Nitrification inhibitor effects on potato yields and soil inorganic nitrogen

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Title:
Nitrification inhibitor effects on potato yields and soil inorganic nitrogen
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xxiii, 308 leaves : ill. ; 28 cm.
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English
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Martin, Harris Warthman, 1954-
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bibliography   ( marcgt )
theses   ( marcgt )
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Thesis:
Thesis (Ph. D.)--University of Florida, 1990.
Bibliography:
Includes bibliographical references (leaves 280-306).
Statement of Responsibility:
by Harris Warthman Martin.
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Typescript.
General Note:
Vita.

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University of Florida
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All applicable rights reserved by the source institution and holding location.
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notis - AHM7551
oclc - 23245362
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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




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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














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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.












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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
























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