• TABLE OF CONTENTS
HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 Introduction
 Review of literature
 Oats
 Pearlmillet
 Discussion
 Summary and conclusions
 Bibliography
 Biographical sketch














Title: Defoliation of oats and pearlmillet as related to herbage yield
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 Material Information
Title: Defoliation of oats and pearlmillet as related to herbage yield
Physical Description: xii, 171 leaves : ill. ; 28 cm.
Language: English
Creator: Hoveland, Carl Soren, 1927-
Publication Date: 1959
Copyright Date: 1959
 Subjects
Subject: Agriculture -- Research   ( lcsh )
Feeds   ( lcsh )
Oats   ( lcsh )
Agronomy thesis Ph. D
Dissertations, Academic -- Agronomy -- UF
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Thesis: Thesis (Ph. D.)--University of Florida, 1959.
Bibliography: Includes bibliographical references (leaves 162-169).
Additional Physical Form: Also available on World Wide Web
General Note: Typescript.
General Note: Vita.
Statement of Responsibility: by Carl Soren Hoveland.
 Record Information
Bibliographic ID: UF00098002
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000410335
oclc - 36794605
notis - ACF7103

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Table of Contents
    Title Page
        Page i
        Page i-a
    Acknowledgement
        Page i-b
    Table of Contents
        Page ii
        Page iii
    List of Tables
        Page iv
        Page v
        Page vi
        Page vii
        Page viii
        Page ix
    List of Figures
        Page x
        Page xi
        Page xii
    Introduction
        Page 1
        Page 2
    Review of literature
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
    Oats
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
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        Page 43
        Page 44
        Page 45
        Page 46
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        Page 48
        Page 49
        Page 50
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        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
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        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
    Pearlmillet
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 78
        Page 79
        Page 80
        Page 81
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        Page 103
        Page 104
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        Page 107
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        Page 109
        Page 110
        Page 111
        Page 112
        Page 113
        Page 114
        Page 115
        Page 116
        Page 117
        Page 118
        Page 119
        Page 120
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
        Page 129
        Page 130
        Page 131
        Page 132
        Page 133
        Page 134
        Page 135
        Page 136
        Page 137
        Page 138
        Page 139
        Page 140
        Page 141
        Page 142
        Page 143
        Page 144
        Page 145
        Page 146
    Discussion
        Page 147
        Page 148
        Page 149
        Page 150
        Page 151
        Page 152
        Page 153
        Page 154
        Page 155
        Page 156
        Page 157
    Summary and conclusions
        Page 158
        Page 159
        Page 160
        Page 161
    Bibliography
        Page 162
        Page 163
        Page 164
        Page 165
        Page 166
        Page 167
        Page 168
        Page 169
    Biographical sketch
        Page 170
        Page 171
        Page 172
        Page 173
        Page 174
Full Text










DEFOLIATION OF OATS AND PEARLMILLET

AS RELATED TO HERBAGE YIELD












By
CARL SOREN HOVELAND


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











UNIVERSITY OF FLORIDA
January, 1959













ACKNOWLEDGEMENTS


The writer wishes to express his appreciation to

Doctors G. B. Killinger and D. E. McCloud for serving as

chairmen of the Supervisory Committee and guiding the re-

search program; to Doctors W. 0. Ash, G. K. Davis, J. H.

Davis, D. B~ Duncan, G. R. Noggle, and D. O. Spinks for

serving as members of the Committee; to V. Chew for ad-

vice on the experimental design; to Dr. H. C. Harris for

assistance in laboratory analyses; to Mr. P. E. Loggins

for furnishing sheep in the grazing study; and to Dr.

F. H. Hull for financial encouragement. Especial thanks

are due Mr. L. Burgess for serving as field assistant and

enduring the irritations of collecting seemingly innumer-

able forage samples. The author is indebted to his wife

for much encouragement and exercising unlimited patience

throughout the study.













TABLE OF CONTENTS


LIST OF TABLES . . . . . . . . . .

LIST OF FIGURES . . . . . . . . .

INTRODUCTION . . . . . o . .

REVIEW OF LITERATURE . . . . .

Perennial Grasses . . . . ..

Effect of plant height at time of cutting
or grazing
Effect of stubble height
Root growth as affected by defoliation

Annual Grasses . . . . . .

OATS . . . . . . . . .

Materials and Methods . . . . .

Effect of cutting treatments varieties,
and irrigation, winter 1955-56
Effect of cutting treatments varieties,
and irrigation, winter 1956-57'
Effect of sheep grazing treatments,
winter 1956-57

Results . . . . . . o. . . .

Effect of cutting treatments, varieties,
and irrigation, winter 1955-56
Effect of cutting treatments, varieties,
and irrigation, winter 1956-57-
Effect of sheep grazing treatments,
winter 1956-57

PEARLMILLET . . . . . .

Materials and Methods . .. . *

Effect of cutting treatments and irriga-
tion, 1955


- ii -


Page

iv

x

1

3

3

3
8
11

13
18

18

18

24

29

33

33

53
65

70

70

70











Page
Effect of cutting treatments, varieties,
row spacings, and irrigation, 1956 72
Effect of cutting treatments and row
spacings, 1957 78
Effect of cutting treatments and nitrogen
levels, 1958 79
Effect of planting date, 1956 and 1957 82
Results * .* * * * . . 86

Effect of cutting treatments and irriga-
tion, 1955 86
Effect of cutting treatments, varieties,
row spacings, and irrigation, 1956 92
Effect of cutting treatments and row
spacings, 1957 109
Effect of cutting treatments and nitrogen
levels, 1958 121
Effect of planting date, 1956 and 1957 137
DISCUSSION . . . . . ... 147

Oats . . . . . . . . . . . 147
Pearlmillet ........ .. . . 151

SUMMARY AND CONCLUSIONS ...... .... . 158
LITERATURE CITED . . .. . . . . 162

BIOGRAPHICAL SKETCH . .. ....... . . 170


- iii -













LIST OF TABLES


Table Page
1. Season total yields of irrigated oats as
influenced by date when clipping ceased,
variety, and clipping treatment, winter
1955-56 34
2. Season total yields of unirrigated oats'as
influenced by date when clipping ceased,
variety, and clipping treatment, winter
1955-56 35
3. Analysis of variance: Forage yields of
oats as influenced by irrigation variety,
date when clipping ceased and clipping
treatments, winter 1955-56 36

4. Summary of oat forage yields as influenced
by irrigation variety, date when clipping
ceased and clipping treatment, winter
1955-56 37
5. Analysis of variance: Forage yields of
three irrigated oat varieties as affected
by clipping, winter 1955-56 42
6. Effect of clipping treatments on forage
yields of three irrigated oat varieties,
winter 1955-56 43

7. Crude protein content of oat forage as
affected by clipping management, winter
1955-56 48
8. Pounds per acre grain of irrigated oats as
influenced by date when clipping ceased,
variety, and clipping treatment, winter
1955-56 49
9. Pounds per acre grain of unirrigated oats
as influenced by date when clipping ceased,
variety, and clipping treatment, winter
1955-56 50
10. Summary of grain yields of oats as affected


- iv -










Table Page
by date when clipping ceased variety, and
clipping treatment, winter 1955-56 51
11. Analysis of variance: Grain yields of
three oat varieties as affected by clipping
treatment and date when clipping ceased,
winter 1955-56 52
12. Pounds per acre oven dry forage of three
irrigated oat varieties as influenced by
cutting treatment, winter 1956-57 54

13. Pounds per acre oven dry forage of three
unirrigated oat varieties as influenced by
cutting treatment, winter 1956-57 55

14. Analysis of variance: Effect of cutting
treatment-on forage yield of three oat
varieties, irrigated and unirrigated,
winter 1956-57 58

15. Analysis of variance: Effect of cutting
treatments on forage-yields of irrigated
Arlington, Floriland, and Seminole oats,
winter 1956-57 59
16. Root and crown yields of three oat vari-
eties as affected by clipping treatment,
winter 1956-57. 61

17. Analysis of variance: Effect of cutting
treatments on root and crown yields of three
irrigated oat varieties, winter 1956-57 62
18. Air temperatures in degrees Fahrenheit-be-
tween rows of irrigated Floriland oats,
winter 1956-57 63
19. Analysis of variance: Pounds per acre oven
dry forage harvested from quadrats in sheep
grazing trial on Arlington oats, winter
1956-57 67
20. Pounds per acre oven dry forage harvested
from quadrats in sheep grazing trial on
Arlington oats, winter 1956-57 68
21. Fertilization schedule for Starr millet


- v -










Table Page
clipping study, 1958 80
22. Pounds per acre of nitrogen applied to
Starr millet date of planting test, 1956 84
23. Pounds per acre actual nitrogen applied to
Starr millet date of planting experiment,
1957 85
24. Total season forage yields of common pearl-
millet as affected by cutting treatment and
irrigation, 1955 87
25. Analysis of variance: Effect of cutting
treatment and irrigation on the forage pro-
duction of common pearlmillet, 1955 88
26. Effect of cutting treatment on the crude
protein content of irrigated common pearl-
millet, 1955 91
27. Effect of cutting treatments on-root yield
of irrigated common pearlmillet, 1955 93
28. Analysis of variance: Effect of clipping
treatments on root-production of irrigated
common pearlmillet, 1955 94
29. Summary of irrigated pearlmillet forage
yields as affected by-row spacing, variety,
and cutting treatment, 1956 96

30. Analysis of variance: Forage yields of
irrigated pearlmillet as affected by row
spacing, variety, and cutting treatment, 1956 97

31. Forage yields of irrigated pearlmillet as
affected by row spacing, variety, and cut-
ting treatment, 1956 98

32. Number of clippings obtained under various
row spacings and cutting treatments of two
pearlmillet varieties, 1956 100

33. Analysis of variance: Effect of cutting
treatment on the season yield of Starr mil-
let grown in 19- and 38-inch rows, 1956 101


- vi -











Table Page

34. Effect of cutting treatments on the
season yield of Starr millet grown in
19- and 38-inch rows, 1956 102

35. Crude protein content of irrigated pearl-
millet forage as affected by variety, row
spacing, and cutting treatment, 1956 106

36. Effect of variety and row spacing on
pounds per acre of oven dry forage from
unirrigated pearlmillet cut when 30 inches
tall to leave a four-inch stubble, 1956 107

37. Analysis of variance: Effect of variety
and row spacing on forage yield of unirri-
gated pearlmillet, 1956 108

38. Pounds per acre of oven dry Starr millet
forage as influenced by row spacing and
cutting treatment, 1957 110

39. Analysis of variance: Effect of row
spacings and cutting treatments on forage
production of Starr millet, 1957 111

40. Analysis of variance: Effect of cutting
treatments on forage production of Starr
millet at seven-, 19-, and 38-inch row
spacings, 1957 112

41. Number of clippings obtained from Starr
millet as influenced by cutting treatments
and row spacings, 1957 116

42. Percent crude protein in Starr millet as
influenced by cutting treatment and row
spacing, 1957 118

43. Pounds per acre oven dry Starr millet
forage as influenced by nitrogen fertili-
zation and cutting treatment, 1958 122

44. Number of clippings obtained from Starr
millet as influenced by cutting treatment
and row spacing, 1958 123

45. Analysis of variance: Forage yield of


- vii -










Table Page

Starr millet as affected by nitrogen
levels and cutting treatment, 1958 124

46. Analysis of variance: Effect of cutting
treatments on forage production of Starr
millet receiving 60 pounds per acre nitro-
gen biweekly, 1958 125

47. Percent crude protein of Starr millet
forage as influenced by cutting treatment
and nitrogen fertilization, 1958 130

48. Pounds per acre nitrogen contained in
Starr millet under three clipping treat-
ments and three nitrogen fertilizer levels,
1958 133
49. Analysis of variance: Pounds per acre
nitrogen contained in Starr millet under
three clipping treatments and three nitro-
gen fertilizer levels, 1958 134

50. Number of live Starr millet shoots per one
foot of row as affected by nitrogen and
cutting treatments, 1958 135

51. Analysis of variance: Effect of nitrogen
levels and cutting treatments on numbers
of live Starr millet shoots, 1958 136

52. Grams of oven dry Starr millet roots per
four-inch diameter core zero to six inches
deep as influenced by cutting treatments
and nitrogen levels, 1958 138

53. Analysis of variance: Effect of nitrogen
levels and cutting treatments on grams of
oven dry Starr millet roots per four-inch
diameter core, zero to six inches deep, 1958 139

54. Pounds per acre of oven dry Starr millet
forage as affected by planting date, 1956 140

55. Pounds per acre of oven dry Starr millet
forage as affected by date of planting,
1957 141


- viii













56. Analysis of variance: Pounds per acre
of oven dry Starr millet forage as affected
by planting date, 1956 142

57. Analysis of variance: Pounds per acre of
oven dry Starr millet forage as affected by
planting date, 1957 143

58. Percent crude protein of Starr millet planted
at five different dates, 1957 146


- ix -


Table


Page













LIST OF FIGURES


Figure Page

1. Mercury tensiometers located in oats 22

2. Hand cutting of oats using a two-inch
red board 22

3. Hand cutting of oats using a nine-inch
blue board 23

4. The irrigated portion of the 648 plots in
the 1955-56 oat clipping study 23

5. A portion of the irrigated 1956-57 oat
clipping experiment 27
6. Minimum thermometer with shields mounted
on pole at five-foot level 27
7. *linimnur thermometers mounted at heights
of three and six inches in oat plots 28

8. Sheep grazing the holding area of oat
management study 32
9. Paddocks of oat management study 32

10. Seasonal distribution of forage for three
irrigated oat varieties cut when six inches
tall to leave a two-inch stubble, winter
1955-56 38
11. Seasonal distribution of irrigated Floriland
oats as affected by height of plants when cut,
winter 1955-56 41

12. Effect of irrigation on the seasonal forage
distribution of Arlington oats when cut at
12 inches to leave a five-inch stubble,
winter 1955-56 46

13. The effect of irrigation on the seasonal
forage production of Seminole oats when cut
at six inches to leave a two-inch stubble,
winter 1955-56 47


- x -











Figure Page
14. Seasonal distribution of irrigated Flori-
land oat forage-as influenced by three cut-
ting treatments, winter 1956-57 57

15. Uninjured Arlington oats where plants were
not closely grazed prior to freezing tempera-
ture on December 28, 1956 69
16. Total loss of closely grazed Arlington oat
stand by freezing 69

17. Over-all view of pearlmillet clipping study 75
18. Pearlmillet plants clipped when 30 inches
tall to leave a four-inch stubble 75
19. Pearlmillet plants clipped when 30 inches
tall to leave a 10-inch stubble 76
20. Pearlmillet plants clipped when 30 inches
tall to leave an 18-inch stubble 76
21. Pearlmillet clipping operation 77
22. Seasonal production of irrigated common
pearlmillet, 1955 90
23. Seasonal distribution of Starr millet grown
in 19-inch rows-and subjected to three cut-
ting treatments, 1956 104
24. Seasonal distribution of common and Starr
pearlmillet varieties when cut at 12 inches
to leave a four-inch stubble, 19-inch row
spacing, 1956 105
25. Regrowth of Starr millet after clipping
30-inch plants, 1957 113
26. Thirty-inch plants of Starr millet clipped back
to four- and 10-inch stubble heights, 1957 114

27. Regrowth of Starr millet as affected by
stubble heights, six days after cutting,
1957 114


- xi










Pa e


Figure

28. Seasonal distribution of forage as affec-
ted by cutting treatments, Starr millet
in 19-inch rows, 1957


29. Seasonal production of
utilized with 15 pounds
biweekly, 1958

30. Seasonal production of
utilized with 30 pounds
biweekly, 1958

31. Seasonal production of
tilized with 60 pounds
biweekly, 1958


Starr millet fer-
per acre nitrogen

Starr millet fer-
per acre nitrogen

Starr millet fer-
per acre nitrogen


32, Effect of planting date on seasonal dis-
tribution of Starr millet forage, 1957


- xii -














INTRODUCTION


Forage plants differ from most other crop plants in

that they are commonly subjected to frequent drastic de-

foliation of leaves and stems. Too often in the past, the

consequences of defoliation of pasture plants have been ig-

nored as animals practiced uncontrolled grazing. In recent

years rotational and strip grazing have been increasingly

used to augment productivity per acre. The problems facing

the grazier using more intensive pasture system have been

outlined by Myers (62) in Australia.
Two questions must be decided in rota-
tional grazing or close folding: (1) the height
of the pasture at the beginning of grazing which
depends on the frequency of grazing and (2) the
height of the pasture at the finish of grazing
(i.e., the severity of grazing).

The above mentioned questions have been answered

to a large degree for cool season perennial grasses and to

a more limited extent for warm season perennial grasses.

Annual forage grasses have received little attention inso-

far as plant management is concerned. Consequently, oats

(Avena sativa L.) and pearlmillet (Pennisetum glaucum (L.))

have been selected for this study, the former being a cool

season plant and the latter a warm season species. Both

have been cited in Florida work (56, 55) as being the most

productive dairy pasture species during their respective


- 1 -




- 2 -


growing seasons.

The questions raised at the inception of this in-

quiry concerned the consequences of defoliation on total

yields and seasonal distribution of forage and to a lesser

extent the effects on crude protein content and root pro-

duction. This series of experiments attempted to evaluate

the effects of plant height when defoliated and the stubble

height on forage and root production of oats and pearlmil-

let. The effects of varieties, row spacings, irrigation,

and nitrogen levels on forage yields were studied to a

more limited extent.














REVIEW OF LITERATURE

Perennial Grasses

Effect of plant height at time of cutting or grazing

The literature is replete with references to vari-

ous frequency of clipping experiments with cool season per-

ennial grasses. One of the earliest studies was made by

Crozier (21) with timothy and reported in 1897. He found

that frequent mowing reduced total yield to one-fourth of

the yield under hay conditions. Although the percentage of

crude protein was highest in forage from frequently cut

plots, Crozier did not feel that it made up for the loss in

yields. Cotton (18) in 1910 ascribed the deterioration of

pastures in New York and New England to overgrazing, caus-

ing less food storage in perennial plants. Several years

later Carrier and Oakley (16) and Hutcheson and Wolfe (42)

reported that heavy grazing of Kentucky bluegrass resulted

in larger gains per acre than light grazing. Somewhat dif-

ferent conclusions were made by Ellett and Carrier (27) in

1915 from their work with Kentucky bluegrass sod. They

found that the total yield of forage varied inversely with

the number of times the plants were cut but that the de-

crease in protein content at the mature stage more than

counterbalanced the increase in dry matter. Early work by


- 3




- 4 -


Waters (87) pointed out the importance of maturity of top-
growth on subsequent yields and permanence of stands of

timothy.

Stapledon and Beddows (74) in England reported in

1926 that repeated cutting of orchardgrass reduced the num-
ber of new shoots. Another English worker, Fagan (28),

compared orchardgrass and Italian ryegrass cut monthly and

every fourteen days, finding that the crude protein content

was highest from plants cut most frequently but the total

protein quantity secured during April and May was greater

from plants cut at monthly intervals. Work by Hudson (41)

in New Zealand also points out the decrease in yields from

frequent clipping of ryegrass and clover.

Graber (30) in 1931 at the University of Wisconsin

found that the amount of root and top growth of bluegrass,

red top, fescue, and timothy varied inversely with the fre-
quency of defoliation. Similar results were reported by

Robertson (68) in 1933.. In contrast, Ahlgren (1) obtained
increased productivity from cutting bluegrass when four to

five inches tall instead of at heading time. Mott (61) in
Indiana found that bluegrass-white clover clipped when the
herbage reached four to six inches produced three times

more forage than when clipped weekly. Dibbern (26), work-
ing with bromegrass, substantiated previous investigations

in that dry weights of tops and roots were in inverse




5 -






proportion to frequency of clipping. Tincker (81) noted

that a plant produces more additional dry weight in a month

by adding to its old growth than when it is clipped and

produces new leaves.

Wagner (84) subjected mixtures of orchard-ladino,

brome-ladino, orchard-alfalfa, and brome-alfalfa to various

cutting intervals and stubble heights of six and twelve

inches. He concluded that frequency of cutting had the

greatest over-all effect on total yield and distribution

of production.

The adverse effect of frequent defoliation on for-

age production of native range grasses is well known.

Studies with native grasses of mostly cool season species

in the western United States by Sarvis (72), Sampson and

Malmsten (71), Biswell and Weaver (8), and Gernert (29) all

point out the decline in forage production under frequent

clipping or grazing.

The time of the year when frequent defoliation oc-

curs may be important. Blaisdell and Pechanec (9) found

that the greatest reduction in yield of bluebunch wheat-

grass the following year occurred from clippings made in

late May and early June. Stoddart (77) reported that Agro-

pyron spicatum in Utah was most severely damaged by clip-

ping in midsummer due to drouth conditions normally exist-

ing at that time. This same grass was also found to be




- 6 -


most vulnerable to clipping damage at the middle of its

vegetative stage and that cutting intensified maximum vul-
nerability and prolonged its duration (58).

Cutting or grazing management may alter the season-
al distribution of forage. English workers (75) found that

when cutting does not begin until late May, the May to No-

vember growth curve is much more level than when cutting
begins earlier in the year. Bird (7) emphasized that stage

of plant growth at the time of the first cutting determines

the period of aftergrowth.

Frequency of clipping studies with warm season
grasses were reported by Leukel, Camp, and Coleman (52) at
the Florida Experiment Station in 1934. Bahia, carpet, and

centipede grasses cut frequently maintained more vegetative
growth and made a better sod. In 1935 Leukel and Barnette

(51) reported that although Bahiagrass cut when mature pro-
duced the most dry matter, the largest quantity of nitrogen
was produced by frequently cut plants. Studies with napier-

grass in Trinidad (65) and Hawaii (89) also indicate de-

creased dry matter production with frequent cutting. The
Hawaii workers found that the greatest amount of palatable
forage was produced by cutting every eight weeks.
Lovvorn (53, 54) in North Carolina studied the ef-
fects of clipping on Dallis, carpet, Bermuda, and Kentucky
bluegrass, concluding that although Dallis was most




- 7 -


seriously injured by frequent cutting, all the species re-

quired more careful management under high fertility. He

also found that frequent cutting was more deleterious at

high temperature. Prine and Burton (67) studied the effect

of nitrogen rate and clipping frequency on Coastal Bermuda-

grass in Georgia. They found that increasing the clipping

interval from one to eight weeks increased hay yield, stem

and leaf length, plant height, seed head frequency, and

internode length and number. This had little effect on

protein yield and percentage nitrogen recovery and de-

creased the protein percentage and leaf percentage of this

grass.

To recapitulate then, forage grass yields are gen-

erally in inverse proportion to the frequency of defolia-

tion; the response to clipping being influenced by the

species, time of year when clipping is practiced, and soil

fertility. Protein yields, on the other hand, may be as

high or higher under more frequent defoliation.

Unfortunately, most clipping studies have been

based on a chronological schedule rather than on the height

of the plant. Kohler (47) points out in his studies on the

chemistry of grasses that cutting treatments in variety and

fertilizer tests should be on the basis of physiological

age rather than on a time interval.

The problem immediately arises as to what is meant











by plant height, Heady (37) defines the height of a plant

as "the perpendicular distance from the soil at its base

to the highest point reached with all parts in their natu-

ral position." In clipping studies with plant varieties

having different growth habits, it is difficult to use this

definition and remove an equivalent amount of forage from

each of the plants. In the case of decumbent and upright

oat varieties, too often clipping experiments have disre-

garded the amount of forage left on the decumbent plants.

Cattle grazing, however, tend to remove much more of the

basal growth on the decumbent plants. For this reason it

would seen highly desirable to lift decumbent forage into

an erect position to determine its true "height" or length

before cutting.

Effect of stubble height

The influence of stubble height on top and root

growth of perennial grasses has been investigated by a num-

ber of workers. Stapledon and Milton (76) reported in 1930

that orchardgrass plants cut to leave a six-inch stubble

considerably outyielded those cut to the ground level.

Graber and Ream (32) found that closely clipped bluegrass

did not respond to additional nitrogen but that leaving a

one and one-half-inch stubble greatly increased production

both with and without additional nitrogen fertilizer. A

number of other studies point out that bluegrass can be


- 8 -




- 9 -


clipped or grazed closely without ill effect (31, 60, 5,
12). Bromegrass, on the other hand, requires that higher

stubble be left if forage production is to remain high (90,

2). Quite obviously, the growth habit of a forage species
determines the response to close clipping. Lang and Barnes

(49) and Newell and Keim (63) noted that native short
grasses produced greater yields when cut frequently to
ground level than when cut only once at the end of the
season.

Harrison (35) and Harrison and Hodgson (36) deduced
from clipping studies with several cool season grasses that

the shorter the stubble, the less top growth and roots were

produced. Harrison (35) concluded that the deleterious ef-

fect of frequent cutting may be offset partially by cutting

the plants at a greater height above the soil. Dexter (25)
and Johnson and Dexter (44) found that quackgrass could be

severely injured and often killed by close clipping.

Aldous (3) found in clipping studies with big and
little bluestem that a four-inch stubble height gave 25

percent more forage than a two-inch stubble. Holscher (38)

reported that with bluestem, wheatgrass, and blue grama

even a stubble height of four centimeters was not suffi-
cient to maintain yields and prevent killing of the plants.
Research on tropical grasses by Paterson (66) in
Trinidad showed that close clipping sharply reduced yields




- 10 -


of para, elephant, Guinea, and Guatemala grasses. He re-
commended that a cutting height of six to ten inches should

be used for these tropical grass species.

Torstensson (82) in Sweden found that meadow fescue

and Italian ryegrass grown in the greenhouse were most pro-

ductive when cut to leave a five-centimeter stubble every

15 days. Jantti and Heinonen (43) in Finland reported that
a mixed sward of fescue-orchard-timothy-red and white clo-
ver showed a striking reduction in yield when clipped

closely. Defoliation to leave a stubble of one centimeter,

while the soil moisture was at or near permanent wilting

percent down to a depth of 40 centimeters, arrested growth

almost completely but the growth rate of plants with a
four- or 12-centimeter stubble was 70 to 90 percent of the

corresponding rate on moist soil. They concluded that de-
foliation alone causes heavy reductions in forage yield

even in moist soil, and these reductions are more important

quantitatively than those resulting from the interaction
with soil moisture. Similar results were noted by Canfield

(15) with black grama and tobosa grasses where close clip-
ping nullified the value of high rainfall years under range
conditions. Tobosa grass clipped to leave a four-inch
stubble yielded 110 percent more forage than two-inch stub-
ble over an 11-year period.
Robinson and Sprague (70) found that clipping




- 11 -


bluegrass-white clover sod to a height of two inches pro-

duced a more dense sod of grass with less clover than when

shorter stubble heights were used. Brougham (10, 11) found

tha a perennial ryegrass, white, and red clover mixture in

New Zealand defoliated to five inches yielded 20 percent

more herbage than pasture cut to one inch during a 32-day

period. During the first 14 days of regrowth the yield

difference was 100 percent. He inferred that excess light

changed the growth habit. The more intense the defolia-

tion, the lower the initial leaf efficiency.

In contrast to the preceding papers which point

out the advantages of higher stubble, Cooper (17) found

that the yield of Nevada bluegrass and sedges from a native

mountain meadow in Oregon decreased as the cutting height

was increased from two to four or six inches. Protein per-

cent of the forage showed only a slight increase with high-

er stubble height. The lack of response to higher stubble

heights here may probably be attributed to the low quality

forage plants and unfavorable wet environment.

Root growth as affected by defoliation

Forage plant roots are often decreased in size and

number by frequent defoliation of the top growth. Dibbern

(26) concluded that clipping of smooth bromegrass was more

adverse in its effects on root growth than top growth.
Sturckie (78) reported that any cutting of Johnsongrass





- 12 -


reduced rootstalk development and the more frequent the

cutting, the greater was the reduction. Similar results

have been reported for orchardgrass (76), Kentucky blue-

grass (46), and wheatgrass (33). Parker and Sampson (64)

noted that frequent removal of aerial growth of purple

needlegrass and soft chess caused poorly developed roots

with a reduction in the diameter of the stele and entire

root.

Baker (6) in England found that cutting of top

growth reduced the number of roots and tillers per ryegrass

plant but increased the'number of roots per tiller. The

root weight of cut plants was found to be lower than on

uncut plants a few weeks after defoliation.

Crider (2), in a detailed study of 13 cool and warm

season grasses including bunch, rhizomatous, and stoloni-

ferous types, showed that root growth stopped for a time

after each removal of aerial growth. He concluded that the

growing top cannot be reduced more than half without ad-

versely affecting the functioning of the root system and

the plant as a whole. At variance with this work, Laird

(48) concluded that mowing of centipede and Bermudagrasses
increased the root growth. The difference of opinion as

expressed by the latter paper can probably be attributed to

poor control of environmental factors in root investiga-
tions. This fact is stressed by Williams and Baker (88)




- 13 -


who point out that root studies should be conducted on
plants grown in their natural habitat, or on field experi-
mental plots, rather than in the artificial environment

provided by containers.

Annual Grasses

Clipping studies with annual forage plants have

been limited in number. Many of these experiments were

concerned with grain production of oats, rye, and wheat.

Field studies in Pennsylvania by Washko, Edge, and Haskins

(86) showed that fall clipping of oats did not affect grain

yields but that spring clipping decreased grain yields.

Robinson (69) in England found that if grazing of winter

wheat is continued into mid or late April the loss of grain
will be 20 to 25 percent of the potential crop. Applying

100 to 150 pounds per acre of ammonium sulfate immediately

after the last grazing reduced the loss of grain by one-
half. :orris and Gardner (59) in north Georgia found that

clipping to March 15 resulted in 75 percent or more reduc-

tion in grain yields of oats, wheat, and rye. Research

work in north rlorida (58) indicated that clipping oats
until February 15 reduced grain yields 25 percent while

an additional two weeks of clipping resulted in 50 percent

yield reduction. High nitrogen fertilization was effective
in maintaining yields of oats and rye clipped to mid






- 14 -


February. Cutler, Pavez, and Mulvey (22) in Indiana found

that clipping wheat during early April increased the yield

and quality of grain. Clipping reduced plant height by

shortening the lower internodes and thus decreased lodging

of the grain.

Davies (23) in England reported that winter grazing

of oats caused a much sharper decrease in grain yields than

did spring grazing. His results indicate that the reduced

yields of grain are probably due to the height of the

plants grazed and the stubble heights used but he attri-

butes the difference to season of the year. In this ex-

periment, the plants were two to three inches tall and

grazed to leave a three-quarter-inch stubble on the winter

grazed paddocks while in the spring grazed paddocks the

plants were six to seven inches tall and grazed to leave a

one to one and one-half-innh stubble.

Washko (85) found in Tennessee sheep grazing trials

on erect and prostrate types of oats, wheat, barley, and

rye that the habit of growth had no effect on forage pro-

duction. Grazing was found to be detrimental to grain pro-

duction on all species. Thurman (79) reports that upright

varieties of oats produce more forage in the fall than

prostrate types but that the total production for the

season is about the same.

Hubbard and Harper (40) in Oklahoma found that




- 15 -


severe clipping of small grain produced slightly less for-

age and appreciably lower grain yields than did moderate

clipping. Yields were affected most by severe clipping in

unfavorable growing seasons. The chemical composition of

forage from severe and moderately clipped plots was simi-

lar.

Thurman and Grissom (80) in Arkansas reported that

clipping very young oat plants reduced root growth and

forage yields as compared to delayed clipping. The re-

growth of oats was reduced when the growing point of the

short stems was clipped along with the leaves. Clipping

above the terminal growing point and after the plants had

a good start more than doubled forage yields. Laudc (50)

in a greenhouse experiment with soft chess noted that

growth was faster from a cut shoot when the terminal bud

was retained and the culm continued elongation, than when

the bud was removed and regrowth was by tillering. In ad-

dition, the tiller was smaller and lighter than the main

shoot. Justus and Thurman (45) also report decreased

yields of oats by frequent clipping. Burton and Prine

(14) found that forage yields of Abruzzi rye, Southland
oats, and ryegrass were greatly increased by cutting at

bi-monthly instead of monthly intervals late in the season.

Early in the season this had little effect on yields.

Hoveland (39) in Texas found that oats clipped




- 16 -


back to one inch whenever they reached three to four inches

in height produced 83 percent less forage than where the

plants were oermitted to grow 10 to 12 inches tall before

clipping. Marshall (55), in a Florida trial with dairy

heifers on oats, concluded that increasing the height of

forage to about eight to ten inches before grazing as com-

pared to six to eight inches was responsible for obtaining

a higher yield of total digestible nutrients. Verbeek (83)

in South Africa also stated the desirability of having oat

plants at that height for grazing. He also cautioned that

oat and wheat plants should not be allowed to get much

higher than 12 inches because the recovery power of the

plants is reduced with consequent fewer grazings being ob-

tained per season.

The effect of cutting sudangrass at two- and six-

inch stubble heights was studied by DePeralta (24) in

Nebraska. 'iields of forage and roots were markedly reduced

by close clipping. Seeding rate was also studied but this

factor had little effect on yield response under the two

cutting treatments. Burger, Jackobs, and Hittle (13), in

an Illinois study, found that herbage yields of four sudan-

grass varieties were much lower when cut at 18 to 20 inches

tall than when harvested at hay stage. Little difference

existed between varieties when cut at the shorter height.

Row spacings may influence the response to cutting




17






of oats (73) and pearlmillet (19). In general, narrower row

spacings favor higher forage yields but defoliation systems

may alter this pattern.














OATS

Materials and Methods

All of the experiments in this study were estab-

lished on Arredondo loamy fine sand located at the Agronomy

Farm, University of Florida, Gainesville, during the win-

ters of 1955-56 and 1956-57.

Effect-of cutting treatments, varieties, and irrigation,
winter. 1955-56

A split plot design was employed, consisting of

three varieties as main plots, subplots of three dates when

clipping stopped in order to produce grain, and sub-sub-

plots of six defoliation or cutting treatments. All combi-

nations of these were used. Oat varieties were selected on

the basis of representative growth habit: decumbent-Arling-

ton; intermediate-Floriland; and upright-Seminole. The

dates to stop clipping on each variety were based on the

usual time of heading at Gainesville. The average heading

dates at Gainesville are: Arlington-April 1, Floriland-

March 1, and Seminole-February 20. Six cutting heights
were selected to obtain a range from very intensive to light

defoliation. The treatments were replicated six times.

The entire experiment was grown under both irri-

gated and non-irrigated conditions, making a total of 648


- 18 -




- 19 -


plots. The irrigation schedule was determined from mer-

cury tensiometers, placed at depths of three and nine

inches. A tensiometer location is shown in Figure 1.

After the plants had become established, irrigation water

was applied by sprinklers whenever the soil moisture ten-

sion reached 500 centimeters at the nine-inch level. Due

to the low water-holding capacity of this soil, only one

inch of water was applied per irrigation. During the win-

ter, a total of 18 inches of water was applied in order to

maintain adequate soil moisture. One-half of this water

was applied from February 25 to April 20. Very hard winds

and blowing sand during the last two weeks of March and

the first week of April made it difficult to supply suffi-

cient moisture for plant growth.

All oat varieties were planted October 18 at the

rate of four bushels per acre in nine-inch rows using a

Planet Jr. 300A planter. The fertilization at planting

consisted of: 800 pounds per acre 8-8-8, 100 pounds cal-

cium sulfate, 40 pounds magnesium sulfate, 10 pounds copper

sulfate, 10 pounds manganese sulfate, 10 pounds zinc sul-

fate, one pound fertilizer borax, and one-fourth pound sodi-

um molybdate. Additional applications of 100 pounds per

acre ammonium nitrate were made on November 28, January 3,

February 3, and March 9, making a total of 196 pounds of

actual nitrogen per acre for the season. Subsequent




- 20 -


nitrogen applications were made on the basis of plant tis-

sue tests. Both irrigated and unirrigated portions of the

experiment received the same fertilization.

Each plot consisted of three rows seven feet long;

the two outer rows serving as borders and being cut the

same as the inner yield row. A 5,8-foot strip of the cen-

ter row, 0.0001 acre in area, was harvested and weighed for

yield.

Cutting was done by hand using paring knives. The

proper height of cut (two, five, or nine inches) was main-

tained by using as a knife guide a plywood board of the

proper height. Nails 5.8 feet apart on top of the board

indicated the exact length of row. Bamboo stakes driven

into the ground at one end of each yield row indicated the

height to which the plants were to be grown before cutting.

The heights of stubble were color coded on both stakes and

the wooden cutting boards (red two inch, white = five

inch, blue = nine inch). This feature eliminated much of

the potential chance for error in the field. Views of the

field experiment and the cutting technique are shown in

Figures 2 to 4.

The question of when to cut a particular treatment

was determined by visual inspection of the plots. Decum-

bent oat forage was lifted to an erect position to deter-

mine its true height and also for the cutting operation




- 21 -


itself. Green forage was not weighed but only oven dry

weights were recorded in grams. Plot yields were converted

to pounds per acre and then subjected to statistical analy-

sis.

Forage was collected in December, January, and

March from two replications of each treatment, dried and

ground for nitrogen analysis by the Kjeldahl method (4).

Grain yields were obtained by harvesting a .0001

acre strip, drying, and threshing with a Vogel machine.

Weight of grain per plot was recorded in grams and later

converted to pounds per acre.





- 22 -


Fig. l.--Mercury tensiometers located in oats.

k --- I


Fig. 2.--Hand cutting of oats using a two-inch red board.




- 23 -


Fig. 3.--Hand cutting of oats using a nine-inch blue board.


Fig. 4.--The irrigated portion of the 648 plots in
the 1955-56 oat clipping study. Bamboo stakes with colored
tips indicate the height at which plants are cut.





- 24 -


Effect of cutting treatments, varieties, and irrigation,
winter 1956-57

In continuation of the clipping studies with oats,

a split plot experiment was planted October 18, 1956 using
Arlington, Floriland, and Seminole oat varieties as main
plots. Subplots consisted of eight clipping treatments as


follows:

(1) Clipped all winter when
two-inch stubble.

(2) Clipped all winter when
inch stubble.

(3) Clipped all winter when
five-inch stubble.

(4) Clipped all winter when
inch stubble.

(5) Clipped all winter when
five-inch stubble.


six inches tall to leave a


12 inches tall to leave a two-


12 inches tall to leave a


18 inches tall to leave a two-


18 inches tall to leave a


(6) Clipped the first time at six inches to leave a two-
inch stubble. Clipped remainder of winter when 12

inches tall to leave a two-inch stubble.

(7) Clipped the first time when six inches tall to leave
a two-inch stubble. Clipped remainder of winter when
12 inches tall to leave a five-inch stubble.

(8) Clipped the first time when 12 inches tall to leave a
two-inch stubble. Clipped remainder of the winter
when six inches tall to leave a two-inch stubble.




- 25 -


The experiment was replicated five times and grown

under both irrigated and unirrigated conditions, making a

total of 240 plots. Fertilization at the October 18 plant-

ing date on both irrigated and unirrigated areas consisted

of 800 pounds per acre of 6-8-8, 100 pounds calcium sul-

fate, 50 pounds magnesium sulfate, and 50 pounds fritted

trace elements. In addition, the irrigated experiment re-

ceived 200 pounds per acre sodium nitrate on November 6,

November 26, December 20, January 9, January 30, and March

11 making a total of 240 pounds of actual nitrogen per acre

for the season. The unirrigated experiment received addi-

tional applications of 200 pounds per acre sodium nitrate

on November 6, December 20, and January 30 making a total

for the season of 144 pounds of actual nitrogen.

A total of 11 one-inch applications of water were

made to the irrigated plots; the irrigation schedule being

determined as in the 1955-56 experiment. Planting and har-

vesting operations were carried out as in the previous year.

An over-all view of the experiment is shown in Figure 5.

In order to obtain information on root production

under the various regimes of cutting, two cores six inches

deep and four inches in diameter were collected from each

plot of the irrigated experiment on January 15. Cores were

obtained directly from the row, the top growth being clipped

off to the ground level. Each plot sample was washed on a





- 26 -


screen to remove soil and the root material, was dried and

then weighed.

It was noted early in the winter that freezing in-

jury appeared to be dependent on the stubble height at the

time of the freeze. The question was posed as to tempera-

ture differences within plots. Consequently, minimum ther-

mometers were mounted between the rows of two- and five-

inch stubble height plots of Floriland oats at heights of

three and six inches as shown in Figures 6 and 7. Unfor-

tunately, only two moderate freezes occurred after mounting

the thermometers on January 17 so that only limited infor-

mation was obtained.




- 27 -


Fig. 5.--A portion of
clipping experiment.


the irrigated 1956-57 oat


Fig. 6.--Minimum thermometer with shields mounted
on pole at five-foot level.















































Fig. 7.--Minimum thermometers mounted at heights
of three and six inches in oat plots.


- 28 -




- 29 -


Effect of sheep grazing treatments, winter 1956-57

In order to ascertain yields of forage and effects

on the plants under different intensities of grazing, a

small paddock sheep grazing study was initiated where the

animals were used only as a tool in removing the forage.

Animal gains were not considered in this study.

Arlington oats were seeded with a grain drill on a

one-fourth acre area after fertilizing with 800 pounds per

acre 8-8-8, 100 pounds calcium sulfate, 50 pounds magnesium

sulfate, and 500 pounds per acre fritted trace elements.

Additional nitrogen applications of 200 pounds per acre of

sodium nitrate were made on November 6, November 26, and

December 28, making a total of 160 pounds of actual nitro-

gen for the season. Eight inches of irrigation water were

applied during the winter.

A randomized block design was employed with five

grazing treatments and four replications, thus dividing the

area into 20 paddocks. The treatments were as follows:
(1) Grazed when the plants reached six inches, leaving a
two-inch stubble.

(2) Grazed when the plants reached 12 inches, leaving a
two-inch stubble.

(3) Grazed when the plants reached 12 inches, leaving a
five-inch stubble.

(4) Grazed the first time when plants were six inches tall





- 30 -


with a two-inch stubble, thereafter when plants were

12 inches tall, leaving a two-inch stubble.

(5) Grazed the first time when plants were 12 inches tall
leaving a two-inch stubble, thereafter when plants

were six inches tall leaving a two-inch stubble.

The estimated yields of forage were calculated for

each of the treatments using data from the clipping experi-

ment of the previous year and the size of the paddock ad-

justed so that it could be grazed down within a day by one

sheep. It was later discovered that one sheep would not

stay and graze well alone, so two animals per paddock were

used, making it possible to graze down the area to the de-

sired height in about two hours.

Woven wire fence three feet high and creosoted

posts were used in construction of the paddocks. The one-

half acre reserve area of oats near the paddocks was fenced

with woven wire four feet high to discourage fence jumping.

In one corner of this area was constructed a small shelter

of sheet metal closed on the north and west as protection

against inclement weather. The eight native breed sheep

were shut up in the shelter each night as protection against

dogs. Figures 8 and 9 show views of the experiment.
Before grazing, yields were taken by cutting to the

desired stubble height three quadrats (0.0001 acre each) at

random in each paddock. The three quadrat yields were




31 -






averaged together and the statistical analysis determined

on the four replications for each treatment. After clip-

ping, the sheep were turned into the paddock and allowed to
graze it down to the stubble height of the clipped quad-

rats. It was found that the sheep grazed the two-inch

stubble paddocks somewhat closer than desired, usually one

to two inches, while the five-inch stubble paddocks were

grazed to leave a stubble of four to six inches.





- 32 -


Fig, 8.--Sheep grazing in the holding area of oat
management study.


'.I
r~- F.Y
`~ ~'-
.li.
~c ";~.
'"C~~
~:j. 'cl
lr
rJ1:
r ''

'I
~i~h~i-4~:--T'L:


Fig. 9.--Paddocks of oat management study. Two
sheep were used in each of the four replications of a par-
ticular grazing treatment.




- 33 -


Results

Effect of cutting treatments, varieties, and irrigation,
winter 1955-56

In Tables 1 and 2 are shown the average yields per

treatment combination. The statistical analysis summary in

Table 3 was calculated from the original plot yields in

grams oven dry forage per 0.0001 acre. Results of the

over-all statistical analysis shown in Table 4 indicate

that the highest forage yield for the winter was obtained

with the Arlington variety, followed by Floriland, and then

Seminole. All three varieties generally responded much the

same to irrigation, the yield increases ranging from 44 to

48 percent.
As shown by Figure 10, there was little difference

in the earliness of forage production by the three varie-

ties. The Seminole variety is usually classed as an early

forage producer but this is probably due to its upright

habit of growth, giving an appearance of greater forage

production than the more decumbent types. Tables 1 and 2

indicate that Seminole made most of its production late in

the growing season. Continued high production throughout

the winter was found to be better with Arlington and Flori-

land than with the Seminole variety, regardless of the cut-

ting treatment used.

The comparison of dates when clipping was stopped






- 34 -


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- 35 -


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- 36 -




- 37 -


TABLE 4
SUMMARY OF OAT FORAGE YIELDS AS INFLUENCED BY IRRIGATION,
VARIETY, DATE WHEN CLIPPING CEASED, AND CLIPPING
TREATMENT, WINTER 1955-56


Pounds per Acre Oven Dry Forage
Irrigated Unirrigated

Varieties:
Arlington 3,890 2,660
Floriland 2,720 1,870
Seminole 2,040 1,410
L.S.D. at 5% 290 110
Date when clipping ceased
in order to produce grain:
Clipped all season 3,910 2,830
Clipped until 2 weeks
before average heading
datea 3,020 2,170
Clipped until 6 weeks be-
fore average heading
date 1,720 930
L.S.D. at 5% 170 110
Clipping treatments:
6 in. tall, 2 in. stubble 2,340 1,910
12 in. tall, 2 in. stubble 2,990 2,480
12 in. tall, 5 in. stubble 2,980 2,090
18 in. tall, 2 in. stubble 3,380 2,160
18 in. tall, 5 in. stubble 3,230 1,850
18 in. tall, 9 in. stubble 2,370 1,370
L.S.D. at 5% 200 170

aAverage heading dates at Gainesville:

Arlington April 1
Floriland March 10
Seminole February 20













-P



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- 38 -




- 39 -


to produce grain gives an indication as to the amount of

forage produced late in the growing season. Approximately

23 percent less forage was obtained when the removal of

forage was stopped two weeks before the average heading

date. When clipping ceased six weeks prior to heading,

forage yields were reduced 56 percent in the irrigated and

67 percent in the unirrigated plots.

Clipping treatments did not have as much effect on

oat forage yields as expected, Low temperatures during the
winter months limited the growth of oats and thus probably

masked much of the response to clipping encountered in sum-

mer forage crops such as pearlmillet. Growth in the unir-

rigated plots was very slow until spring due to drouth and

only one clipping was obtained from the 18-inch plants. As

would be expected, the 18-inch plants with two- or five-

inch stubble produced the most forage under irrigation.

Yields were sharply reduced with a nine-inch stubble.

Forage yields were generally reduced by clipping

plants when six inches tall. Under irrigation this decline
in yield was most pronounced with the Floriland variety as

shown by the data for the total season forage production in

Table 1. Under conditions of inadequate moisture, close

clipping of this variety decreased the yield early in the

growing season but was not detrimental later in the season

as shown in Table 2. It is possible that close and frequent





- 40 -


clipping may have stimulated increased tillering of this

variety. However, intensive clipping under unirrigated

conditions reduced the yield of the Seminole and Arlington

varieties, indicating that varieties differ in response to

defoliation, depending on the moisture available.

The effect of clipping treatments on seasonal dis-

tribution of forage is typified by the results for Flori-

land oats shown in Figure 11. Generally, plants allowed to

grow 12 inches tall before clipping produced a greater

quantity of forage in midwinter than did the other treat-

ments.

Since there was a highly significant interaction

between varieties and clipping treatments under irrigation,

it was desirable to ascertain how each variety responded to

clipping. Separate analyses of variance (Table 5) were cal-

culated for each variety. As shown in Table 6, the three

varieties responded somewhat differently to clipping. Ar-

lington, a decumbent type, gave increased yield with the

higher stubble height on 18-inch plants. Seminole, an up-

right type oat, was quite different in that highest yields

were obtained when 18-inch plants were cut with a two-

inch stubble. This was also true under unirrigated condi-

tions (Table 2). The reason for this is somewhat difficult

to understand since Seminole has an erect habit of growth

and close clipping results in loss of the growing point.





- 41 -


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- 44 -


With 12-inch plants, leaving a five-inch stubble did not

significantly increase the forage yield of any variety.

The efficacy of irrigation is shown in Figure 12

where the distribution of forage throughout the season is

graphed for the Arlington variety when cut at 12 inches to

leave a five-inch stubble. The major contribution of ir-

rigation was in furnishing early forage during December

and January. The value of irrigation was erased by im-

proper defoliation management. Figure 13 illustrated this

fact in the case of Seminole oats but similar results oc-

curred with the other two varieties. Close and frequent

cutting resulted in low production despite adequate mois-

ture being present. The sharp production dips during Janu-

ary on all of these graphs are due to freezes which seri-

ously limited forage growth.

The crude protein content of forage from most of

the clipping treatments was high, as shown in Table 7. The

protein content remained highest throughout the season with

six-inch plants clipped back to two inches. Plants 18

inches tall with a two-inch stubble were lowest in protein.

In the case of 12-inch plants, those having a five-inch

stubble were somewhat higher in crude protein during the

month of March than plants with a two-inch stubble.
Grain yield data are summarized in Table 8. Very

low grain yields were obtained as shown in Tables 9, 10,




- 45 -


and 11, particularly with the Arlington and Floriland vari-

eties where losses due to bird damage were appreciable. Ir-

rigation increased the yield of Seminole oats by 50 percent

but even so, the yield was low. As expected, grain yields

decreased when the forage was removed as late as two weeks

before the average heading date. However, the yield re-

duction was much less pronounced where moisture was not
limiting.
Under unirrigated conditions, clipping treatments

had little effect on the yield of grain except in the case

of closely defoliated plants six inches tall with two-inch

stubble where the yield was reduced. With adequate mois-

ture, grain yields were greatly affected by defoliation.

Plants clipped when 12 inches tall to leave a five-inch

stubble produced considerably more grain than any other

treatment.






- 46 -


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- 51 -


TABLE 10
SUMMARY OF GRAIN YIELDS OF OATS AS AFFECTED BY DATE
WHEN CLIPPING CEASED, VARIETY, AND CLIPPING
TREATMENT, WINTER 1955-56


Pounds per Acre of Grain
Irrigated Unirrigated

Varieties:
Arlington 490 210
Floriland 580 450
Seminole 1,040 660

L.S.D. at 5% 110 80
Date when clipping ceased:
Clipped until six weeks be-
fore average heading date 790 604
Clipped until two weeks be-
fore average heading date 610 281
L.S.D. at 5% 30 80
Effect of clipping treatments:
6 inches tall, 2-inch stubble 760 310
12 inches tall, 2-inch stubble 700 400
12 inches tall, 5-inch stubble 950 450
18 inches tall, 2-inch stubble 540 450
18 inches tall, 5-inch stubble 560 510
18 inches tall, 9-inch stubble 720 520
L.S.D. at 5% 110 90





- 52 -


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- 53 -


Effect of cutting treatments, varieties, and irrigation,
winter 1956-57

The interpretation of yield data from the irrigated

and unirrigated experiments, as shown in Tables 12 and 13,

was complicated by several hard freezes. The recovery power

of plants in plots cut closely just prior to a freeze was

impaired much more than those cut closely just after a

freeze. Furthermore, a serious infestation of Victoria

blight (Helminthosporium victoria) destroyed the Arlington

variety during February in the irrigated area but caused

little damage on the dryland oats. Quite obviously, it be-

comes difficult to make conclusions concerning the vari-

eties and the effects of cutting treatments upon them.

Clipping oat plants when six inches tall back to a

two-inch stubble resulted in considerable reduction in

herbage yields. Height of the stubble apparently had lit-

tle effect on forage yields except in the case of 18-inch

plants where five-inch stubble reduced yields. Close clip-

ping of six-inch plants the first time followed by cutting

the plants when 12 inches tall did not change season yields

appreciably from that of plants clipped all season at 12

inches. Differences between irrigated and non-irrigated

plots were least when plants were clipped at six inches in

height to leave a two-inch stubble.

Seasonal distribution of forage was affected very

little by cutting treatments. Although the six- and 12-inch





- 54 -


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- 55 -


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- 56 -


plants cut back to two inches gave quite different total

yields for the year, the production curves for Floriland

oats in Figure 14 point out the sharp early peak with

gradual decline in production for these two treatments.

Plants having a five-inch stubble generally tended to re-

main more productive late in the season.

Since there were interactions between varieties

and cutting treatments (Table 14), individual varieties

were analyzed separately as shown in Tables 12 and 15.

Under irrigation, the Floriland variety generally performed

better than Seminole. Seminole, with an erect growth habit,

performed best when cut at 18 inches while Floriland was

most productive at 12 inches. Floriland showed a serious

decrease in forage yield when the first cutting was made

at six inches followed by cuttings at 12 inches to leave

a two-inch stubble. When a five-inch stubble was used with

this variety the remainder of the season, apparently the

close early defoliation of young plants was not harmful.

This is perhaps explained by the location of the growing

point when cutting occurs. Monthly measurement of the grow-

ing point heights showed that the growing point of the

Seminole variety was at a height of five to seven inches

in early January while for Floriland this did not occur

until March.

Data from the root samples collected from the




- 57 -


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- 59 -


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irrigated oat plots January 15 are shown in Table 16.

Close frequent clipping, as with the six-inch plants cut

back to two inches, seriously decreased root and crown

weights. Allowing the plants to grow 12 inches tall before

beginning the intensive defoliation treatment of cutting

when six inches tall did not increase the root production.

Differences between varieties were highly significant as

shown in Table 17. Floriland produced a much larger quan-

tity of roots as compared to the other two varieties. The

reason for this is probably twofold. First, Arlington

growth was severely retarded by the fungal infestation.

Secondly, the growing point of an erect growing variety

like Seminole is more easily destroyed by clipping, thus

disturbing root development. The data for Seminole root

yields indicate that root growth was decreased to a greater

extent under two than under five-inch stubble for both 12-

and 18-inch plants. This suggests the likelihood that re-

tardation of root growth may be more serious with close

clipping of erect growing than decumbent oat varieties.

Freeze damage to irrigated Floriland oats was se-

vere in early January on plots which had recently been cut

to leave a two-inch stubble. Minimum daily temperatures in

Table 18 indicate that under very cold conditions the air

between plants with high stubble may be two or three degrees

warmer than where stubble is short. Unfortunately, no more


- ou -













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- 65 -


low temperatures occurred after mid January. Conse-

quently, no further checks on these results were ob-

tained.

Effect of sheep grazing treatments, winter 1956-57

Yield responses to the various grazing treatments

were significantly different as shown in Table 19. Highest

yields were achieved by deferring grazing until the plants

were 12 inches tall as shown in Table 20. Grazing whenever

the plants reached six inches resulted in production being

halved but grazing the first time at 12 inches and there-

after at six inches caused a substantial rise in yield.

Apparently, stubble height had no effect on the total yield
of forage obtained. Height of the plants when grazing was
begun determined the subsequent production. The herbage
yields of Arlington oats obtained from quadrat studies

under grazing conditions compared quite favorably with

those obtained in the clipping experiments (Tables 12 and

20).
A serious freeze on December 28 completely killed

oats in paddocks which had been recently grazed down to

leave a one- to two-inch stubble. As shown in Figures 15

and 16, oat plants having a four- to six-inch stubble were
uninjured. This same effect was observed in the clipping

experiment under irrigation. Victoria blight (Helmintho-
sporium victoria) caused a great deal of damage during





66 -





January and February until finally the experiment had to
be abandoned.




- 67 -


TABLE 19

ANALYSIS OF VARIANCE: POUNDS PER ACRE OVEN DRY FORAGE
HARVESTED FROM QUADRATS IN SHEEP GRAZING
TRIAL ON ARLINGTON OATS,
WINTER 1956-57

Sum of Mean
Source D.F. Squares Square

Replications 3 1,596.0 532.0**
Grazing treatments 4 20,638.7 5,159.7**
Error 12 650.4 54.2

Total 19 22,885.1

**Significant at one percent level.




- 68 -


TABLE 20

POUNDS PEP ACRE OVEN DRY FORAGE HARVESTED FROM QUADRATS
IN SHEEP GRAZING TRIAL ON ARLINGTON OATS,
1956-57


Pounds per Number
Acre Oven of Times
Dry Forage Grazed

Grazed when plants reached 12
inches, 5-inch stubble 2,860 3

Grazed when plants reached 12
inches, 2-inch stubble 2,780 2

Grazed first time-when plants
12 inches tall, 2-inch stub-
ble; thereafter grazed when
6 inches tall, 2-inch stubble 2,320 3

Grazed when plants reached 6
inches, 2-inch stubble 1,340 3

Grazed first time when plants
6 inches tall, 2-inch stub-
ble; thereafter grazed when
12 inches tall, 2-inch stub-
ble. 1,190 2

L.S.D. at 5% 250




- 69 -


-18
ARLINGTON FIVE INCH
JAN 3 STueBLE

-^ -v nii


' '


Fig. 15.--Uninjured Arlington oats where plants
were not closely grazed prior to freezing temperature on
December 28, 1956.

12

i 6
:---6----


Fig. 16.--Total loss of closely grazed Arlington
oat stand by freezing. Plants were grazed to leave a one-
to-two-inch stubble prior to low temperature on December
28, 1956.















PEARLMILLET

Materials and Methods

All of the experiments in this study were estab-
lished on Arredondo loamy fine sand located at the Agronomy

Farm, University of Florida, Gainesville, during the period

1955 through 1958. Weed control in experiments with 19-
and 38-inch row spacings was effected by a hand-operated

push cultivator equipped with a wide sweep. No weed con-

trol was practiced in plots with a seven-inch row spacing.

Effect of cutting treatments and irrigation. 1955

Common pearlmillet was planted in 38-inch rows on

April 27 at the rate of 15 pounds per acre. Thirteen cut-

ting treatments, in a randomized block design, were used to

simulate different management practices with respect to

frequency and severity of defoliation. The plants, on dif-
ferent plots, were cut when they reached heights of 12, 18,

30, and 54 inches. These treatments produced different
frequencies of cutting based not on a fixed time interval,

but on the rapidity of plant development. Four heights of

cut or height of stubble were used: four, six, 10, and 18
inches. These four heights of cut combined in all likely
combinations with the four heights at cutting composed a
series of 13 defoliation treatments.




- 71 -


Two replications received only rainfall and three

replications received two supplemental irrigations of two

inches each. The experiment contained a total of 65 plots.

On the irrigated plots, 800 pounds of 3-12-12 fertilizer

was applied at planting with four supplemental applications

of ammonium nitrate, making a season total of 214 pounds

actual nitrogen per acre. The unirrigated plots received

the same initial fertilization at planting and four supple-

mental applications of ammonium nitrate, making a season

total of 179 pounds actual nitrogen per acre. Rapid plant

tissue tests were used to determine when supplemental

nitrogen should be applied.

Height of the plants was ascertained by lifting

the forage to an erect position to determine its true

height. The cutting was done by means of hand sickles,

using as a guide an aluminum pole, the ends of which rested

on stakes of the desired height. A 13.8-foot strip, 0.001

acre in size, was removed for yield. Adjacent rows on

either side were cut similarly and served as borders on the

three-row plot. The samples were dried at 1300 F., weighed

and yields recorded as pounds of dry matter per acre.
Forage samples were collected from two of the ir-

rigated replications at monthly intervals during the clip-

ping season for nitrogen analysis by the Kjeldahl method

(4).





- 72 -


An attempt was made to study root production under
the different clipping treatments in the irrigated portion

of the experiment. One core was collected from each plot

at a depth of zero to six inches using a Soil Conservation
Service bucket type F-7 four-inch diameter soil auger.

Cores were obtained directly from the row on August 29, the

top growth being clipped off at the ground level. Each

sample was washed on a screen to remove soil and the root

material dried and then weighed.

Effect of cutting treatments, varieties, row spacinps. and
irrigation. 1956

Results of the 1955 pearlmillet management study

indicated the need for a more intensive study of the fac-

tors influencing forage production. Since only 38-inch

rows were used in the 1955 test it became evident that

closer row spacings should be studied together with vari-

ous defoliation practices. The introduction of the higher

quality Starr millet (a variety developed at the Georgia

Coastal Plain Experiment Station) made it desirable to

expand the experiment to include two varieties.

A split plot design was employed, consisting of two
varieties as main plots, three row spacings as subplots,

and four replications, making a total of 144 plots. The

same seeding rate per foot of row was used with all row

spacings, resulting in the following rates of seed per




- 73 -


acre: 38-inch rows 10 pounds, 19-inch rows 20 pounds,

and seven-inch rows 54 pounds.

Prior to planting on March 26, the following ferti-

lizers were applied: 500 pounds per acre 4-12-12, 50

pounds magnesium sulfate, 40 pounds fitted trace elements,

and 10 pounds zinc sulfate. Good stands were obtained but

a severe sandstorm on April 16 ruined the entire planting

so it had to be disced up and replanted on April 24. Addi-

tional broadcast applications of 200 pounds per acre ammo-

nium nitrate were made on April 24, June 6, June 25, and

July 20, making a total of 284 pounds actual nitrogen for

the season. Irrigation water was applied as needed; the

total amount applied to the replanted millet being three

and one-half inches during the month of May.

Each plot was nine feet long but the width was de-

pendent on the row spacing. With a 38-inch row spacing, a

three-row plot was used, the 0.0005 acre harvest area being

6.9 feet of the center row. With the 18-inch row spacing,

a five-row plot was used, the 0.00025 acre harvest area

being 6.9 feet of the center row. Plots having the narrow

row spacing of seven inches had seven rows, of which 6.9

feet of the three center rows were harvested, making a

yield area of 0.00028 acre. In all cases, the border rows

were cut at the same time and in the same manner as the


yield areas.




- 74 -


Cutting was done by hand, using butcher knives.

The proper height of cut (four, 10, or 18 inches) was main-

tained by using as a knife guide a plywood board of the

proper height. The board was seven feet long, the exact

length of plot to be harvested. Views of the stubble
heights and the cutting operation are shown in Figures 17

to 21. Bamboo stakes driven into the ground at one end of

each yield row indicated the height to which plants were to
be grown before cutting. The height of the stubble was

color coded on both stakes and the wooden cutting boards

(red = four inch, white = ten inch, blue = 18 inch).

Both green and oven dry weights of forage were re-

corded. Dry weights from each of the plots were converted

to equivalent per acre yields and subjected to statistical

analysis. Forage samples for nitrogen analysis were col-

lected in June and July, dried, ground in a Wiley mill, and

analyzed for nitrogen by the Kjeldahl method (4).

In order to check on the effectiveness of irriga-
tion, a smaller unirrigated experiment was planted nearby

on similar soil. This experiment was of a split plot de-

sign with Starr and common varieties of pearlmillet as main
plots and three row spacings (seven, 19, and 38 inches) as

the subplots. Using three replications, this made a total
of 18 plots. All plots were clipped back to a four-inch

stubble whenever the plants reached 30 inches tall. Plot




- 75 -


Fig. 17.--Over-all view of pearlmillet


clipping study.


Fig. 18.--Pearlmillet plants clippea wnen
tall to leave a four-inch stubble.


inches




- 76 -


Fig. 19.--Pearlmillet plants clipped when 30 inches
tall to leave a 10-inch stubble.


Fig. 20.--Pearlmillet plants clipped when 30 inches
tall to leave an 18-inch stubble.




- 77 -


Fig. 21.--Pearlmillet clipping operation. A 10-
inch white board is being used to maintain proper stubble
height.




- 78 -


sizes and fertilization were as in the larger irrigated
experiment,

Effect of cutting treatments and row spacings. 1957
In order to confirm the rather interesting findings

of 1956, the experiment was repeated with the exception
that only the Starr variety was used, The experimental de-
sign was a split plot with row spacings of seven, 19, and

38 inches as main plots and six cutting treatments as sub-
plots:

(1) Cut when 54 inches tall to leave a four-inch stubble.
(2) Cut when 30 inches tall to leave a four-inch stubble.

(3) Cut when 30 inches tall to leave a 10-inch stubble,
(4) Cut when 30 inches tall to leave an 18-inch stubble.

(5) Cut when 18 inches tall to leave a four-inch stubble.
(6) Cut when 12 inches tall to leave a four-inch stubble.
An initial fertilization of 400 pounds per acre
8-8-8, 50 pounds magnesium sulfate, and 50 pounds of fritted

trace elements was made prior to planting the experiment on
April 22. Additional applications of 200 pounds per acre
sodium nitrate were made on May 9, May 17, June 6, June 12,

July 3, July 30, and August 15, giving a total of 256
pounds actual nitrogen for the season. An additional ap-
plication of 200 pounds per acre 0-8-24 was made on June
12. Planting and harvesting procedures were similar to the




- 79 -


methods used the previous year except that irrigation water

was applied only at planting to insure a uniform stand.
Recovery rate after defoliation was determined by measur-

ing the regrowth of 30-inch plants over a seven day period

after the first clipping. Three measurements of regrowth
were made in each plot of the four replications for the

three stubble heights and three row spacings. Forage sam-

ples were collected from two replications on approximately

every other harvest date, dried, ground in a Wiley mill,

and analyzed for nitrogen by the Kjeldahl method (4).

Effect of cutting treatments and nitrogen levels. 1958

In 1958 a field experiment was begun to test the
effect of cutting treatments and nitrogen levels on forage

production of Starr pearlmillet. The experimental design

was a split plot with nitrogen levels as main plots and

cutting treatments as subplots. Six replications were

used, making a total of 54 plots. Three nitrogen ferti-

lizer rates were used:

(1) Low 15 pounds per acre of actual nitrogen applied

biweekly.

(2) Medium 30 pounds per acre of actual nitrogen applied

biweekly.

(3) High 60 pounds per acre of actual nitrogen applied
biweekly.
Total amounts of fertilizer applied are shown in Table 21.






























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- 80 -




- 81 -


Three cutting treatments were imposed on each of

the nitrogen levels:

(1) Cut when 12 inches tall to leave a four-inch stubble.

(2) Cut when 30 inches tall to leave a four-inch stubble.

(3) Cut when 30 inches tall to leave a ten-inch stubble.
The experiment was planted May 2 and the stand was

destroyed by a sandstorm. Another planting made May 8 was

washed out by unusually heavy rain., A successful planting

was made May 28 in another area. The Starr variety was

planted at ten pounds per acre in 19-inch rows. Each plot

was nine feet long and consisted of four rows, of which

0.0005 acre was harvested from the two center rows for

yield data. Harvesting methods were similar to those em-

ployed in proceeding experiments. Forage samples were col-

lected from two replications on each harvest date, dried,

ground in a Wiley mill, and analyzed for total nitrogen by

the Kjeldahl method (4). Crude protein was expressed by

multiplying the nitrogen content by 6.25.
Changes in the stand of plants were studied by

counting the numbers of live plants in a one-foot strip of

row. One count was made in each plot on three different
dates.
A crude measure of the effect of nitrogen level and

cutting treatment on root production was obtained by taking

a core four inches in diameter and six inches deep from











each plot on June 28 and August 1. Each core was washed on

a screen to remove the soil and the root material was dried

and then weighed. Trash and rocks were carefully removed.

Cores were obtained immediately adjacent to the row of

plants rather than directly below the row. Previous ex-

perience had shown that it was difficult to decide between

crowns and roots so this problem was circumvented by samp-

ling adjacent to the row of plants and excluding the crowns.

Effect of planting date. 1956 and 1957.

Pearlmillet is usually considered to be a plant

which makes its production over a very short period of

time. The question arose as to whether this growing period

is influenced by the date of planting, stimulating the fol-

lowing experiments during 1956 and 1957.

The 1956 experiment originally consisted of six

dates of planting at monthly intervals from March to August

arranged in a randomized block design with four replica-

tions. Severe sandstorms destroyed both the March and

April plantings; consequently, the yield data are based

only on four planting dates. The Starr variety was

planted at ten pounds per acre in 38-inch rows. Each plot

was 16 feet long and consisted of three rows, of which

0.001 acre of the center row was harvested for yield.

Plants were clipped by hand to leave a four-inch stubble

whenever they reached 30 inches. At each planting, the


- 62 -











following fertilizers were applied: 400 pounds per acre

8-8-8, 50 pounds magnesium sulfate, and 50 pounds fritted

trace elements. Additional nitrogen was supplied by am-
monium nitrate whenever the plots were cut as shown in

Table 22.

In 1957 the experiment was modified, the changes

being based on results from the 1956 season. The Starr

variety again was planted, this time in 19-inch rows. In-

dividual plots consisted of six rows nine feet long, of

which 0.0005 acre of the two center rows was harvested for

yield data. Plantings were made monthly from March through

July, using a randomized block design with five replica-

tions. Plants were clipped when they reached a height of

30 inches, leaving a ten-inch stubble. The initial fer-
tilizer application at each planting date was the same as

in the 1956 experiment. Nitrogen applications are shown in

Table 23. Samples were collected at a number of harvests,

dried, ground, and analyzed for nitrogen by the Kjeldahl
method (4).


- 83 -




- 84 -


TABLE 22
POUNDS PER ACRE OF NITROGEN APPLIED TO STARR MILLET
DATE OF PLANTING TEST, 1956


Date Fertilizer Planting Dates
Applied May 1 June 4 July 6 August 3

Initial planting
application 32 32 32 32
June 21 66

July 3 66
July 6 66
August 10 66 66 66

Total 164 164 98 98
















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- 85 -












Results

Effect of cutting treatments and irrigation, 1955

The results as summarized in Tables 24 and 25 indi-

cate that irrigation had little effect on forage yield of

pearlmillet. It is probable that the irrigation at plant-

ing coupled with the two and one-half inches of rainfall

during May prevented a severe water shortage and minimized

the drouth effect.

Highest yields of forage were obtained with the 54-

inch growth, cut near the ground leaving a minimum of stub-

ble. Season yields of dry forage in the test ranged from

13,950 down to 5,520 pounds of dry matter per acre in the
irrigated plots. Forage production of pearlmillet in-

creased progressively as the plants were permitted to grow

taller before clipping.

Plants 54 inches tall showed a progressive decline

in forage yield as the cutting height was increased. Cut-

ting of 54-inch plants at 18 inches decreased the yield of

forage by one-third as compared to that of the 54-inch

plants with a four-inch stubble. There were no significant

differences in total yield between the four-, six-, 10-, and

18-inch stubble heights of 30-inch plants. In spite of con-

siderable forage not harvested in the high stubble of the

30-inch plants, the season total yield was similar to that
for the low stubble plants. Pearlmillet plants harvested


- 86 -




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