 1.0732 NS NS NS X NS NS 1983 1.0841 1.0854 X 1.0845 1.0832 1.0851 1.0857 1.0854 1.0846 NS NS NS NS NS DCD Q X NR DCD v Nty X NR Hastings 1984 1.0769 1.0787 1.0796 L*** 1.0778 1.0773 1.0781 1.0787 1.0798 1. 0786 NS NS NS NS None 1985 1.0775 1.0791 1.0784 Q* 1.0786 1.0779 1.0762 1.0787 1.0797 1.0789 ** NS NS *** NS None Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. sNty = nitrapyrin. 1 Ih = inhibitors. --.J w

PAGE 97

74 an increase in N rate from 67 to 134 kg ha1 then decreased to 1.0784 with a further increase in N rate to 202 kg ha1 Tuber specific gravity was not influenced by N rate in 1983 or 1984 at Gainesville. Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on tuber specific gravity (Table 4-13). With 202 kg ha1 N, tuber specific gravity decreased from 1.0862 to 1.0818 with an increase in DCD rate from Oto 5.6 kg ha1 With a further increase in DCD to 11.2 kg ha1 tuber specific gravity increased to 1.0856. With 134 kg ha1 N, DCD rate had no effect on tuber specific gravity. In 1985 at Hastings, tuber specific gravity decreased from 1.0786 to 1.0762 with an increase in DCD rate from Oto 11.2 kg ha1 (Table 4-12). In 1983 at Gainesville, tuber specific gravity decreased from 1.0932 to 1.0880 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 (Table 4-12). Tuber specific gravity was not influenced by nitrapyrin rate in 1983, 1984, or 1985 at Hastings, or in 1984 at Gaines ville. In 1984 at Gainesville and Hastings, and in 1985 at Hastings, tuber specific gravity was higher with the nitra pyrin treatments than with the DCD treatments (Table 4-12). In 1984 at Gainesville, tuber specific gravity was 1.0760 with nitrapyrin and 1.0730 with DCD. In 1984 at Hast i ngs tuber specific gravity was 1.0792 with nitrapyrin and 1.0777

PAGE 98

75 Table 4-13. Interaction (DCD Q X NR *) of DCD and N rate effects on tuber specific gravity (Hastings, 1983). DCD Rate (kg/ha) N Rate 0 5.6 11.2 kg/ha 134 1.0828 1.0845 1.0846 NS 202 1.0862 1.0818 1.0856 Q* X NS NS Nonsignificant (NS) or significant at the 0.1 (x), or 0.05 (*) probability levels, respectively. Table 4-14. Interaction (DCD v nitrapyrin X NR *) of DCD v nitrapyrin, and N rate effects on tuber specific gravity (Hastings, 1983). N Rate kg/ha 134 202 DCD 1.0845 1.0837 NS Nitrapyrin 1. 0841 NS 1.0870 ** Nonsignificant (NS) or significant at the 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 99

with DCD. In 1985 at Hastings, tuber specific gravity was 1.0792 with nitrapyrin and 1.0770 with DCD. 76 In 1983 at Hastings, the DCD v nitrapyrin contrast interacted with the N rate effect on tuber specific gravity (Table 4-14). With 202 kg ha1 N, tuber specific gravity was higher with nitrapyrin (1.0870) than with DCD (1.0837). With 134 kg ha1 N, tuber specific gravity was similar with the two inhibitors. Tuber N Concentration N rate effects. Tuber N concentration means increased with increases in N rate in all five year-location combin ations (Table 4-15). In 1983 at both locations, tuber N concentration increased from 0.98% with 134 kg ha1 N, to 1.07-1.08% with 202 kg ha1 N. In 1984, with an increase in N rate from 67 to 202 kg ha1 tuber N concentration in creased from 1.23 to 1.62% at Gainesville, and from 1.12 to 1.33% at Hastings. In 1985 at Hastings, tuber N concentra tion was not measured. Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on tuber N concentration (Table 4-16). With 134 kg ha 1 N, tuber N concentration increased from 0.92 to 1.02% with an increase in DCD rate from Oto 5.6 kg ha1 and d i d not increase further with an increase in DCD to 11.2 kg ha 1 With 202 kg ha 1 N, tuber N concentration was not affected by an increase in DCD rate

PAGE 100

Table 4-15. Effects of N rate and amendment on tuber N concentration in 1983 and 1 984 Treatment 1983 N Rate (kgLha) 67 _t 134 0.98(22)* 202 1.08(21) L** Amendment Control 0.97(8) 5.6 kg/ha DCD 1.01(7) 11.2 kg/ha DCD 1. 00 ( 7) 0. 56 kg/ha Nty 5 1. 02 ( 8) 1.12 kg/ha Nty 1. 06 ( 8) IBDU (1/3 of N) 1.13(5) Significance DCD Linear NS DCD Quadratic NS Nty Rate X DCD v Nty NS IBDU v Ih 1 X Gainesville 1984 % N 1. 23 1.46 1.62 L*** 1 40 1.44 1.45 1.43 1. 45 1.45 NS NS NS NS NS 1983 0.98 1.07 L*** 0.98 1.02 1.06 0 96 1.10 1.02 NS *** NS NS Hastings 1984 1.12 1. 21 1.33 L*** 1. 22 1.19 1.23 1. 24 1.20 1.22 NS NS NS NS NS Interactions NS DCD L X NR L DCD Q X NR DCD v Nty X NR L x Nty RX NR Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 1 Ih = inhibitors. -....I -....I

PAGE 101

Table 4-16. Interaction (DCD Q X NR *) of DCD and N rate effects on tuber N concentration (Hast i ngs, 1983). DCD Rate, (kg/ha) N Rate 0 5.6 11.2 kg/ha % N 78 134 0.92 1.02 0.98 Qx 202 1.05 1.04 1.13 LxQx NS NS NS Nonsignificant (NS) or significant at the 0.1 (x), or 0.05 (*) probability levels, respectively. Table 4-17. Interaction (DCD L X NR L *) of DCD and N rate effects on tuber N concentration (Gainesville, 1984). DCD Rate (kg/ha) N Rate 0 5.6 11.2 kg/ha % N 67 1.26 1.24 1.15 134 1.40 1.43 1 .50 202 1.55 1.64 1.69 L*** L*** L*** Qx Nonsignificant (NS) or signi f icant at the 0.10 ( x ) 0. 05 (*), 0.01 (**), or 0.001 (***) probability l e v e l s, respectively. L* Lx L**

PAGE 102

79 from Oto 5.6 kg ha1 but increased from 1.04 to 1.13% with an increase in DCD rate to 11.2 kg ha1 In 1984 at Gainesville, DCD rate interacted with N rate effects on tuber N concentration (Table 4-17). With 67 kg ha1 N, tuber N concentration decreased from 1.26 to 1.15% with an increase in DCD rate from Oto 11.2 kg ha1 With 134 kg ha1 N, tuber N concentration increased from 1.40 to 1.50% with an increase in DCD rate from Oto 11.2 kg ha1 With 2 02 kg ha1 N, tuber N concentration increased from 1.55 to 1.69% with an increase in DCD rate from Oto 11. 2 kg ha1 In 1983 at Gainesville, tuber N concentration increased from 1.02 to 1.06% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 (Table 4-15). In 1983 at Hastings, nitrapyrin rate interacted with N rate effects on tuber N concentration (Table 4-18). With 202 kg ha1 N, tuber N concentration increased from 0.99 to 1.20% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha 1 With 134 kg ha1 N, tuber N concentration was not affected by nitrapyrin rate. In 1984 at Hastings, the DCD v nitrapyrin contrast interacted with N rate effects on tuber N concentration means (Table 4-19). With 202 kg ha1 N, tuber N concen tration means were higher with DCD (1.36%) than with nitrapyrin (1.27%). With 67 and 134 kg ha 1 N, tuber N concentration means were similar with the two inhibitors.

PAGE 103

80 Table 4-18. Interaction (Nty RX NR *) of nitrapyrin and N rate effects on tuber N concentration (Hastings, 1983). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha % N 134 0.93 1.00 NS 202 0.99 1.20 *** NS Nonsignificant (NS) or significant at the 0.05 (*) or 0.001 (***) probability levels, respectively. Table 4-19. Interaction (DCD v nitrapyrin X NR L x) of DCD v nitrapyrin, and N rate effects on tuber N concentration (Hastings, 1984). N Rate kg/ha 67 134 202 DCD Nitrapyrin --------% N--------1.10 1.19 1.36 L*** 1.14 NS 1.25 NS 1.27 X L* Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively.

PAGE 104

81 In 1983 at Gainesville, tuber N concentration means were higher with IBDU (1.13%) than with inhibitors (1.02%) (Table 4-15). Plant Shoot Biomass at Harvest N rate effects. In 1983 at Gainesville, plant shoot biomass (Table 4-20), increased from 0.89 to 1.08 t ha1 with an increase in N rate from 134 to 202 kg ha1 while at Hastings, plant shoot biomass increased from 0.65 to 0.81 t ha1 with the same increase in N rate. In 1984 at Gaines ville, plant shoot biomass increased from 0.88 to 1.41 t ha1 with an increase in N rate from 67 to 202 kg ha1 while at Hastings, plant shoot biomass decreased from 1.12 to 0.71 t ha1 with the same increase in N rate. Amendment effects. In 1984 at Gainesville, nitrapyrin and N rate interacted in their effects on plant shoot bio mass (Table 4-21). With 202 kg ha1 N, plant shoot biomass decreased from 1.55 to 1.16 t ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 67 and 134 kg ha1 N, plant shoot biomass was not influenced by nitra pyrin rate. Total Biomass at Harvest N rate effects. Total potato plant (plant shoots plus tubers) biomass at harvest (Table 4-22) increased with increases in N rate in all tests except in 1983 at Gaines ville. In 1983 at Hastings, total biomass at harvest

PAGE 105

Table 4-20. Effects of N rate and amendment on plant shoot biomass at harvest in 1983 and 1984. Treatment 1983 N Rate (kgLha) 67 _t 134 0.89(23)* 202 1.08(22) Amendment Control 0.89(8) 5.6 kg/ha DCD 0.99(8) 11.2 kg/ha DCD 0.86(7) 0. 56 kg/ha Nty 5 1.08(7) 1.12 kg/ha Nty 1.01(8) IBDU (1/3 of N) 1.08(6) Significance DCD Linear NS DCD Quadratic NS Nty Rate NS DCD v Nty NS IBDU v Ih 1 NS Interactions NS Gainesville 1984 t/ha 0.88 1.19 1.41 L*** 1.09 1.17 1.15 1.15 1.09 1.26 NS NS NS NS NS Nty RX NR L 1983 0.65 0.81 *** 0.64 0.73 0.75 0.75 0.81 0.76 NS NS NS NS NS NS Hastings 1984 1.12 0 81 0.71 L*** 0.89 0.90 0.83 0.83 0.86 0.86 NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 1 Ih = inhibitors. (X) N

PAGE 106

83 Table 4-21. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on plant shoot biomass at harvest (Gainesville, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha t/ha 67 0.80 0.94 NS 134 1. 25 1.17 NS 202 1.55 1.16 ** L** Lx Nonsignificant (NS) or significant at the 0.10 ( X) t 0.05 ( *) I or 0.01 ( **) probability levels, respectively.

PAGE 107

Table 4-22. Effects of N rate and amendment on total biomass at harvest in 1983 and 1984. Gainesville Hastings Treatment 1983 1984 1983 1984 t/ha N Rate (kgLha) 67 _t 6.50 4.90 134 7.53(22)* 7.87 4.86 5.61 202 7.99(21) 7.93 5.80 6.16 NS L*** *** L*** Q* Amendment Control 7.92(8) 7.80 4.76 5.54 5.6 kg/ha DCD 7.58(7) 7.80 5.46 5.79 11.2 kg/ha DCD 7.40(7) 7.51 5.63 5.63 0. 56 kg/ha Nty 5 7.77(8) 7.12 4.80 5.33 1.12 kg/ha Nty 7.61(8) 6.96 5.78 5.41 IBDU (1/3 of N) 8.28(5) 7.41 5.54 5.63 Significance DCD Linear NS NS NS DCD Quadratic NS NS NS NS Nty Rate NS NS NS DCD v Nty NS NS X IBDU v Ih' NS NS NS NS Interactions NS Nty RX NR L DCD Q X NR * NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (* *) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 1 Ih = inhibitors. (X) ,i:,.

PAGE 108

85 increased from 4.86 to 5.80 t ha1 with an increase in N rate from 134 to 202 kg ha1 In 1984 at Hastings, total biomass increased from 4.90 to 6.16 t ha1 with an increase in N rate from 67 to 202 kg ha1 In 1984 at Gainesville, total biomass increased from 6.50 to 7.87 t ha1 with an increase in N rate from 67 to 134 kg ha1 A further increase in N rate to 202 kg ha1 did not influence total biomass at harvest. Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on total biomass (Table 4-23). With 134 kg ha 1 N, total biomass increased from 3.75 to 5.66 t ha1 with an increase in DCD rate from Oto 5.6 kg ha1 A further increase in DCD rate did not influ ence total biomass. With 202 kg ha1 N, DCD rate did not influence total biomass at harvest. In 1983 at Hastings, total biomass at harvest increased from 4.80 to 5.78 t ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha 1 (Table 4-22). In 1984 at Gainesville, nitrapyrin rate interacted with N rate effects on total biomass at harvest (Table 4-24). With 67 kg ha1 N, total biomass increased from 5.62 to 7.13 t ha1 with an increase in nitrapyrin rate. With 134 and 202 kg ha1 N, nitrapyrin rate had no effect on total biomass. In 1984 at both locations, the DCD treatments resulted in higher total biomass at harvest than did the nitrapyrin treatments (Table 4-22). At Gainesville, total biomass

PAGE 109

86 Table 4-23. Interaction (DCD Q X NR **) of DCD and N rate effects on total biomass at harvest (Hastings, 1983). N Rate kg/ha 134 202 DCD Rate (kg/ha) 0 5.6 11.2 ----------t/ha---------3.75 5.77 5.66 5.27 NS 5.01 L*Q** 6.26 NS NS Nonsignificant (NS) or significant at the 0.05 (*) or 0.01 (**) probability levels, respectively. Table 4-24. Interaction (Nty RX NR L *) of nitrapyrin rate and N rate effects on total biomass at harvest (Gainesville, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha t/ha 67 5.62 7.13 134 7.91 7.01 NS 202 7.84 6.74 NS L** NS Qx Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 110

means were 7. 66 t ha1 with DCD and 7. 04 t ha1 with nitra pyrin. At Hastings, total biomass means were 5.71 t ha1 with DCD and 5.37 t ha1 with nitrapyrin. Plant Shoot N Concentration at Harvest 87 N effects. In 1983 at Gainesville, plant shoot N concentration at harvest (Table 4-25) increased from 2.04 to 2.34% with an increase in N rate from 134 to 202 kg ha1 In 1984, shoot N concentration increased from 2.16 to 3.38% at Gainesville, and from 1.40 to 2.02% at Hastings, with an increase in N rate from 67 to 202 kg ha1 Amendment effects. In 1984 at Hastings, DCD and N rate interacted in their effects on plant shoot N concentra tion at harvest (Table 4-26). With 67 kg ha1 N, shoot N concentration decreased from 1.52 to 1.38% with an increase in DCD rate from Oto 5.6 kg ha1 With a further increase in DCD to 11.2 kg ha1 shoot N concentration was not affected. With 134 and 202 kg ha1 N, plant shoot N concen tration at was not affected by DCD rate. In 1984 at Hastings, plant shoot N concentration at harvest was influenced by an interaction between nitrapyrin and N rate effects (Table 4-27). With 202 kg ha1 N, shoot N concentration increased from 1.83 to 2.07% with an in crease in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 67 and 134 kg ha1 N, plant shoot N concentration was not affected by nitrapyrin rate.

PAGE 111

Table 4-25. Effects of N rate and amendment on plant shoot N concentration at harvest in 1983 and 1984. Treatment N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Ntys 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih' Interactions Gainesville 1983 1984 _t 2.16 2.04(23)* 2.64 2.34(22) 3.38 L** L*** 2.06(8) 2.98 2.24(8) 2.81 2.05(7) 3.17 2.13(8) 2.90 2.19(8) 2.79 2.48(6) 2.96 NS NS NS NS NS NS NS NS NS NS NS 1983 % N 2.47 2.56 NS 2.47 2.56 2.52 2.57 2.54 2.41 NS NS NS NS NS N Hastings 1984 1.40 1.71 2.02 L*** 1.70 1.71 1.69 1.66 1.72 1.79 NS NS NS NS X DCD Q X NR L x Nty RX NR L IBDU v I h X NR L * Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. sNty = nitrapyrin. 1 Ih = inhibitors. co co

PAGE 112

89 Table 4-26. Interaction (DCD Q X NR L x) of DCD and N rate effects on plant N concentration at harvest (Hastings, 1984). DCD Rate (kg/ha) N Rate 0 5.6 11.2 kg/ha % N 67 1.52 1. 38 1.40 134 1.60 1.65 1.71 202 1. 96 2.10 1.95 L*** L*** L*** Q** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. L*Qx NS NS Table 4-27. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on plant shoot N concentration at harvest (Hastings, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha % N 67 1. 43 1.37 134 1.73 1.71 202 1.83 2.07 L*** L*** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. NS NS X

PAGE 113

90 In 1983 at Gainesville, plant shoot N concentration means were higher with the IBDU treatment (2.48%) than with the inhibitor treatments (2.15%). In 1984 at Hastings, the IBDU v inhibitor contrast interacted with N rate effects on shoot N concentration (Table 4-28). The trend in the data reversed as N rate increased. With 67 kg ha1 N, shoot N concentration means were higher with inhibitors (1.40%) than with IBDU ( 1.29%). With 202 kg ha1 N, however, shoot N concentration means were higher with IBDU (2.23%) than with inhibitors (1.99%). With 134 kg ha1 N, plant shoot N con centration means were similar with the two amendment types. N Uptake by Plant Shoots at Harvest N Effects. In 1983 the amount of N uptake by plant shoots at harvest (Table 4-29) increased from 18.3 to 25.6 kg ha1 at Gainesville, and from 16. 3 to 20. 7 kg ha1 at Hastings, with an increase in N rate from 134 to 202 kg ha 1 In 1984 at Gainesville, an increase in N rate from 67 to 202 kg ha 1 resulted in an increase in shoot N uptake from 19.0 to 47.8 kg ha 1 while at Hastings, there was no N rate effect. Amendment effects. In 1984 at Gainesville, nitrapyrin and N rate effects interacted in their effects on shoot N uptake (Table 4-30). With 202 kg ha 1 N, shoot N uptake decreased from 54 .1 to 36. 0 kg ha 1 with an increase i n nitrapyrin rate from 0.56 to 1.12 kg ha 1 With 67 and 1 3 4 kg ha 1 N, nitrapyrin rate had no effect on shoot N uptake.

PAGE 114

91 Table 4-28. I nteraction ( IBDU v Ih X NR L **) of IBDU v inhibitors, and N rate effects on plant shoot N concentration at harvest (Hastings, 1984). N Rate kg/ha 67 134 202 IBDU Inhibitors --------% N---------1.29 1.83 2.23 L*** 1.40 ** 1. 70 NS 1.99 L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 115

Table 4-29. Effects of N rate and amendment on N uptake by plant shoots at harvest in 1983 and 1984. Gainesville Hastings Treatment 1983 1984 1983 1984 -kg/ha----------N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Ntys 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih 1 Interactions _t 18.3(23)* 25.6(22) L** 18.2(8) 22.6(8) 17.6(7) 24.0(8) 22.4(8) 26.8(6) NS NS NS NS NS DCD v Nty X NR x 19.0 32.0 47.8 L*** 30.4 31. 8 34.8 34.7 29.3 36.8 NS NS NS NS NS Nty RX NR L 15.7 16.3 14 1 20.7 15 0 L** NS 16 2 14.8 19.1 15.2 18.9 13.2 18.9 13.2 20.4 14 6 18.5 15 5 NS N S NS NS NS NS NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (* *) probabil it y levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 1 Ih = inhibitors. \D N

PAGE 116

93 Table 4-30 I nteraction ( Nty RX NR L *) of nitrapyrin and N rate effects on N uptake by plant shoots at harvest (Gainesville, 1984). N Rate kg/ha 67 134 202 0.56 Nitrapyrin Rate (kg/ha) 1.12 --------kg/ha-------18.0 32.1 54.1 L** 19.9 NS 32.0 NS 36.0 *** Lx Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 4-31. Interaction (DCD v nitrapyrin X NR x) of DCD v nitrapyrin, and N rate effects on N uptake by plant shoots at harvest (Gainesville, 1983). N Rate kg/ha 134 202 DCD Nitrapyrin ------kg/ha ----17.9 22.4 NS 16.2 NS 30.3 NS L** Nonsignificant (NS) or significant at the 0.10 (x) or 0.01 (**) probability levels, respectively.

PAGE 117

94 In 1983 at Gainesville, the DCD v nitrapyrin contrast interacted with N rate effects on shoot N uptake means (Table 4-31). Shoot N uptake was influenced by N rate with the nitrapyrin treatments but not with the DCD treatments. With nitrapyrin, shoot N uptake increased from 16.2 to 30.3 kg ha1 with an increase in N rate from 134 to 202 kg ha1 N Uptake by Tubers N effects. The amount of N uptake by tubers (Table 4-32) increased with increases in N rate in both years at both locations. In 1983, tuber N uptake increased from 65.8 to 74.7 kg ha1 at Gainesville, and from 41.3 to 53.7 kg ha 1 at Hastings, with an increase in N rate from 134 to 202 kg ha1 In 1984 at Gainesville, tuber N uptake increased from 69.2 to 96.8 kg ha1 with an increase in N rate from 67 to 134 kg ha1 Tuber N uptake was not influenced by a further increase in N rate to 202 kg ha1 In 1984 at Hastings, tuber N uptake increased from 42 .1 to 72. 4 kg ha1 with an increase in N rate from 67 to 202 kg ha 1 Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on tuber N uptake (Table 4-33) With 134 kg ha1 N, tuber N uptake increased from 30.1 to 50.3 kg ha 1 with an increase in DCD rate from Oto 5. 6 kg ha1 A further increase in DCD rate to 11. 2 kg ha1 resulted in a reduction of tuber N uptake to 43.2 kg ha1 which was higher than tuber N uptake with O DCD. With 202 kg ha1 N, DCD rate had no effect on tuber N uptake.

PAGE 118

Table 4-32. Effects of N rate and amendment on N uptake by tubers in 1983 and 1984. Gainesville Hastings Treatment 1983 1984 1983 1984 -kg/ha --N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Ntys 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih 1 Interactions _t 65.8(22)* 74.7(21) L* 68 1(8) 67.7(7) 65.5(7) 69.1(8) 70.4(8) 80.8(5) NS NS NS NS NS 69.2 96.8 104.8 L*** Q* 94.2 96.1 91. 6 85.2 84.5 90.0 NS NS NS X NS Nty RX NR L 41.3 53.7 L*** 41.4 47.8 52.0 39.7 55.5 48.5 NS *** NS NS DCD Q X NR ** DCD v Nty X NR x 42.1 58.2 72.4 L*** 57.1 59.2 60.7 54.1 55.3 59.0 NS NS NS X NS DCD v Nty X NR L x Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. sNty = nitrapyrin. 1 Ih = inhibitors. \0 l11

PAGE 119

96 Table 4-33. Interaction (DCD Q X NR **) of DCD and N rate effects on N uptake by tubers (Hastings, 1983). N Rate 0 kg/ha 134 202 30.1 52.8 X DCD Rate (kg/ha) 5.6 kg/ha 50.3 45.3 NS 11.2 43.2 L**Q*** 60.7 NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 4-34. Interaction (Nty RX NR L *) of nitrapyrin and N rate effects on N uptake by tubers (Gainesville, 1984). N Rate kg/ha 67 134 202 Nitrapyrin Rate (kg/ha) 0.56 1.12 --------kg/ha------57.2 95.8 102.8 L*** Q* 77.5 X 88.2 NS 87.9 NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively.

PAGE 120

97 In 1983 at Hastings, tuber N uptake increased from 39.7 to 55.5 kg ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 (Table 4-32). In 1984 at Gaines ville, nitrapyrin and N rate interacted in their effects on tuber N uptake (Table 4-34). With 67 kg ha1 N, tuber N uptake increased from 57. 2 to 77. 5 kg ha 1 with an increase in nitrapyrin rate from 0 56 to 1.12 kg ha1 With 134 and 202 kg ha1 N, tuber N uptake was not affected by nitrapyrin rate. In 1983 at Hastings, the DCD v nitrapyrin contrast interacted with N rate effects on tuber N uptake ( Table 4-35). With 134 kg ha 1 N, tuber N uptake means were greater with DCD (46.8 kg ha 1 ) than with nitrapyrin (38.9 kg ha1 ). With 202 kg ha 1 N, tuber N uptake means were similar with the two inhibitors. In 1984 at both locations, tuber N uptake means were higher with DCD than with nitrapyrin. At Gainesville, tuber N uptake means were 93. 8 kg ha 1 with DCD and 84. 8 kg ha1 with nitrapyrin. In 1984 at Hastings, the DCD v nitrapyrin contrast interacted with N rate effects on tuber N uptake (Table 4-36). With 202 kg ha 1 N, tuber N uptake means were higher with DCD (79.9 kg ha 1 ) than with nitrapyrin (65.9 kg ha 1 N). With 67 and 1 34 kg ha 1 N, tuber N uptake means were similar with the two inhibitors. In 1983 at Gaines ville, tuber N uptake means were higher with IBDU (80.8 kg ha 1 ) than with inhibitors (68.2 kg ha 1 N) (Table 4-32).

PAGE 121

98 Table 4-35. Interaction (DCD v nitrapyrin X NR x) of DCD v nitrapyrin, and N rate effects on N uptake by tubers (Hastings, 1983). N Rate kg/ha 134 202 DCD Nitrapyrin --------kg/ha-------46.8 53.0 NS 38.9 ** 56.3 NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.01 (**) probability levels, respectively. Table 4-36. Interaction (DCD v nitrapyrin X NR L x) of DCD v nitrapyrin, and N rate effects on N uptake by tubers (Hastings, 1984). N Rate kg/ha 67 134 202 DCD Nitrapyrin --------kg/ha-------41.9 58.2 79.9 L*** 39.8 NS 58.5 NS 65.9 ** L*** Nonsignificant (NS) or significant at the 0.1 (x), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 122

99 Total N Uptake by Plant Shoots and Tubers N effects. Total N uptake by plant shoots and tubers (Table 4-37) increased with increases in N rate in all tests. In 1983, with an increase in N rate from 134 to 202 kg ha1 total N uptake increased from 83. 8 to 100. 3 kg ha1 at Gainesville, and from 57.6 to 74.4 kg ha1 at Hastings. In 1984 at Gainesville, total N uptake increased from 88.2 to 128.8 kg ha1 with an increase in N rate from 67 to 134 kg ha1 A further increase in N rate to 202 kg ha1 did not influence total N uptake. In 1984 at Hastings, total N uptake increased from 57. 7 to 87. 5 kg ha1 with an increase in N rate from 67 to 202 kg ha1 Amendment effects. In 1983 at Hastings, DCD rate interacted with N rate effects on total N uptake (Table 4-38). With 134 kg ha1 N, total N uptake increased from 42.4 to 68.6 kg ha1 with an increase in DCD rate from Oto 5. 6 kg ha1 A further increase in DCD to 11. 2 kg ha1 did not influence total N uptake. In 1983 at Hastings, with 202 kg ha 1 N, total N uptake was not influenced by DCD rate. In 1983 at Hastings, total N uptake by plant shoots and tubers increased from 57. 6 to 75. 9 kg ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha 1 In 1984 at Gainesville, nitrapyrin and N rate interacted in their effects on total N uptake (Table 4-39). With 67 kg ha 1 N, total N uptake increased from 7 5. 3 to 9 7. 4 kg ha1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg

PAGE 123

Table 4-37. Effects of N rate and amendment on total N uptake by plant shoots and tubers at harvest in 1983 and 1984. Gainesville Hastings Treatment 1983 1984 1983 1984 ----------------kg/ha------------N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Nty 5 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih 1 Interactions _t 83.3(22)* 100.3(21) ** 86.2(8) 89.2(7) 83.1(7) 93.1(8) 92.9(8) 107.7(5) NS NS NS NS NS 88.2 128.8 152.6 L*** Q* 124.6 128.0 126.4 120.0 113.8 126.7 NS NS NS NS Nty RX NR Q ** 57.6 74.4 *** 57.6 67.0 70.9 57.6 75.9 67.0 NS ** NS NS DCD Q X NR ** 57.7 72.3 87.5 L*** 72.0 74.4 73.9 70.5 69.9 74.4 NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. tRate not included in 1983. *Gainesville 1983 means are least square means. Number of observations are in parentheses. 5 Nty = nitrapyrin. 1 Ih = inhibitors. I-' 0 0

PAGE 124

101 Table 4-38. Interaction (DCD Q X NR **) of DCD and N rate effects on total N uptake by plant shoots and tubers at harvest (Hastings, 1983). N Rate 0 kg/ha 134 202 42.4 72.8 X DCD Rate (kg/ha) 5.6 11.2 kg/ha 68.6 59.9 L*Q** 65.3 81.9 NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.01 (**) probability levels, respectively. Table 4-39. Interaction (Nty RX NR Q **) of nitrapyrin and N rate effects on total N uptake by plant shoots and tubers at harvest (Gainesville, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha kg/ha 67 75.3 97.4 X 134 127.9 120.0 NS 202 156.8 12 3. 9 X L*** NS Nonsignificant (NS) or significant at the 0.10 (x), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 125

102 ha1 With 202 kg ha1 N, however, total N uptake decreased from 156.8 to 123.9 kg ha1 with an increase in nitrapyrin rate. With 134 kg ha1 N, total N uptake was not influenced by nitrapyrin rate. In 1984 at Gainesville, total N uptake means were greater with DCD (127.2 kg ha 1 ) than with nitrapyrin ( 116.9 kg ha1 ) (Table 4-37). In 1983 at Gainesville, total N uptake means were higher with IBDU (107 7 kg ha 1 ) t han w i th inhibitors (89.6 kg ha1 ). Leaf N Concentration at Tuber Initiation N effects. In 1983 at Hastings, concentration of leaf Nat tuber initiation (LNTI) (Table 4-40) increased from 3.57 to 3.75% with an increase in N rate from 134 to 202 kg ha 1 In 1984 at Hastings, LNTI concentration increased from 5.01 to 5.55% with an increase in N rate from 67 to 202 kg ha1 In 1985 at Hastings, LNTI concentration increased from 5.62 to 6.17% with an increase in N rate from 67 to 134 kg ha1 A further increase in N to 202 kg ha 1 did not influence LNTI concentration. Leaf N concentration at tuber initiation was not influenced by N rate in 1983 or 1984 at Gainesville. Amendment effects. In 1983 at Hastings, LNTI con centration increased from 3.45 to 3.86% with an increase in DCD rate from Oto 11.2 kg ha 1 (Table 4-40). I n 1984 at Gainesville, LNTI concentration decreased from 4.87 t o 4 .65 % with an increase in DCD rate from Oto 11 .2 kg ha 1 I n th e

PAGE 126

103 Table 4-40. Effects of N rate and amendment on leaf N concentration at tuber initiation. Treatment N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0. 56 kg/ha Nty 1 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih 1 Interactions 1983[43]t -* 5.65(23) 5.76(22) NS 5.70(8) 5.68(8) 5.76(7) 5.61(8) 5.75(8) 5.73(6) NS NS NS NS NS NS Gainesville 1984(48] % N 4.76 4.87 4.80 NS 4.87 4.83 4.65 4.86 4.73 4.92 NS NS NS Nty RX NR Q Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNwnbers in brackets represent days after planting. *Rate not included in 1983. sGainesville 1983 means are least square means. Nwnber of observations are in parentheses. 1 Nty = nitrapyrin. 'Ih = inhibitors.

PAGE 127

104 Table 4-40.--Extended Hastings 1983[54] 1984[55] 1985[51] --------------% N1----------------3.57 3.75 ** 3.45 3.62 3.86 3.61 3.85 3.58 ** NS NS X Nty RX NR x DCD v Nty X NR x 5.01 5.22 5.55 L*** 5.20 5.20 5.37 5.22 5.25 5.31 ** X NS NS NS IBDU v Ih X NR L *** 5.62 6.17 6.40 L*** Q** 6.09 6 06 6.17 6.15 6.03 5.90 NS NS NS NS ** DCD v Nty X NR Q

PAGE 128

105 same year at Hastings, LNTI concentration was not influenced by an increase in DCD rate from Oto 5.6 kg ha1 A further increase in DCD to 11.2 kg ha1 resulted in an increase in LNTI concentration from 5.20 to 5.37%. Leaf N concentration at tuber initiation was not influenced by DCD rate in 1983 at Gainesville or in 1985 at Hastings. In 1983 at Hastings, LNTI concentration increased from 3.61 to 3.85% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 In 1984 at Gainesville, nitrapyrin and N rate interacted in their effects on LNTI concentration (Table 4-41). With 67 kg ha1 N, LNTI concentration de creased from 4.90 to 4.69% with an increase in nitrapyrin rate. With 134 and 202 kg ha1 N, nitrapyrin rate had no effect on LNTI concentration. In 1985 at Hastings, the DCD v nitrapyrin contrast interacted with N rate effects on LNTI concentration (Table 4-42). With 134 kg ha1 N, LNTI concentration means were higher with DCD (6.32%) than with nitrapyrin (6.08%). With 67 and 202 kg ha1 N, LNTI concentration means were similar with the two inhibitors. Leaf N concentration at tuber initiation was higher with IBDU (4.92%) than with inhibitors (4.77%) in 1984 at Gainesville (Table 4-40). In 1983 at Hastings, IBDU resulted in lower LNTI concentration means (3.58%) than did inhibitors (3.74%). In 1984 at Hastings, the IBDU v inhib itors contrast interacted with N rate (Table 4-43). With 67

PAGE 129

106 Table 4-41. Interaction (Nty RX NR *) of nitrapyrin rate and N rate effects on leaf N concentration at tuber initiation (48 dap) (Gainesville, 1984). N Rate kg/ha 67 134 202 Nitrapyrin Rate (kg/ha} 0.56 1.12 --------% N-------4.90 4.76 4.94 NS 4.69 X 4.86 NS 4.64 NS NS Nonsignificant (NS) or significant at the 0.10 (x) or 0.05 (*), probability levels, respectively. Table 4-42. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on leaf N concentration at tuber initiation (51 dap) (Hastings, 1985). N Rate kg/ha 67 134 202 DCD Nitrapyrin --------% N--------5.62 6.32 6.40 L*** Q*** 5.70 NS 6.08 6.49 NS L*** Nonsignificant (NS) or significant at the 0.05 (*) or 0.001 (***) probability levels, respectively.

PAGE 130

Table 4-43. Interaction ( IBDU v Ih X NR L ***) of IBDU v inhibitors, and N rate effects on leaf N concentration at tuber initiation (55 dap) (Hastings, 1984). 107 N Rate IBDU Inhibitors kg/ha 67 134 202 --------% N-------5.23 5 31 5.40 Lx 4.96 *** 5.22 NS 5.60 ** L*** Nonsignificant (NS) or significant at the 0.10 (x), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 131

108 kg ha1 N, LNTI concentration means were higher with IBDU (5.23%) than with inhibitors (4.96%). With 202 kg ha1 N, LNTI concentration means were higher with inhibitors (5.60%) than with IBDU (5.40%). With 134 kg ha1 N, LNTI concentra tion means were similar with the two types of amendments. Leaf N Concentration at Flowering N effects. In 1983 at Gainesville, leaf N concentration at the flowering or tuber bulking stage (LNF) increased from 3.92 to 4.22% with an increase in N rate from 134 to 202 kg ha1 (Table 4-44). In 1984, LNF concentration increased from 3.75 to 4.65% at Gainesville, and from 2.88 to 3.80% at Hastings, with an increase in N rate from 67 to 202 kg ha1 In 1985 at Hastings, LNF concentration in creased from 3.50 to 5.13% with an increase in N rate from 67 to 202 kg ha1 Amendment effects. Leaf N concentration at flowering increased with an increase in DCD rate in three of four year-location combinations. Increasing DCD rate resulted in an increase in leaf N concentration at flowering from 3.84 to 4.12% in 1983 at Gainesville, from 4.13 to 4.28% in 1984 at Gainesville, and from 4.28 to 4.42% in 1985 at Hastings. In 1984 at Hastings, DCD rate interacted with N rate effects on LNF concentration (Table 4-45). With 202 kg ha1 N, LNF concentration was not affected by an increase in DCD rate from Oto 5.6 kg ha1 but with a further increase in DCD to 11.2 kg ha 1 LNF concentration decreased from 3.95 to

PAGE 132

109 Table 4-44. Effects of N rate and amendment on leaf N concentration at flowering. Gainesville Treatment 1983[66]t 1984[74] --------% N--------N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11. 2 kg/ha DCD 0. 56 kg/ha Nty' 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih# Interactions -* 3.92(23)s 4.22(22) ** 3.84(8) 3.78(8) 4.12(7) 4.05(8) 4.11(8) 4.47(6) X NS NS NS ** IBDU v Ih X NR 3.75 4.18 4.65 L*** 4.13 4.16 4.28 4.21 4.16 4.21 NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after planting. *Rate not included in 1983. sGainesville 1983 means are least square means. Number of observations are in parentheses. 1 Nty = nitrapyrin. #Ih = inhibitors.

PAGE 133

110 Table 4-44--Extended. Hastings 1984[81] 1985[73] --------------% N------------2.88 3.40 3.80 L*** 3.38 3.38 3.18 3.34 3.44 3.43 ** X NS X DCD Q X NR L Nty RX NR Q x DCD v Nty X NR IBDU v Ih X NR Q ** Q 3.50 4.36 5.13 L*** 4.28 4.36 4.42 4.39 4.37 4.17 X NS NS NS ** IBDU v Ih X NR L

PAGE 134

111 Table 4-45. Interaction (DCD Q X NR L *) of DCD and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 1984). DCD Rate (kg/ha) N Rate 0 5.6 11.2 % N 2.80 2.84 NS 3.40 3.15 NS kg/ha 67 134 202 2.91 3.37 3.87 3.95 3.55 L**Q** L*** L*** L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 4-46. Interaction (Nty RX NR Q *) of nitrapyrin and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha % N 67 2.83 2.94 134 3.62 3.53 202 3.58 3.86 L*** L*** Q*** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. X NS **

PAGE 135

112 3.55%. With 67 and 134 kg ha1 N, DCD rate had no effect on LNF concentration. In 1984 at Hastings, nitrapyrin rate interacted with N rate effects on LNF concentration (Table 4-46). With 67 kg ha1 N, LNF concentration increased from 2.83 to 2.94%, and with the 202 kg ha1 N, LNF concentration increased from 3.58 to 3.86% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 134 kg ha1 N, nitrapyrin rate had no effect on LNF concentration. In 1983 and 1984 at Gaines ville, and in 1985 at Hastings, LNF concentration was not influenced by nitrapyrin rate. In 1984 at Hastings, the DCD v nitrapyrin contrast interacted with N rate effects on LNF concentration (Table 4-47). With 134 kg ha 1 N, LNF concentration means were higher with nitrapyrin (3.57%) than with DCD (3.27%). With 67 and 202 kg ha1 N, LNF concentration means were similar with the two inhibitors. In 1983 at Gainesville, the IBDU v inhibitors contrast interacted with N rate effects on LNF concentration (Table 4-48). With 134 kg ha 1 N, LNF concentration means were higher with IBDU (4.54%) than with inhibitors (3.80%). With 202 kg ha 1 N, LNF concentration means were similar with the two types of amendments. In 1984 at Hastings, the IBDU v inhibitors contrast interacted with N rate effects on LNF concentration (Table 4-49). With 67 kg ha1 N, LNF concentration means were

PAGE 136

113 Table 4-47. Interaction (DCD v nitrapyrin X NR Q **) of DCD v nitrapyrin, and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 19 84) N Rate kg/ha 67 134 202 DCD Nitrapyrin --------% N--------2.82 3.27 3.75 L*** Q** 2.89 NS 3.57 ** 3.72 NS L*** Nonsignificant (NS) or significant at the 0.01 (**) or 0.001 (***) probability levels, respectively. Table 4-48. Interaction (IBDU v Ih X NR *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering (66 dap) (Gainesville, 1983). N Rate IBDU Inhibitors kg/ha 134 202 --------% N--------4.54 4.41 NS 3.80 ** 4.24 NS NS** Nonsignificant (NS) or signif i cant at the 0.05 (*) or 0.01 (**) probability levels, respectively.

PAGE 137

114 Table 4-49. Interaction (IBDU v Ih X NR Q *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering (81 dap) (Hastings, 19 84) N Rate kg/ha 67 134 202 IBDU Inhibitors --------% N--------2.98 3.34 3.98 L*** Q** 2.85 3.42 NS 3.74 ** L*** Q* Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 4-50. Interaction (IBDU v IH X NR L *) of IBDU v inhibitors, and N rate effects on leaf N concentration at flowering (73 dap) (Hastings, 1985). N Rate kg/ha 67 134 202 IBDU Inhibitors --------% N--------3.47 4.25 4.80 L*** Qx 3.51 NS 4.43 5.22 ** L*** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 138

115 higher with IBDU (2.98%) than with inhibitors (2.85%). With 202 kg ha1 N rate as well, LNF concentration means were higher with IBDU (3.98%) than with inhibitors (3.74%). With 134 kg ha1 N, LNF concentration means were similar with the two types of amendment. In 1985 at Hastings, LNF concentration means were lower with the IBDU treatment than with the inhibitor treat ments with the 134 and 202 kg ha1 N rates (Table 4-50). With 134 kg ha1 N, LNF concentration means were 4.25% with IBDU and 4. 43% with inhibitors. With 202 kg ha1 N, LNF concentration means were 4.80% with IBDU and 5.22% with in hibitors. With 67 kg ha1 N, LNF concentration means were similar with the two types of amendment. Leaf N Concentration at Tuber Maturation N effects. Concentration of leaf Nat tuber matur ation (LNTM) increased with increases in N rate in all years and locations years where LNTM was measured (Table 4-51). In 1983, LNTM concentration increased from 2.69 to 2.91% at Gainesville, and from 2.85 to 3.11% at Hastings, with an increase in N rate from 134 to 202 kg ha1 In 1984 at Gainesville, an increase in N rate from 67 to 134 kg ha 1 did not influence LNTM concentration. With an increase in N rate from 134 to 202 kg ha1 however, LNTM concentration increased from 3.13 to 3.80%. In 1984 at Hastings, an increase in N rate from 67 to 134 kg ha1 did not influence LNTM concentration. With an increase in N rate from 134 to

PAGE 139

Table 4-51. Effects of N rate and amendment on leaf N concentration at tuber maturation in 1983 and 1984. Gainesville Treatment 1983[93]t 1984[94] Hastings 1983[95] 1984[98] ----------------% N---------------N Rate (kg/ha) 67 134 202 Amendment Control 5.6 kg/ha DCD 11.2 kg/ha DCD 0.56 kg/ha Nty 1 1.12 kg/ha Nty IBDU (1/3 of N) Significance DCD Linear DCD Quadratic Nty Rate DCD v Nty IBDU v Ih# -* 2.69(23) 5 2.91(22) 2.74(8) 2.84(8) 2.79(7) 2.59(8) 2.83(8) 2.98(6) NS NS NS NS NS 2.98 3.13 3.80 L*** Q*** 3.31 3.18 3.38 3.28 3.26 3.40 NS X NS NS NS 2.85 3.11 ** 3.04 2.87 3.16 2.94 3.03 2.84 NS X NS NS NS 2.19 2.37 2.68 L*** Q* 2.45 2.42 2.37 2.37 2.41 2.46 NS NS NS NS NS Interactions NS Nty RX NR Q *** DCD v Nty X NR Q NS DCD Q X NR L Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after planting. *Rate not included in 1983. 5 Gainesville 1983 means are least square means. Number of observations are in parentheses. 1 Nty = nitrapyrin. #Ih = inhibitors. I-' I-' O'\

PAGE 140

117 202 kg ha1 however, LNTM concentration increased from 2.37 to 2.68%. Amendment effects. In 1984 at Gainesville, LNTM concentration decreased from 3.31 to 3.18% with an increase in DCD rate from Oto 5.6 kg ha1 A further increase in DCD to 11.2 kg ha1 increased LNTM to a concentration that was not different from that with O DCD. In 1983 at Has tings, LNTM concentration decreased from 3.04 to 2.87% with an increase in DCD rate from Oto 5.6 kg ha1 A further increase in DCD to 11.2 kg ha1 increased LNTM to a concen tration that was not different from that with O DCD. In 1984 at Hastings, DCD and N rate interacted in their effects on LNTM concentration (Table 4-52). With 67 kg ha1 N, LNTM concentration decreased from 2.26 to 2.12% with an increase in DCD rate from Oto 5.6 kg ha1 With a further increase in DCD to 11.2 kg ha1 LNTM increased to a concentration that was not different from that with O DCD. With 134 and 202 kg ha1 N, LNTM concentration was not in fluenced by DCD rate. In 1984 at Gainesville, nitrapyrin and N rate inter acted in their effects on LNTM concentration (Table 4-53). With 67 kg ha1 N, LNTM concentration increased from 2.78 to 3.15% with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 134 kg ha1 N, however, LNTM concentration decreased from 3.30 to 2.68% with an increase in nitrapyrin

PAGE 141

118 Table 4-52. Interaction (DCD L X NR L *) of DCD and N rate effects on leaf N concentration at tuber maturation (98 dap) (Hastings, 1984). DCD Rate (kg/ha) N Rate 0 5.6 11.2 kg/ha % N 67 2.26 2.12 2.29 Q* 134 2.40 2.44 2.24 NS 202 2.69 2.70 2.58 NS L*** L*** L*** Q*** Nonsignificant (NS) or significant at the 0.05 ( ) or 0.001 (***) probability levels, respectively. Table 4-53. Interaction (Nty RX NR Q ***) of nitrapyrin rate and N rate effects on leaf N concentration at tuber maturation (94 dap) (Gainesville, 1984). N Rate kg/ha 67 134 202 0.56 2.78 3.30 3.77 L*** Nitrapyrin Rate (kg/ha) 1.12 % N 3.15 2.68 3.95 L*** Q*** ** *** NS Nonsignificant (NS) or significant at the (***) probability levels, respectively. 0.01 (**) or 0.001

PAGE 142

119 rate. With 202 kg ha 1 N, nitrapyrin rate had no effect on LNTM concentration. In 1984 at Gainesville, the DCD v nitrapyrin contrast interacted with N rate effects on LNTM concentration (Table 4-54). With 134 kg ha1 N, LNTM concentration means were higher with the DCD treatments (3.22%) than with the nitra pyrin treatments (2.99%). With 67 and 202 kg ha1 N, LNTM concentration means were similar with the two inhibitors.

PAGE 143

120 Table 4-54. Interaction (DCD v nitrapyrin X NR Q *) of DCD v nitrapyrin, and N rate effects on leaf N concentration at tuber maturation (94 dap) (Gainesville, 1984). N Rate kg/ha 67 134 202 DCD Nitrapyrin --------% N-------2.94 3.22 3.68 L*** 2.97 NS 2.99 X 3.86 NS L*** Q** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 144

CHAPTER 5 EXTRACTABLE N AND DCD IN SOILS PLANTED TO POTATO Soil Inorganic N To be beneficial to crop growth and yield, nitrif ication inhibitors should inhibit nitrification, thereby increasing the supply of plant-available Nin the soil rooting zone. Therefore, data in Chapter 5 are presented as total extractable soil inorganic N (SIN) concentration, e.g., NH/-N plus NO 3 --N in the O to 30 cm depth rather than as NH/-N and NO 3 --N separately. Soil inorganic N concentra tion data for six potato plant growth stages are shown in the tables in this chapter. Most treatment interactions shown in the main effect tables in this chapter were exam ined in detail in separate interaction tables. Some inter actions were not presented in separate tables because they contributed no additional information about the data. Graphic depictions of SIN concentration with selected treatments are shown in Appendix C. Analysis of variance tables for extractable NH/-N and NO 3 --N concentrations separately, and the ratio of NO 3 --N/ (NO 3 --N + NH/-N), are shown in Appendix D. Fertilizer and amendment applications were carried out simultaneously with planting of the potato crops. Thus, the 121

PAGE 145

122 days after fertilizer application referred to in this chap ter, are equivalent to the days after planting referred to in Chapter 4. Planting+ one week. Soil samples were taken in the first week after planting at Hastings only. Samples were taken five and six days after fertilizer application in 1983 and 1984, respectively. In 1984 on day 6, SIN concentration increased from 77.4 to 193.9 mg kg1 with an increase in N rate from 67 to 202 kg ha1 (Table 5-1). In 1983 on day 5, SIN concentration was not influenced by Nor DCD rate. In 1984 on day 6 at Hastings, DCD rate interacted with N rate effects on SIN concentration (Table 5-2). With 67 kg ha1 N, SIN concentration decreased from 83. 2 to 63. 7 mg kg1 with an increase in DCD rate from Oto 11.2 kg ha1 With 134 kg ha1 N, DCD rate had no effect. With 202 kg ha1 N, SIN concentration decreased from 202.0 to 147.6 mg kg1 with an increase in DCD rate from Oto 5.6 kg ha 1 With a fur ther increase in DCD rate to 11.2 kg ha1 SIN concentration increased to 214.5 mg kg 1 which was not different from the concentration with O DCD. Soil was not sampled from the nitrapyrin or IBDU amended plots on day 5 in 1983. In 1984 on day 6, nitra pyrin rate interacted with N rate effects on SIN concentra tion (Table 5-3), with the nitrapyrin rate effect present only with 67 and 202 kg ha 1 N. With 67 kg ha 1 N, an

PAGE 146

123 Table 5-1. Effects of N rate and amendment on soil inorganic N concentration at the planting+ one week stage of potato (Hastings). Independent Variable N Rate 67 kg/ha 134 kg/ha 202 kg/ha DCD Rate 0.0 kg/ha 5.6 kg/ha 11. 2 kg/ha Ntys Rate 0.56 kg/ha 1.12 kg/ha DCD v Nty IBDU as 1/3 of N IBDU v Ih* Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU X Ih X NR 1983[5]t 1984[6] ------~mg/kg N--------* 6.6 7.5 NS 6.0 8.0 7.1 NS -' NS NS 77.4 129.6 193.9 L*** 137.1 120.0 132.3 NS 137.6 160.7 ** 114.0 ** NS L** Q* NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumber in brackets represents days after fertilizer application. *Rate not included in 1983. sNty = nitrapyrin. 'These plots were not sampled. *Ih = inhibitors.

PAGE 147

Table 5-2. N Rate kg/ha 67 134 202 124 Interactions (DCD Q X NR L **) of DCD rate and N rate effects on soil inorganic N concen tration 6 days after fertilizer application (Hastings, 1984). 0 83.2 126.2 202.0 L*** DCD Rate (kg/ha) 5.6 g/kg N 87.7 124.6 147.6 L*** 11.2 63.7 Lx 118.8 NS 214.5 Q* L*** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 5-3. N Rate kg/ha 67 134 202 Interaction (Nty RX NR Q x) of nitrapyrin rate and N rate effects on soil inorganic N concen tration 6 days after fertilizer application (Hastings, 1984). Nitrapyrin Rate (kg/ha) 0.56 1.12 mg/kg N 69.2 94.7 152.0 145.9 NS 191. 5 241.6 X L*** L*** Nonsignificant (NS) or sign ifi cant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 148

125 increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 resulted in an increase in SIN concentration from 69.2 to 94. 7 mg kg1 With 202 kg ha1 N, increased nitrapyrin rate resulted in an increase in SIN concentration from 191.5 to 241. 6 mg kg1 In 1984 on day 6 (Table 5-1), mean SIN concentration was higher with nitrapyrin (149.2 mg kg1 ) than with DCD (126.2 mg kg1 ). Mean soil inorganic N concentration was higher with the inhibitors (137.6 mg kg1 ) than with IBDU (114.0 mg kg1 ). Pre-emergence stage. Soil was sampled at the pre emergence stage at 16, 13, and 18 days after fertilizer application in 1983 at Gainesville and Hastings, and in 1984 at Hastings, respectively. At the pre-emergence stage, SIN concentration means increased with increases in N rate in all year-location combinations that were sampled (Table 5-4). In 1983 on day 16 at Gainesville, SIN concentration increased from 7 4. 5 to 9 7. 1 mg kg1 with an increase in N rate from 134 to 202 kg ha1 In 1984 on day 13 at Gaines ville, SIN concentration increased from 33.1 to 68.2 mg kg1 with an increase in N rate from 67 to 202 kg ha 1 In 1984 on day 18 at Hastings, SIN concentration increased from 85.0 to 211.1 mg kg1 with an increase in N rate from 67 to 202 kg ha 1 In 1984 on day 13 at Gainesville, DCD rate interacted with N rate effects on SIN concentration (Table 5-5). With

PAGE 149

126 Table 5-4. Effects of N rate and amendment on soil inorganic N at the pre-emergence stage of potato. Gainesville Hastings Independent Variable 1983[16]t 1984[13] 1984[18] g/kg N N Rate 67 kg/ha _; 33.1 85.0 134 kg/ha 74.5 48.1 157.7 202 kg/ha 97.1 68.2 211.1 ** L*** L***Q* DCD Rate 0.0 kg/ha 85.8 51.5 165.5 5.6 kg/ha 96.2 40.2 147.2 11.2 kg/ha 71.8 50.2 151.6 NS Q*** L*Q* NtyS Rate 0.56 kg/ha 79.7 49.3 164.3 1.12 kg/ha 96.9 49.6 153.3 NS NS NS DCD v Nty NS X X IBDU as 1/3 of N 84.4 58.1 125.9 IBDU V Ih' NS *** *** Interactions DCD L X NR NS NS Qx DCD Q X NR NS Q* L* Nty RX NR NS L** DCD v Nty X NR NS Lx NS IBDU v Ih X NR NS L** L** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumber in brackets represents days after fertilizer application. *Rate not included in 1983. sNty = nitrapyrin. 1 Ih = inhibitors.

PAGE 150

Table 5-5. N Rate kg/ha 67 134 202 Interactions (DCD Q X NR Q *, DCD L X NR Q x, and DCD Q X NR L *) of DCD and N rate effects on soil inorganic N concentration at the pre-emergence stage of potato (1984). Gainesville r 131t Hastings (18] DCD Rate (kgLha) DCD Rate (kgLha) o.o 5.6 11.2 0.0 5.6 11.2 g/kg N 35.7 31.6 35.5 NS 87.5 88.3 72.5 X 54.8 33.4 50.5 Q*** 159.9 146.3 164.6 NS 127 64.0 55.6 74.4 NS 249.0 207.0 217.8 L*Q* L*** L*** L*** L*** L*** L*** Q** Q* Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumber in brackets represents days after fertilizer application. Table 5-6. N Rate kg/ha 67 134 202 Interactions (Nty RX NR and Nty RX NR L **) of nitrapyrin and N rate effects on soil inorganic N concentration at the pre-emergence stage of potato. Gainesville 1983 (16]t Nitrapyrin Rate (kg/ha) 0.56 1.12 -* 73.92 63.2 NS 85.5 130.6 NS NS g/kg N Hastings 1984 (18] Nitrapyrin Rate (kgLha) 0.56 1.12 88.7 99.3 NS 167.3 166.7 NS 236.8 193.8 ** L*** L*** Qx Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application. *Rate not included in 1983.

PAGE 151

128 134 kg ha1 N, SIN concentration decreased from 54.8 to 33.4 mg kg1 with an increase in DCD rate from O to 5. 6 kg ha 1 With a further increase in DCD to 11.2 kg ha1 SIN concen tration increased to 50. 5 mg kg1 With 67 and 202 kg ha1 N on day 13, SIN concentration was not influenced by DCD rate. In 1984 on day 18 at Hastings, DCD rate interacted with N rate (Table 5-5). With 67 kg ha1 N, SIN concen tration decreased from 87.5 to 72.5 mg kg1 with an increase in DCD rate from O to 11. 2 kg ha 1 W ith 134 kg ha 1 N, DCD rate had no effect. With 202 kg ha1 N, SIN concentration decreased from 249.0 to 207.0 mg kg1 with an increase in DCD rate from Oto 5.6 kg ha1 A further increase in DCD to 11.2 kg ha1 had no effect on SIN concentration. In 1983 on day 16 at Gainesville, nitrapyrin rate interacted with N rate (Table 5-6). With 202 kg ha1 N, SIN concentration increased from 85. 5 to 130. 6 mg kg1 with an increase in nitrapyrin rate from O. 56 to 1.12 kg ha 1 With 134 kg ha1 N, nitrapyrin rate had no effect. In 1984 on day 18 at Hastings, nitrapyrin rate inter acted with N rate ( Table 5-6) With 2 02 kg ha 1 N, SIN con centration decreased from 236.8 to 193.8 mg kg 1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 67 and 134 kg ha 1 N, nitrapyrin rate had no effect. In 1984 on day 13 at Gainesville, the DCD v nitrapyrin contrast i nteracted with N rate (Table 5-7). With 134 kg ha1 N, mean SIN concentration was higher with nitr a pyr i n

PAGE 152

Table 5-7. N Rate kg/ha 67 134 202 129 Interaction (DCD V Nty X NR L x) of DCD V nitrapyrin and N rate effects on soil inorganic N concentration 13 days after fertilizer appli cation (Gainesville, 1984). DCD Nitrapyrin ------~ug/kg N------33.6 42.0 60.0 L*** Qx 30.5 NS 49.3 68.5 NS L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 153

130 ( 49. 3 mg kg1 ) than with DCD ( 41. 0 mg kg1 ). With 67 and 202 kg ha1 N, mean SIN concentration was similar with the two inhibitors. In 1984 on day 18 at Hastings, mean SIN concen tration (Table 5-4) was higher with nitrapyrin (158.8 mg kg1 ) than with DCD ( 149. 4 mg kg1 ). In 1984 on day 13 at Gainesville, the IBDU v inhib itors contrast interacted with N rate (Table 5-8). With 202 kg ha1 N, mean SIN concentration was higher with IBDU (88.2 mg kg1 ) than with inhibitors ( 64. 3 mg kg1 ) With 67 and 134 kg ha1 N, mean SIN concentration was similar with the two amendment types. In 1984 on day 18 at Hastings, the IBDU v inhibitors contrast interacted with N rate (Table 5-8). With all N rates, SIN concentration means were higher with inhibitors than with IBDU, but the magnitude of the difference in mean SIN concentration between the two amendment types, increased with increasing N rate. Vegetative stage. Soil was sampled at the vegetative stage of potato growth on 35, 31, 31, and 32 days after fertilizer application in 1983 and 1984 at Gainesville, and 1983 and 1984 at Hastings, respectively. At the vegetative stage, SIN concentration increased with increases in N rate in all year-location combinations (Table 5-9). In 1983 on day 35 at Gainesville, SIN concentration increased from 47.5 to 61.0 mg kg 1 with an increase in N rate from 134 to 202 kg ha1 In 1984 on day 31 at Gainesville, SIN

PAGE 154

Table 5-8. N Rate kg/ha 67 134 202 131 Interaction (IBDU v Ih X NR L **) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration at the pre-emergence stage of potato (1984). Gainesville [ 131t Hastings [18] IBDU Inhibitors IBDU Inhibitors g/kg N 34.6 32.1 NS 74.0 87.2 X 51.4 45.6 NS 141.5 161.2 X 88.2 64.3 ** 162.3 213.9 *** L*** L*** L*** L*** Q** Qx Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application.

PAGE 155

132 Table 5-9. Effects of N rate and amendment on soil inorganic N concentration at the vegetative stage of potato. Gainesville Hastings Independent Variable 1983[35]t 1984[31] 1983[31] 1984[32] g/kg N N Rate 67 kg/ha -* 27.0 21.7 134 kg/ha 47.5 41. 7 2.4 32.2 202 kg/ha 61.0 52.7 3.1 41.0 ** L*** X L*** DCD Rate 0.0 kg/ha 46.9 41.3 2.4 26.1 5. 6 kg/ha 57.2 34.6 3.1 29.4 11.2 kg/ha 47.2 43.2 2.4 28.8 NS Q** NS NS Ntys Rate 0.56 kg/ha 50.3 38.7 2.3 29.7 1.12 kg/ha 57.0 36.6 2.7 29.6 NS NS NS NS DCD v Nty NS NS NS NS IBDU as 1/3 of N 66.8 48.3 3.4 46.4 IBDU V Ih' *** NS *** Interactions DCD L X NR NS Q* NS NS DCD Q X NR Q* NS NS Nty RX NR NS L** NS NS DCD v Nty X NR NS NS NS NS IBDU v Ih X NR NS Q** NS L** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application. *Rate not included in 1983. sNty = nitrapyrin. 1 Ih = inhibitors.

PAGE 156

133 concentration increased from 27. 0 to 52. 7 mg kg1 with an increase in N rate from 67 to 202 kg ha1 In 1983 on day 31 at Hastings, SIN concentration increased from 2.4 to 3.1 mg kg1 with an increase in N rate from 134 to 202 kg ha1 In 1984 on day 32 at Hastings, SIN concentration increased from 21.7 to 41.0 mg kg1 with an increase in N rate from 67 to 202 kg ha1 In 1984 on day 31 at Gainesville, DCD rate interacted with N rate (Table 5-10). With 67 kg ha1 N, DCD had no effect. With 134 kg ha1 N, SIN concentration decreased from 45. 7 to 31. 6 mg kg1 with an increase in DCD rate from 0 to 5.6 kg ha1 With a further increase in DCD to 11.2 kg ha1 SIN concentration increased to 39. 3 mg kg1 which was less than the concentration with 0 DCD. With 202 kg ha1 N, a similar pattern of SIN concentration occurred, decreasing from 5 0 8 to 4 5 6 mg kg1 then increasing to 61. 3 mg kg 1 with increases in DCD rate from 0, to 5.6, to 11.2 kg ha1 respectively. At this N rate, however, the SIN concentra tion with 11.2 kg ha 1 DCD was higher than that with 0 DCD on day 31 in 1984 at Hastings. At the vegetative stage, SIN concentration was not influenced by DCD rate in either year at Hastings. In 1984 on day 31 at Gainesville, nitrapyrin rate interacted with N rate effects on SIN concentration (Table 5-11). With 67 kg ha1 N, an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 resulted in an increase in SIN

PAGE 157

Table 5-10. N Rate kg/ha 67 134 202 134 Interactions (DCD L X NR Q and DCD Q X NR Q *) of DCD and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 1984). 0 27.3 45.7 50.8 L*** Q* DCD Rate 5.6 g/kg 26.5 31.6 45.6 L*** (kg/ha) 11.2 N 29.0 NS 39.3 LxQ*** 61.3 LxQx L*** Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. Table 5-11. N Rate kg/ha 67 134 202 Interaction (Nty RX NR Q ***) of nitrapyrin and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 1984). Nitrapyrin Rate (kg/ha) 0.56 1.12 -------mg/kg N--------18.2 41.4 56.6 L *** 27.6 *** 35. 6 X 46.6 NS L *** Nonsignificant (NS) or significant at the 0.1 (x), or 0.001 (***) probability levels, respectively.

PAGE 158

135 concentration from 18. 2 to 27. 6 mg kg1 With 134 kg ha1 N, an increase in nitrapyrin rate resulted a decrease in SIN concentration from 41.4 to 35.6 mg kg1 With 202 kg ha1 N, nitrapyrin rate had no effect on SIN concentration on day 31 in 1984 at Gainesville. At the vegetative stage, SIN concentration means were higher with IBDU than with inhibitors in 1984 at both loca tions, and in 1983 at Gainesville (Table 5-9). In 1983 on day 35 at Gainesville, mean SIN concentration was 66.8 mg kg1 with IBDU and 52. 9 mg kg1 with inhibitors. In 1984 on day 31 at Gainesville, the IBDU v inhibitors contrast inter acted with N rate (Table 5-12). With 67 kg ha1 N, mean SIN concentration was 33. 0 mg kg1 with IBDU and 25. 3 mg kg1 with inhibitors. With 134 kg ha1 N, mean SIN concentration was 56. 6 mg kg1 with IBDU and 37. 0 mg kg1 with inhibitors. With 202 kg ha1 N, mean SIN concentration was similar with the two types of amendments. In 1984 on day 32 at Hastings (Table 5-9), mean SIN concentration was 46.4 mg kg1 with IBDU and 29.4 mg kg1 with inhibitors. The interaction between N rate and IBDU v inhibitors (data not shown) indicated a greater N rate effect with IBDU than with inhibitors. Tuber initiation stage. The soil was sampled at the tuber initiation stage of potato growth only in 1984, 45 and 46 days after fertilizer application at Gainesville, and Hastings, respectively. At tuber initiation, SIN

PAGE 159

Table 5-12. N Rate kg/ha 67 134 202 Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration 31 days after fertilizer application (Gainesville, 1984). 136 IBDU Inhibitors -------~mg/kg N------33.0 56.6 55.3 L*** 25.3 *** 37.0 *** 52.5 NS L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 160

137 concentration increased with increases in N rate at both locations (Table 5-13). On day 45 at Gainesville, SIN concentration increased from 14.7 to 39.3 mg kg1 with an increase in N rate from 67 to 202 kg ha1 On day 46 at Hastings, SIN concentration increased from 12.3 to 40.1 mg kg1 with an increase in N rate from 67 to 202 kg ha1 On day 45 at Gainesville, SIN concentration decreased from 25.4 to 21.1 mg kg1 with an increase in DCD rate from 0 to 5.6 kg ha1 (Table 5-13). With a further increase in DCD to 11.2 kg ha1 SIN concentration increased to 26.5 mg kg1 which was not different that with O DCD. On day 45 at Gainesville, nitrapyrin rate interacted with N rate (Table 5-14). With 67 kg ha1 N, SIN concen tration increased from 9. 4 to 14. 4 mg kg1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 202 kg ha1 N, SIN concentration decreased from 39. 9 to 20. 8 mg kg1 with an increase in nitrapyrin rate. With 134 kg ha1 N, nitrapyrin rate had no effect. At both locations, SIN concentration at tuber initi ation was influenced by an interaction between DCD v nitra pyrin and N rate. On day 45 at Gainesville (Table 5-15), mean SIN concentration was higher with DCD than with nitra pyrin with 67 (14.5 v 11.9 mg kg 1 and 202 kg ha1 N (39.2 30.3 mg kg1 ), but was lower with 134 kg ha1 N (17.6 v 24.8 mg kg 1 ). On day 46 at Hastings (Table 5-16), mean SIN concentration was higher with nitrapyrin than with DCD, with

PAGE 161

138 Table 5-13. Effects of nitrogen rate and amendment on soil inorganic N concentration at the tuber initiation stage. Independent Variable N Rate 67 kg/ha 134 kg/ha 202 kg/ha DCD Rate 0.0 kg/ha 5.6 kg/ha 11.22 kg/ha Nty: Rate 0.56 kg/ha 1.12 kg/ha DCD v Nty IBDU as 1/3 of N IBDU v Ihs Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR Gainesville 1984[45]t Hastings 1984[46] -------mg/kg N------14.7 25.9 39.3 L*** 25.4 21.1 26.5 Qx 24.2 20.5 NS NS 42.1 *** NS NS L** Q** Q* 12.3 24.4 40.1 L*** 26.6 23.6 24.8 NS 23.2 26.1 NS NS 29.7 *** NS NS NS L*Q* NS Nonsignificant (NS) or signi f icant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application. *Nty = nitrapyr i n. sih = inhibitors.

PAGE 162

Table 5-14. N Rate kg/ha 67 134 202 139 Interactions (Nty RX NR L **) of nytrapyrin and N rate effects on soil inorganic N concentration 45 days after fertilizer application (Gainesville, 1984). Nitrapyrin Rate (kg/ha) 0.56 1.12 g/kg N 9.4 14.4 23.5 26.2 NS 39.9 20.8 ** L*** Qx Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 5-15. N Rate kg/ha 67 134 202 Interaction (DCD v nitrapyrin X NR Q **) of DCD v nitrapyrin, and N rate effects on soil inorganic N concentration 45 days after fertilizer application (Gainesville, 1984). DCD Nitrapyrin -------ug/kg N-----14.5 17.6 39.2 L*** Q** 11.9 X 24.8 30.3 X L*** Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 163

Table 5-16. N Rate kg/ha 67 134 202 140 Interaction (DCD v nitrapyrin X NR L and X NR Q *) of DCD v nitrapyrin, and N rate effects on soil inorganic N concentration 46 days after fertilizer application (Hastings, 1984). DCD Nitrapyrin ------iug/kg N-------10.5 21.8 40.4 L*** Qx 12.4 26.2 X 35.3 L*** Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.001 (***) probability levels, respectively.

PAGE 164

141 67 (12.4 v 10.5 mg kg1 ) and 134 kg ha1 N (26.2 v 21.8 mg kg1 ), but was lower with 202 kg ha1 N (35.3 v 40.4 mg kg1 ). At the tuber initiation stage, mean SIN concentration was higher with IBDU than with inhibitors at both locations (Table 5-13). On day 45 at Gainesville, mean SIN concentra tion was 42 .1 mg kg1 with IBDU and 23 .1 mg kg1 with inhib itors. On day 46 at Hastings, mean SIN concentration was 29. 7 mg kg1 with IBDU and 24. 4 mg kg1 with inhibitors. Tuber bulking stage. Soil was sampled at the tuber bulking (enlargement) stage of potato growth on 59, 69, 61, and 74 days after fertilizer application in 1983 and 1984 at Gainesville, and in 1983 and 1984 at Hastings, respectively. Increases in N rate increased SIN concentration at tuber bulking in 1983 at Gainesville, and in 1984 in both loca tions (Table 5-17). In 1983 on day 59 at Gainesville, SIN concentration increased from 18.5 to 27.2 mg kg1 with an increase in N rate from 134 to 202 kg ha1 In 1984 on day 69 at Gainesville, SIN concentration was not influenced by an increase in N rate from 67 to 134 kg ha1 With a fur ther increase in N rate to 202 kg ha1 however, SIN concen tration increased from 10 .1 to 23. 2 mg kg1 In 1983 on day 59 at Gainesville, SIN concentration at tuber bulking increased from 18. 9 to 24. 6 mg kg1 with an increase in DCD rate from Oto 5.6 kg ha 1 With a further increase in DCD rate to 11.2 kg ha1 SIN concentration

PAGE 165

Table 5-17. Effects of nitrogen rate and amendment on soil inorganic N concentration at the tuber bulking stage. Gainesville Hastings 142 Independent Variable 1983[59]t 1984[69] 1983[61] 1984[74] N Rate 67 kg/ha 134 kg/ha 202 kg/ha DCD Rate 0.0 kg/ha 5.6 kg/ha 11.2 kg/ha NtyS Rate 0.56 kg/ha 1.12 kg/ha DCD v Nty IBDU as 1/3 of N IBDU v Ih 1 Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR ---------_mg/kg N-----------* 18.5 27.2 *** 18.9 24.6 17.0 Q* 22.4 22.9 NS NS 30.6 *** NS NS NS NS ** 7.8 10.1 23.2 L*** Q*** 11.2 12.8 14.6 L* 13.9 12.2 NS NS 17.5 *** Lx NS Lx NS L** Q** 11.2 13.2 NS 10.1 12.5 14.4 NS 14.5 10.9 NS NS 10.8 NS NS NS NS NS NS 6.9 8.6 15.5 L*** Q*** 9.5 9.8 9.5 NS 9.9 10.0 NS NS 13.3 *** NS NS NS NS L** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application *Rate not included in 1983. sNty = nitrapyrin. 'Ih = inhibitors.

PAGE 166

143 decreased to 17.0 mg kg1 which was not different from that with 0 DCD. In 1984 on day 69 at Gainesville, DCD rate interacted with N rate (Table 5-18). With 67 kg ha1 N, an increase in DCD rate from O to 5. 6 kg ha1 had no ef feet on SIN concen tration. A further increase in DCD to 11.2 kg ha1 resulted in an increase in SIN concentration from 6.8 to 8.4 mg kg1 With 134 kg ha1 N, DCD rate had no effect on SIN concentra tion. With 202 kg ha1 N, SIN concentration increased from 16. 9 to 24. 6 mg kg1 with an increase in DCD rate from O to 11. 2 kg ha1 In 1984 on day 69 at Gainesville, nitrapyrin rate interacted with N rate (Table 5-19). With 202 kg ha1 N, SIN concentration decreased from 23. 7 to 17. 4 mg kg1 with an increase in nitrapyrin rate from 5.6 to 1.12 kg ha1 With 67 and 134 kg ha1 N, nitrapyrin rate had no effect on SIN concentration. In 1983 at both locations and in 1984 at Hastings (Table 5-17), the IBDU v inhibitors contrast interacted with N rate effects on SIN concentration at tuber bulking. In 1983 on day 59 at Gainesville (Table 5-20), with 202 kg ha1 N, mean SIN concentration was higher with IBDU (40.5 mg kg1 ) than with inhibitors ( 25. 8 mg kg 1 ). With 134 kg ha 1 N, SIN concentration means were similar with the two amend ments types. In 1984 on day 69 at Gainesville (Table 5-20), with 67 kg ha1 N, mean SIN concentration with IBDU was

PAGE 167

Table 5-18. N Rate kg/ha 67 134 202 144 Interaction (DCD L X NR L *) of DCD and N rate effects on soil inorganic N concentration 69 days after fertilizer application (Gaines ville, 1984). 0 7. 1 9.8 16.9 L*** Q* DCD Rate 5.6 g/kg 6.8 8.8 22.7 L*** Qx (kg/ha) 11.2 N 8.4 L*Q* 10.6 NS 24.6 L* L*** Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. Table 5-19. N Rate kg/ha 67 134 202 Interaction (Nty RX NR L x) of nitrapyrin and N rate effects on soil inorganic N concen tration 69 days after fertilizer application (Gainesville, 1984). Nitrapyrin Rate (kg/ha) 0.56 1.12 g/kg N 7.3 7.3 NS 10.8 11.8 NS 23.7 17.4 X L*** L*** Qx Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), or 0.001 (***) probability lev e ls, respectively.

PAGE 168

145 Table 5-20. Interactions (IBDU v Ih X NR **, IBDU v Ih X NR L **, and X NR Q **) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration at the tuber bulking stage. Gainesville 1983 [59]t N Rate IBDU Inhibitors kg/ha mg/kg N 67 -* 134 20.6 18.0 NS 202 40.5 25.8 ** L* L*** Gainesville 1984 [69] IBDU 9.8 8.9 33.9 L*** Q*** Inhibitors 7.5 *** 10.5 22.1 *** L*** Q*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application. *Rate not included in 1983. Table 5-21. N Rate kg/ha 67 134 202 Interaction (IBDU v Ih X NR L *) of IBDU v inhibitors, and N rate effects on soil inor ganic N concentration 74 days after fertilizer application (Hastings, 1984). IBDU Inhibitors -------mg/kg N-----7.9 10.5 21.5 L*** Q*** 6.9 8.2 ** 14.3 *** L*** Q* Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 169

146 higher (9.8 mg kg1 ) than with inhibitors (7.5 mg kg1 ). With 134 kg ha1 N, mean SIN concentration was higher with inhibitors (10.5 mg kg1 ) than with IBDU (8.9 kg ha1 ). With 202 kg ha1 N, mean SIN concentration was higher with IBDU (33.9 mg kg1 ) than with inhibitors (22.1 mg kg1 ). In 1984 on day 74 at Hastings (Table 5-21), at all N rates SIN concentration means were higher with IBDU than with inhib itors but the magnitude and significance of this difference increased with increasing N rate. At tuber harvest. Soil was sampled at tuber harvest on 98, 108, and 103 days after fertilizer application in 1983 and 1984 at Gainesville, and 1984 at Hastings, respec tively. In 1983 on day 98 at Gainesville (Table 5-22), SIN concentration was not influenced by N rate. In 1984 on day 108 at Gainesville (Table 5-22), SIN concentration increased from 7.8 to 10.3 mg kg1 with an increase in N rate from 67 to 202 kg ha1 In 1984 on day 103 at Hastings, SIN concen tration was not influenced by an increase in N rate from 67 to 134 kg ha 1 but with a further increase in N to 202 kg ha1 SIN concentration increased from 10.1 to 20.9 mg kg1 In 1984 on day 103 at Hastings, DCD rate interacted with N rate (Table 5-23). With 202 kg ha1 N, SIN concen tration decreased from 24.8 to 16 7 mg kg 1 with an increase in DCD rate from Oto 11 2 kg ha 1 With 67 and 134 kg ha1 N, DCD rate did not influence SIN concentration.

PAGE 170

147 Table 5-22. Effects of N rate and amendment on soil inorganic N concentration at potato harvest. Independent Variable N Rate 67 kg/ha 134 kg/ha 202 kg/ha DCD Rate 0.0 kg/ha 5.6 kg/ha 11.2 kg/ha NtyS Rate 0.56 kg/ha 1.12 kg/ha DCD v Nty IBDU as 1/3 of N IBDU v Ih 1 Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR Gainesville 1983[98]t 1984(108] Hastings 1984(103] ----------mg/kg N--------* 5.3 5.6 NS 5.7 4.8 5.4 NS 4.9 5.2 NS NS 6.8 NS NS NS NS X 7.8 9.4 10.3 L*** 8.2 8.8 8.4 NS 9.2 10.3 NS 10.1 NS NS NS L** NS NS 8.7 10.1 20.9 L*** Q*** 14.7 13.7 11.8 L* 13.0 13.9 NS NS 12.1 NS L* NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tNumbers in brackets represent days after fertilizer application. *Rate not included in 1983. 5 Nty = nitrapyrin. 1 Ih = inhibitors.

PAGE 171

148 Table 5-23. Interaction (DCD L X NR L *) of DCD and N rate effects on soil inorganic N concentration 103 days after fertilizer application (Hastings, 1984). N Rate kg/ha 67 134 202 DCD Rate (kg/ha) 0 5.6 11.2 ----------mg/kg N-------9.2 10.3 24.8 L*** Q** 9.5 9.1 22.5 L*** Q* 8.6 NS 10.1 NS 16.7 L* L*** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Table 5-24. Interaction (Nty RX NR L **) of nitrapyrin and N rate effects on soil inorganic N concen tration 108 days after fertilizer application (Gainesville, 1984). Nitrapyrin Rate (kg/ha) N Rate 0.56 1.12 kg/ha g/kg N 67 8.6 7.2 134 9.7 10.5 202 9.2 13.2 NS L** Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. **

PAGE 172

149 In 1984 on day 108 at Gainesville, nitrapyrin rate interacted with N rate effects on SIN concentration (Table 5-24). With 67 kg ha1 N, SIN concentration decreased from 8.6 to 7.2 mg kg1 with an increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 With 134 kg ha1 N, SIN concentration increased from 9.7 to 10.5 mg kg1 with an increase in nitrapyrin rate. With 202 kg ha1 N, SIN concentration in creased from 9.2 to 13.2 mg kg1 with an increase in nitra pyrin rate. In 1984 on day 108 at Gainesville, mean SIN concentra tion was higher with nitrapyrin (9.8 mg kg1 ) than with DCD (8.6 mg kg1 ) (Table 5-22). In 1983 on day 98 at Gaines ville, the IBDU v inhibitors contrast interacted with N rate (Table 5-25). With 134 kg ha1 N, mean SIN concentration was higher with IBDU (7.7 mg kg1 ) than with inhibitors (4.6 mg kg1 ). With 202 kg ha1 N, SIN concentration means were similar with the two amendment types. Extractable Soil DCD Extractable Soil DCD Over Time Extractable soil DCD concentration was quite variable from one year-location combination to another. The highest soil DCD concentration means observed in 1983 and 1984 at Gainesville, were in the 0.6 to 1.2 and 1.4 to 1.6 mg kg1 ranges for the 5.6 and 11.2 kg ha 1 DCD rates, respectively (Figures 5-1 and 5-2). Measured soil DCD concentrations

PAGE 173

Table 5-25. Interaction (IBDU v Ih X NR x) of IBDU v inhibitors, and N rate effects on soil inorganic N concentration 98 days after fertilizer application (Gainesville, 1983). 150 N Rate IBDU Inhibitors kg/ha 134 202 ------mg/kg N-------7.7 5.8 X 4.6 ** 5. 6 NS Nonsignificant (NS) or significant at the 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 174

..-. Cl 1.6 1.2 i _, 0. 8 0.4 Gainesville 1983 ,,,_ \,_ '\. Rainfall ,. ,. ,. ,. ........ .. ..... \ t .?<', ; I .. 1 , ,.,., .. .,. .. .. . .... ... . . ,. i .. / .... ,_ ~,: .. i: .... .. j -, , ... ,, .......... ... .................. 5.6 kg/ha DCD ....... ,::) ....... .. 11.2 kg/ha DCD 600 500 ....... Ii -400 r-1 rl Id ,:: -,-f 300 Id p:: rt 200 r-1 / ................ .. .-. .. .;~ . --;-;,_,;_ .. .;,. __ .,_; j 100 0 . ........ ,.,.. 0 Figure 5-1. 20 Days 40 After 60 Fertilizer 80 Application 100 0 Effects of DCD rate on soil DCD concentration (Gainesville, 1983). I--' U1 ....

PAGE 175

1.6 ,--------------------------------------------, 600 ...... C'l ....... i 1.2 ---o.a 0.4 0 0 Figure 5-2. Gainesville 1984 ;.. !5,6 kg/ha DCD u a ";;t" cco ; Rainfall ,:-; r, / / ', I 20 Days 40 After 60 Fertilizer 80 Application 100 500 ...... 6 ..., 400 ,-I ,-I ell 11-1 Q ri 300 Gl > .-1 +I 200 Ill r-1 j 100 0 Effects of DCD rate on soil DCD concentration (Gainesville, 1984 ) ..... l11 "'

PAGE 176

153 were not more than 0.8 mg kg1 in 1983 at Hastings, and increased with time with the 11.2 kg ha1 DCD rate (Figure 5-3). The highest concentrations of soil DCD occurred in 1984 at Hastings (Figure 5-4), with as much as 5 and 11 mg kg1 with the 5. 6 and 11. 2 kg ha1 DCD rates, respectively. To estimate the time required for half of the applied DCD to disappear from a 30 cm deep rooting zone, a 1.35 g cm3 soil bulk density was assumed (USDA, 1983) in convert ing observed soil DCD concentration means to a kg ha1 basis. An extrapolated line was then assumed between the amount of DCD applied and the amount observed with the first sampling. The time required for half of the applied DCD to disappear from the rooting zone will be referred to as resi dence half time. This parameter is not a half life as not all DCD loss from the soil is due to decomposition. It was approximated that in 1983 at Gainesville, the DCD residence half time values were 50 and 30 days for the 5.6 and 11.2 kg ha1 DCD rates, respectively. In 1984 at Gainesville, the estimated residence half time was 70 days with both DCD rates. In 1983 at Hastings, it was not possible to estimate the DCD residence half time because soil DCD concentration values did not decrease with time. In 1984 at Hastings, the estimated residence half time was 30 days with both DCD rates. At Gainesv i lle, where overhead irrigation was used, less than 0. 2 mg kg 1 DCD remained in the soil at the end of

PAGE 177

,.. 0) ....... 1.6 600 Hastings 1983 500 1.2 400 Rainfall ..... ,.. n ._.. r-1 r-1 Ill 11,.1 r-1 i1 ....... 0.8 ..... ... .. .... .. ........................ .... ... . 300 0. 4, :) ( .. _, 0 0 20 _. . ./ ... _ ________ __ __ ~_) Days 40 A f ter 60 Fertilizer 80 Appli c a t ion 5 6 ltg/ha DCD ,.. .. t r .. 11 2 kg-/ha DCD 10 0 Figure 5-3. Effects of DCD rate on soil DCD concentrati o n ( Ha s ti ngs, 1983). 4l > .... .jJ 2 00 I r-1 100 0 ..... l.11

PAGE 178

12 ,--------------------------------------------~ 600 ..... DI ....... g E 6 3 0 0 ,-.. \ ( -~ --" _, \ \ \ \ \ Hastings 1984 Rainfall 5. 6 kg/ha DCD \\ ... ..J \ ...... 11.2 kg/ha DCD i \ / '\ i \ ..'~ I ....... ~7---"t:) "' r (:~ -.... ... : 20 Days 40 After 60 Ferti1izer 80 Application 100 500 ..... 6 ..... 400 r-1 r-1 ell 14-1 J:: ei 300 Ql > r-l .jJ 200 ft! r-1 100 0 Figure 5-4. Effects of DCD rate on soil DCD concentration (Hastings, 1984). 1--' u, u,

PAGE 179

156 the potato growing season in both years. At Hastings, where subsurface irrigation was used, as much as 0.6 mg kg1 DCD remained in the soil at the end of the potato growing season. DCD Rate Effects In 1983 at Gainesville, DCD rate had no effect on soil DCD concentration (Figure 5-1, and Table 5-26). In 1984 at Gainesville, soil DCD concentration (Figure 5-2) was in creased with an increase in DCD rate from 5.6 to 11.2 kg ha1 on all but day 45. In 1983 at Hastings, soil DCD concentration was not influenced by DCD rate (Table 5-27). In 1984 at Hastings, on days 6 and 18, DCD rate had no effect on soil DCD concentration. On days 32, 46, 74, and 103, and with the mean of all sampling dates, soil DCD concentration means were increased with an increase in DCD rate from 5.6 to 11.2 kg ha 1 (Table 5-27). Rainfall Recorded cumulative rainfall amounts at Gainesville and Hastings, in 1983 and 1984, are shown in Figures 5-1 to 5-4. In 1983 at Gainesville (Figure 5-1), rainfall amounts were high and evenly spaced throughout the growing season. In 1984 at Gainesville (Figure 5-2), total rainfall was adequate but droughts occurred from day 18 to day 38 and from day 46 to day 95. During these droughts water was

PAGE 180

Table 5-26. Effects of N and DCD rates on soil DCD concentration (Gainesville). 1983 1984 Days After Days After Fertilizer AQQlication Fertilizer AQQlication Independent Variable 16 35 59 98 Mean 13 31 45 69 108 N Rate NS NS NS NS NS NS NS NS NS DCD Rate NS NS NS NS NS X NS X X DCD RX NR NS NS NS NS NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively. Mean NS *** NS t--' l.11 -..J

PAGE 181

Table 5-27. Effects of N and DCD rates on soil DCD concentration (Hastings). 1983 1984 Days After Fertilizer AQQlication Days After Fertilizer AQQlication Independent Variable 5 31 61 Mean 6 18 32 46 74 103 N Rate NS NS X NS NS NS NS NS NS DCD Rate NS NS NS NS NS NS *** *** ** *** DCD RX NR NS NS NS NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. Mean NS *** NS I-' u, 00

PAGE 182

159 supplied by overhead irrigation, sufficient to provide for crop requirements without promoting leaching of soil inor ganic N. In 1983 at Hastings (Figure 5-3), total rainfall was low but evenly distributed except at the end of the growing season. In 1984 at Hastings (Figure 5-4), rainfall was low and poorly distributed, with relative droughts occurring from days Oto 19, 34 to 53, and 62 to harvest. In both years at Hastings, supplemental water was provided from a subsurface irrigation system.

PAGE 183

CHAPTER 6 UREA AND DCD APPLIED TO A FALLOW QUARTZIPSAMMENT Soil NH/-N Analysis of variance of DCD effects on soil NH/-N concentrations for all sampling dates and depths are shown in Table 6-1. Soil NH/-N concentrations at five depths in the typic Quartzipsamrnent 14 days after urea and DCD appli cation are shown in Figure 6-1. Soil NH/-N concentration was not influenced by DCD rate at any of the sampled depths on day 14 (Table 6-1). On day 31 at the 15 to 30 cm depth, soil NH/-N concentrations (Figure 6-2 and Table 6-1) were 21.8, 27.2, 14.0, and 22.0 mg kg1 with DCD rates of 0, 20, 40, and 60 kg ha1 respectively (a cubic effect). At the 91 to 122 cm depth, NH/-N concentration decreased from 2.1 to 1.7 mg kg1 with an increase in DCD rate from Oto 60 kg ha1 At other depths, DCD rate did not influence soil NH/-N concentration on day 31. On day 46, NH4+-N concentration (Figure 6-3) was not influenced by DCD rate at any soil depth (Table 6-1). On day 60 (Figure 6-4), soil NH/-N concentration at the 15 to 30 cm depth was increased from 7.7 to 21.1 mg kg 1 with an increase in DCD rate from Oto 60 kg ha1 160

PAGE 184

0 20 fl 40 -5 60 A r-i .... 0 ti) 80 100 120 0 Ammonium-N 20 40 60 80 (mg/kg) 100 120 140 ----~-~ '1/ -----------------~-.... =-=-=-=-=-=-=-=---------------A ,.-w... .. .. .. .. .......... .. .................... ............ .. ........ ............ .. .. .......... .. .. .. ... -,, I ,. ,. .. ..... ...... .... .... ............ .. .. .. ... ... ............ .. ........ ..... ...... ... .. .... .. ., ........ .. .. .............. .. .. ........ ........ .. .. ...... ........ ... .. .... .. . 'f / .. .. .. .... _, V "' I . ,,, . ,:.' \ .... . . ' i I jf .' l'f ~, I f. I I I I
PAGE 185

Table 6-1. Depth ( cm) 0-15 15-30 30-61 61-91 91-122 Profile 162 Effects of oeo rate on soil NH/-N concentra tion at five depths over six sampling dates in a Quartzipsamment at Live Oak. Days Fertilizer After Application 14 31 46 60 81 116 NS NS NS NS NS NS NS e* NS Lx NS NS NS NS NS NS NS NS NS NS NS NS Lx NS Q*ex NS Lx NS NS Lx NS ex ex NS NS L* NS Nonsignificant (NS) or significant at the 0.1 ( X) or a.as ( ) probability levels, respectively.

PAGE 186

0 0 20 ..... 40 fl ...... .c: 4-> GI 60 0 r-1 ..-i 0 (I) 80 100 120 Ammonium-N 20 (mg/kg) 40 60 ...... E .... .... .... _________ .,,. ----------'" -------~. .-,, .. .. : .. .. ,., ..................................... .. .................... ,-::::. : :::.:::.:: :::.:::: ::. :: : :: : .: .: :::: ... ... ...... ............ c.~ .,"" ,........... .... ............ .... ................................................. ..... ... / ,, ..... ..... .. .; ,,,,. ' .;' ..,,,,, , ,., ' ,,; .,,,. .. .;' .. ,,, ,. .... ,,,.. i ,-.t'r/ I I < : \ I a I i I \ r I \ I : ;L&. ,t, "'", :.p I : I I ,. JI JI f I' f ,. ,, I I 1/ DAY 31 no :Cr~1J.1zr 0 kg / ha DCD "'20 kg/ha DCD r ..................... . .. ..... 40 kg / ha DCD ___ )I( __ ,., 60 kg / ha DCD ,._ .. -r..;r Figure 6-2. Effects of DCD rate on soil NH/-N concentration with depth 31 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. f--' O'I w

PAGE 187

0 0 20 ..... 40 s u ..., .a .> 60 0 ori 0 {I) 80 100 120 Ammonium-N 20 (mg/kg) 4.0 60 ... ,,"' ; ; ......................... (~) .......... .. ,, __,,..,.,t,.,:.,::.:::: ::: ........ .. --=--------------------------------___ ,._ ,, ,,.,,. ; ; ""' , ~"' ; .,. .,. ,,.:-~, .. ..:,~ ,,, ,,, .. ~. .,. e ,:; .,,,,,., ; .,. ~,p'"' ~r""-.: !I: I irf f .. I! I! I! I ll I! DAY 46 no 1:ertilizer 0 k9/ha DCD 71-.20 kg/ha. DCD r-. ............ ,.,. ... .... , ..... 40 kg/ha DCD ___ )I( __ ,. .... 60 kg/ha. DCD "':,;.r-'' Figure 6-3. Effects of DCD rate on soil NH/-N concentration with depth 46 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. ..... O'\ ,i:,.

PAGE 188

0 0 20 .,.... 40 fl ...... .c: 60 0 ,-j ..-1 0 {I) 80 1 00 120 Ammonium N (mg/kg) 40 20 .. ""'' = .. :.E ; It .. ~: .. lo\ ... .. .. ....,,, :.. -.. !'.. .. ., . .. .. .. . j :'-...._ .-.: ,., .,. ; ;.: : )'!' ""' I ' _,, ,,' ,,. ,,,, ,,,, , I ,,, ,,, ; ; , ,, ,,, ,,,, I ,,.,,:, _,, _,, "'~ ,,,,,, I ,, ,,, ,,_,, I ~I" '~ ~~~:,: 'I! r 1/i f .,; ,/ 1 t i 1 JI/ /! l I I I I It DAY 60 60 no rertil.izer e 0 k9 / ha DCD ""20 kg / ha DCD .,. ._ 110 1 011 11 1. tl tl ltltU t H ... .. 40 kg / ha DCD ___ )I( __ ,., 60 kg / ha DCD ,.. .. ..... ..,.~,_ ... .. . Figure 6-4. Effects of DCD rate on soil NH/-N concentration with depth 60 days after application of 200 kg N ha 1 to a fallow Quartzipsamment at Live Oak. ..... O'I u,

PAGE 189

166 On day 81, soil NH/-N concentration (Figure 6-5) increased with an increase in DCD rate at the 61 to 91 and 91 to 122 cm depths. At the 61 to 91 cm depth, an increase in DCD rate from 0 to 20 kg ha1 had no effect on soil NH/-N concentration. With an increase in DCD rate from 20 to 40 kg ha1 soil NH 4 -N concentration decreased from 2. 7 to 2. 0 mg kg1 With an increase in DCD rate to 60 kg ha1 soil NH 4 -N concentration increased from 2. 0 to 4. 0 mg kg1 which was higher than that with 0 DCD. At the 91 to 122 cm depth, soil NH 4 -N concentration increased from 2. 2 to 3. 1 mg kg1 with an increase in DCD rate from Oto 60 kg ha1 On day 116 (Figure 6-6) soil NH/-N concentration was not influ enced by DCD rate (Table 6-1). Soil NH/-N concentration data for each of the five depths were converted from mg NH 4 -N kg1 of soil, to kg of NH 4 -N ha1 The sum of these values was presented as the total kg NH/-N ha1 in the 1. 22 m soil profile (Figure 6-7). This calculation assumed a soil specific gravity of 1.40 g cm3 for the 0 to 15 cm depth, and 1. 57 g cm3 for the other depths, as reported for this soil series (USDA, 1983). On day 14, quantities of total kg NH/-N ha1 in the 1.22 m profile were 307, 485, 275, and 332 kg ha1 with DCD rates of 0, 20, 40, and 60 kg ha1 respectively. On day 31, quantities of total kg NH/-N ha 1 in the profile were 167, 286, 159, and 222 kg ha1 with DCD rates of 0, 20, 40, and 60 kg ha 1 respectively. On days 14 and 31, quant i ties

PAGE 190

-..c: .L) Q r-1 -rl 0 l'I) 0 0 20 40 60 80 100 120 Figure 6-5. 0.5 DAY 81 a, .Ammonium N (mg/kg) 2.5 1 1.5 2 3 3.5 no t'ertilizer 0 kg/ha DCD :~": YI ft'; ... .. 11 "' i ,,,,, "' /, .,,,.,, .. ,,,. j"' ,,,,,, ,, / ,, ,; f / . -"" "' /4 ./ .. .... ,-,.\;,i < ~. \ ,, \ \ \ ... ., \ \ \ \ \ \ \ ', \ \ \ ',. \ \ \ "i:V .J:..., :t{ ; :..v /"' -~. / ', \ ' \/ ' .X ., / , ,., \ /, \ / \ ', / \ / \ ', 4 ,., --"""'-/ 0 :;L .. '"' ~; 20 kg/ha DCD .,. ......... ,o kg/ha DCD --~-60 kg/ha DCD ....... (_), ....... ,/ ,,.. ,,,; ,,/ .,', ,., ,. X ,' ' ( _,. , ' ''"" ,,;' / / / / ,, ' ,.. J,/ .. I \.... ' :,: .~ ;:,.:; -~ -. ,I' ,,, ,,, Effects of DCD rate on soil NH/-N concentration with depth 81 days after application of 200 kg N ha 1 to a fallow Quartzipsamrnent at Live Oak. -...J

PAGE 191

..... .q JJ Q r-i ..-l 0 l'I) 0 0 20 40 60 80 100 120 Figure 6-6. 0.5 1 DAY 116 .Ammoni\lill N (mg/kg) 2.5 1.5 f: I I 2 I I ff -~ _I I i I I i I I I j I i I : I I f I i I l ..J, J ,-t, ,+., :,'t_ ,.., ~, \ f \ \ I : \ i, : \,\;; ,'IY vi I 1\\ .I. .~;., = .. ~: .. > \ : \\ !\ \ \ :\ \ H H, :i \ \ I ' \ \ .~':. ..,,,...,r ''"'' 3 3.5 no fertilizer 0 kg/ha DCD ,., --""-~o kg/ha DCD .... ..... .. ,J, .. .. ,; 40 kg/ba DCD ---~--,o kg /ha OCD ........ -E~l,.., ..... Effects of DCD rate on soil NH/-N concentration with depth 116 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. 4 .... C'\ 00

PAGE 192

500 400 ...... ,IS .c : 300 ...... z -rl c 200 0 100 : ~ \ \ \ \ \ \ \ \ \ // ... .. . .. \ \ Rainfall \ ... \ : !!'..;. \ .-, ,. \ '-:..: \ ..... ,. ,-:i \ ' -, ' \ ,. \ ,. .. ,. t..:, :!it;, ,..... .. , ?K '< / .. ,, , ' ... / ~ <:, '{;v:.".'. ....... . .. .. .. .. ~ : -_-. ....... ,'. ~~ ::_. ,,>~ :" ~ ;::_-~~ .. ....... .. .. i ; ~' .. .. ., .. .. .. ......... ... .. ..... .......... ...... ........ .. .. .... .... : ':-::, -:-::.~ : ~ .: ~ .... .. .. .. :c.o tez;ti1izez; 0 k9 / ht1. OCO ._ .... 20 kg/ha DCD ---'jf._---&0 kg/ha OCO -(j-60 kg / ha DCD " , .. /: ~ : : :~: ;:;.:.;;;:;;.:;::;;.:;;,:; 0 .... / 0 ()....___ .A.----~ 0 Figure 6-7. 20 Days 40 After 60 Fertil.izer 80 Application 100 Effects of DCD rate on soil NH/-N in the 1.22 rn profile of a fallow Quartzipsarnrnent at Live Oak. 400 300 ...... Id 16-l c -rl 200 G> :> -rl Cl! ;j 1 00 a 0 120 .... O'\ l,O

PAGE 193

170 of total soil NH/-N with 60 kg ha1 DCD were not different from those with 0 DCD because DCD rate effects were cubic (Table 6-1). On day 81, total NH/-N in the 1.22 m profile in creased from 43 to 63 kg ha1 with an increase in DCD rate from 0 to 60 kg ha1 (Table 6-1). Total NH / -N in the 1.22 m profile was not influenced by DCD rate on days 46, 60, or 116. Soil N0 3 -N On day 14, soil NO 3 --N concentrations at the 0 to 15, 15 to 30, and 61 to 91 cm depths, decreased with an increase in DCD rate from Oto 60 kg ha1 (Figure 6-8 and Table 6-2). These decreases were from 10.7 to 4.6, 4.7 to 3.2, and 2.3 to 1.3 mg kg1 at the Oto 15, 15 to 30, and 61 to 91 cm depths, respectively. On day 31 at all depths, soil NO 3 --N concentrations were reduced with increases in DCD rate (Figure 6-9 and Table 6-2). At the 0 to 15 cm depth, soil NO 3 --N con centration decreased from 43 to 11 mg kg1 with an increase in DCD rate from Oto 40 kg ha 1 A further increase in DCD rate to 60 kg ha 1 had no effect at the Oto 15 cm depth. With an increase in DCD rate from Oto 60 kg ha1 soil NO 3 -N concentrations decreased from 13 to 3.8, 3.7 t o 1 9, 2.3 to 1.3, and 1.9 to 1.1 mg kg 1 at the 15 to 30, 30 to 61, 61 to 91, and 91 to 122 cm depths, r espectively.

PAGE 194

0 0 20 ,._ 40 s u ...... .c: 60 0 ..-1 -.-l 0 {I) 80 100 120 Figure 6-8. Jl 'itI i/f i 1 I i ,i 1 tf I I i I ,f.~~i 'ri' i I : 2 i I i i I l i I l i I 11 l i I l l ,r...l' Nitrate-N 4 (mg/kg) 6 8 10 .. }" / / / ./ . ;(;, ., ....... ...... .. .............. . 0 ~ .. .. .... .... .. .... .. .. ........ .. ......... .... .... .... .. ... .... ...... ...... .. .. ........ .. .... _______ ,.. ~,.. .... -. / , / _, ,I //, :,I ,I /. ~ ,I ,I , ,I ~ ,I I I I I I I I 1' I I I I I ,I DAY 14 no rert:ilizer 0 k9 / ha DCD .,.._20 kg / ha. DCI> r .. .. .. ... ... ..... . ... ... .. 40 kg / ha DCD ___ )If __ ,., 60 kg/ha. DCI> A .. .... .. ~,- Effects of DCD rate on soil N0 3 --N concentration with depth 14 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. I-' -...I I-'

PAGE 195

172 Table 6-2. Effects of DCD rate on soil NO 3 -N concentration at five depths over six sampling dates in a Quartzipsamment at Live Oak. Days After Fertil i zer Application Depth ( cm) 14 31 46 60 81 116 0-15 L** L*** L* NS NS NS Q** 15-30 Lx L** L** NS NS NS Q* 30-61 NS L** L* L* NS Lx 61-91 L* Lx Lx L* NS NS 91-122 NS L* NS L* NS NS Profile L** L*** L** L* NS NS Q** Nonsignificant (NS) or significant at the 0.1 ( X) 0.05 ( *) 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 196

-r-i -ri 0 11') 0 0 :a 0 40 60 80 100 120 10 20 Nitrate -N 30 (mg/kg) 40 ,fl'-; :'" : ,j 11 .. .,/,,, .. "'~ ,,,,,' "'"' ..... ,' ;.:,( r;," ,r. r .... I f ,,I ; I f ,, I I' ,, i I' ,, ,, '-'~~ ~ :I I I I I I fl, If' I: I 11, 1 DAY 31 50 no fertil.izer e 0 l<:9/ha DCD ,., ---;"__ 20 kg/ha DCD ~-... .... .. &,,,,o,,, ..... . ._, 40 l<:9/ha DCD ------6 0 kg/ha DCD Figure 6-9. Effects of DCD rate on soil N0 3 --N concentration with depth 31 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. 60 I-' -..J w

PAGE 197

174 On day 46, soil NO 3 --N concentrations decreased with increases in DCD rate at all but the deepest (91 to 122 cm) depth (Figure 6-10 and Table 6-2). At the Oto 15 cm depth, soil NO 3 --N concentration decreased from 60 to 34 mg kg1 with an increase in DCD rate from Oto 60 kg ha1 At the 15 to 30 cm depth, soil NO 3 --N concentration decreased from 35 to 16 mg kg1 with an increase in DCD rate from 0 to 20 kg ha1 Further increases in DCD rate had no effect on soil NO 3 --N concentration at the 15 to 30 cm depth. With an increase in DCD rate from 0 to 60 kg ha1 soil NO 3 --N con centrations decreased from 7.4 to 4.0 and 3.1 to 2.1 mg kg1 at the 30 to 61 and 61 to 91 cm depths, respectively. On day 60 ( Figure 6-11), soil NO 3 --N concentrations decreased with an increase in DCD rate at the 30 to 61, 61 to 91, and 91 to 122 depths (Table 6-2). These decreases in soil NO 3 --N concentration were from 26 to 17, 13 to 5.3, and 5.9 to 2.2 mg kg1 at the 30 to 61, 61 to 91, and 91 to 122 depths, respectively. On day 81 (Figure 6-12), soil NO 3 --N concentrations were not influenced by DCD rate at any depth (Table 6-2). On day 116 (Figure 6-13) at the 30 to 61 cm depth, soil NO 3 -N concentration increased from 2. 0 to 2. 7 mg kg 1 with an increase in DCD rate from 0 to 60 kg ha1 As with the NH/-N data, soil NO 3 -N concentrations f or all five depths were transformed to kg ha1 of NO 3 --N and summed to calculate the total kg NO 3 -N ha 1 in th e 1. 22 m

PAGE 198

fl fl c:l .-i 0 tll 0 0 20 40 60 80 100 120 10 20 Nit:rate-N 30 (mg/kg) 40 50 60 .. ... .. .. .......... ... ...... .. .. .. ,.. .. ::::::::: =-----------------------"' A ,;,,; ..,.,,. .......... ........... .. .. .. .. .. ...... .. ......... .... ................... ...... .. .... .............. ......... .. ........... ............ .. .... ...... .. ....... ..... ,., .. ... ~, ., . ..... .. .. ---,,. ..... ---------/ ..... ---.... ---.,.. .,, ,,,' ___ .. ~ t.: ,,,,' .,., .11 '-' ........ ;I, J I f I I! f I I! j 1 l' f I f I j I If I J I I "j, '!I, jJ I I I DAY 46 no fertil.izer 0 k9/ha DCD ,., ; ..... 20 kg /ha DCD .... ............ , 0,,, ..... . _, 40 k9/ha DCD ___ ., __ 6 0 kg/ha DCD .. .... ~=~.. .... Figure 6-10. Effects of DCD rate on soil N0 3 --N concentration with depth 46 days after application of 200 kg N ha 1 to a fallow Quartzipsamrnent at Live Oak. I-' -..J U1

PAGE 199

A e-1 Ti 0 tl.l 0 ~o 40 60 80 100 120 0 /I JI fl .f I i I/ 10 20 Nit:r::ate-N 30 (mg/kg) ~"';'; ..... l ,,:,(,, ,711i; ;,, ;',',, I ,.,:.',' I ,,; I ",,'' I
PAGE 200

0 0 20 .,.... 40 fl ..... .i:: Oi CD 60 0 ,-f -.-4 0 fll 80 1.00 1.20 Figure 6-12. 2 -=; : 9\ ~,.,..;.; .... J / I~"( 4 Nitrate-N (mg/kg) 6 8 ~ If.: ., : . t, DAY 81 ,, '\?: \\ \\ .. .. .. ...... .. ' \ ., .. .. ..... ., ~ ........ "'" '-,( ' ';. ',... '',,, \ ' ,, \ ........ .... -..._. .. .... ": -=-i:::......... ;. :::-~ ' .... ',. \ :;:-., ,,': ..... :\.. .... ... '.""; . '1:::-~, . , ,, ~= ~1 :\" ~ -, ,, \ .. . '\ -.. ', ... -. ,, ,:: :' "'-: ~ ... \ . \ \'\ ., ,,, \ '\ ... . ~., '\. ,t--. v; :..;.,; 10 no t:rtilizr e 0 kg / ha DCD ~'"' 20 kg/ha DC) ~ .. .. ., ... 40 kg / ha DCD ___ ),!( __ oO kg/ha DC) .. ..... .. ... . Effects of DCD rate on soil N0 3 --N concentration with depth 81 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. I-' ...., ....,

PAGE 201

0 0 20 ,,... 40 fl ...... .c: 60 GI 0 r-i 0 ti) 80 100 120 Figure 6-13. 2 : ;: 41'. ~ \1 ,' f , j l~ ~:, \~ 1 '1 \ ,\ \ i. i~tt, Nitrate-N \ '\. '\. '". \ ' .. \ .. ' \\ '\. \_\ ' --.}. \ -:;~ ', .. ,~; ,. ',fi_ : ~\ I l f i \' I i '. J i \ I l ,, i \ ,, l )Y:' t~: ,.~.. ';,.' ... V "" (mg/kg) 6 DAY 116 8 10 no :C'ertil.1:z:er O k9/ha DCD 7t,..20 kg/ha DCD ,., .. ..... ,,, 11 ..... 40 kg/ha DCD ___ ':II{ __ ,., 60 kg/ha DCD A Effects of DCD rate on soil N0 3 --N concentration with depth 116 days after application of 200 kg N ha1 to a fallow Quartzipsarnment at Live Oak. I-' --..I (X)

PAGE 202

179 profile (Figure 6-14). Total NO 3 --N in the profile de creased with increases in DCD rate on days 14, 31, 46, and 60 (Table 6-2). On day 14, total NO 3 --N decreased from 67 to 40 kg ha1 with an increase in DCD rate from Oto 60 kg ha1 On day 31, total NO 3 --N decreased from 160 to 78 kg ha1 with an increase in DCD rate from 0 to 20 kg ha1 With further increases in DCD rate, total NO 3 --N decreased to 54 kg ha1 With an increase in DCD rate from 0 to 60 kg ha1 total NO 3 --N in the profile decreased from 273 to 139 and from 373 to 247 kg ha1 on days 46 and 60, respectively. On days 81 and 116, total NO 3 --N in the 1.22 m profile was not influenced by DCD rate. Total Soil Inorganic N Total soil NH/-N and NO 3 --N (SIN) concentrations decreased with increases in DCD rate at several depths on days 14, 31, 46, and 60. On day 14 at the 61 to 91 cm depth, SIN concentration decreased (Figure 6-15 and Table 6-3) from 5. 0 to 3. 0 mg kg1 with an increase in DCD rate from Oto 60 kg ha1 On day 31, SIN concentrations (Figure 6-16 and Table 6-3) decreased from 35 to 18 and 4.0 to 2.8 mg kg1 at the 15 to 30 and 91 to 122 cm depths, respectively. On day 46, SIN concentrations (Figure 6-17) decreased from 59 to 32 and 11. 7 to 8. 0 mg kg1 at the 15 to 30 and 30 to 61 cm depths, respectively, with an increase in DCD rate from Oto 60 kg ha1 On day 60 (Figure 6-18), with an

PAGE 203

500 4.00 .-.. Ill ..c: ....... tn 300 ..I( ._ z I 4) .jJ Ill :aoo M .jJ .... :z 100 0 0 .. .. . "" ~ : _/.//_ . //:\\ . ._/ /_M\ \ _:,:,, /f \\ \ __ / / _; :. \~ \ / / ;.,;; \\, ... ..... / i / \\ \ _./ / / '' \ .. .... // _,/ .. \~ ........ f ...// .,\ i ./ / (?, / ., .. \ f (::i / r/ -~' ~ .. I / _, .'. 'i. .. / i ~f. ........ .. ...... .... ... ... .. . . .... ).}!\ / / / ,,.... i '} \ .-' I i / \.\\ .. / / / ,,, , .. i Rainfall no !:i::t1l.1zr O kg/ha DCD ,., .. 20 kg/ha DCD ---~=--40 kg/ha DCD ,, --,_1-oO kg/ha DCD .. .. f : .......... ..... .. '2,~/:> ~~: ~ ::7 :: :-(J / ---~'.'~ / ......... .,,, .. ,:', ;: :. ~ ~--~!,l.t-.,, ,::::. ::-:.= :. :';l . ....... ~ '!":-/ .,..;"" : ~.;.:-G:: ~---. _..._._ ..... .... .. 20 Days 40 After 60 Fe:ctili.ze:r 80 Appl.icati.on 100 400 300 ffl ._, r-1 r-1 cs 11-1 A ..-1 cl 200 P: CD > ..-1 cl r-1 1 00 0 120 Figure 6-14. Effects of DCD rate on soil N0 3 --N in the 1.22 m profile of a fallow Quartzipsamment at Live Oak. ..... 00 0

PAGE 204

..... fl ..c: i 0 ,-l 0 tll 0 20 40 60 0 Nitrogen 80 (mg/kg) 100 120 140 160 20 :.,,;, . --------""" .. t :, ..:--; ~,;::.,::.,::.,::. :: ......................................................................................................... ,,, I . " _., ..... ,::, ......................................................................................................................................................................... "<.; I ........ .. .... . 40 ,_., \ I.-' r .. l,, I "' I 60 J ,' w !f / if : I I I d!l, 80 H-~t !I. ,~ -~ ,, J! 11 r 100 120 DAY 14 no :Cr~111zer 0 kg/ha DCD 7t,.,,20 kg/ha DCD ..... .... ,0,,., ..... 40 kg/ha DCD ___ 'lll{ __ ,., 60 kg/ha DCD A Figure 6-15. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concen tration with depth 14 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. ..... (X) .....

PAGE 205

Table 6-3. Depth ( cm) 0-15 15-30 30-61 61-91 91-122 Profile 182 Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) at five depths over six sampling dates in a Quartzipsamment at Live Oak. Days After Fertilizer Application 14 31 46 60 81 116 NS NS NS NS NS NS NS Lx Lx NS L* NS NS NS L* Lx NS NS L* NS NS L** NS NS NS L* NS L* NS NS Qx ex Cx NS NS NS NS Nonsignificant (NS) or significant at the 0.1 ( X) 0.05 ( *) or 0.01 (**) probability levels, respectively.

PAGE 206

0 0 20 ..... 40 fl ..., .c: 60 0 .-i .... 0 fll 80 1.00 120 20 Nit:rogen 40 (mg/kg) 60 80 ---------~--------------,., --------. . ...... .. .?"-.a ,., ,, .... -"' .. .. .. .. ....................................................................................... ,,., / ......... ,
PAGE 207

fl ...., Q r-i ..,,j 0 ti) 0 0 20 4.0 60 80 100 120 20 40 Niti:ogen 60 (mg/kg) 80 100 1410 A _ ... ., ......... ..... ........ .. .. ...... ,., .. ., -. ::.-:.-----------------..... ......... ,.,.,. ., ., ., .,,, ., .,.;::;,:.:;..-.. ___ .. ,,,,(.{ .. .,.. ,J>r , ., ., ;,:-;;, .... ,!(,,';,, .. ~,,. .. ,, .. ..,. .. t~---. : i I :I i f I f I i f I ,,, j ;J, I f I ; I I DAY 46 no trtiliz:i: 0 kg/ha DCD --~';!' __ ,., 20 leg/ha DCD .,.,. ......................... ,., 40 kg/ha DCD __ .,. __ GO k9/ha DCD ..... ... : Figure 6-17. Effects of DCD rate on soil inorganic N (NH/-N + NO 3 --N) concen tration with depth 46 days after application of 200 kg N ha1 to a fallow Quartzipsamment at Live Oak. .... co

PAGE 208

0 0 20 ...... 40 fl ..... 60 0 r-i ori 0 {I) 80 100 120 Nitrogen 20 (mg/kg) ~o 60 {~) i .. iii.:. .. : ,,,.,. .,. .. .,. .,. .. . ~ .. ~..... . .. .,. .,. .,. : . .. ,tit .. .. ., ~ j..;,;. \. / ~~ .., / .. .... ,.., ., .. : .. ------"" / -------... .. .. ... ,,, . -------... .. .. ,,,:.:..--~ -~-------:.~ ..... ..,.., -~ :: ,"-11/ _i / -; /.Ii-. _i, ., ... ,I ... "' ..,, "' ,,., ,I ., / ,I .,:;,' .. . "' ,;:~ .. "'"' ,I,>. . . "' ,I . / . .. "' '-ii!,~,,,. ,I r -~; ,I /! f' ', /! j I p. I , DAY 60 no :Cer-cilizer O kg / h a DCD JI\.20 kg / ha DCD r .. .... . , 0 11 ... . I i j ,i j :X1/ /! J I I I 40 kg / ha DCD ___ )I( __ ,., ~/ .... I 60 kg / ha DCD .. .. ..... ...;,-.. Figure 6-18. Effects of DCD rate on soil inorganic N (NH / -N + NO 3 --N) concen tration with depth 60 days after application of 200 kg N ha1 to a fallow Quartzipsamrnent at Live Oak. I-' C0 Ln

PAGE 209

186 increase in DCD rate from Oto 60 kg ha1 SIN concentra tions decreased from 32 to 23, 16 to 7.5, and 8.3 to 4.1 mg kg1 at the 30 to 61, 61 to 91, and 91 to 122 cm depths, respectively (Table 6-3). The only instance where increases in DCD rate resulted in increased SIN concentration (from 3.5 to 4.8 mg kg1 ), was on day 81 at the 15 to 30 cm depth (Figure 6-19 and Table 6-3). On day 116, SIN concentrations were not influ enced by DCD rate at any depth (Figure 6-20). Again, these data were transformed to kg SIN ha 1 and summed for the 1.22 m profile (Figure 6-21). On days 14 and 41, DCD rate effects on total kg SIN ha1 in the profile were cubic (Table 6-3). On day 14, quantities of total SIN in the profile were 376, 538, 315, and 373 kg ha1 with 0, 20, 40, and 60 kg ha1 DCD, respectively. On day 31, quan tities of total SIN in the profile were 327, 364, 219, and 276 kg ha1 with 0, 20, 40, and 60 kg ha1 DCD, respectively. Total kg SIN ha 1 in the 1.2 m profile was not influenced by DCD rate on days 46, 60, 81 or 116. Soil N0 3 --N/ (N0 3 --N + NH / -N) Ratio The soil NO 3 --N concentration was divided by SIN concentration for each date-depth combination. This ratio has been referred to as the nitrification ratio (Lossaint and Roubert, 1964) and the nitrification rate (Sahrawat, 1980). Data derived from this equation gave some ind ic a ti on

PAGE 210

g. Q ,-j -.-1 0 t/l 0 0 :a 0 40 60 80 100 120 Figure 6-19. 2 Nitrogen 4 f'!:~ -~,,1,,r l ., f / f ., f I f ,, f I f J''ll 'I. '~ \ ,,... ., ,, .. ' \',,,,,, ',. \ \ \ .. ,, (mg/kg) 6 \ ,..,,,,,,, \ \ ', \., ... -. .. "a . ... \., ,:(' -...:r,.... "'ur ' ..... ' ' ......... \ 8 ... ', ... ''' ""--:~ 10 DAY 81 no fertilizer ... -\. ......... ""iiiii ~....... \ ... .. .... ... 0 k9/ha DCD ,,., 20 kg/ha DCD ......................... ..... 40 k9/ha DCD ---4--60 kg/ha DCD ,, . ... "'' \ .. ... .. ... ,, .... \. .. ... .. ... ,, . .... ,--~ ', .. ~i"~ ... ~> ... \ \ \ \. 1 ~ \ ,, ',, \ \ ',, ,, ',, \ ,, ,,, \ \ \. ',, \ \ ',,, \ ..... ., .,. .. ;,. ~) ._;,J 12 Effects of DCD rate on soil inorganic N (NH/-N + N0 3 -N) concen tration with depth 81 days after application of 200 kg N ha 1 to a fallow Quartzipsamrnent at Live Oak. ..... co .....,

PAGE 211

Cl Ti 0 Ol 0 0 20 40 60 80 100 1.20 Figure 6-20. 2 Nitrogen (mg/kg) 4 ,, i"! J!, fl !' (:U) --rn"1 hi I! I: \! t 1 E I ,I, .-i a ~" ;.1~ \ ..... ,, \ 6 ....... ......... \ \\ ', \ \ ..... \ \ \\ \ \\ '\. :,,:\ lt .~> ;r '' l \ I ': i I !-\ I : '\ , I \ I : I E \ I : ,1 \ 1, ~) ~ 8 10 DAY 116 n.o fertilizer 0 k9/ha DCD ,., ---n,--20 kg/ha DCD .. .. ......... ......... ... _, o k9/ha DCD ------60 kg / ha DCD ....... l.2 Effects of DCD rate on soil inorganic N (NH/-N + NO 3 -N) concen tration with depth 116 days after application of 200 kg N ha 1 to a fallow Quartzipsamment at Live Oak. ..... 0) 0)

PAGE 212

500 400 ..... ell ..c: bl .... 300 s:: Gl bl 0 .u .-I 200 z 100 \ ~ : \ .. ~, \ .. . \ \ .... ,. \ \ .. . : \ : ,. .,, ~, \ .. ". ... ... ~ \ \ "' -'?I! : \ ,., . } \ ., .i \ ... ~' ,,..~ \ \ ..~ . '. \ '. \ \ .,;,, I / \ \\ \ ,.. \ ,.-;' i / \ \ '. \ f \. / i .., '. \ '. .. ; 'at-\ .. .. . )II": / i ./ \ ~ ~' \ .. / .. ,,, \ S'. \ ,,; "' '" \ i . , . i \ i , .. i, ,.. ., \ l .. ,, .. ; ' . \ ',: ,! ' I \ '. : ~., ; .; lo ; 'I \ '-. I ~ ', .; it . : ~ ,, ; ,, .. , . . . no !eztiliiz:e:c 0 kg/ha DCD .... ....... 20 kg/b& DCD ---:~--40 kg/b& DCD -I \60 kg/ha DCD : \\);. 'tii! : :: :-: :-:::;::; ;:; :;; :::: ~ ............ .............. .... .. .. :~ -"' : ~ ... --.. ----0 400 .... 300 i ...., ,--t ,--t G -..i s:: Tl G 200 Pl Q) > Tl G ,--t ;:j 100 a . .... 0 0 Figure 6-21. 20 Days 40 After 60 P'ert:1.1izer 80 Applica t ion 100 0 120 Effects of DCD rate on soil inorganic N (NH/-N + N0 3 --N) in the 1.22 m profile of a fallow Quartzipsamment at Live Oak. CX) \0

PAGE 213

190 of the extent to which nitrification was inhibited by DCD. Inhibition of nitrification should lower the magnitude of this ratio. The means of these data are not shown but analysis of variance is shown in Table 6-4. The N0 3 --N/ (N0 3 --N + NH/-N) ratio decreased with increases in DCD rate on day 14 at the Oto 15 and 15 to 30 cm depths. On day 31, this ratio decreased at the Oto 15 and 15 to 30 cm depths with increasing DCD rate. On day 46, this ratio de creased with increases in DCD rate at all five depths. On day 60, this ratio decreased at the Oto 15, 15 to 30, and 30 to 61 cm depths with increases in DCD rate. On day 81, this ratio decreased at the Oto 15 and 30 to 61 cm depths with increases in DCD rate. The only increase in the NO 3 --N/ (NO 3 --N + NH/-N) ratio with increased DCD rate, occurred at the 30 to 61 cm depth on day 116. The NO 3 --N/(NO 3 --N + NH/-N) ratio for the entire 1.22 m profile (Figure 6-22), was computed from the total kg NO 3 --N and SIN ha1 in the profile. On day 14, DCD rate had no effect on the NO 3 --N/(NO 3 -N + NH/-N) ratio in the 1.22 m profile as a whole (Table 6-4). On days 31, 46, 60, and 81, the NO 3 -N/ (NO 3 -N + NH/-N) ratio in the profile decreased with an increase in DCD rate. On day 116, DCD rate had no effect on the NO 3 --N/(NO 3 -N + NH / -N) ratio i n the 1.22 m profile as a whole. These data indicate that DCD had an inhibiting effect on nitrification throughout all or most of the 1.22 m

PAGE 214

191 Table 6-4. Effects of DCD rate on soil NO 3 --N/ (NO 3 --N + NH/-N) ratio at five depths over six sampling dates in a Quartzipsamment at Live Oak. Days After Fertilizer Application Depth ( cm) 14 31 46 60 81 116 0-15 L* L*** L* Lx L* NS Q* Qx 15-30 L* L*** L** L** NS NS Qx QxC* Q* 30-61 NS NS Lx L* L* L* 61-91 NS NS Lx NS Qx QxCx 91-122 NS NS Lx NS NS NS Profile NS L*** L* L* L** NS Q*C* Nonsignificant (NS) or significant at the 0.1 ( X)' 0.05 ( *) 0.01 ( **) or 0.001 (***) probability levels, respectively.

PAGE 215

80 60 0 .... .u IIS C: 0 .... 40 .u IIS u .... 4M .... ),,I .u ... z 20 r : : ; .. .. .=.: :{ . .. .. .. .. .. .. ... .... .. .... .. .. /..... . / \!> ,. / I '-, / /.*" .. . . .. / .' _, ,_ .. / I , , / ;/ f / --"'' ,. ~ , "" ,.-, .. "' ,., ....~---,.~' ,,,-, . . ... .. ,,. ; :c.~--, ~" --, , I ,., I // 't!C>,,.... ... .. I . J ~ . I ~ ~ -v,,"{l; .. .. I t I /i I// 1// no frt:i1iz:r 1/ / ~ / 1 : 'tfi' / o kg/ha DCD 'JI:/ "' ... i / .. Rainfall ...... . .. . .. . .... ... . , ,o kg/ha DCD ---~--/// / I .,-/ .. i ii\ r ..... .. . / / : {tf'""~, ., : . .......... . . . .. .. . j ~o kg / ha DCD ~ ~ ./' 60 kg / ha DCI> 7it 400 ,..... 300 i ...... r-1 r-1 cl i::: Ti Ill 2 00 Q) > 4J Cl r-! 100 . / 0 0 Figure 6-22. 20 Daye 40 After 60 Ferti1izer 80 App1ication 100 0 120 Effects of DCD rate on soil nitrification rat i o, i e (N0 3 --N x 100/(Ntt 4 -N + NH 3 -N) in the 1.22 rn profile of a fallow Quartzipsarnrnent at Live Oak. 1--' \.0

PAGE 216

193 profile from 31 to 81 days after urea and DCD application, and in at least portions of the profile from 14 to 81 days after application. Soil DCD Fourteen days after DCD application, soil DCD concen tration increased with an increase in DCD rate from 20 to 60 kg ha1 (Figure 6-23 and Table 6-5) at the Oto 15, 15 to 30, and 61 to 91 cm depths. On day 31, soil DCD concentra tion increased with an increase in DCD rate (Figure 6-24) at the Oto 15, and 15 to 30 cm depths. Similar DCD rate effects on soil DCD concentration were observed on day 46 (Figure 6-25) at the 15 to 30 and 61 to 91 cm depths, and on day 60 (Figure 6-26) at the Oto 15 and 30 to 61 cm depths. Soil DCD concentration increased with increases in DCD rate on day 81 (Figure 6-27) at all but the Oto 15 cm depth. On day 116 (Figure 6-28), soil DCD concentration increased with increases in DCD rate at the 61 to 91, and 91 to 122 cm depths. Total kg soil DCD ha1 in the 1.22 m profile (Fig ure 6-29) increased with increases in DCD rate at all sampling dates (Table 6-5). Based on these data, an estimate of the residence half time of DCD in the 1.22 m profile was calculated by means of regression. This calculation assumed the amounts of DCD applied as the points of origin on the X axis of Figure 6-29. Because of the shapes of the curves in Figure 6-29, these residence half times can only be considered rough

PAGE 217

..... s u ...., .c: Pi GI 0 r-i ..-I 0 fl} 0 2 4 0 0 DCD (mg/kg) 6 8 ~' ' .,. .. . 10 20 40 ,. ... . ' --' -----,-. ...... ..................................................................................................................................................................................................................................... ,., 0 60 80 01: ,\ \ '\ \ 1, \ r, \ :'!.'-: f f \ / f \ f 100 fl-!, f ~;i( 120 DAY 14 20 kg/ha DCD 4.0 k9/h DCD ~-',., 60 kg/ha. DCD .. .......... _. ............... Figure 6-23. Effects of DCD rate on soil DCD concentration with depth 14 days after DCD application to a fallow Quartzipsamment at Live Oak. .... U)

PAGE 218

195 Table 6-5. Effects of DCD rate on DCD at five depths over six sampling dates in a Typic Quartzipsamrnent at Live Oak. Days After DCD Application Depth (cm) 14 31 46 60 81 116 0-15 L** L* NS L** Q* NS Qx 15-30 Lx L*** Lx NS L* NS Q*** 30-61 NS NS NS Lx Lx NS 61-91 Lx NS L* NS L* L* 91-122 Q** NS NS NS L*** L* Q* Qx Profile L* L** Lx L* L* LX Q* Nonsignificant (NS) or significant at the 0.1 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 219

0 0 20 ..... 40 fl ..., .c: 60 0 r-t ori I=~ 0 ti) 80 100 120 DCD (mg/kg) 2 4 6 ~ ,.:-: ; ,,. ,,. .... .. ,#~ I' ..... .. ~.,: I' ..... .. ...... . ..... .. ............ .... ........... ...... ,,, ,, , ... ... .. ............................ . . .... ................ .. r ;j / DAY 31 '/ 1i .. .... . 8 10 20 kg / ha DCD e 40 k9 / ha DCD ~ ,., 60 kg / ha DCD . ... ... ... ,i;, .. c. ........ .. Figure 6-24. Effects of DCD rate on soil DCD concentration with depth 31 days after DCD application to a fallow Quartzipsamrnent at Live Oak. .... \0 0\

PAGE 220

0 0 20 ..... 40 fl ....... 2 DCD (mg/kg) ict""'" : t;. 6 ~ '-. ...... ... .,. ,, -:: .... ., .... ,, 21 .. ... ,.., ..u .i:" .:: .::~ 3... ""~ ----.. .. . -:'o" "' "' "' .. .. .. .. ;::.::: .... .. .. ...... -5, ~ .. ..... ... ..... .. ... .... .. ..... :' 8 10 .c: Pi 60 // DAY 46 CD 0 ,-t 0 fl) 80 100 120 : I : I ./ / / ,,, (p I f 1 I f d 1. I: Figure 6-25. 20 kg / ha DCD 40 kg / ha DCD ~',., 60 kg/ha DCD ., .1 ... ... .. .. .. , Effects of DCD rate on soil DCD concentration with depth 46 days after DCD application to a fallow Quartzipsamment at Live Oak. I-' \D .....,

PAGE 221

0 0 20 ..... 40 s u ...... .: i 60 0 r-1 0 ti) 80 100 120 DCD (mg/kg) 2 4 iE,,.. ... :.: .. ...,, ... .. ... \ -... ... "' ... V, .. ;r= .... ,._ ; ,, : ,, ,, f ,, : ,, ). ,, ; }.; / _..i._ ., ,,, ,A; .. ,,, ,,' ,,, ,., ,,, ,,, ,,, ,,, ,, ., ,,, ,,, ,,.,,. ,,, ,.,, ,,, ,,, .. ,,, ,,,,' ,,, ,., ,,, .. !"1t' I -.;; I I : \ I ; f f I f 6 DAY 60 8 10 20 k'1/b11. DCD 40 kg/ha DCD ~-: ---~-6 0 k'1/b11. DCD .,.._ .............. ,. .... ..... ..... Figure 6-26. Effects of DCD rate on soil DCD concentration with depth 60 days after DCD application to a fallow Quartzipsamrnent at Live Oak. .... \0 CX)

PAGE 222

fl .c: 0 0 20
PAGE 223

..... a ..c: ., Cl 4) Q rl ...t 0 en 0 0 ~0 40 60 60 100 120 Figure 6-28. o.os -----------------DCD (mg/kg) 0.1 0.15 0.2 0.25 DAY 116 20 kg/ha OCD ,o kg/ha OCD -, ., /i ~60 kg/ha DCD .. : / / / , .... .. ... .. ...... .. .. ................................. .... ,, .. / .. ... / .. ..... ............ ......... .... ... ... ... .,: .. : ---. .... : Effects of DCD rate on soil DCD concentration w it h de pt h 116 days after DCD application to a fallow Quartzipsamment at Live Oak. "' 0 0

PAGE 224

" ....... Ol 60 50 40 ._,. 30 20 l.0 0 0 G Q 0 .. ~ ~ .\ .,... / \ I ' / \ i \ ; \ \ :, v. / \ .. . . .. .. ... .. //" ........ .... ... Rainfall // :lO kg/ba DCD ___ l'.,l_ __ '-' 40 kg/ba DCD J "' 60 kg/bA DCD .. .. .. . .. .. /1 -r ........................ .. ............. '.\\\ ,.,. -------=--"'-, ., "' er ........ ~, ,. .. .. .... .. ,. ...................... :.:.................. .. ........... '' ';:-',, ''''' ...__ . .. .. ....... .. .. .. .. .. . ............ ,; . ',~~ ------------~) rT----! .. I / I / I ~-; I I 20 Days 40 After 60 Ferti1izer 80 APp1ication 100 400 300 6 _. r-i r-i ell 14-1 rl 200 Q) > ri +.I ell r-i 100 0 120 Figure 6-29. Effects of DCD rate on total DCD in the 1.22 m profile of a fallow Quartzipsamment at Live Oak. IV 0 ....

PAGE 225

202 estimates. This is particularly true in the case of the 40 and 60 kg ha1 DCD rates. The residence half ti.mes thus obtained were 61 (r 2 = -0.9697), 66 (r 2 = -0.7487), and 63 (r 2 = -0.9524) days for the 20, 40, and 60 kg ha1 DCD rates, respectively.

PAGE 226

CHAPTER 7 DISCUSSION Plant Yield/N Content and Soil N and DCD Tuber Yields Marketable tuber yields ranged from 26 to 30 t ha1 in 1983, and from 24 to 30 t ha1 in 1984, at Gainesville. At Hastings, marketable yields ranged from 18 to 22 t ha1 in 1983, 16 to 24 t ha1 in 1984, and 29 to 35 t ha1 in 1985. Average potato yields for commercial production in the Gainesville area were 19 and 24 t ha1 for 1983 and 1984, respectively. Average yields in the Hastings area (the primary spring crop potato producing area of Florida) were 26, 31, and 30 t ha 1 in 1983, 1984, and 1985, respectively (Florida Crop & Livestock Reporting Service, 1986). Thus, yields obtained in this study were above state averages in 1983 and 1984 at Gainesville and in 1985 at Hastings while being below state averages in 1983 and 1984 at Hastings. In 1983 and 1984 the low yields observed at Hastings were likely due to a combination of rainfall distribution and severe leaching of fertilizer salts by the subsurface irrigation systems. 203

PAGE 227

204 Tuber Quality Since these tubers were largely intended for proces sing into potato chips, high specific gravity values were very desirable. Tuber specific gravity values in this study ranged from 1.0723 to 1.0910. Generally tuber specific gravity values between 1.061 and 1.090 are considered normal for most types of potatoes (Curwen et al., 1982). Tuber specific gravity was increased by N rate in two out of five year-location combinations and was decreased by DCD in one of the five year-location combinations. Nitra pyrin effects were mixed, but resulted in higher tuber specific gravity values than did DCD in three out of five year-location combinations. In all cases tuber specific gravities with the IBDU treatment were similar to those with the inhibitor treatments. The proportion of marketable yield that was grade A (~ 4.8 cm tuber diameter) is an important measure of crop quality, particularly in areas such as Northeast Florida where most of the potato crop is processed into potato chips. Grade B tubers are too small to be processed into potato chips, thus they are usually sold at a lower price. A direct relationship was observed between proportions of marketable yield that were grade A, and tuber yields. The proportion of total yield that was marketable, as reported by Sanderson and White (1987), reflects the pro portion of marketable v cull tubers. Cull tubers are either

PAGE 228

205 rotten, misshapen, or damaged by the harvester or grader, and are of no economic value in most situations. If a treatment increases the proportion of total yield that is marketable, then the value of the crop is increased. An inverse relationship was observed between proportions of total yield that were marketable and tuber yields. Reasons for this were not apparent. Treatment Effects Nitrogen rate effects. When 67, 134, and 202 kg ha1 N were applied, soil NH/-N, NO 3 --N, and SIN concentrations increased with increases in N rate on all sampling dates, including at harvest. In 1983 when only 134 and 202 kg ha1 N were applied, N rate effects on NH/-N, NO 3 --N and SIN were limited to the first 60 days after fertilizer application. In 1984 and 1985, a lower N rate (67 kg ha1 ) was included with the 134 and 202 kg ha1 N rates. Thus the probability of obtaining N responses was greater than in 1983. A posi tive tuber yield response to an increase in N rate from 67 to 134 kg ha1 did occur in 1984 at both locations and in 1985 at Hastings. In all cases this yield increase was approximately 4 t ha1 Only in 1983 at Hastings, was tuber yield increased (3 t ha1 ) by an increase in N rate from 134 to 202 kg ha 1 These N rate effects on potato were similar to those obtained by other workers (Giroux, 1982; Kleinkopf et al., 1981; Meisinger, 1976; Murphy and Goven, 1975; Painter and Augustin, 1976). In no case was a "no N"

PAGE 229

206 control included in any of the trials because on most Florida soils, essentially no yield would be obtained. Positive N rate effects on soil inorganic N concentrations led to increases in many potato plant parameters such as yield (Table 7-1). Interactions between inhibitor and N rate effects. In several cases inhibitor effects were more pronounced or only present at lower N rates. This was the case in several instances in 1984 at Hastings. The reasons for this type of interaction were somewhat different with the soil inorganic NH/-N and N0 3 -N data than with the plant yield and plant N data, though a cause and effect relationship sometimes appeared to be present. In some cases inhibitors had greater inhibiting effects on nitrification at low N rates. This was likely a result of a greater ratio between inhib itor and NH/ concentrations with the low N rates i.e., more inhibitor per unit of NH/. An explanation was needed for why nitrification inhi bition often had more favorable effects on total soil inor ganic N concentrations at low than at high N rates. At low N rates, when inhibitors were effective, though soil N0 3 -N concentrations were reduced for a time, soil NH / -N concen trations were sometimes increased. I f increases in soil NH 4 + _N concentration exceeded decreases in soil N0 3 -N con centrations, the result was an increase in total soil

PAGE 230

Table 7-1. Summary of positive N rate effects on potato plant parameters. Number of Tests Plant Parameters 4/5 Marketable and total yield. 207 4/5 Proportion of marketable yield that was Grade A. 1/5 Proportion of total yield that was marketable. 2/5 Specific gravity. 4/4 Tuber N concentration. 3/4 Plant shoot biomass. 3/4 Total biomass. 3/4 Plant shoot N concentration at harvest. 3/4 N uptake by plant shoots. 4/4 Total N uptake by plant shoots and tubers. 3/5 Leaf N concentration at tuber initiation. 4/4 Leaf N concentration at flowering. 4/4 Leaf N concentration at tuber maturation.

PAGE 231

208 inorganic N. This was the case in 1983 at Hastings with the 134 kg ha1 N rate. Similar effects were observed by Touch ton (1981b) when DCD and urea were applied to winter wheat. At higher N rates however, reductions in soil NO 3 --N concen trations often equaled increases in soil NH/-N concentra tions. Thus, SIN concentrations did not increase. Graetz et al. (1981) observed a similar effect 67 days after DCD and nitrapyrin were applied with 224 kg ha1 N as NH 4 NO 3 to a mulched soil planted to tomato at the Horticulture Unit near Gainesville. Randal and Malzer (1981) also observed this type of DCD effect when 168 kg ha1 N was applied to corn in Minnesota. In several instances, reductions in soil NO 3 --N concentrations exceeded increases in soil NH/-N concentra tions. Thus SIN concentrations were reduced by the inhib itors. This occurred in 1984 at Hastings. Similar results were observed by Touchton (1981a) 4 weeks after application of nitrapyrin and urea to grain sorghum. This may have been because much of any increase in soil NH/-N was consumed by soil heterotrophic microorganisms (Norman et al., 1989; Walters and Malzer, 1990a, 1990b), lost due to leaching, (Walters and Malzer, 1990b), or lost due to NH 3 volatilization (Rodgers, 1983). It may be that for a given soil and climate, there is a maximum limit to the soil inorganic NH/-N concentration that can be maintained. Such maximum limits exist for soil organic N and organic C concentrations (Alexander, 1977).

PAGE 232

Such a maximum limit in soil NH 4 T -N concentration is less likely to be reached with a low N rate such as 67 kg ha1 than with a higher N rate such as 2 02 kg ha1 209 Walters and Malzer (1990b) found that with 90 and 180 kg ha1 N, immobilization of fertilizer N was increased when 0.56 kg ha1 nitrapyrin was applied. They observed that a greater proportion of applied N was leached with 180 than with 90 kg ha1 N. Thus, a greater proportion of applied N was immobilized with 90 than with 180 kg ha1 N. This relationship was accentuated when nitrapyrin was applied. With 80 kg ha1 N, however, plant uptake of N did not decrease with nitrapyrin. This was because in the first year, fertilizer N lost to plant uptake as a result of nitrapyrin induced immobilization was compensated for by nitrapyrin induced mineralization of soil organic N. In succeeding years, this immobilized fertilizer N was miner alized and taken up by the plants. With 180 kg ha1 N, however, stimulation by nitrapyrin of immobilization was apparently exceeded by stimulation by nitrapyrin of miner alization. As a result, in some cases nitrapyrin resulted in an increase in N leachin g loss with the 180 kg ha1 N rate. In some cas es inhibitor s or IBDU did increase SIN concentration at all N rates but plant yield or plant N conten t increased only with the low N rate. This type of interaction was likely due to N supply to the plant being

PAGE 233

210 limiting with the low N rate but not with the high N rate, with or without inhibitors. If N supply to the plant is not growth limiting at a high N rate, then amendments that in crease SIN concentration over time, will not increase plant growth or yield (BlacJaner, 1986). This assumes that inhibi tion of nitrification will conserve soil N and increase the supply of SIN available to the plant. As was shown in Chap ters 5 and 6 and by Norman et al. (1989) and Walters and Malzer (1990a, 1990b), this assumption is often invalid in the field. In some cases, since inhibition of nitrification only increased soil inorganic N with the low N rate, plant yield or plant N content parameters were only increased with the low N rate. In such a case, a direct cause and effect rela tionship would be indicated, with the effects of nitrifi cation inhibition on soil inorganic N concentrations being reflected by similar effects on the means of plant param eters. Interactions were not consistent, often following no logical pattern. In several cases inhibitor effects were greater or only significant at a medium or high N rate. No explanation for this was apparent. The data in Table 5-7 are an example of this. These kinds of patterns may have been due to some soil microbiological or plant physiological relationships that was not understood but more likely they were a result of high variability in the data.

PAGE 234

211 More interactions were observed with leaf Nat flower ing than with any other plant parameter. The reason for this was likely a high sensitivity on the part of leaf N status at flowering to SIN concentrations. Leaf Nat flowering (66 to 81 dap) is reflective of a time during which the tuber bulking stage is well under way and leaves must compete with tubers for N taken up by the roots (Klein kopf et al., 1981). Several workers have suggested that the ideal stage of potato plant growth for leaf tissue sampling is at the 10% bloom stage (McKay et al., 1966). The early (43 to 55 dap) leaf N samplings provide information on the N status of the plant during the latter portion of the vegetative growth stage or the tuberization stage, prior to the tuber growth (bulking or enlargement) stage (Kleinkopf et al., 1981). During the vegetative stage there is no competition for soil N uptake between the plant shoots and tubers. Gardner and Jones (1975) were of the opinion that leaf samples should be taken on at least two separate dates (earlyand mid-season) to reliably determine the nutrient status of a given field of potato. In Flor ida's subtropical climate, maximum total dry matter accumu lation occurs between 52 and 69 days after planting (corre sponding to the time between the earlyand at-flowering sampling dates in this study), followed by a rapid decline with the onset of hot weather; this is about 30 days earlier than that reported in northern trials (O'Hair, 1985). By

PAGE 235

212 the time of the late leaf sampling (93 to 98 dap) the plants were past the tuber bulking stage and in the latter part of the tuber maturation stage. During this last stage, N and carbohydrates move from the shoots and roots into the tubers (Kleinkopf et al., 1981). Dicyandiamide rate effects. Dicyandiamide did not in hibit nitrification in 1983 at Gainesville, since it did not decrease soil N0 3 --N concentrations or the N0 3 --N/(N0 3 --N + NH/-N) ratio (see Appendix C for data and Appendix D for analysis of variance). Dicyandiamide at rates of 5.6 and 11. 2 kg ha 1 did not increase soil NH/-N or SIN concentra tions. The only positive DCD rate effect on potato plant parameters in 1983 at Gainesville, was leaf N concentration at flowering. Potato leaf N concentration at flowering is quite sensitive to soil inorganic N status. The NO 3 --N/ (NH/-N + NO 3 --N) ratio was increased with DCD on day 59 at the 134 kg ha1 N rate, indicating a greater proportion of soil Nin the NO 3 form available to the plant ten days before these leaf samples were taken. In 1984 at Gainesville, increasing DCD rate resulted in an increase in soil NH/-N concentration on only one of five sampling dates (see appendices C and D). All soil NO 3 -N concentrations were very low in 1984 at Gainesville. This was l i kely due to th i s s oil r e c e iving 506 mm of rain during the growing season, a s well as supplemental ove r head irrigation. Soil NO 3 --N conc e nt r ations were generally

PAGE 236

213 decreased by DCD with 67 kg ha1 N but increased with 202 kg ha1 N. The NO 3 --N/(NO 3 --N + NH/-N) ratio was decreased on all but day 13 with the 67 kg ha1 N rate. Thus, inhibition of nitrification was limited to the lowest N rate. The total soil inorganic N concentration was increased by DCD only on day 69. Leaf N concentration at tuber initiation was decreased by DCD in 1984 at Gainesville. The soil inorganic N data do not indicate why this should have been the case. Leaf N concentration at flowering was increased by DCD. This may have been related to DCD induced increases in soil NH/-N and total soil inorganic Non day 69. No relationship was apparent between soil inorganic N concentrations and the quadratic DCD rate effect on late leaf N concentration. With increases in DCD rate, tuber N concentration decreased with the low N rate and increased with the medium and high N rates. This may have been due to effects of the soil NO 3 --N/(NO 3 -N + NH/-N) ratio on tuber N. This ratio was decreased by DCD with the low N rate while it was increased with increases in N rate. Potato has a preference for NO 3 --N (Volk and Gammon, 1954: Pollizotto et al., 1975) thus increases in the soil NO 3 -N/ (NO 3 -N + NH/-N) ratio may tend to increase tuber N concentration. Touchton (1981b) observed a similar decrease in wheat grain N concentration with DCD applied at a low N rate (34 kg ha1 ).

PAGE 237

214 Severe leaching and/or denitrification occurred in 1983 at Hastings, possibly induced by the failure of the sub-irrigation system to keep the water table far enough below the fertilizer band (B.L. McNeal, personal commun ication, see further discussion below). This led to potato yields that were quite low. Soil inorganic N concentrations decreased followed by an increase. Soil NH/-N concentra tion was increased substantially by DCD but there were no effects on soil N0 3 --N. Graetz et al (1981) also observed an increase in soil NH/-N concentration without a decrease in soil N0 3 --N concentration on one of the sampling dates in one of their nitrification inhibitor studies. Because of favorable effects of DCD on soil inorganic Nin 1983 at Hastings, DCD had positive effects on several potato plant parameters. Tuber yield was increased by DCD with the low N rate. In a similar study nitr i fication inhibitor increased SIN concentration at both of two N rates but increased corn grain yield only at the l ow N rate (Touchton et al., 1979). In 1984 at Hastings, soil NH/-N concentrations were initially decreased by DCD up to day 18 (particularly at the 202 kg ha1 N rate), and subsequently increas e d by DCD (see Appendices C and D). Decreases in soil N0 3 -N concentra tions on most sampling dates were caused by DCD, partic ularly with the 67 kg ha 1 N rate. The N0 3 -N/(NH/-N + N0 3 -N) ratio was decreas e d by DCD throughout the latt er t wo

PAGE 238

215 thirds of the season thus DCD quite effectively inhibited nitrification. The SIN concentration was, however, not increased by DCD at any time. It decreased on two sampling dates, particularly with the 202 kg ha1 N rate because decreases in N0 3 --N concentrations exceeded increases in NH 4 + _N concentrations. Because there were no favorable DCD effects on SIN concentrations in 1984 at Hastings, there were only a few mixed DCD effects on potato plant parameters in 1984 at Hastings. Early leaf N concentration was increased, prob ably due to the increase in soil NH/-N concentration on day 32, but leaf N concentration at flowering was reduced by DCD. No soil inorganic N data was collected in 1985 at Hastings, but the only DCD effects on potato plants were a decrease in specific gravity and a slight increase in leaf N concentration at flowering. Among all five year-location combinations the effects of DCD led to an increase in several plant parameters, though in some cases only at certain N rates. These param eters included tuber yield, the proportion of marketable yield that was grade A, tuber N concentration, total bio mass, and total N uptake. Application of DCD led to decreases in specific grav ity and plant shoot N concentration at one year-location combination each. Leaf N concentration at flowering

PAGE 239

216 increased with increased DCD rate in three out of four year location combinations. In the fourth year-location combin ation, DCD resulted in decreased leaf N concentration at flowering. A similar study was conducted in 1983 and 1984 at the Horticulture Unit near Gainesville on a Typic Ochraquult (Mohamad, 1985) less than 100 m from where potato was grown in this study. Mohamad (1985) applied 67, 134, and 202 kg ha1 N with 0, 11.2, or 22.4 kg ha1 DCD to sweet corn. Soil was sampled only from plots receiving 202 kg N ha1 In 1983, 22.4 kg ha1 DCD resulted in increased soil NH/-N concentrations for up to 56 days while 11.2 kg ha1 DCD increased soil NH/-N concentration for 28 days after urea fertilizer application. Soil NO 3 --N concentration was decreased with DCD for 28 days (Mohamad, 1985). In our study in 1983 at Gainesville, DCD had very little effect on soil inorganic N concentrations. In 1984, Mohamad (1985) found that soil NH/-N con centration was increased only at the 42 day sampling with 22.4 kg ha 1 DCD but was little affected with 11.2 kg ha1 DCD. In that same year, 22.4 kg ha1 DCD resulted in decreased soil NO 3 -N concentration only on day 28. With 11.2 kg ha 1 DCD, soil NO 3 -N concentration was not affected (Mohamad, 1985). In our study in 1984 at Gainesville, soil NO 3 -N and NO 3 -N/ (NH/-N + NO 3 -N) ratio data indicated that

PAGE 240

217 11.2 kg ha1 DCD did not inhibit nitrification with 202 kg ha1 N although SIN concentration increased on one of five sampling dates. In 1983 Mohamad (1985) observed no DCD effect on total marketable sweet corn yield. In 1984 sweet corn yield increased with an increase in DCD rate from Oto 11.2 kg ha1 but decreased with a further increase in DCD rate to 22.4 kg ha1 Dicyandiamide had no effect on plant biomass in either year. In 1983 DCD decreased sweet corn shoot N concentration at harvest with 134 kg ha1 N. Nitrapyrin rate effects. In 1983 at Gainesville, nitrapyrin rate had no effect on potato plant parameters because there were no nitrapyrin rate effects on any soil inorganic N parameters. In 1984, however, effects of increasing nitrapyrin rate on soil N parameters tended to be favorable with the low N rate and unfavorable with the high N rate at Gainesville. Thus, it was reasonable that tuber N uptake increased with an increase in nitrapyrin rate with the low N rate but was not affected with the high N rate. Plant shoot N uptake decreased with an increase in nitra pyrin rate with the high N rate but was not affected with the low N rate. No logical explanation was apparent why one plant parameter should have been affected with the low N rate and the other with the high N rate, other than natural biological variation or experimental variation in the data.

PAGE 241

218 No effects of nitrapyrin rate were observed on soil inorganic N concentration in 1983 at Hastings. However, soil samples were not taken beyond day 61 because the potato plants were of such an unthrifty appearance, it was thought that no additional useful information would have been gained thereby. There may have been nitrapyrin rate effects on inorganic soil N that were missed. This was likely because an increase in nitrapyrin rate increased tuber yield (134 kg ha1 N rate only), the proportion of marketable tubers that were grade A, tuber N concentration (particularly with 202 kg ha1 N), total biomass (particularly with 134 kg ha1 N), plant shoot N concentration ( 134 kg ha1 N only), and total N uptake. In 1984 at Hastings, an increase in nitrapyrin rate from 0.56 to 1.12 kg ha 1 resulted in decreased N0 3 --N/ (NH/-N + N0 3 --N) ratios on days 32 and 46. Thus, nitrifi cation was reduced mid-way through the season by nitrapyrin. Increasing nitrapyrin rate resulted in increased N0 3 --N and SIN concentrations on one sampling date and increased NH/-N concentration on another. These favorable effects on soil inorganic N concentration were reflected by an increase in tuber specific gravity and increases in leaf N concentration at flowering at two of three N rates. With 202 kg ha1 N, however, an increase in nitrapyrin rate resulted in decreased plant shoot biomass in 1984 at Hastings.

PAGE 242

219 Dicyandiamide v nitrapyrin. The results for this contrast were mixed. Nitrapyrin seemed to inhibit nitri fication somewhat more effectively than DCD in 1983 at Gainesville. No differences were observed, however, between the inhibitors in their effects on SIN concentrations. Thus, no differences were observed between the two inhib itors in their effects on any potato plant parameters. In 1984 at Gainesville, the two inhibitors seemed about equally as effective at inhibiting nitrification in this soil. Though SIN concentrations were higher with nitrapyrin early and late in the season, these were not times of critical N supply for the potato plant. Apparently higher concentrations of soil N0 3 --N with DCD during the tuber enlargement stage were sufficient to result in higher values for tuber yield and several other potato plant param eters with DCD than with nitrapyrin. This may have been due to the preference by potato for N0 3 --N over NH/-N. The only plant parameter f or which values were greater with nitra pyrin was tuber specific gravity. In a similar study NH 4 N0 3 DCD and nitrapyrin were applied to tomato at Gainesville (Graetz et al., 1981). Their data indicated that at all soil sampling dates, while DCD resulted in higher soil NH / -N and SIN concentrations, nitrapyrin resu l ted i n higher soil N0 3 --N concentrations. As a result, tomato yields were slightly higher with nitra pyrin.

PAGE 243

220 No differences were observed between the two inhib itors in their effects on any soil inorganic N parameters in 1983 at Hastings. The only difference between the inhib itors in their effects on potato plant parameters, was a greater N uptake by tubers with the DCD treatments, and this only with the 134 kg ha1 N rate. In 1984 at Hastings, comparison between the two inhib itors gave mixed results. Soil N0 3 --N and N0 3 --N/ (NH/-N + N0 3 --N) ratio data indicated that nitrification was inhi bited somewhat more effectively by DCD than nitrapyrin. Nitrapyrin, however, resulted in higher soil NH/-N, N0 3 --N, and SIN concentrations. It is reasonable therefore, that nitrapyrin resulted in higher concentrations of leaf Nat flowering. Nitrapyrin also resulted in higher tuber specific gravity values than did DCD. With other plant parameters, however, there appeared to be an inverse rela tionship between soil N effects and plant effects. Dicyan diamide resulted in higher values for several potato plant parameters including tuber yield. Two of these differences were present only with the 202 kg ha 1 N rate. Soil N levels were apparently not a good predictor of yield in this test. Yields were below state average in spite of appar ently adequate soil inorganic N levels. This was the only test where values for a plant parameter (plant shoot biomass at harvest) decreased with increases in N rate. Possible

PAGE 244

221 explanations for this may have included high soil salinity or hail damage. In 1985 at Hastings, the DCD treatments resulted in higher values for yield and leaf N concentration at tuber initiation (with the medium N rate only) while tuber specific gravity values were higher with the nitrapyrin treatments. Considering all year-location combinations, the potato yield, biomass, and plant N concentration data were in most cases reflective of the trends in the soil N data for this comparison. Tuber yields were higher with DCD in three of five tests. Tuber specific gravity values, however, were higher with nitrapyrin in three of five tests. No explan ation can be offered as to why tuber specific gravity values were higher with nitrapyrin than with DCD. Inhibitors v IBDU. In many cases, the IBDU treatment resulted in higher soil inorganic N concentrations than did the inhibitor treatments. Higher soil N values with IBDU in 1983 at Gainesville, were responsible for higher tuber and shoot N uptake and concentration and higher leaf N concen tration at flowering. There was no difference, however, between IBDU and the inhibitors in their effects on tuber yield, tuber quality, or biomass in 1983 at Gainesville. Overwhelmingly favorable effects by IBDU on soil inorganic N concentrations did little to improve potato plant growth in 1984 at Gainesville. The only plant

PAGE 245

222 parameter, the means of which were higher with IBDU than with inhibitors, was leaf N concentration at tuber initi ation. The reasons for this discrepancy in 1984 at Gaines ville, were not apparent. In 1983 at Hastings, the IBDU v inhibitors contrast was contradictory. Soil N0 3 --N concentrations were higher with IBDU on one date while the percent of total yield that was marketable at the high N rate and leaf N concentration at flowering were higher with inhibitors. In 1984 at Hastings, in the first 18 days of the growing season, soil NH/-N, N0 3 --N, and SIN concentrations were generally higher with inhibitors. By day 32 or 46, the trend was reversed with IBDU resulting in higher soil inor ganic N values. This pattern was most likely due to the slow release character of IBDU, which was added as one-third of total applied N. In several cases, the advantage with IBDU increased with increasing N rate. Potato plant param eters showed mixed IBDU v inhibitors contrasts and inter actions with N rate effects as a result of these soil inor ganic N differences. Leaf Nat flowering was higher with IBDU and tuber yields with 67 kg ha1 N were higher with IBDU because soil inorganic N values were higher with IBDU after tuber initiation. In 1985 at Hastings, leaf Nat flowering was higher with inhibitors but the percent of total yield that was marketable was higher with IBDU.

PAGE 246

223 In 1983 and 1984 at both locations, IBDU was more effective than the nitrification inhibitors, for maintaining plant available Nin the rooting zone during the middle and latter portions of the growing season. This difference was reflected in only a few cases, however, by greater tuber yield, plant N concentration and N uptake with IBDU. Irrigation and Rainfall Effects Most of the NH/-N and NO 3 --N leached out or was other wise lost from the soil in 1983 at Hastings, less than five days after fertilizer application. The SIN concentration was less than 10 mg kg1 on the fifth day after fertilizer application. The rainfall data does not indicate that rainfall caused this N loss. Figure 5-3 does not show any substantial amount of rain falling during this time period. The total recorded rainfall during the growing season was 329 mm, not an excessive amount. The possibility of intense leaching rainfall cannot be entirely ruled out in this case, however. Immediately after planting and fertilizer appli cation in 1983 at Hastings, an intense rain occurred at the field site which was not recorded by the rain gauge posi tioned a few hundred meters away and thus, was not reflected in the rainfall data. Thus, it is possible that much of the N fertilizer was very rapidly leached below the rooting zone, with little remaining for subsequent upward movement. It is possible that an excess of water from the sub irrigation system rose up into the fertilizer band,

PAGE 247

224 dissolving the fertilizer N. Then the water level dropped, leaching the N downward, and draining it away. This hypoth esis was supported by the fact that the low concentrations of soil NH/-N and N0 3 --N increased from the second to the third sampling dates, indicating a capillary rise of N dis solved in the sub-irrigation water. The DCD appeared to have largely been leached out as well. As with the soil N, soil DCD concentrations increased with time with the higher of the two DCD rates, lending further credence to the hypothesis just mentioned. Graetz et al. (1981), however, observed similar increases in soil DCD concentrations in a well drained soil with overhead irrigation. With overhead irrigation, soil N0 3 and other soluble salts move downward and decrease in concentration as the crop growing season progresses. Elkashif et al. (1983) observed this to be the case at the University of Florida Horticulture Unit near Gainesville. At the Hastings AREC, however, where potato was grown with subsurface irrigation, they observed that in the rooting zone (upper 30 cm) soil soluble salts increased as the season progressed, due to low rainfall and upward movement of soluble salts as water evap orated during dry periods. These explanations are not sufficient to explain the suddenness and magnitude of the soil inorganic N loss in 1983 at Hastings. Recent unpublished studies of fertilizer N movement in nonrnulched, bedded soil with banded fertilizer

PAGE 248

225 over very shallow water tables in South Florida, indicate that a previously undescribed mechanism of fertilizer N loss may be operative in soils planted to potato and other vege tables under these conditions (B. L. McNeal, personal com munication). These conditions include fertilizer bands that are approximately 10 cm below the top of the soil bed, and drainage and/or subsurface irrigation systems that are designed to maintain the water table level at about 30 to 40 cm below the top of the soil bed, and just below the soil surface in the furrows between the soil beds. When the water table rose up into the lower portion of the soil beds, capillary movement of water even in these very sandy soils, was sufficient to lead to water saturated conditions in the soil just below the fertilizer band. The presence of the band of fertilizer salts just above the saturated zone, led to a wick effect, with the salinity gradient pulling water up into the fertilizer band. When this situation was concurrent with heavy rainfall occurring within a day or two of planting and fertilizer application, the fertilizer band became saturated with water. The fertilizer in the fertilizer band had not had sufficient time to become encrusted and the fertilizer salts had not had sufficient time to diffuse out from the band. An unexpected phenomenon was then observed. A dense layer of highly saline water formed in and around the fertilizer band. The difference in density between this

PAGE 249

226 saline water and the fresh water below it, caused the saline water to flow rapidly (within a few hours) downward below the soil bed and rooting zone. Solute movements that were expected, such as gradual downward diffusion of fertilizer salts, or a slow downward mass flow of dissolved fertilizer salts as water table levels receded downward, were not observed. It was likely therefore that fertilizer N, and possibly fertilizer Kand other plant nutrient salts, were lost from the rooting zone in this manner in 1983 at Hastings. Soil NH/-N and N0 3 --N concentrations in 1984 at Hastings, increased from the first to the second sampling. This increase was followed by a substantial decrease in these values beginning approximately 18 days after fertil izer application, concurrent with 83 mm of rainfall within three days and 32 mm of rainfall a few days later. Soil N0 3 --N concentration increased from the third to the fourth sampling. As in 1983, this field had a sub-irrigation system, but heavy rainfall did not occur until 19 days after fertilizer application. Thus relatively large(> 30 mg kg 1 ) amounts of soil NH/-N and N0 3 -N remained for at least 18 days after fertilizer application and "inversion" of dis solved fertilizer salts was delayed and was not as complete as it had been the previous year. This does not adequately explain the very low tuber yields observed in 1984 at Has tings. Possibly the delay i n fertilizer salt loss was o f

PAGE 250

227 sufficient duration to allow some retention of fertilizer derived soil inorganic N by means of biological immobil ization, but not of sufficient duration to allow retention of other essential plant nutrient salts such as K, thus the low yields. No measurements of extractable soil K were con ducted, thus it was not possible to test this hypothesis in 1984 at Hastings. In 1985 at Hastings, soil inorganic N data were not collected. Yields were quite high, probably because intense rainfall (47 mm) did not occur until 26 days after fertil izer application, and because a split application of K fertilizer was made, as recommended (G. Kidder, personal communication). It may also be likely that because only 175 mm of rainfall occurred during the growing season, the water table levels were subject to more control during that year. Sampling for Soil N When Fertilizer is Banded In quite a few cases, relatively large absolute dif ferences in soil inorganic N concentrations between treat ments were not statistically significant. This was especi ally true early in the season, particularly with soil NH/-N concentrations. This phenomenon was observed in the studies with potato as well as in the upper 30 cm in the fallow Quartzipsamment. These observations may have been due to nonlinear inhibitor rate effects on soil N immobilization and mineralization.

PAGE 251

228 A more likely reason for this, however, was the high degree of variability commonly encountered with soil inor ganic N data. A likely reason for such variability being more extreme early in the season, was the fact that potatoes were grown in bedded soil with all the fertilizer being banded. Soon after planting and fertilizer application (which were simultaneous in all cases), the fertilizer N had not fully diffused from the fertilizer band, causing dis tribution of inorganic Nin the soil bed to be very heter ogeneous. When fertilizer is applied in a band in raised beds or mounds of soil, rather than broadcast on flat ground, col lecting a representative sample of soil inorganic N0 3 --N and NH/-N is difficult. Even with the best conventional equipment and tractor operator, normal flexibility of the hitch between the tractor and the planter allows several centimeters of movement, which results in inexact row placement (Sanchez et al., 1987). As a result of this and other factors, fertilizer bands are not always straight horizontally or vertically in relation to the seed pieces, nor are they uniform in thickness of deposition. In addi tion to the heterogeneity of initial fertilizer concentra tions in the soil, downward movement of water and fertilizer salts in potato soil beds is quite irregular (Lesczynski and Tanner, 1976; Saffinga e t al., 1976, 1977; Tanner et al., 1982; Simpson and Cunningham, 1982; Rourke, 1985).

PAGE 252

229 The accuracy of soil sampling is also affected by sample volume, with the variance of the observations usually decreasing as the sample size increases (Peck, 1983). Has san et al. (1983) found that the coefficient of variation for an extracted element that had been uniformly applied to the soil, was greatly reduced by using a wider diameter soil sampling tube, although the mean was the same. Attempts at using a standard 2.2 cm diameter sampling tube for sampling soil into which fertilizer has been banded have resulted in difficulties in obtaining a representative sample, resulting sometimes in suspiciously low measured soil NH/-N and N0 3 concentrations (Fiskell and Robertson, 1957; Graetz et al., 1981). This was why a large diameter sampling tube was used in this study. When sampling bedded soil planted to potato, the sam pling depth should include the entire rooting zone of the plants (Linford and McDole, 1977). This was why soil in these potato field experiments was sampled down to the hardpan, which consistently occurred at about 30 to 33 cm. Considering these obstacles, we were fortunate to observe as many significant treatment effects on soil inorganic N as we did. Other Observations While DCD and nitrapyrin sometimes reduced soil N0 3 --N concentrations, increases in soil NH/-N concentrations occurred less frequently. Therefore, the inhibitors

PAGE 253

230 generally did not increase the total inorganic N extracted from the soils except in 1983 at Hastings, in which case salt inversion, leaching and/or denitrification were severe. Chancy and Kamprath (1982) obtained similar results with nitrapyrin on corn. They observed that nitrapyrin resulted in more of the total inorganic N being in the NH/ form, but this did not significantly increase the total inorganic N concentration. In contrast, Graetz et al. (1981) observed at the Horticulture Unit near Gainesville, that 45 and 61 days after application of urea to soil under mulched tomato, DCD and nitrapyrin treatments resulted in substantial increases in SIN concentrations. In that same experiment, however, SIN concentrations were decreased by inhibitors on some sampling dates. The unusual results obtained by Graetz et al. (1981) may have been due to the effects of plastic mulch on NH 3 volatilization, N leaching and/or N immobilization. Recentwork with 15 N labeled fertilizer and DCD applied to paddy rice (Norman et al., 1989) and nitrapyrin applied to corn on field lysimeters (Walters and Malzer, 1990a, 1990b) sheds light on what is now an old enigma. Their work indicates that the reason why nitrification inhibitors often do not increase SIN concentrations is the confounding effects of inhibitors on N immobilization and mineralization. Thus, these effects, not the lack of

PAGE 254

231 leaching rainfall, are the primary reason why nitrification inhibitors usually do not increase crop yields. With NH 4 N0 3 as the fertilizer N source in 1983 and 1984, soils began the season with an equal amount of fertil izer derived NH / -N and N0 3 --N. The data described in these studies show that even in these very sandy soils of low clay and organic carbon content, N0 3 --N was much more rapidly leached or otherwise removed from the soil, than was NH / -N. The only year-location combination where substantial amounts of N0 3 --N persisted in the soil for even 18 days after fer tilizer application, was in 1984 at Hastings. This was likely due to low rainfall during the season (294 mm) and use of sub-irrigation. The inhibitors usually had little or no inhibiting effect on nitrification, or favorable effects on soil NH/-N concentrations with the earliest sampling dates. This may have been due in part to the fact that the fertilizer N was applied as NH 4 N0 3 Ammonium nitrate is generally not the best N source to apply when studying the effects of nitrifi cation inhibitors. However, potatoes require a mixed N source for optimum growth (Chen and Li, 1978; Davis, 1983; Davis et al., 1986b; Hendrickson et al., 1978; Loescher, 1981; Meisinger et al., 1978; Middleton et al., 1975; Pa i nter and Augustin, 1976; Pollizotto et al., 1975; Terman et al., 1951; Volk and Gammon, 1954).

PAGE 255

232 Other workers, however, have observed similar results with NH 4 -N and urea. Touchton (1981a) added 60 mg kg 1 NH/-N to an Alabama soil with nitrapyrin and DCD. Nitrapyrin and one of two DCD rates appeared to have decreased SIN concen tration 28 days after application. Ten days after applica tion of urea to a mulched soil at Gainesville, Graetz et al. (1981) found that DCD and nitrapyrin resulted in decreased soil NH 4 -N, NO 3 --N, and SIN concentrations. Twenty-eight days after application of urea to an unmulched soil at Gainesville, Graetz et al. (1981) found that 10% N as DCD-N decreased soil NH/-N and SIN concentrations substantially. This was attributed to inhibition of urea hydrolysis by DCD. Though Sommer and Rossig (1978) attributed urease inhibiting activity to DCD, they showed no evidence for this. Amberger and Vilsmeier (1979c) demonstrated that DCD does not inhibit urease. Nitrapyrin has also been shown to have no effect on urease activity (Goring, 1962a; Bundy and Bremner, 1974; Westerman et al., 1981). Initial nitrifi cation inhibitor inactivity and initial reductions in soil inorganic N concentrations due to DCD and n i trapyrin, are more likely caused by a combination of several other fac tors. These include inhibitor effects on fertilizer N immobilization (Smirnov et al., 1968; 1972a; 1972b; 1973; 1976a; 1976b; 1977; Ashworth, 1986; Norman et al., 1989; Walters and Malzer, 1990b) and NH 3 volatilization (Rodgers 1983). In addition, such inhibitor e ffects may b e

PAGE 256

233 confounded by the initial priming effect of fertilizer Non organic N mineralization (Walters and Malzer, 1990b). Soil DCD. It was approximated that the ti.me required for half of the DCD applied to disappear from the potato rooting zone ranged from 30 to 70 days. Residual DCD concentrations on the last sampling dates 98 to 108 days after fertilizer application ranged from 0. 1 to 0. 6 mg kg1 for the three location year-combinations where late samples were taken. The higher residual values occurred at Hastings, where rainfall amounts were low and subsurface irrigation was used, resulting in incomplete leaching and upward as well as downward movement of DCD and other solutes in the soil beds. Comparison of these data with those of Mohamad (1985) indi cate that at Gainesville with 202 kg ha1 N, 11. 2 kg ha1 DCD is sometimes not sufficient for effective inhibition of nitrification. No conclusion can be drawn, however, regard ing the mini.mum concentrations of soil DCD necessary for inhibition at Hastings, or at either location when 67 or 134 kg ha 1 N are applied. Urea and DCD Applied to a Fallow Quartzipsamment So i l Inorganic N Though DCD would be expected to increase soil NH/-N concentrations (Goring, 1962b; Hauck, 1980), only three out

PAGE 257

234 of thirty time-depth combinations showed increases and two of these occurred below 60 cm in depth (Table 6-1). In one case soil NH/-N concentrations were reduced by DCD appli cation. Most nitrification inhibition activity by DCD would be expected in the upper 30 cm of the soil. The reasons for this activity not being observed in the surface soil may have included confounding effects of DCD on immobilization and mineralization (Smirnov et al. 1972b), DCD induced increases in NH 3 volatilization (Rodgers, 1 983), the priming effect of fertilizer Non soil organic N mineralization (Walters and Malzer, 1990b), and extreme variability in NH/-N concentrations. Inhibiting activity may have been greater below 60 cm of depth because the DCD appeared to move downward with NH/ in the soil and because the low organic carbon concentration in the subsoil likely minimized immobilization and mineralization effects. Application of DCD decreased soil N0 3 --N concentra tions in fifteen out of twenty time-depth combinations during the first four samplings (Figures 6-8 to 6-11 and Table 6-2). Several of these decreases were of large magnitude. No increases in soil NO 3 --N concentration were observed on any of these dates. With the last two samplings (Figures 6-12 and 6-13), however, DCD increased soil NO 3 --N concentrations in one out of ten time-depth combinations. When all of the soil NO 3 -N in the measured profile was considered together (Figure 6-14), DCD decreased NO 3 -N

PAGE 258

235 concentrations on four out of six sampling dates (Table 62). Three of these decreases were of large magnitude, and all occurred during the first 60 days. The SIN concentrations were increased by DCD appli cation in only one case, and that increase was small (day 81, Table 6-3). In contrast, with eight out of thirty time depth combinations, DCD application resulted in decreases in soil inorganic N concentration. Five of these eight were of large magnitude and all of the eight occurred during the first 60 days after fertilizer application. Decreases in SIN concentrations with increases in DCD rate occurred because substantial reductions in NO 3 --N concentrations were not balanced by increases in NH/-N concentrations. Such negative effects on soil inorganic N are certainly not likely to be favorable for crop plant growth. The SIN concentrations for the whole profile were very high, considering that 200 kg ha1 of ureaand DCD-N was applied. Calculated total NH/-N ha1 values were as high as 400 kg ha1 on day 14 while calculated NO 3 --N values were as high as 300 kg ha1 on day 60. The same formula was used to calculate kg soil DCD ha1 in the 1.22 m profile as was used for soil inorganic N, and the resulting DCD values were less than the amounts applied. When the soil inorganic N values for the unfertilized control were subtracted from those for the fertilized treatments (data not shown), the magnitudes were still very high. A likely explanation for this was a

PAGE 259

priming effect on mineralization of organic soil N stimu lated by application of the urea-N. 236 Such an effect has been proposed by Alexander (1977), Broadbent and Nakashima (1971), Kissel et al. (1977), Legg et al. (1971), and Westerman and Kurtz (1973). Walters and Malzer (1990b) observed a priming effect that was of greater magnitude than previously observed by other workers. They also observed that this effect can cause discrepancies between the 15 N and difference methods for quantifying leaching and plant uptake of fertilizer N. They concluded that this was because of the confounding effects of N immobilization and mineralization. Smith et al. (1989) observed that soil metabolism of organic N (immobilization and mineralization) is regulated by the concentration of soil inorganic N. They found that this effect was trans itory, however, and had little long-term effect on mineral ization or assimilation of the C contained in organic N. Figure 6-21 shows some rather peculiar patterns for SIN concentration. Soil inorganic N concentration decreased from day 14 to day 31, increased until day 60, then declined rapidly. The shape of these curves was a result of two processes. Soil NH/-N concentrations decreased steadily as NH/-N was leached, immobilized, nitrified, and possibly volatilized to NH 3 Soil NO 3 -N concentrations increased to a maximum on day 60 due to nitrification of fertilizer N possibly combined with nitrification of mineralized organic

PAGE 260

237 N. This NO 3 --N maximum was followed by a rapid decrease in the second half of the season due to leaching. In the first two samplings, a logical pattern of DCD effect was not present due to variability in the NH/-N data and possible nonlinear DCD rate effects on immobilization and mineraliza tion. The decrease from the first to the second sampling date, and subsequent increase with the next two sampling dates, could not have been due to breakdown of DCD and release of DCD-N (DCD contains 66% N). This is because the same pattern occurred with the zero DCD treatment and the unfertilized control. This increase in SIN concentration may have been indirectly due to rather low rainfall amounts from 20 to 75 days after fertilizer application. During this ti.me only 43 cm of rainfall occurred and most of this fell on day 53. An additional contributing factor may have been the disking of the soil for weed control. Soil cultivation normally results in a temporary increase in mineralization of soil organic N (Alexander, 1977). Even under environmentally controlled and undisturbed conditions, however, Mohamad (1985) observed substantial fluctuations in inorganic N concentrations when NH/-N and DCD were applied to soil. Reddy (1964a), in incubation studies with DCD and (NH 4 ) 2 SO 4 in a Lakeland sand (Quartzipsamment) from Georgia, found that 25 mg kg 1 DCD inhibited nitrification for up to 90 days, with some inhibition still occurring after 150

PAGE 261

238 days. Ten mg kg-1 DCD also had some inhibiting effect (Reddy, 1964a). In our study, the soil NO 3 --N (Table 6-2) and NO 3 --N/NH/-N ratio data (Table 6-4) indicate that high rates of DCD (20-60 kg ha1 ) inhibited nitrification in a Lakeland fine sand for at least 81 days but less than 116 days. In this Lakeland fine sand, even though DCD was effective in inhibiting nitrification, it did not increase the total soil inorganic Nin the profile relative to the control. This means that even in a deep sandy soil receiv ing average rainfall and overhead irrigation, nitrification inhibition did not improve the efficiency of surface incor porated urea as a source of N. Though no data was collected to show this, it is quite possible that these observations were due to inhibitor-induced increases in biological immo bilization of fertilizer NH/ as noted by Smirnov (1968), Smirnov et al. (1968; 1972a, 1972b; 1973), Juma and Paul (1983), Ashworth et al. (1984), Norman et al. (1989), and Walters and Malzer (1990a, 1990b). Contributing factors may also have included the high N rate used, the priming effect of fertilizer Non N mineralization (Walters and Malzer, 1990b), and volatilization of NH 3 (Rodgers, 1983). Soil DCD The DCD concentration at the Oto 15 and 15 to 30 cm soil depths remained fairly stable for at least the first 46 days after surface application, though a gradual reduction

PAGE 262

239 occurred with the 60 kg ha1 DCD treatment. Initially the DCD concentration at the 15 to 30 cm depth was about the same as that at the Oto 15 cm depth. This can be attrib uted largely to mixing of these two soil depths by disking. Early in the study, small amounts of DCD leached below the 15 to 30 cm depth. Leaching down to the 30 to 61 cm depth became more substantial by day 46. Substantial amounts of DCD had reached the 30 to 61 cm depth by day 60 with lesser amounts reaching the 61 to 91 cm depth. Mean while, concentrations in the top soil were lower by this time. After 60 days, soil concentrations of DCD dropped rapidly. Considering the N0 3 --N concentrations observed in the subsoil, this was most probably due more to decom position than leaching. By the 81 st day DCD concentrations at all depths were fairly low and spread more or less evenly throughout the profile. By day 116 the DCD concentrations were generally a half an order of magnitude less than they were at day 81. Most of this remaining DCD was in the lower depths since it had decomposed in and/or leached out of the topsoil. These data confirm the conclusion of Graetz et al. (1981), that DCD was quite stable in deep sandy soils of North Florida under field conditions. The increase in total soil DCD with the 46 and 61 day samplings with the 40 and 60 kg ha 1 DCD rates, was peculiar and coincided with an increase in total inorganic Nat those

PAGE 263

240 dates. This pattern may have been due to upward movement of DCD from below the measured portion of the profile during a period of low rainfall. Graetz et al. (1981) observed a similar increase in soil DCD concentration. Bock et al. (1981) observed separation between DCD and NH/ as they were leached down a soil column in the laboratory. They did not observe this in the case of urea, however, since DCD and urea moved with the soil solution at about the same rate. In our study urea movement was not measured since under field conditions, it was likely to have hydrolyzed within a few days of application. If one examines the movement (change in concentration with depth over time) of NH/-N in Figures 6-1 to 6-6 and the movement of DCD in Figures 6-23 to 6-28, it can be concluded that in this study the bulk of the DCD did not separate from the bulk of the NH/ in the soil.

PAGE 264

CHAPTER 8 CONCLUSIONS Plant Yield/N Content and Soil N and DCD The nitrification inhibitors did not increase potato yields except with the 134 kg ha1 N rate in the one year location combination where they increased inorganic N levels in the soil. In that year-location combination, severe N leaching and low yields for all treatments were observed. The inhibitors did, however, increase leaf N concentration at flowering in three out of four year-location combin ations. Increases in DCD rate resulted in increases in several plant parameters, though in some cases only at certain N rates. These parameters included the proportion of marketable yield that was grade A, tuber N concentration, total biomass, and total N uptake. Application of DCD led to decreases in specific gravity and plant shoot N concen tration in one year-location combination each. An increase in nitrapyrin rate from 0.56 to 1.12 kg ha1 resulted in increases in tuber yield and several other plant parameters with the 134 kg ha1 N rate in the one test where severe leaching was observed. When DCD and nitrapyrin inhibited nitrification, they generally did not increase inorganic N levels in the potato 241

PAGE 265

242 rooting zone, but simply changed the ratio between N0 3 and NH/ N forms. This was the primary reason why the nitrifi cation inhibitors usually did not increase potato crop yields. In the one test where inhibitors did increase soil inorganic N concentrations, these concentrations were ex tremely low due to a previously un-described mechanism of fertilizer salt loss. This mechanism involves a very rapid downward movement of nearly all fertilizer salts due to a difference in water density. Potato yields with the DCD treatments were higher than those with nitrapyrin treatments in three of five year location combinations. These differences were usually attributable to differences in soil N0 3 --N or total soil inorganic N concentrations. Tuber specific gravity values, however, were higher with nitrapyrin than with DCD in three of five tests. No explanation can be offered as to why tuber specific gravity values were higher with nitrapyrin than with DCD. At the rates applied in this study, DCD and nitrapyrin were about equally effective as inhibitors of nitrification. Soil inorganic N concentrations were higher with the treatment where one-third of applied N was IBDU-N, than with the inhibitor treatments in the middle and late parts of the growing season. In some cases favorable effects of IBDU on soil inorganic N concentrations resulted in increases in tuber yield and other plant parameters.

PAGE 266

243 Nitrogen and inhibitor rate and IBDU effects on plant response parameters could in most cases be attributed to the effects of these treatments on soil inorganic N concentra tions. This was particularly true with the sum of NH/-N and N0 3 --N concentrations. Most exceptions to this direct relationship occurred in 1984 at Hastings where yields were low for reasons other than soil inorganic N concentrations. Urea and DCD Applied to a Fallow Quartzipsamment In the fallow Quartzipsamment study DCD had an inhibiting effect on nitrification in all or part of the 1.22 m profile on all but the last sampling date (day 116). All DCD rates inhibited nitrification for at least 60 days. Nitrification was inhibited for up to 81 days with the 40 and 60 kg ha1 DCD rates. In general, DCD application lowered soil N0 3 --N levels to a greater extent than it raised NH/-N levels. Thus, DCD generally decreased the total amount of inorganic Nin the soil rather than increased it. With urea as the N source, NH/ and DCD moved downward in the soil profile at about the same rate. Nitrate leaching was reduced by DCD application for approximately 60 days. Concentrations of DCD incorporated with urea into the surface 15 cm of the soil, remained relatively stable for 46 days after application. A substantial portion of the DCD remaining at 60 days had leached to 45 cm. Most of this DCD

PAGE 267

244 apparently decomposed in the upper 60 cm of soil after about 60 days, with the remainder leaching deep into the profile. After 6 O days only 1 mg DCD kg1 remained in the surface soil with the lowest DCD application rate while 4 mg kg1 soil persisted with the two higher application rates. Only a very small amount(< 0.25 mg DCD kg1 soil) persisted in the soil after 116 days, with this having leached to a depth of 1.2 m. The residence half times of DCD in the 1.2 m profile were 61 (r 2 = -0.9697), 66 (r 2 = -0.7487), and 63 (r 2 = -0.9524) days for the 20, 40, and 60 kg ha1 DCD rates, respectively. General Conclusions When nitrification inhibitors increase crop yields, this can be attributed to their favorable effects on total soil inorganic N concentrations rather than the lack of leaching rainfall. Because of inhibitor effects on N immobilization and mineralization in soil, inhibitors usually do not increase soil inorganic N concentrations unless N is applied below recommended rates and leaching of fertilizer N is severe. Nitrification inhibitors can be recommended for potato production in Northeast Florida if N is applied at less than recommended rates and if sub-surface irrigation systems are unreliable in their control of water table levels. If N fertilizer r 3tes are equal to or greater than those recom mended or if irrigation and drainage systems provide

PAGE 268

245 reliable control of water table levels, then nitrification inhibitors can not be recommended for potato production in Northeast Florida. Recommendations For Future Research Ashworth (1986) recommended that long term studies with nitrification inhibitors and 15 N labeled fertilizer should be conducted in the field to assess the effect of inhibitors on N immobilization and other components of the N cycle. This year, Walters and Malzer (1990a, 1990b) pub lished such a study. If this type of study is repeated, several rates of nitrification inhibitor should be included rather than split N applications. Such studies should also monitor the effects of inhibitor rates on NH 3 volatilization and total soil inorganic N concentrations. If possible, several soils should be used in such studies. Soils should vary in pH, texture, and organic C and N content and represent several soil taxonomic orders. It should not be necessary to conduct a great deal of research comparing several types of nitrification inhibitor. This is because at comparable effective concentrations, most nitrification inhibitor compounds appear to have similar effects on soil N transformations. McCormick et al. (1984) and several European workers have observed much larger crop yield increases due to nitrification inhibitors with manure than with synthetic N fertilizers. Thus, studies should be conducted on the

PAGE 269

interaction between organic amendment rates and nitrifi cation inhibitor rates. 246 Separate studies should be conducted on effects of inhibitors on NH 3 vola~ilization from NH 4 N0 3 and urea applied to sandy and fine textured, and acid and calcareous soils. An 15 N labeled DCD should be produced with the 15 N occurring on different specific positions in the DCD structure. Bio chemical studies could then be conducted on the mechanism of nitrification inhibition by DCD and the breakdown and fate of DCD in soil. It would be worthwhile to assess the abil ity of a variety of native and cultured nitrifying organisms to acquire a tolerance for various nitrification inhibitors. Research should be carried out for the purpose of improving the analytical method for DCD in soil extracts. Such a study should determine the effects of (1) time of equilibration of naphthol reagent with DCD solutions of known concentrations; (2) degree of mixing of naphthol reagent and DCD standard solutions; (3) filtration v centrifugation of naphthol reagent; (4) ca 2 , K, and N0 3 concentrations of soil extracts on accuracy of the method; (5) 0 2 concentration of naphthol reagent on accuracy of the method; (6) alternative complexing reagents; (7) alternative soil extractants; (8) varying pH of soil extractants; and (9) addition of reducing agents to naphthol reagent. Other methods for analysis of DCD in soil extracts should be pursued, including high pressure liquid

PAGE 270

247 chromatography (HPLC) of volatile DCD derivatives, gas chromatography, UV spectrophotometry, and thin layer chromatography. Subsequent to these studies, adsorption isotherms and degradation kinetics for DCD should be determined for a variety of soils. Soil retention characteristics of DCD could be determined by a continuous flow technique as proposed by the late J.G. Fiskell. There are in the literature many studies of inhibitor effects on yield of crops in the field. There is, however, insufficient reported research in the literature on the effects of nitrification inhibitors on environmental quality parameters such as long term total N leaching into surface and subsurface drainage systems. Such studies should be conducted with 1 5 N on the same soils for at least four years. Studies should be conducted on the effects of inhib itor, N, and organic Crates and environmental conditions on soil and fertilizer N immobilization, mineralization, leach ing, ''aerobic" denitrification, and gaseous N losses. Nitrification inhibitors can be used as tools in various types of soil N cycle studies in the field, green house, or laboratory. Dicyandiamide, because of its phys ical and chemical properties, is a useful nitrification inhibitor for these types of studies.

PAGE 271

APPENDICES

PAGE 272

APPENDIX A SOIL CHARACTERIZATION Potato soils. The results of the soil character ization analyses shown in Table 3-2, indicate that all of these soils are quite sandy as is characteristic of most Florida soils, with sand contents exceeding 90% in all but the Millhopper sand which has approximately 84% sand. All have silt contents of 6% or less except the Millhopper sand with approximately 11%. Clay contents are in all cases less than 5%. Organic carbon contents in the top soils are all fairly low with the Plummer fine sand having the least and the Millhopper sand the most. Organic N contents in the top soils are less than 0.07% except in the case of the Millhopper sand with almost 0.13% organic N. Cation exchange capacities are all 4 cmol kg1 or less except in the Millhopper sand with approximately 8 cmol kg 1 These low CEC values are to be expected s i nce the sand contents are so high. The pH values are all below 5.5 which is favorable for potato production. Lime is used sparingly for potato production in Florida, thus the pH values reported here are probably not much higher than the native pH values for these soils. 249

PAGE 273

250 The Millhopper sand used in 1983 at Gainesville stands out as being a more fertile soil than the others. This is likely because of its greater silt content and the fact that it had been cleared from forest for only a few years. As a result of these factors, this soil was much higher in organic carbon, total N, and CEC than the other soils. Fallow soil. The properties of the Lakeland fine sand shown in Table 3-2 indicate that the sand content is fairly consistent with depth while the clay content tends to increase slightly with depth. Silt, organic C and organic N contents as well as CEC and pH decline steadily with depth. These data are normal for Typic Quartzipsarnrnents in Florida.

PAGE 274

APPENDIX B SAMPLE ANALYSIS OF VARIANCE TABLE Table B-1. Analysis of variance table for plant response parameters in the studies with potato. Source Model Error Corrected Total Block DCD Linear (DCD L) DCD Quadratic (DCD Q) Nitrapyrin Rate (Nty R) DCD v Nty IBDU V DCD and Nty ( IBDU v Ih) N Rate Linear (NR L) N Rate Quadratic (NR Q) DCD L X NR L DCD L X NR Q DCD Q X NR L DCD Q X NR Q Nty RX NR L Nty RX NR Q DCD v Nty X NR L DCD v Nty X NR Q IBDU v Ih X NR L IBDU v Ih X NR Q OF 20 51 71 3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Sum of Squares 2428.7 1031.6 3460 3 1804.0 3.6 12.3 0.4 80.2 0.3 212.9 74.1 0.3 28.8 11.1 13.2 73.1 19.1 30.8 6.7 0 5 10.0 Mean Square 121.4 20.2 F Value 6.00 29.73 0.18 0.61 0.02 3.96 0.02 10.53 3.66 0.01 1.43 0.55 0.65 3.61 0.94 1.52 0.33 0.03 0.49 Dependent Variable--Marketable Potato Yield at Gainesville in 1984. 251 Pr> F 0.0001 0.0001 0.6741 0.4392 0.8904 0.0519 0.9010 0.0021 0.0612 0.9032 0.2381 0.4615 0.4226 0.0630 0.3357 0.2231 0.5688 0.8705 0.4860

PAGE 275

APPENDIX C INORGANIC N CONCENTRATIONS IN SOILS PLANTED TO POTATO AS AFFECTED BY SELECTED TREATMENTS

PAGE 276

100 80 Cl .!Iii 60 Ol a 0 40 M rl z Gainesville 1983 .. \ C\_ r Rainfall ,. ,. ,. , .. .. .. "" 1 t~ '\ .! ><<., ! /. ,. 134 kg/ha N 202 kg/ha N 20 i / / / 0 0 Figure C-1. 20 Days 40 After 60 Fertil.izer 80 Ar;>pl.ication 100 Effects of N rate on soil inorganic N concentration (Gaines ville, 1983). 600 500 i -400 ..... ,-i Id 1H J::l rl 300 Id rl 200 ..... 100 0 "-> U'1 w

PAGE 277

80 60 -C'I ....... C'I l:l ._, 40 A (I) t,i 0 1-l ..-l z 20 : ;:fl; : . .. Gainesville 1983 . NH+ 8 4 , . .... .. .. ....... .. ... .. .... ', ,.. / Rainfall : ~ : :-~ \ ' : '\. . . / ... .... . . 1..'Y\ ' \ i .._ ' ,, ,, .. ,, ... . ., \ \ . .J ', \., \ No .. .f \ 3 "~ f 17' ~~ ~ . Anmonium at 134 kg/ha N ---c,-AJrmoni um at 202 kg/ha N ---*~ -Nit:ca.t a.t 134 kg/ha N ..... --,,, Nit:cat at 202 kg/ha N ..... ~-'?II: r.___ .. i / / ', ,., ., ,c. -G ~:: =~~~~:::::: "" "' 0 .. 0 Figure C-2. 20 Da.ys 40 After 60 Fertilizer 80 Application 100 Effects of N rate on soil NH 4 + and N0 3 concentrations (Gainesville, 1983). 600 500 400 300 I l 200 100 0 ...... I ..... ,.... r-1 elf t! rl G) > rl .jJ Ill ,.... j N u,

PAGE 278

80 60 ...... Ol Ol f:l ......
PAGE 279

120 100 ...... 80 ........ Cl ....,. i: 60 Q) g, ,IJ ri z 40 20 0 0 <> ., ,,. \ _,. \ ;,' .. \ ,-" \ ,:); NH4 \ ., \ / o, / / / \ \ \ \ \ ,\ \ .\ \ \ \ \ \ \ \ \ \ \ \ .. \ \ ,.: .. ~ ;) \ .. . \ \ \ -~ \ \ \ : .. : : ;;; ; \ \ \ .... ::,,"\ \ \ \ '_ ... \ \ \\ ;I!'\ \ \ \ Hastings \ '. \ \ \ ; \ ~\. \ ....... ...... . ...... ........ ... .. N03~~-----,~, \ .. . . .,.< .., :: : .. , --.. >:-., .. Anmonium at 67 ]qJ/ba. N 1984 ---w--Annlonium at 134 kg/ha N __ .../::; __ '.J Anmonium at 202 kg-/b& N -: :. Rainfall Nitrate at 67 kg/ha N c ~ -N.i.trate at 134 leg/ha N ,-. .. .. .... ., ... .. N1trate at 202 kg/ha N > .. >.J '\ ........... ,,, .. ... .. / ',., \ ~.~: :~~;~~==~~~?~?~ ~~E~!~~ : ~~~::::::~oc::=-".,=i 20 Days 40 A:!ter 60 P'exti1izer 80 App1ice.tion 100 Figure C-4. Effects of N rate on soil NH/ and No 3 concentrations (Hastings, 1984). 600 500 ,.. I ...... 400 r-1 r-i l\j 1M ri 300 nf ri ,IJ 200 l\j r-i 100 0 I\.) u,

PAGE 280

100 80 tii .!Ill 60 t,, a 40 0 H .jJ rl z ~ : ;f\. '. \ ,:;z\\ \ Gainesville 1983 \ \. .. \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ !"' ':-. ,.. / , ' ' . / l( :: ~ , ,. ,. /_ ... :--\ ~ Rainfall 0 k9 / h.a D CD --~~--.5 6 k g / h a DCD l.1, 2 kg / ba DCD 20 \. ,, ,, .... .. ... .... .. ....... . ::,...,., ... ...... ---....... ... . ---............... ... .. ----..... . .... -/,/l 0 0 Figure C-5. 20 Days 40 After 60 FertiJ.izer 80 At>pJ.ication 100 Effects of DCD rate on soil inorganic concentration N (Gainesville, 1983). 600 500 ....... e -400 r-1 rl td 1M rl 300 QI > rl 200 r-1 a 100 0 I'.) l.11 ...J

PAGE 281

80 60 ...... DI ....... DI f:; ....., 40 gi M .jJ ri :z; 20 0 0 I "1 uu-~ .. l { Ga1.nesv1._ . . ~'\. . . .... '\. ,. '\. '\. NH/ '\. : ... ... .. Ra inf all ' ' :"~; ' V,. '\ ' ' ',. r".\ ' \ \ \ \ .. ") \ ... \ : \ \, . .. ;,< ..... \ .. ,, \ . .... ,, \ .. \ \ / \, \ / \ \ .. .. .. \ NO t. : ::.... / \. ,~ '\ 3 .; \ -lflllr ,...~~-~-u~11e 1983 .Amll\onium at 0 kg/b.a DCD -A-: .Amlllonium a.t S.6 kg/ha DCD --f7--Arnrnon1um at 1 1. 2 kg / ha DCD '/ N1t:rate at 0 kg / bn DCD Nitrate a t S. 6 kg / b.a DCD Nitra. t at ..,: .............. \ '~ '' .. -: .. ........ ......._ //i .. .. ~ :t, ~ ::~~~ -:~ :: ~~~ : ~:~=:~:;~===~==~ ~:' 11.2 k 9 / ba DCD 20 Days 40 At:ter 60 Ferti1izer 80 App1i c ation 100 Figure C-6. Effects of DCD rate on soil NH/ and N0 3 concentrations (Gainesville, 1983). 600 500 0 -400 r-i r-i Id 4+--1 ri 300 Id ri .jJ 200 Id r-1 l.00 0 I\.) u, CX)

PAGE 282

80 .. .. . . Gainesville 1984 60 ...... Cl .i.: Cl i::: ....... /' 40 gi o'!< i . , --. . ... ... ... ... .. .. .. ... ........ . Rainfall 0 k9/ha DCD ---t4---H J.J r-t z 20 / .. 0 0 Figure C-7. .. '. ..,,, .. ~" '\: f. f ., ,, 5 6 k9 / b.a DCD .f ', . . ;11,..~. ... .. ... . . ----. ::: ::, ,, .... "'-:~: ::::::::: ::::: :c~_ 11. 2 kg/b.a DCD 20 Days 40 Aj!ter 60 Fertil.izer 80 Appl.ication 100 Effects of DCD rate on soil inorganic N concentration (Gainesville, 1984). 600 500 i 400 r-l .-1 rd 11-1 J:: r-t 300 Id r-t J.J 200 rd .-1 100 0 "" V, 1.0

PAGE 283

80 60 ...... t,) ....... t,) El ...... 40 ij gi M .u .... z 20 0 0 Gainesville 1984 -.,: ..... NHt ~ >., ', ~ "'' :~: . . .-. ~'), A&rmoni um at Ni.trtlte at \;>-.. / ................... ~.. .... ................. ., .. / .... .c:-, . r, i '-, ; 'i . .. .. ', :::. :::., , ... . 0 kg / ha OCD 0 kg / ha DCD ---,;.. ----:,rr: Ammonium a. t Ni tr ate at 5.6 kg/ha DCD 5.6 kg / ha DCD ---G--........ ,.,( ~) Ammon.i um at Ni.t:rate at -~.... .... ... ..... '--. ', ,. 11.2 kg / ha DCD l.1.2 kg / ha DCI> ...... ... .. I'. / ... ....... ) N0 3 / @;.'""' .. .... -Iii> 20 Days ....... ....... ..... .. .. .. A ,...._, , V ..... , -~-"*. ----. =:::i,.f:~ 5:~ili "'",; ;:;: ;.::;,::;: ;.::E;;.;.::::1 40 After 60 Ferti1izer 80 App1ication 100 Figure C-8. Effects of DCD rate on soil NH/ and N0 3 concentrations (Gainesville, 1984). 600 500 0 400 ,-t ,-t Id 111 J:: .... 300 Id Ill > r-i .u 200 Id r-1 100 0 "-> 0

PAGE 284

15 ,.. 10 01 ....... 01 ..... G) M JJ ri z 5 0 0 Hastings 1983 ,., ~' / / / _i _; ,. / I"'\ .. "-, / / / / -=:: / / ~ .. / / / I / ,. / / .. / / '-"/ / / Rainfall , .. / ' / ... / ... , / / ', , I ,. / : ,.... ..,, ...... / / .... . : / >, )/ // r I 20 Days 40 Aftex 60 P'exti1izex 80 App1ication o kg / ha DCD , ---c::r--5. 6 kg / b.a DCD ;;~ l.1 2 kg / ha DCD 100 Figure C-9. Effects of DCD rate on soil inorganic N concentration (Hastings, 1983). 600 500 0 ...... 400 ,-I ,-t td CM ri 300 Id II:: ri JJ 200 td ,-t j 100 0 Iv I-'

PAGE 285

160 140 120 ...... 01 ........ 01100 E; ...,, i 80 ,IJ .... 60 z 40 20 0 0 / / ~) / \ / / /;( Hastings 1984 '--/ -,. ...... .... ..... .. / .. .. .... / 20 Days 40 Afte:r: -... . . .. .. . I 60 P'e:r:tilize:r: Rainfall 80 Application 0 kg / 11.A DCD ___ .L'.:L __ 5. 6 kg/ha DCD ~11. 2 kg/ha DCD .... _....~.., ...,. .... .:. 0 100 Figure C-10. Effects of DCD rate on soil inorganic N concentration (Hastings, 1984). 600 500 fi ._. 400 ,-I ,-1 .... 300 ... ,IJ 200 ,-1 100 0 "' CTI "'

PAGE 286

100 80 .... t,) 60 ....... t,) ...., i::: Q) gi 4.0 M ,I.J .... z 20 0 0 "" / I / \ I + \ N H / <. I 4 / /'n, I ,14)_ / / \\ / , \' I I ... / \\ ,, ,, / ; f' / \ \ I ), / \\ \ / \\ I / \\' ,< ~ -; \\ \ (~ t, \', I \\ I (-)' '-' i1 i1 'Hastings 1984 N03 \ \ \ \ ....... \ ,, ;, \ ........................ .. .... .. .. . t:,:.., ' Anmonium at 0 kg/ha DCD ~II; Anntonium at 5.6 kg/ha OCD ---L.~--.... ,, Ammonium at 11.2 kg / ha OCD ... .......... ... ... .. .... .. .. Rainfall : l ,\/ It.;. , ./!~ ... ;;,;~ ... ',,-;..-.: . ... ... .... ... ... >:..._ "?( ... .. .. , .. __ ... .... ....... ... < -.. .. .. ;::-.,..__ ,, ... .. -.......... -:::.-:::.---~:::.-s:: ::.:./ :. ~< ............ )i~ ..... .. .. -... ... .. .. : .~ . ... . ..... .. .. ... J .. Ni t :cate at o kg/ha DCD ;t:_,_ Nit:i:ate at 5 6 kg/ha DCD .. .. .... ..... . . Nit:i:ate at 1l..2 kg /ha DCD ,; .. : ~= I 20 Days 40 Atte:r 60 P'e:z::ti1ize:r 80 App1ication 100 Figure C-11. Effects of DCD rate on soil NH/ and N0 3 concentrations (Hastings, 1984). -l I I I 600 500 0 -400 r-1 r-f Ill 1H i::: .... 300 td 1k: .-1 ,I.J 200 Ill r-f 100 0 Iv O'I w

PAGE 287

100 ..... 'y 80 Cl 60 Ol a .__. i Cl 0 40 1-1 +I rl z 20 .. ..................... .. ... .. Gainesville 1983 ... ......... Rainfall ... . ... ~~ I \I ..... ,. ,. ,. ,. .. .. !, I' ..... .. .. ... .. ; .: <, ,., I-:} / . .. ........ ... J:BDU' .. '... J:nhihitore 600 500 i 400 ,-f rl Id '1-1 r-4 300 Id ii:: rl 200 ,-f 100 // ..... ...... .... ................ .. .... .. .. .. . .. .. .. I 0 0 Figure C-12. 20 Days 40 After 60 Fertilizer 80 At,pl.ication 100 0 Contrast of IBDU and inhibitor effects on soil inorganic N concen tration (Gainesville, 1983). I',.) O'I

PAGE 288

80 60 ...... Cl Cl e .._, -C.0 ti g, JJ rl z Gainesville 1984 ~.x. .. .............. .. Rainfall .,,, ... .. . . .. / ... . ,. ,. ,. IBD U ,...,_ -.. ~ I nhi b itor s 600 500 i .... 400 r-i r-i Ill 11-1 i:: .... 300 Id ll'.: ri JJ 200 Ill r-i 20 ~... . ~ .. .. _.,_ . .. ,. .. .. .. .. .. . .. .. .. .. _ .. ., __ , .. /, .... .. 100 0 r' 0 Figure C-13. 20 Days 40 A~ter 60 Fertil.izer 80 .A,ppl.ication 100 0 Contrast of IBDU and inhibitor effects on soil inorgan i c N concen tration (Gainesville, 1984). N C'\ u,

PAGE 289

160 140 120 ..... r ....... Cl 100 El ...... ij 80 g, r-t 60 :z; 40 20 0 0 ~ ''" \ . .:.:.~ . \ . --"' \ "'' \,... .. ,..:, \ \ \ \ \ \ \ ' J 20 Days 40 A:fter Hastings 1984 ; . ... .. : 60 P'ertil.izer Rainfall 80 Appl.ication J:BDU -{} J:nhibitor 100 600 500 6 400 r-i ri Ill 11-1 J;;: r-t 300 Gl > r-t 200 Ill .-i 100 0 Figure C-14. Contrast of IBDU and inhibitor effects on soil inorganic N concen tration (Hastings, 1984). N '

PAGE 290

APPENDIX D ANALYSIS OF VARIANCE OF INORGANIC NIN SOILS PLANTED TO POTATO

PAGE 291

Table D-1. Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty R X NR DCD V Nty X IBDU v Ih X 268 Analysis of variance of nitrogen and amendment rate effects on soil NH/-N concentration (Gainesville, 1983). 16 ** NS NS NS NS NS NS NR NS NR NS Days After Application 35 ** NS NS NS NS NS NS NS NS 59 X NS NS X NS NS NS NS NS 98 NS NS NS NS NS NS NS NS NS Mean *** Q* NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 292

269 Table D-2. Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N concentration (Gainesville, 1983). Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR Days After Application 16 ** Qx NS NS NS NS NS X NS NS 35 X NS NS NS NS NS X NS NS NS 59 *** NS NS NS NS NS NS NS ** 98 NS NS NS NS NS NS NS X X Mean *** Q* NS NS NS NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 293

270 Table D-3. Analysis of variance of nitrogen and amendment rate effects on soil N0 3 --N/ (N0 3 --N + NH/-N) ratio (Gainesville, 1983). Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR 16 NS NS NS X NS NS NS NS NS Days After Application 35 NS NS NS NS NS NS NS NS NS NS 59 NS L* NS NS NS NS NS 98 X NS NS NS NS NS NS NS NS NS Mean ** L* NS X NS NS NS NS X Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 294

Table D-4. Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR 271 Analysis of variance nitrogen and amendment rate effects on soil NH/-N concentration (Gainesville, 1984). 13 L*** Q*** NS NS *** Days After Application 31 L** Q** NS NS *** 45 L*** Qx NS NS *** NS NS Qx NS L* L** 69 L*** Q*** L* NS NS 108 L* NS *** *** NS Mean L*** Q*** NS NS *** DCD v Nty X NR IBDU v Ih X NR NS Q* NS Lx L* NS Qx Q*** Q** NS NS Lx Lx Q* NS NS L** L* NS NS LxQ** L** L*Q* Q** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 295

272 Table D-5. Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N concentration (Gainesville, Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR 19 84) DCD v Nty X NR IBDU v Ih X NR 13 L*** Q** NS NS X NS NS NS NS NS L**Qx Days After Application 31 L*** NS NS NS NS L*** Q* NS NS NS 45 L*** Q* NS NS NS NS NS NS L*Q* L* 69 L*** Q*** NS NS X NS NS NS L**Q* L***Q* 108 L*** Qx X *** NS NS NS NS NS Mean L*** Q* NS NS NS *** L** NS NS L**Q** L***Q** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 296

Table D-6. Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR 273 Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N/ (NO 3 --N + NH/-N) ratio (Gainesville, 1984). 13 L*** Q** NS NS NS NS Days After Application 31 NS Q* NS ** L** Q*** NS 45 Lx Q* Qx NS NS NS 69 L*** L* Q* NS NS NS NS NS 108 L** L* *** *** *** Mean L*** L** NS NS NS NS NS DCD v Nty X NR IBDU v Ih X NR NS L* Qx NS L* L** L**Q** L* Qx NS L** L** NS L**Q* L** NS NS L* NS NS NS L***Q* L***Q** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 297

Table D-7. Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih 274 Analysis of variance of nitrogen and amendment rate effects on soil NH/-N and N0 3 --N concentration (Hastings, 1983). Days After Application 5 31 61 Mean ------------NH/-N------------NS NS NS Qx NS NS NS NS L* NS NS NS NS L** Qx NS NS NS Interactions NS NS NS NS -----------N0 3 --N-------------N Rate NS * ** DCD Rate NS NS NS NS Nty Rate NS NS NS DCD v Nty NS NS NS IBDU v Ih NS NS Interactions NS IBDU v Ih X NR DCD Q X NR x DCD Q X NR ** Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.01 (**) probability levels, respectively.

PAGE 298

Table D-8. Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions 275 Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N/(NO 3 --N + NH/-N) ratio (Hastings, 1983). 5 NS NS NS Days After Application 31 NS NS NS NS NS NS 61 NS L*** Qx NS NS NS Nty RX NR x Mean NS L* NS NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), or 0.001 (***) probability levels, respectively.

PAGE 299

276 Table D-9. Analysis of variance of nitrogen and amendment rate effects on soil NH/-N concentration (Hastings, 1984). Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR L IBDU v Ih X NR L 6 L*** NS NS NS NS L*** NS NS NS Days After Application 18 L*** Qx L* Q* NS X *** LxQx L** L** NS L* 32 L*** Lx NS NS *** NS NS NS NS L*** 46 L*** Q** L*** * NS L** NS NS L** NS 74 L** Lx NS NS *** NS NS NS NS L*** 103 L*** L** NS NS Lx NS NS NS L** Mean L*** NS NS X NS NS L** NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 300

277 Table D-10. Analysis of variance of nitrogen and amendment rate effects on soil NO 3 --N concentration (Hastings, 1984). Independent Variable N Rate DCD Rate Nty Rate DCD v Nty IBDU v Ih Interactions DCD L X NR DCD Q X NR Nty RX NR DCD v Nty X NR IBDU v Ih X NR 6 L*** Q** NS * *** NS L* Qx NS NS Days After Application 18 L*** NS X *** Qx NS L** NS L** 32 L*** L* NS NS NS NS NS NS Q* NS 46 L*** Q*** L*** Q* NS ** *** L* L* NS Q*** NS 74 L*** Q*** NS NS NS NS NS LxQx NS NS 103 L*** L** NS NS NS L* NS NS NS NS Mean L*** Lx NS ** ** NS L* NS NS NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively.

PAGE 301

278 Table D-11. Analysis of variance of nitrogen and amendment rate effects on soil N0 3 -N/(N0 3 --N + NH / -N) ratio (Hastings, 1984). Days After AQQlication Independent Variable 6 18 32 46 74 103 Mean N Rate L*** L*** Qx L*** L*** L*** L*** Q*** Q* Q* Q*** DCD Rate NS NS L*** L*** L** L*** L*** Q* Q** Qx Nty Rate NS NS X *** NS NS DCD V Nty NS NS NS *** NS X *** IBDU v Ih *** *** *** *** NS NS Interactions DCD L X NR NS L*** NS Qx L* NS NS DCD Q X NR NS Q* Q* NS NS NS NS Nty R X NR NS NS Qx L* NS NS Lx DCD V Nty X NR NS NS NS Q*** NS LxQx Q** IBDU v Ih X NR L NS Qx NS Q** NS L*** NS Nonsignificant (NS) or significant at the 0. 1 0 (x), 0.05 (*), 0.0 1 (**), or 0.001 (***) probabilit y levels, respectively.

PAGE 302

279 Table D-12. Analysis of variance of nitrogen and amendment rate effects on total soil inorganic N means for all sampling dates. Gainesville Hastings Independent Variable 1993t 1984 1983 1984 N Rate *** L** L*** Qx DCD Rate Q* Q*** L* Nty Rate NS NS NS DCD V Nty NS NS NS IBDU v Ih X **** NS Interactions DCD L X NR NS Qx NS DCD Q X NR ** Q* NS Nty R X NR NS L** NS DCD V Nty X NR NS Q** NS IBDU v Ih X NR NS L** NS Nonsignificant (NS) or significant at the 0.10 (x), 0.05 (*), 0.01 (**), or 0.001 (***) probability levels, respectively. tsee Chapter 5 for data for individual sampling dates. NS NS X NS L** NS NS NS

PAGE 303

REFERENCES AERO. 1964. Dicyandiamide. American Cyanamid Company, Wayne, NJ. Alexander, Martin. 1977. Introduction to soil microbiology. John Wiley & Sons, Inc., New York. Allison, F. E. 1965. Evaluation of incoming and outgoing processes that affect soil nitrogen. In W. V. Bartholomew and F. E. Clark (ed.) Soil nitrogen. Agronomy 10:573-606. Amberger, A. 1978. Belasten Giillenahrstoffe das Grundwasser. Mitteilgn. Dtsch. Landw. Ges. 93:836-841. Amberger, A. 1981a. Didin as a nitrification inhibitor. p. 20-33. In Proc. Syrop. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschafliches Jahrbuch" No. 7, 1981. Amberger, A. 1981b. In Heyland, K. U. Podium discussion. 3. Significance of ammonium and nitrate nutrients to crops. p. 100-101 In Proc. Syrop. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschafliches Jahrbuch" No. 7/1981. Amberger, A. 1984. Effects and applicability of dicyandiamide as a nitrification i nhib i tor. Nitrification inhibition Symposium. VDLUFA Verlag, Darmstadt, West Germany. Amberger, A., and R. Guster. 1978. T ransformation and effect of urea-dicyandiamide and ammonium sul f ate dicyandiamide products with ryegrass and rice. ( In German). Z. Pflanzenern., Diingg., Bodenk. 141:553-566. (Chem. Abstr. 90:21370). 280

PAGE 304

281 Amberger, A., and R. Guster. 1979. N-effect of liquid cattle manure with application of dicyandiamide to ryegrass. (In German.) Zietschrift fur Acker-und Pflanzenbau. 148(3):198-204. (Soils and Fert. Abstr. 43 (11):1042, 1980). Amberger, A., and K. Vilsmeier. 1979a. Breakdown of dicyandiamide in quartz sand and soils. (In German.) Z. Pflanzenern., Diingg., Bodenk. 142(6):778-785. (Chem. Abstr. 92:109896). Amberger, A., und K. Vilsmeier. 1979b. Umsetzungen von Kalkstickstoff in Quarzsand und verschiedene Boden. z. Acker-u. Pflanzenbau 148:1-12 Amberger, A., und K. Vilsmeier. 1979c. Inhibition of the nitrification of liquid manure nitrogen by dicyan diamide. (In German.) z. Acker-u. Pflanzenbau 148(3):239-246. (Chem Abstr. 91:156570). Asfary, A. F., A. Wild, and P. M. Harris. 1983. Growth, mineral nutrition and water use by potato crops. J. Agric. Sci. Camb. 100:87-101. Ashworth, J. 1986. Comments on "Nitrification inhibition by nitrapyrin and volatile sulfer compounds". Soil Sci. Soc. Am. J. 50:268-269. Ashworth, J., S.S. Malhi, D. C. Penny, N. A. Flore, A. T. Blades, and A. M. F. Hennig. 1984. The use of nitrification inhibitors in attempts to improve the efficiency of plant uptake of fertilizer-N and soil mineral-N. Proc. Annu. Alberta Soil Sci. Workshop 1984:115-127. Ashworth, J., A. Penny, F. V. Widdowson, and G. G. Briggs. 1980. The effects of injecting nitrapyrin ('N-Serve'), carbon disulfide or trithiocarbonates, with aqueous ammonia, on yield and %N of grass. J. Sci. Food Agric. 31:229-237. Ashworth J., and G. A. Rogers. 1981. The compatibility of the nitrification inhibitor dicyandiamide with injected anhydrous ammonia. Can. J. Soil Sci. 61:461-463. Barker, A. V., D. N. Maynard, and W. H. Lachman. 1967. Induction of tomato stem and leaf lesions, and potassium deficiency by excessive ammonium nutrition. Soil Sci. 103:319-327.

PAGE 305

282 Barker, A. V., and H. A. Mills. 1980. nutrition of horticultural crops. Ammonium and nitrate Hort. Rev. 2:395-423. Bazilevich, S. D. 1968. Effect of cyanoguanidine on rhizosphere and radicle microorganisms of corn and rnicroflora of the soil. (In Russian.) Doklady TSKhA (Tirniryazevskya Sel'skokh o zyaistvennaya Akaderniya) (Reports of the Tirniryazev Agricultural Academy) 138:7580. Bazilevich, S. D., and N. A. Kabanova. 1973. Effects of nitrification inhibitors on the reactions in soil, loss and use by plants of the ammonium nitrogen of fertil izers as illustrated by experiments with nitrogen 15 labeled ammonium sulfate. (In Russian.) p. 200-213. In D. A. Karen'kov, N. A. Sapozhnikov, and P. M. Srnirnov (ed.) Prirnenenie Stabil 'nogo Izotopa 15 N v Issle dovaniyakh po Zernledeliyu (Utilization of the stable isotope 1 5 N in agricultural research) ti Kolas ti : Moscow, USSR. (Chern. Abstr. 82:56640). Belser, L. w., and E. L. Schmidt. 1981. Inhibitory effect of nitrapyrin on three genera of ammonia-oxidizing nitrifiers. Appl. Envir. Microbial. 41:819-821. Blackmer, A. M. 1986. Potential yield response of corn to treatments that conserve fertilizer nitrogen in soils. Agron. J. 78:571-575. Blue, W. G., and D A. Graetz. 1977. The effect of split nitrogen applications on nitrogen uptake by pensacola bahiagrass from an Aerie Haplaquod. Soil Sci. Soc. Arn. J. 41:927-930. Bock, B. R., J.E. Lawrence, and H. M. Williams. 1981. Relative mobility of dicyandiamide ammonium, and urea by mass flow in soils. p. 25-37. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyand i amide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Boswell, F. C. 1977. Seasonal anhydrous ammonia comparison for corn with and without a nitri fi cation i nh i bitor. Agron. J. 69:103-106. Bremner, J.M. 1965. Inorganic forms of nitrog e n. I n C. A. Black (ed.) Methods of soil ana l ys i s. Part 2 Chemical and microbiological properties. Agr o nomy 9:1179-1237.

PAGE 306

283 Bremner, J.M., and R. W. Radley. 1966. Studies in potato agronomy. II. The effects of variety and time of planting on growth, development, and yield. J. Agric. Sci. Carnb. 66:253-266. Bremner, J.M., and M.A. Taha. 1966. Studies in potato agronomy. I. The effects of variety, seed size, and time of planting on growth, development, and yield. J. Agric. Sci. Carnb. 66:241-252. Briggs, G. G. 1975. The behavior of the nitrification inhibitor "N-Serve" in broadcast and incorporated applications to soil. J. Sci. Food Agric. 26:1083-1092. Brioux, C. X. 1910. Contributions to the study of calcium cyanarnide and dicyandiarnide. (In French.) Ann. Sci. Agron. (Ser. 3), 5:241-281. (Chern. Abstr. 4:2025. 1910; and 5:1723. 1911). Broadbent, F. E., and T. Nakashima. 1967. Reversion of fertilizer nitrogen in soils. Soil Sci. Soc. Arn. Proc. 31:648-652. Bundy, L. G., and J.M. Bremner. 1974. Effects of nitrification inhibitors on transformations of urea nitrogen in soils. Soil Biol. Biochem. 6:369-376. Bundy, L. G., R. P. Wolkowski, and G. G. Weis. 1986. Nitrogen source evaluation for potato production on irrigated sandy soils. Arn. Potato J. 63:385-397. Chamberland, E., and A. Scott. 1968. N-P-K experiments with potatoes in the lower St. Lawrence Region of Quebec. Arn. Potato J. 45:93-102. Chancy, H.F., and E. J. Karnprath. 1982. Effects of deep tillage on N response by corn on a sandy coastal plain soil. Agron J. 74:657-662. Chen, H. H., and P.H. Li. 1978. Comments on report by 'Meisinger et al. 1978. Potato growth and development in relation to NO 3 and NH 4 forms of nitrogen source. Arn. Potato J. 55:227-234.' Arn. Potato J. 55:467-469. Chisso Corporation, Tokyo, Japan. 1981. Controlled release urea fertilizers: urea dicyandiarnide fertilizer coating. Chem. Abstr. 95:17-18. Colliver, G. M. 1980. Nitrification inhibitors can increase yields. Farm Chem. 143:114-117.

PAGE 307

284 Cribbs, w. H., and H. A. Mills. 1979. Influence of nitrapyrin on the evolution of N 2 0 from an organic medium with and without plants. Commun. Soil Sci. Plant Anal. 10:785-795. Curwen, D., K. A. Kelling, J. A. Schoenemann, W.R. Stevenson, and J. A. Wyman. 1982. Commercial potato production and storage. Wisc. Agric. Exp. Stn. Bull. A2257. Curwen, D., and L. R. Massie. scheduling in Wisconsin. 1984. Potato irrigation Am. Potato J. 61:235-241. Davis, J.M. 1983. The effects of soil fumigation on the nitrogen nutrition of potatoes. MS Thesis, Wash. State Univ., Pullman. Davis, J.M., W. H. Loescher, M. w. Hammond, and R. E. Thornton. 1986a. Response of Russet Burbank potatoes to soil fumigation and nitrogen fertilizers. Am. Potato J. 63:71-79. Davis, J.M., W. H. Loescher, M. W. Hammond, and R. E. Thornton. 1986b. Response of potatoes to nitrogen and to change in nitrogen form at tuber initiation. Am. Soc. Hortic. Sci. 11(1):70-72. Day, P. 1965. Particle fractionation and particle size analysis. In C. A. Black (ed.) Methods of soil analysis. Part 1. Physical and mineralogical properties, including statistics of measurement and sampling. Agronomy 9:545-567. Department of Agronomy, Kansas State University. 1976. Kansas fertilizer research report of progress-1976. Agric. Exp. Stn. Rep. Progr. 285. Dec. 1976. Department of Agronomy, Kansas State University. 1977. Kansas fertilizer research report of progress-1977. Agric. Exp. Stn. Rep. Progr. 313. Dec. 1977. Department of Agronomy, Kansas State University. 1978. Kansas fertilizer research report of progress-1978. Agric. Exp. Stn. Rep. Progr. 343. Dec. 1978. form J. Dibb, D. W., and L. F. Welch. 1976. Corn growth as affected by ammonium versus nitrate absorbed from soil. Agron. J. 68:89-94.

PAGE 308

285 Elkashif, M. E., S. J. Locascio, and D.R. Hensel. 1983. Isobutylidene diurea and sulfur-coated urea as N sources for potatoes. J. Am. Soc. Hort. Sci. 108:523-526. Elliott, J.M. 1970. Effects of rates of ammonium and nitrate nitrogen on bright tobacco in Ontario. Tobacco Sci. XIV:131-137. El Wali, A. M. O., F. Le Grand, and G. J. Gascho. 1979. Effect of urea, N-Serve and sulphur coated urea on growth, nutrient uptake, and yield of corn (Zea mays L.). Soil Crop Sci. Soc. Fla. Proc. 38:1-3. Endelman, F. J., D.R. Keeney, J. T. Gilmour, and P. G. Saffinga. 1974. Nitrate and chloride movement in the Plainfield loamy sand under intensive irrigation. J. Envir. Qual. 3:295-298. Fiskell, J. G. A., and W. K. Robertson. 1957. Comparison of broadcast and row fertilization for potatoes on Kanapaha fine sand. Proc. Fla. State Hort. Soc. 70:96103. Florida Crop & Livestock Reporting Service. 1986. agricultural statistics, vegetable crop summary. Crop & Livestock Rep. Serv., Orlando, FL. Florida Fla. Freund, R. J., and R. C. Littel. 1981. SAS for linear models. A guide to the ANOVA and GLM procedures. SAS Institute Inc., Cary, NC. Frye, W.W., R. L. Blevins, L. W. Murdock, K, L. Wells, and J. H. Ellis. 1981. Effectiveness of nitrapyrin with surface-appl i ed f ertilizer nitrogen in no-tillage corn. Agron. J. 73:287-289. Gardner, B. R., and J.P. Jones. 1975. Petiole analysis and the nitrogen fertilization of Russet Burbank potatoes. Am. Potato J 52:195-200. Garita, R. 1981. Use of dicyandiamide-containing fertilizer i n Banana plantations of Costa Rica under humid tropic conditions. p. 95-104. In R. D. Hauck and H. Behnke (ed.) Proc. Tech. Workshop on Dicyandiamide. Muscle Shoals, AL. 4 5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Gasser, J. K. R., and A. Penny. 1964. Inhibiting the nitrification of ammonium salts. Rothamsted Exp. Sta. Rep. 1 963. p. 46.

PAGE 309

286 Giroux, Marcel. 1982. Effet des doses, et du mode d'apport de l'azote sur rendernent et la rnaturittte de la pornrne de terre cultivee sur differents types se sols du Quebec. Can. J. Soil Sci. 62:503-517. Goring, C. A. L. 1962a. Control of nitrification by 2chloro-6-(trichlorornethyl)pyridine. Soil Sci. 93:211218. Goring, C. A. I. 1962b. Control of nitrification of ammonium fertilizers and urea by 2-chloro-6(trichlorornethyl)pyridine. Soil Sci. 93:431-439. Goring, C. A. I., and H. H. Scott. 1976. Control of nitrification by soil fumigants and N-Serve nitrogen stabilizers. Down Earth 32:14-17. Gaus, P. J., T. A. Terrill, and W. Kroontje. 1971. Effects of soil fumigation and the form of nitrogen on the growth yield and value of tobacco grown on two soil types. I. Plant growth and yield. Agron. J. 63:221-224. Graetz, D. A., J. G. A. Fiskell, S. J. Locascio, and W. K. Robertson. 1981. Improving nitrogen fertilizer efficiency using dicyandiamide as a nitrification inhibitor. p. 62-84. In R. D. Hauck and H. Behnke (ed.) Proc. Tech. Workshop on Dicyandiamide, Muscle Shoals, AL. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Guster, K. 1981. Pot and field experiments on the N-effect of liquid manure with Didin. (In German.) Bayer. Landw. Jb. 7. Gysi, Chu, und K. Stroll. 1980. Der Einflufl der Stickstofform (NH 4 oder NO 3 ) auf das Auftreten van Blattpunktnecrosen bei Langerkohl. z. Pflanzenern., Diingg., Bodenk. 143:14-25. Harger, Rolla N. 1920. The changes taking place in cyanamide when mixed with fertilizer materials. J. Ind. Eng. Chern. 12:1111-1116. (Chern. Abstr. 15:287). Hassan, H. M., A. W. Warrick, and A. Arnoozegar-Fard. 1983. Sampling volume effects on determining salt in a soil profile. Soil Sci. Soc. Arn. J. 47:1265-1267. Hauck, R. D. 1972. Synthetic slow release fertilizers and fertilizer amendments. p. 633-690. In C. A. I. Goring and J. W. Hamaker (ed.) Organic chemicals in the environment. Vol. 2. Marcel Dekker, Inc., New York.

PAGE 310

287 Hauck, R. D. 1980. Mode of action of nitrification inhibitors. p. 19-32. In M. Stelly (ed.) Nitrification inhibitors potentials and limitations. ASA Spec. Publ. 38. ASA, CSSA, and SSSA, Madison, WI. Hauck, R. D., and M. Koshino. 1971. Slow release and amended fertilizers. p. 455-495. In R. A. Olson, T. J. Army, J. J. Hanway, and V. J. Kilmer (ed.) Fertilizer technology and use. 2 nd ed. ASA, CSSA, and SSSA, Madison, WI. Helwig, J. T. 1983. SAS introductory guide. SAS Institute Inc. Cary, NC. Hendrickson, L. L., and D.R. Keeney. 1979. Effect of some physical and chemical factors on the rate of hydrolysis of nitrapyrin. Soil Biol. Biochem. 11:47-50. Hendrickson, L. L., D.R. Keeney, L. M. Walsh, and E. A. Liegel. 1978. Evaluation of nitrapyrin as a means of improving N efficiency in irrigated sands. Agron J. 70:699-703. Hergert, G. w., and R. A. Wiese. 1980. Performance of nitrification inhibitors in the Midwest (West). p. 89105. In J. J. Meisinger et al. (ed.) Nitrification inhibitors-potentials and limitations. ASA Spec. Publ. 38. ASA, CSSA, and SSSA, Madison, WI. Herlihy, M., and W. Quirke. 1975. The persistence of 2chloro-6-(trichloromethyl)pyridine in soil. Commun. Soil Sci. Plant Anal. 6(5):513-520. Hewitt, E. J., D. P. Hucklesby, and B. A. Notton. 1976. p. 633-681. In J. Bonner and J.E. Varner (ed.) Plant Biochemistry. Academic Press, New York. Hooper, A. A., and K. R. Terry. 1973. Specific inhibitors of ammonia oxidation in Nitrosomonas. J. Bacterial. 115:480-485. Huber, D. M., P. D. Karamesines, H. L. Warren, and D. W. Nelson. 1981. Equipment to mix chemical additives with anhydrous ammonia during application to soil. Agron. J. 73:1046-1048. Huber, D. M., G. A. Murry, and J.M. Crane. 1969. Inhibition of nitrification as a deterrent to nitrogen loss. Soil Sci. Soc. Am. Proc. 33:975-976.

PAGE 311

Huber, D. M., and R. D. Watson. 1970. Effect of organic amendment on soil-borne plant pathogens. Phytopath. 60:22-26. 288 Janssen, K. A. 1969. The influence of 2-chloro-6(trichloromethyl)pyridine with anhydrous ammonia on corn yield, N uptake and conversion of ammonium to nitrate. M.S. Thesis, Univ. of Nebr.-Lincoln. Dept. Agron. Jaworski, C. A., and D. J. Morton. 1967. Tomato transplant growth, production and uniformity, in relation to source and levels of nitrogen. Hort. Res. 7:1-12. Ju.ma, N. G., and E. A. Paul. 1983. Effect of a nitrifi cation inhibitor on N immobilization and release of 15 N from non-exchangeable ammonium and microbial biomass. Can. J. Soil Sci. 63:167-175. Jung, J., und J. Dressel. 1978. Unsetzungsvorgange und Inhibierungsmoglichkeiten bei Bodenund Diinger stickstoff. Landw. Forsch. Sonderheft 34:74-89. Kappan, H. 1907. On decomposition of cyanamide by mineral constituents of soil. (In German.) Fuhlings Landw. Ztg. 56:122-127. (Chem. Abstr. 5:1149, 1911). Kapusta, George, and E. C. Varsa. 1972. Nitrification inhibitors do they work? Down Earth 28(1):21-23. Kelling, K. A., L. G. Bundy, M. J. Mlynarek, D.R. Keeney, and R. P. Wolkowski. 1984. Usefulness of nitrification inhibitors on irrigated sands in Wisconsin. p. 319-324. In Proc. Wisc. Fert., Aglime and Pest Mgmt. Conf., Madison, WI., 17-19 Jan. 1984. Univ. Wisc., Madison, WI. Kiangsi Prov. Sci. Res. Inst. of Light and Chem. Industries (PRC). 1976. Nitrification inhibitors chemical agents that improve the availability of nitrogen fertilizers. (In Chinese.) Hua Hsueh Tung Pao 1:14-16, 13 (Chem. Abstr. 85:107846). Kick, H., and H. Poletschny. 1981. Inhibiting nitrifi cation when sewage sludge is used as fertilizer. p. 54-64. In Proc. Symp. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschafliches Jahrbuch" No. 7, 1981.

PAGE 312

289 Kissell, D. E., S. J. Smith, w. L. Hargrove, and D. W. Dillow. 1977. Immobilization of fertilizer nitrate applied to a swelling clay soil in the field. Soil Sci. Soc. Am. J. 41:346-349. Kleinkopf, G. E., D. T. Westermann, and R. B. Dwelle. 1981. Dry matter production and nitrogen utilization by six potato cultivars. Agron. J. 73:799-802. Kostov, O. 1977. Inhibition of nitrification and denitrification in calcareous chernozem soil. 155. In Soil biology and conservation of the Proc. 7 th meeting Soil Biology Sect. Soc. Soil Hungarian Assoc. Agric. Sci., Keszthely Univ. Sept. 1975. Akadeniai Kiado, Budapest (Chem. 89:145718). p. 151biosphere. Sci. of Agric. Abstr. Kreitinger, J.P., T. M. Klein, N. J. Novick, and M. Alexander. 1985. Nitrification and characteristics of nitrifying microorganisms in an acid forest soil. Soil Sci. Soc. Am. J. 49:1407-1410. Krishchenko, V. P., S. D. Bazilevich, and L. G. Gruzdev. 1972. Effect of the nitrification inhibitor cyano guanidine on the yield and quality of oats. (In Russian, title mistranslated.) Vestnik Sel'skokhozyaistvennoi Nauki (Moscow) 6:27-32 (Chem. Abstr. 77:100120). Kuntze, H., and B. Scheffer. 1981. Ways to reduce nitrogen leaching into the water system. p. 41-53. In Proc. Syrop. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschafliches Jahrbuch" No. 7, 1981. Laskowski, D. A., and H. D. Bidlack. 1977. Nitrification recovery in soil after inhibition by nitrapyrin. Down Earth 33:12-17. Laskowski, D. A., A. J. Regoli, and N. H. Kurihara. 1974. Aerobic and anaerobic degradation of 14 C-labeled N-Serve in soil. p. 129. In Agronomy abstracts. ASA, Madison, WI. Lees, H. 1946. Effects of copper enzyme poisons on soil nitrification. Nature 158:97.

PAGE 313

290 Legg, J. O., F. w. Chichester, G. Stanford, and W. H. DeMar. 1971. Incorporation of 15 N tagged mineral nitrogen into stable forms of soil organic nitrogen. Soil Sci. Soc. Am. Proc. 35:273-276. Lesczynski, D. B., and Tanner. 1976. Seasonal variation of root distribution of irrigated, field-grown Russet Burbank potato. Am. Potato J. 53:69-78. Linford, Kent, and R. E. McDole. 1977. Potato rooting habits under soil types and management practices. p. 37-40. In Proc. 9th Annual Potato School., Univ. of Idaho. Liu, Shyilon L., E. C. Varsa, G. Kapusta, and David M. Mburu. 1984. Effect of etridiazole and nitrapyrin treated N fertilizers on soil mineral N status and wheat yields. Agron J. 76:265-270. Loescher, W. 1981. Nitrogen source as it affects potato growth. p. 89-92. In Proc. 20 th Ann. Wash. Potato Conf., Moses Lake, WA. Lossaint, P. and R. M. Roubert. 1964. La mineralisation de l'azote organique dans quelques humus forestiers acides. (Mineralization of organic nitrogen in several acid forest humuses) (In French) Annls. Inst. Pasteur, Paris (suppl. no. 3) 107.178-187 MacLean, A. A. 1983. Sources of fertilizer nitrogen and phosphorous for potatoes in Atlantic Canada. Am. Potato J. 60:913-918. Maddux, L. D., D. E. Kissel, J. D. Ball, and R. J. Raney. 1985. Nitrification inhibition by nitrapyrin and volatile sulfur compounds. Soil Sci. Soc. Am. J. 49:239-242. Makarov, B. N., and L.B. Gerashchenko. 1976. Effect of nitrification inhibitors on oat yields and gaseous losses of fertilizer nitrogen. (In Russian.) Agrokhimiya 9:32-37. (Chem. Abstr. 86:42297). Malzer, G. L., T. J. Graff, and J. Lensing. 1979. Influence of nitrogen rate, timing of nitrogen application and use of nitrification inhibitors for irrigated spring wheat and corn. p. 31-39. In Univ. Minn. Soil Series 105. Report on Field Research in Soils.

PAGE 314

Matsumoto, H., N. Wakiuchi, and E. Takahashi. 1969. The suppression of starch synthesis and accumulation of uridine diphosphoglucose in cucumber leaves due to ammonium toxicity. Physiol. Plant. 22:537-545. 291 May, D.R. 1979. Cyanamides. In M. Grayson (ed.) Kirk Othmer encyclopedia of chemical technology. 3 rd ed. 7:291-306. Wiley Interscience, New York. Maze, P., Vila, and V. M. Lemoigne. 1919. Action of cyanamide and dicyandiamide on the development of corn. (In French.) Compt. Rend. Acad. Sci. (Paris) 169(18):804-807. McBeath, D. K. 1962. The inhibition of nitrification by thiourea and 2-chloro-6-(trichloromethyl)pyridine. (Diss. Abstr. 23:1471., Order No.62-5958). McCall, P. J., and R. L. Swann. 1978. Nitrapyrin volatility from soil. Down Earth 34:21-27. Mccants, C. B., E. O. Skogley, and w. G. Woltz. 1959. Influence of certain soil fumigation treatments on the response of tobacco to ammonium and nitrate forms of nitrogen. Soil Sci. Soc. Am. Proc. 23:446-469. McCormick, R. A., D. W. Nelson, A. L. Sutton, and D. M. Huber. 1983. Effect of nitrapyrin on nitrogen transformations in soil treated with liquid swine manure. Agron. J. 75:947-950. McCormick, R. A., D. W. Nelson, A. L. Sutton, and D. M. Huber. 1984. Increased N efficiency from nitrapyrin added to liquid swine manure used as a fertilizer for corn. Agron. J. 76:1010-1014. McElhannon, w. S., and H. A. Mills. 1981. Inhibition of denitrification by nitrapyrin with field grown sweet corn. J. Am. Soc. Hort. Sci. 106:673-677. Meisinger, J. J. 1976. Nitrogen application rates consistent with environmental constraints for potatoes on Long Island. Cornell Univ., Agronomy 5. Meisinger, J. J., D.R. Bouldin, and E. D. Jones. 1978. Potato yield reductions associated with certain fertilizer mixtures. Am. Potato J. 55:227-234.

PAGE 315

Meisinger, J. J., G. W. Randall, and M. L. Vitosh (ed.) 1980. Nitrification inhibitors potentials and limitations. ASA Spec. Pub. 38. ASA, CSSA, and SSSA, Madison, WI. 292 Meyer, B. 1981. From Heyland, K. U. 1981. What is Didin?, Podium discussion. p. 97-98. In Proc. Syrop. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschafliches Jahrbuch" No. 7, 1981. Middleton, J.E., S. Roberts, D. W. James, T. A. Cline, B. L. McNeal, and B. L. Carlisle. 1975. Irrigation and fertilization management for efficient crop production on a sandy soil. Wash. State Univ. Coll. Agric. Res. Cent. Bull. 811. Mitsui, S., I. Watanabe, and S. Honda. 1962. Effects of pesticides on the denitrification in paddy soil. (In Japanese.) Nippon Dojo Hiryogaku Zasshi (Journal of the Science of Soil and Manure, Japan) 33(10):469-474. (Chem. Abstr. 60:3433f). Mitsui, S., I. Watanabe, M. Honma, and S. Honda. 1964. The effect of pesticides on the denitrification in paddy soil. Soil Sci. Plant Nut. 10(3):15-23. (Chem. Abstr. 62:5822f). Mohamad, A. R. B. 1985. The effect of the nitrification inhibitor, dicyandiamide, on sweet corn (Zea mays var. Sacharata) yield and soil nitrogen levels. M.S. thesis, Univ. of Florida, Gainesville. Moorby, J. 1978. The physiology of growth and tuber yield. p. 153-194. In P. M. Harris (ed.) The potato crop: The scientific basis for improvement. Chapman and Hall Ltd., London. Moore, F. D. 1973. N-Serve nutrient stabilizer. A nitrogen management tool for leafy vegetables. Down Earth 28:4-7. Morris, H. D., and J. Giddens. 1963. Response of several crops to ammonium and nitrate forms of nitrogen as influenced by soil fumigation and liming. Agron. J. 55:372-374.

PAGE 316

293 Muller, G., und Hickisch. 1979. und Nitrifikationsinhibitoren Arch. Acker-u Pflanzenenbau u 23:529-546. Der EinfluB von Ureolyse auf Boderunikroorganismen. Bodenk. (East Germany.) Mullison, W.R., and M. G. Norris. 1976. A review of the toxicological residual and envirorunental effects of nitrapyrin and its metabolite 6-chloropicolinic acid. Down Earth 32:22-27. Muntz, A. 1893. Reserches experimentales sur la culture et l'exploitation des vignes. Ann. Agron. 2:1-167. Munzert, M. 1984. Field experiments on potatoes with ALZON. Nitrification inhibition Symposium. VDLUFA Verlag, Darmstadt, West Germany. Murata, H. 1939. Ammonification of dicyanodiamide and its derivatives in soil. Trans. 3 rd Commission, Int. Soc. Soil Sci. A:137-139. (Chem. Abstr. 34:1791). Murphy, H.J., and M. J. Goven. 1975. Effect of fertil ization on yield and specific gravity of Abnaki, Katahdin, and Sioux grown continuously and in two-year rotation. Res. Life Sci. 22(7):1-5. Neglia, R. G., and O. Verona. 1976. Behavior of soil microorganisms particularly nitrifiers, with regard to dicyanodiamide. (In Italian.) Agricoltura Italiana (Pisa) 76(5-6):255-262 (Chem Abstr. 87:37928). Nelson, D. w., and L. E. Sommers. 1972. A simple digestion procedure for estimation of total nitrogen in soils and sediments. J. Environ. Quality 1(4):423-425. Nelson, D. w., L. E. Sommers, D. M. Huber, and H. L. Warren. 1977. Conserving energy with nitrification inhibitors. p. 361-376. In B. Commoner and W. Lockertz (ed.) Agriculture and energy. Academic Press, New York. Nielsen, K F., and R. K. Cunningham. 1964. The effects of soil temperature and form and level of nitrogen on growth and chemical composition of Italian ryegrass. Soil Sci. Soc. Am. Proc. 28:213-218. Nightingale, G. T. 1948. The Nitrogen nutrition of green plants. II. Bot. Rev. 1 4:185-221

PAGE 317

294 Nishihara, T. 1962. The search for chemical agents which inhibit nitrification in soil and studies on its utilization in agricultural practice. (In Japanese.) Bull. Fae. of Agric., Kagoshima Univ. 12:107-158. Nishihara, T., and T. Tsuneyoshi. 1964. Availability of urea mixed with nitrification inhibitors by direct seeding of paddy rice plants. (In Japanese.) Kagoshima Daigaku Nogakobu Gakujutsu Hokoku (Bull. Fae. of Agric., Kagoshima Univ.) 15:91-99. (Chern. Abstr. 65:9673b). Nornrnik, H. 1958. On decomposition of calcium cyanarnide and dicyandiarnide in the soil. Acta Agric. Scand. 8:404440. (Chern. Abstr. 53:8490f). Nornrnik, H. 1959. Calcium cyanamide and dicyandiarnide as sources of nitrogen for higher plants. Acta Agric. Scand. 9:435-447. (Chern. Abstr. 54:14523). Norman, R. J., B. R. Wells, and K. A. K. Moldenhauer. 1989. Effect of application method and dicyandiamide on urea nitrogen-15 recovery in rice. Soil Sci. Soc. Arn. J. 53(4):1269-1274. Norris, M. G. 1972. N Serve nitrogen stabilizers ... a practical approach to better fertilizer nitrogen management. Down Earth 28:5-9. O'Hair, s. K. Florida. 1985. Potato growth in the subtropics of Arn. Potato J. 62:391-401. Osiname, Olumuyiwa, Heriett van Gijn, and Paul L. G. Vlek. 1983. Effect of nitrification inhibitors on the fate and efficiency of nitrogenous fertilizers under simulated humid tropical conditions. Trop. Agric. (Trinidad) 60:211-217. Painter, C. G., and J. Augustin. 1976. The effect of soil moisture and nitrogen on yield and quality of the Russet Burbank potato. Arn. Potato J. 53:275-284. Peck, A. J. 1983. Field variability of soil physical properties. p. 189-221. In D. Hillel (ed.) Advances in Irrigation Vol. 2. Academic Press, New York. Pill, W. G., and V. N. Lambeth. 1977. Effects of NH 4 and NO 3 nutrition with and without pH adjustment on tomato growth, ion composition, and water relations. J. Arn. Soc. Hort. Sci. 102:78-81.

PAGE 318

295 Poletschny, H., and K. Sommer. 1976. The effect of nitrificide application on the efficiency of different nitrogen fertilizers used for grass. (In German.) Landw. Forsch. 33(2):41-51. Polizotto, K. R., G. E. Wilcox, and C. M. Jones. 1975. Response of growth and mineral composition of potato to nitrate and ammonium nitrogen. J. Am. Soc. Hort. Sci. 100:165-168. Potter, H. S., M. G. Norris, and C. E. Lyons. 1971. Potato scab control studies in Michigan using N-Serve nitrogen stabilizer for nitrification inhibition. Down Earth 27(3):23-24. Prasad, R., and B. A. Lakhdive. 1969. Note on the nitrification of ammonium sulfate and subsequent losses of nitrogen under water-logged conditions as affected by nitrification retarders 'N-Serve' and 'AM'. Indian J. Agric. Sci. 39:259-262. Prasad, R., G. B. Rajale, and B. A. Lakhdive. 1971. Nitrification retarders and slow-release nitrogen fertilizers. Adv. Agron. 23:337-383. Quastel, J. H. 1965. Soil metabolism. Ann. Rev. Plant Physiol. 16:217-240. Quastel, J. H., and P. G. Scholefield. 1951. Biochemistry of nitrification in soil. Bacteriol. Rev. 15:1-53. Quebedeaux, B., and J. L. Ozbun. 1973. Effects of ammonium nutrition on water stress, water uptake, and root pressure in Lycopersicon esculentum Mill. Plant Physiol. 52:677-679. Rajale, G. B., and R. Prasad. 1970. Nitrification/ mineralization of urea as affected by nitrification retarders 'N-Serve' and 'AM'. Curr. Sci. (Current Science Association, Bangalore, India) 39:211-212. Randall, G. W., and G. L. Malzer. 1981. Corn production in South-Central Minnesota as influenced by dicyandiamide. p. 38-46. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyandiamide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Ranney, M. w. 1978. Nitrification and urease inhibitors p. 168-169. In M. W. Ranney (ed.) Fertilizer additives and soil conditions. Noyes Data Corp., Park Ridge, NJ.

PAGE 319

296 Rathstack, K. 1978. The nitrification inhibiting effect of dicyandiamide. (In German.) Landw. Forsch. 31(4):347-358. (Chem. Abstr. 90:5073). Reddy, G. R. 1964a. Effect of mixing varying quantities of dicyandiamide with ammonium fertilizers on nitrification of ammonia in soil. Can. J. Soil Sci. 44:254-259. (Soil and Pert. Abstr. 27:3687). Reddy, G. R. 1964b. Effects of varying quantities dicyandiamide on the utilization of nitrogen by crops from sodium nitrate and ammonium sulfate. Agric. Sci. 62:35-38. (Chem. Abstr. 60:15091f). of several J. Reddy, G. R., and N. P. Datta. 1965. Use of dicyandiamide in nitrogen fertilizers. Indian Society of Soil Science Journal 13(2):135-139. Redemann, C. T., R. w. Meikle, and J. G. Widofsky. 1964. The loss of 2-chloro-6-(trichloromethyl)pyridine from soil. J. Agric. Fd. Chem. 12:207-209. Reeves, D. W., J. T. Touchton, and D. H. Rickerl. Effect of nitrogen source and dicyandiamide on and water relations of cotton. Soil Sci. Soc. 52:281-285. 1988. growth Am. J. Reitter, L. 1975. Dicyandiamide. (In German.) In Ullmanns Encyklopeadie der technischen en Chemie. 10(4):145-149. Verlag Chemie, Weinhei.m, West Germany. (cited in May, 1979). Rhoads, F. M. 1972. A comparison of ammonium and nitrate nitrogen for cigar wrapper tobacco. Agron. J. 64:209210. Rieder, G. 1981. DCD results from Europe. p. 87-94. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyandiamide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Rieder, G., and H. Michaud. 1980. Improving fertilizer efficiency. The use of a dicyandiamide-containing nitrification inhibitor. Nitrogen 124:31-35. Roberts, S. 1979. Evaluation of N-Serve and Dwell as nitrification inhibitors on 'Russet Burbank' potatoes. Res. Rep. Wash. State Univ.

PAGE 320

297 Roberts, S., and H. H. Cheng. 1984. Implications from "spoonfeeding" potato plants with nitrogen-15 fertilizer. p. 29-33 In Proc. 20 th Ann. Wash. Potato Conf., Moses Lake, Wash. Robertson, W. K., J. R. Rich, and F. G. Martin. 1982. Corn grain yield on two sandy soils in response to N sidedressing, N rates, N sources, and two fertilizer pretreatments. Soil Crop Sci. Soc. Fla. Proc. 41:220222. Rodgers, G. A. 1983. Effect of dicyandiamide on ammonia volatilization from urea in soil. Fert. Res. 4:361-367. Rodgers, G. A., J. Ashworth, and N. Walker. 1980. Recovery of nitrifier populations from inhibition by Nitrapyrin or CS 2 Zentralblatt fur Bacteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene, Abt. II. 135:477-483. Roorda van Eysinga, J.P. N. L., R.H. M. Maaswinkel, M. Q. van der Meijs, en P. van der en Roozenboom. 1980. Ein stikstofbemestingsproef met andijvie onder glas metals doel het nitraatgehalte in het gewas te bestunderen. Intern Verslag no. 14, Proefstation voor de Groenten-en Fruitteelt onder Glas te Naaldwijk. Roorda van Eysinga, J.P. N. L., en M. Q. van der Meijs. 1980. A trial with nitrogen fertilizer quantities and nitrification with chinese cabbage grown under glass. (In Dutch). Intern Verslag no. 47, Proefstation voor de Groenten-en Fruitteelt onder Glas te Naaldwijk. Roorda van Eysinga, J.P. N. L., en M. Q. van der Meijs. 1981. Proeven met nitrificatieremmers bij sla, andijvie en spinazie in het voorjaar. Intern Verslag no. 27, Proefstation voor de Groenten-en Fruitteelt onder Glas te Naaldwijk. Rotini, O. T., and N. Guerrucci. 1961. the action of cyanamide compounds on plants. (In Italian, with English summary.) Agrochimica 6:92-100. (Soils Fert. Abstr. 25:1098). Rourke, R. V. 1985. Soil solution levels of nitrate nitrogen in a potato-buckwheat rotation. Am. Potato J. 62:1-8. Rowberry, R. G., G. R. Johnston. 1980. Alternative sources of nitrogen and phosphorous in potato fertilizer. Am. Potato J. 57:543-552.

PAGE 321

298 1979a. Growth and Rudert, B. D., and S. J. Locascio. tissue composition of sweet corn source, nitrapyrin, and season. 104:520-523. as affected by nitrogen J. Arn. Soc. Hort. Sci. Rudert, B. D., and S. J. Locascio. 1979b. Differential mobility of nitrapyrin and ammonium in a sandy soil and its effect on nitrapyrin efficiency. Agron. J. 71:487-489. Sabey, B. R. 1968. The influence of nitrification suppressants on the rate of ammonium oxidation in Midwestern USA field soils. Soil Sci. Soc. Arn. Proc. 32:675-679. Saffinga, P. G., D.R. Keeney, and C. B. Tanner. 1977. Nitrogen chloride and water balance with irrigated Russet Burbank potatoes in a sandy soil. Agron. J. 69:251-257. Saffinga, P. G., C. B. Tanner, and D.R. Keeney. 1976. Non-uniform infiltration under potato canopies caused by interception, stern flow, and hilling. Agron. J. 69:337342. Sahrawat, K. L. 1980. On the criteria for comparing the ability of compounds for retardation of nitrification. Plant Soil 55:487-490. Sampei, M. 1972. with summary Hokoku B (or of the Natl. Fertilizers) Nitrification inhibitors. (In Japanese, in English.) Nogyo Gijutsu Kenkyusho Norinsho Nogyo Gijutsukenkyujo) (Bulletin Inst. of Agric. Sci., Series B: Soils and No. 23:79-145. Sampei, M., and M. Fukushima. 1973. Nitrification inhibitors. II. Injurious effects of nitrification inhibitors on some crops. (In Japanese, with summary in English.) Nogyo Gijutsu Kenkyusho Hokoku B (or Norinsho Nogyo Gijutsukenkyujo) (Bulletin of the Natl. Inst. of Agric. Sci., Series B: Soils and Fertilizers) No.24:5399. Sanchez, C. A., A. M. BlacJaner, R. Horton, and D.R. Timmons. 1987. Assesrnent of errors associated with plot size and lateral movement of nitrogen-15 when studying fertilizer recovery under field conditions. Soil Sci. 144(5):344-351.

PAGE 322

299 Sander, D. J., and A. V. Barker. 1978. Comparative toxicity of nitrapyrin and 6-chloropicolinic acid to radish and cucumber under different nitrogen nutrition regimes. Agron. J. 70:295-298. Sanderson J.B and R. P. White. 1987. Comparison of urea and ammonium nitrate as nitrogen sources for potatoes. Am. Potato J. 64:165-176. SAS Institute Inc. 1982a. A. A. Ray (ed.) SAS user's guide: basics, 1982 edition. SAS Institute Inc., Cary, NC. SAS Institute Inc. 1982b. A. A. Ray (ed.) SAS user's guide: statistics, 1982 edition. SAS Institute Inc., Cary, NC. SAS Institute Inc. 1985a. SAS user's guide: basics, Version 5 edition. SAS Institute Inc., Cary, NC. SAS Institute Inc. 1985b. S A S user's guide: statistics, Version 5 edition. SAS Institute Inc., Cary, NC. Scheffer, B., H. Kuntze, and R. Bortels. 1984. Reducing the nitrate leaching in sandy soils by application of DCD Nitrification inhibition Symposium. VDLUFA Verlag, Darmstadt, West Germany. Schmitt, L. 1937. The question of the action of dicyandiamide on the growth of plants. (In German.) Forschungsdienst, Sonderheft 6:248-258. (Chem. Abstr. 33:5573). Schmitt, L. 1938. The effect of dicyandiamide in calcium cyanamide. (In German.) Landwirtsch. Jb. 86:501-508. (Chem. Abstr. 33:1863). Schollenberger, C. J., and R.H. Simon. 1945. Determin ation of exchange capacity and exchangeable bases in soil ammonium acetate menthod. Soil Sci. 59:13-24. Shattuck, G.E., and M. Alexander. 1963. A differential inhibitor of nitrifying microorganisms. Soil Sci. Soc. Amer. Proc. 27:600-601. Simpson, J. R., J. R. Freeney, W. A. Muirhead, and R. Leuning. 1985. Effects of phenylphosphorodiamidate and dicyandiamide on nitrogen loss from flooded rice. Soil Sci. Soc. Am. J. 49:1426-1431.

PAGE 323

300 Simpson, T. w., and R. L. Cunningham. 1982. The occurrence of flow channels in soils. J. Environ. Qual. 11:29-30. SKW. 1973. Produkstudie Dicyandiamid. Silddeutch Kalkstickstoff-Werke A.G. Trostberg, FRG. SKW. 1979a. (Silddeutch Kalkstickstoff-Werke) A.G. Trostberg, Milnchen. 1979a. Alzodin, Rasendilngen mit Langzeitwirkung Merkblatt 1-7. SKW. 1979b. (Silddeutch Kalkstickstoff-Werke) A.G. Trostberg, Milnchen. 1979b. Alzon, Merkblatt: 1-14. Slangen, J. H. G., and P. Kerkhoff. 1984. Nitrification inhibitors in agriculture and horticulture: A literature review. Fert. Res. 5:1-76. Smirnov, P. M. 1968. Utilization by plants, losses, and transformation in soil of nitrogen of different forms of nitrogen fertilizers. (In Russian with summary in English.) Izvestiya Timiryazevskoi Sel'skokhozyaist vennoi Akademii 6:98-116. (Soil Fert. Abstr. 32:2236). Smirnov, P. M. 1978. Application of nitrification inhib itors for reducing nitrogen losses and raising the affectivity of nitrogen fertilization. (In German.) TagungsberichtAkademie der landwirtschaft swissenschaften der Deutschen Demokratischen Republik 155:165-180. (Chem. Abstr. 89:178761). Smirnov, P. M., S. D. Bazilevich, and N. A. Kabanova. 1972a. Effect of nitrification inhibitors on the transformations of nitrogen fertilizers in the soil and on their efficiency. (In Russian.) Doklady TSKhA (Timiryazevskoi Sel'skokhozyaistvennoi Akademii) 183:131-135. (Chem. Abstr. 80:36265). Smirnov, P. M., S. D. Bazilevich, and N. A. Kabanova. 1973. Effect of nitrification inhibitors on the transform ations of nitrogen fertilizers in the soil and on their efficiency. (In Russian.) Khimiya v Sel'skom Khozyaistve 11(1):19-21. (Chem. Abstr. 78:96492). Smirnov, P. M., S. D. Bazilevich, R. Pedyushyus, and V. I. Bronnikov. 1972b. Action of a cyanoguanidine nitrification inhibitor on transformation in soil and losses and utilization of fertilizer ammonium nitrogen by plants. (In Russian.) Agrokhimiya 2:11-19. (Chem. Abstr. 77:18563).

PAGE 324

301 Smirnov, P. M., N. A. Kabanova, and N. I. Degtyareva. 1968. Effect of nitrification inhibitors on the transformation of nitrogen from ammonia fertilizers in soil, and the uptake of the nitrogen by plants. (In Russian.) Doklady TSKhA 144:25-30. (Chem. Abstr. 70:67211). Smirnov, P. M., V. V. Kidin, R. Pedisius, and V. N. Nazarova. 1977. Losses of fertilizer nitrogen from the soil and their reduction by means of nitrification inhibitors. Izvestiya Timiryazevskoi Sel'skokhozyaistvennoi Akademii (Bulletin of the Timiryazev Agricultural Academy) 6:58-70. (Chem. Abstr. 88:36324). Smirnov, P. M., E. A. Muravin, and S. D. Bazilevich. 1976a. Effectiveness of nitrification inhibitors. (In Russian.) Khimiya v Selskom Khozyaistve 14(6):40-42. (Chem. Abstr. 85:122489). Smirnov, P. M., E. A. Muravin, and S. D. Bazilevich. 1976b. Use of nitrification inhibitors for reducing the loss and increasing the effectiveness of nitrogen fertil izers. (In Russian.) Doklady Sovetskikh Vchastnikov Kongressa-Mezhdunarodnyi Kongress po Mineral'nym Udobreniyam, 8 th Moscow, 1976 (Reports of Soviet participants of the congress-International fertilizer congress) 2:168-176. (Chem. Abstr. 89:74827). Smith, M. Scott, Charles w. Rice, Metabolism of labeled organic lation by inorganic nitrogen. 53(3):768-773. and Elder A. Paul. 1989. nitrogen in soil: Regu Soil Sci. Soc. Am. J. Solansky, S. 1981. SKW Didin nitrogen stabilizer test results and recommendations for use. p. 78-96. In Proc. Syrop. on SKW Didin Nitrogen Stabilizer for Liquid Manure., Augsburg, West Germany. 22 Oct. 1981. SKW Trostberg, Agricultural Division, Trostberg, West Germany. Translated from "Bayerisches Landwirtschaf liches Jahrbuch" No. 7/1981. Sommer, K., M. Mertz, und K. Rossig. 1976. Stickstoff zu Weizen mit Ammoniumnitrificiden. Mitteilung 2:Proteingehalte, Proteinfraktionen und Backfahigkeit. Landw. Forsch. 29:161 169. Sommer, K., and K. Rossig. 1978. Effect of the kind of nitrification inhibition in connection with different nitrogen fertilization and proposal for classification. (In German.) Landw. Forsch. 831:291-299. (Chem. Abstr. 90:5072).

PAGE 325

302 Soubies, L., R. Gadet, and M. Lenain. 1962. The possi bility of controlling the transformation of ammoniacal nitrogen to nitrate nitrogen in the soil. Practical applications in the use of nitrogen fertilizers. (In French.) Compt. Rend. Acad. Agr. France 48(16):798-803. (Chem. Abstr. 60:8579d). Spratt, E. D., and J. K. R. Gasser. 1970. The effect of ammonium sulfate treated with a nitrification inhibitor, and calcium nitrate, on growth and N-uptake of spring wheat, ryegrass and kale. J. Agric. Sci. 74:111-117. Street, H. E., and D. E.G. Sheat. 1958. The absorption and availability of nitrate and ammonia. p. 150-165. In W. Rushland (ed.) Encyclopedia of plant physiology. (Handbuch der Pflanzenphysiologie). Vol. 8. Springer Verlag, Berlin. Swezey, A. W., and G. O. Turner. 1962. Crop experiments on the effect of 2-chloro-6-(trichloromethyl)pyridine for the control of the nitrification of ammonium and urea fertilizers. Agron. J. 54:532-535. Tanner, C. B., G. G. Weis, and D. Curwen. 1982. Russet Burbank rooting in sandy soils with pans following deep plowing. Am. Potato J. 59:107-112. Terman, G. L., A. Hawkins, C. E. Cunningham, and R. A. Struchtemeyer. 1951. Rate, placement and source of nitrogen for potatoes in Maine. Maine Agric. Exp. Stn. Bull. 490. Terry, R. E., D. W. Nelson, and L. E. Sommers. 1981. Nitrogen transformations in sewage sludge-amended soils as affected by soil environmental factors. Soil Sci. Soc. Am. J. 45:506-512. Timmons, D.R. 1984. Nitrate leaching as influenced by water level and nitrification inhibitors. J. Environ. Qual. 13(2):305-309. Touchton, J. T. 1981a. Inhibitor and nitrogen applications for early planted grain sorghum. p. 47-52. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyandiamide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany.

PAGE 326

303 Touchton, J. T. 1981b. Effect of didin on nitrification urea N, wheat growth and grain yield. p. 53-61. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyandiamide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Touchton, J. T., and F. C. Boswell. 1980. Performance of nitrification inhibitors in the South East. p. 63-74. In J.J. Meisinger et al. (ed.) Nitrification inhibitors potentials and limitations. ASA Spec. Publ. 38. ASA, CSSA, and SSSA, Madison, WI. Touchton, J. T., R. G. Hoeft, and L. F. Welch. 1979a. Effect of nitrapyrin on nitrification of broadcast applied urea, plant nutrient concentrations, and corn yield. Agron. J. 71:787-791. Touchton, J. T., R. G. Hoeft, and L. F. Welch. 1979b. Loss of nitrapyrin from soils as affected by pH and temper ature. Agron. J. 71:865-869. Touchton, J. T., R. G. Hoeft, L. F. Welch, D. L. Mulvaney, M. G. Oldham, and F. E. Zajicek. 1979. N-uptake and corn yield as affected by applications of nitrapyrin with anhydrous ammonia. Agron. J. 71:238-242. Tsai, C. J., D. M. Huber, and H. L. Warren. 1978. Relationship of the kernel sink for nitrogen to maize productivity. Crop Sci. 18:399-404. Turner, G. O., L. E. Warren, and F. G. Andriessers. 1962. Effect of 2-chloro-6-(trichloromethyl)pyridine on the nitrification of ammonium fertilizers in field soils. Soil Sci. 94:270-273. Turner, M.A., and A. w. MacGregor. 1978. An evaluation of 'Terrazole' as a nitrificide for improving the effi ciency of use of nitrogenous fertilizers on pasture. N. z. J. Agric. Res. 21:39-45. USDA. 1983. Soil survey of St. Johns County, Florida. USDA-SCS. U.S. Gov. Print. Office, Washington, DC. USDA. 1985. Soil survey of Alachua County, Florida. USDA SCS. U.S. Gov. Print. Office, Washington, DC. Vendrell, P. F., F. M. Hons, and D. Bordovsky. 1981. Effects of nitri f ication inhibitor on nitrate leaching losses and yield of Irish potatoes. p. 192. In Agronomy abstracts. ASA, Madison, WI.

PAGE 327

Verona, O.,and u. Gherarducci. 1980. Einflufl von Dicyandiamid und Dicyandiamid-haltigen Diingern auf Boderunikroorganisrnen. SKW-Versuchsbericht, SKW Trostberg, AG., Trostberg, West Germany. 304 Vilsrneier, K. 1979. A colorimetric method for the determination of dicyandiamide in soils. (In German.) z. Pflanzenern., Diingg., Bodenk. 142(6):792-798. (Chern. Abstr. 92:109728). Vilsrneier, K. 1980. Effect of temperature on the breakdown of dicyandiamide in the soil. (In German.) z. Pflanzenern., Diingg., Bodenk. 143(1):113-118. (Chern. Abstr. 92:162760; Soils and Fert. Abstr. 45(2):168, 1982). Vilsrneier, K. 1981. Action and degradation of dicyandiamide in soils. p. 18-24. In R. D. Hauck, H. Behnke (ed.) Proc. Technical Workshop on Dicyandiamide, Muscle Shoals, Alabama. 4-5 Dec. 1981. SKW Trostberg AG, Trostberg, West Germany. Vilsrneier, K. 1982. An improved colorimetric method for the determination of dicyandiamide in soil extracts. (In German, but have English translation.) z. Pflanzenern., Diingg., Bodenk. 145:122-224. Vilsrneier, K., and A. Arnberger. 1978. The inhibition of nitrification by dicyandiamide in model and pot experiments. (In German.) Landw. Forsch. 35:243-248. (Chern. Abstr. 92:70944). Vitosh, M. L. potatoes. No. 142. 1971. Fertilizer studies with irrigated Mich. State Univ. Agric. Exp. Stn. Res. Rep. Volk, G. M. 1956. Efficiency of various nitrogen sources for pasture grasses in large lysimeters of Lakeland fine sand. Soil Sci. Soc. Arn. Proc. 20:41-45. Volk, G. M., and N. Gammon, Jr. 1952. Effect of liming and fertilization on yield and correction of nutritional leaf roll of Irish potatoes. Fla. Agric. Exp. Stn. Bull. No. 504. Volk, G. M., and N. Gammon, Jr. 1954. Potato production in Florida as influenced by soil acidity and nitrogen sources. Arn. Potato J. 31:83-92.

PAGE 328

305 Walters, D. T., and G. L. Malzer. 1990a. Nitrogen manage ment and inhibitor effects on nitrogen-15-urea: I. Yield and fertilizer use efficiency. Soil Sci. Soc. Am. J. 54(1):115-122. Walters, D. T., and G. L. Malzer. 1990b. Nitrogen management and inhibitor effects on nitrogen-15-urea: II. Nitrogen leaching and ballance. Soil Sci. Soc. Am. J. 54(1):122-130. Warren, H. L., D. M. Huber, C. Y. Tsai, and D. W. Huber. 1980. Effect of nitrapyrin and N fertilizer on yield and mineral composition of corn. Agron. J. 72:729-732. Weast, R. C. (ed.) 1979. physics. 60th edition. CRC handbook of chemistry and CRC Press, Boca Raton, Florida. Welch, L. F. 1979. Nitrogen use and behavior in crop production. Illinois Agric. Exp. Stn. Bull. 761. Welch, N. c., K. B. Tyler, and D. Ririe. 1979. Nitrogen stabilization in the Pajaro Valley in lettuce, celery and strawberries. Calif. Agric. Sept. 1979:12-13. Westermann, D. T., and G. E. Kleinkopf. 1985. Nitrogen requirements of potatoes. Agron. J. 77:616-621. Westerman, R. L., M. G. Edlund, and D. L. Minter. 1981. Nitrapyrin and Etradiazole effect on nitrification and grain sorghum production. Agron J. 73:697-702. Westerman, R. L., and L. T. Kurtz. 1973. Priming effect of 15 N labeled fertilizer on soil nitrogen in field experiments. Soil Sci. Soc. Am. Proc. 37:725-727. Wilcox, G. E., C. A. Mitchell, and J.E. Hoff. 1977. Influence of nitrogen form on exudation rate, and ammonium, amide, and cation composition of xylem exudate in tomato. J. Am. Soc. Hort. Sci. 102:192-196. Wolfe, D. w., E. Fereres, and R. E. Voss. 1983. Growth and yield response of two potato cultivars to various levels of applied water. Irrig. Sci. 3:211-222. Wolkowski, R. P., K. A. Kelling, D.R. Keeney, and L. G. Bundy. 1986. Effect of dicyandiarnide on potato growth and nitrogen nutrition. p. 273. In Agronomy abstracts. ASA, Madison, WI.

PAGE 329

306 Zacherl, B., and A. Arnberger. 1984. Inhibition of ammonia oxidation by Nitrosomonas europae with different nitrification inhibitors. Nitrification inhibition Symposium. VDLUFA Verlag, Darmstadt, West Germany.

PAGE 330

BIOGRAPHICAL SKETCH Harris Martin was born in 1954 in Bala Cynwyd, PA. His parents are J. Stanwood Martin and M. Elizabeth Newkirk Martin, of Philadelphia. His family engaged in part time farming while operating an equipment rental business. Harris graduated from Conestoga High School in Berwyn, PA, where he was the student council president. He earned a B.S. in Environmental Science at Antioch College, in Ohio, in 1979. While at Antioch, he partici pated in an environmental field program, spending a semester studying coastal environments in Georgia and Florida. He earned an M.S. degree in Plant Science at the University of Delaware, under Dr. Donald Sparks. His M.S. research concerned nonexchangeable potassium in coastal plain soils. While in Delaware, he married and started a family. At the University of Florida, Harris conducted his Ph.D. research on nitrification inhibitors and potato. Presently, Harris is a single father with two children, Stanwood, age 6, and Rachel, age 8, of whom he has joint custody. While living in Gainesville, he has been a Cub Scout den leader, a Sunday School teacher, a computer instructor for primary grade children, and president of the local chapter of Parents Without Partners. 307

PAGE 331

308 Harris has worked at a wide variety of positions including farm hand, salesman, assistant manager, gardener, oil exploration jug boy, warehouseman, truck driver, plant taxonomy intern, cave diver, soils consultant, and research assistant. Though most of his spare time is spent with his children, his hobbies include SCUBA diving, camping, gardening, geography, current events, and politics. Upon graduating, Harris's career objective is to work in local, state, or federal government, environmental consulting, private industry, or university teaching and research. He prefers to stay in Florida but is willing to move elsewhere.

PAGE 332

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Donald A. Graetz,C irman Professor of Soil Science I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, a dissertation for the degree of Doctor of Philosophy. Dale R. Hensel Professor of Soil Science as I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. oa &~rt~ h ~~~ Professor of Soil SC'i.ence I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Science

PAGE 333

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. t_ -Y'-. 1 : // ~ ._ J ,;;;~ C (_ Salvadore J. L~scio Professor of Horticultural Science This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor f Philosophy. August 1990 Dean, Dean, Graduate School

PAGE 334

UN IV ERSITY OF FLO RIDA II I II I IIIII Ill Il l lll ll ll l ll II I II II I III I I I l lll llll 1111111111 1 111 1 3 1262 08553 8345