Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 253
Title: Studies on summer cover crops in a pineapple orange grove
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Permanent Link: http://ufdc.ufl.edu/UF00026391/00001
 Material Information
Title: Studies on summer cover crops in a pineapple orange grove
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 18 p. : ill., chart ; 23 cm.
Language: English
Creator: Stokes, W. E ( William Eugene ), 1889-1948
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1932
 Subjects
Subject: Cover crops -- Florida   ( lcsh )
Fruit-culture -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by W.E. Stokes ... et al..
General Note: Cover title.
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Bibliographic ID: UF00026391
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924113
oclc - 18204777
notis - AEN4718
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used only to trace the historic work of
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Copyright 2005, Board of Trustees, University
of Florida







Bulletin 253


October, 1932


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
Wilmon Newell, Director








STUDIES ON SUMMER COVER CROPS

IN A PINEAPPLE ORANGE GROVE

By
W. E. STOKES
R. M. BARNETTE
H. W. JONES
J. H. JEFFERIES




















Bulletins will be sent free upon application to the
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA










EXECUTIVE STAFF
John J. Tigert, M.A., LL.D., President of the
University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
J. Francis Cooper, M.S.A., Editor
R. M. Fulghum, B.S.A., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant


MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist**
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A., Associate*
Fred H. Hull, M.S., Associate
J. D. Warner, M.S., Associate
John P. Camp, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman*
R. B. Becker, Ph.D.. Specialist in Dairy Hus-
bandry
W. M. Neal, Ph.D., Associate in Animal Nutri-
tion
E. F. Thomas, D.V.M., Assistant Veterinarian
W. W. Henley, B.S.A., Assistant Animal Hus-
bandman
P. T. Dix Arnold, B.S.A., Assistant in Dairy In-
vestigations
CHEMISTRY AND SOILS
R. W. Ruprecht, Ph.D., Chemist**
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Assistant
J. M. Coleman, B.S., Assistant
H. W. Winsor, B.S.A., Assistant
H. W. Jones, M.S., Assistant

ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
M. A. Brooker, Ph.D., Associate
Zach Savage, M.S.A., Assistant

ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist**
L. W. Gaddum, Ph.D., Biochemist
C. F. Ahmann, Ph.D., Physiologist

ENTOMOLOGY
J. R. Watson, A.M., Entomologist**
E. F. Grossman, M.A., Entomologist
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
P. W. Calhoun, Assistant, Cotton Insects

HORTICULTURE
A. F. Camp, Ph.D., Horticulturist**
Harold Mowry, B.S.A., Horticulturist
M. R. Ensign, M.S., Associate
A. L. Stahl, Ph.D., Associate
G. H. Blackmon, M.S.A., Pecan Culturist
C. B. Van Cleef, M.S.A., Greenhouse Foreman
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist**
George F. Weber, Ph.D., Plant Pathologist
R. K. Voorhees, M.S., Assistant
Erdman West, M.S., Mycologist

*In cooperation with U.S.D.A.
**Head of Department.


BOARD OF CONTROL
P. K. Yonge, Chairman, Pensacola
A. H. Blanding, Bartow
Raymer F. Maguire, Orlando
Frank J. Wideman, West Palm Beach
Geo. H. Baldwin, Jacksonville
J. T. Diamond, Secretary, Tallahassee



BRANCH STATIONS

NORTH FLORIDA STATION, QUINCY
L. 0. Gratz, Ph.D., Plant Pathologist in Charge
R. R. Kincaid, M.S., Asst. Plant Pathologist
W. A. Carver, Ph.D., Associate Agronomist
R. M. Crown, B.S.A., Assistant Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
John H. Jefferies, Superintendent
Geo. D. Ruehle, Ph.D., Associate Plant Pathol-
ogist
W. A. Kuntz, A.M., Associate Plant Pathologist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Assistant Entomologist

EVERGLADES STATION, BELLE GLADE
R. V. Allison, Ph.D., Soils Specialist in Charge
R. Lobdell, M.S., Entomologist
F. D. Stevens, B.S.. Sugarcane Agronomist
G. R. Townsend, Ph.D., Asst. Plant Pathologist
B. A. Bourne, M.S., Sugarcane Physiologist
J. R. Neller, Ph.D., Biochemist
A. Daane, Ph.D., Agronomist
R. W. Kidder, B.S., Asst. Animal Husbandman
Ross E. Robertson, B.S., Assistant Chemist
SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Assistant Horticulturist
Stacy 0. Hawkins, M.A., Assistant Plant
Pathologist



FIELD STATIONS

Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
W. B. Shippy, Ph.D., Associate Plant Pathol-
ogist
K. W. Loucks, M. S., Asst. Plant Pathologist
J. W. Wilson, Ph.D., Associate Entomologist
C. C. Goff, M.S., Assistant Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
R. E. Nolen, M.S.A., Asst. Plant Pathologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Asso. Plant Pathologist
West Palm Beach
D. A. Sanders. D.V.M., Veterinarian
Monticello
Fred W. Walker, Assistant Entomologist
Bradenton
David G. Kelbert, Asst. Plant Pathologist







STUDIES ON SUMMER COVER CROPS IN
A PINEAPPLE ORANGE GROVE
By
W. E. STOKES, R. M. BARNETTE, H. W. JONES and J. H. JEFFERIES

INTRODUCTION
Summer cover crops have had an important place in citrus
groves since the beginning of citrus culture in Florida and with
the extension of citrus culture in the well drained deep sand areas
of the state the value of cover crops has received increasing recog-
nition. Both leguminous and non-leguminous plants indigenous
to Florida as well as introduced plants are now widely used as
summer cover crops in citrus groves.
Since few experiments have been made under comparable con-
ditions to test the relative value of different summer cover crops
in citrus groves, such an experiment was started at the Citrus
Experiment Station at Lake Alfred, Florida, in 1925. At the end
of seven years, it has become necessary to rearrange the plan of
the experiment. The outline of the original experiment with the
first seven years' observations on cover crop yields, tree growth,
fruit yields and soil changes are given in this bulletin.

PLAN OF EXPERIMENT
Four summer leguminous cover crops, one volunteer non-le-
gume, a rotation, and clean culture have been compared for their
effects on tree growth, fruit yields, and soil conditions. The four
legumes were Crotalaria striata DC., velvet beans, cowpeas, and
beggarweed. The volunteer non-legume was fiatal grass (Trich-
olaena rosea Nees.). The rotation consisted of the four legumes
and natal grass. No vegetation was allowed to grow on the clean
culture plots.
The land on which the experimental grove was located was
cleared in November, 1923, by cutting down trees and cutting
out stumps and removing them. Stumps were not burned out
and no burning was done on the land planted to citrus. The land
was planted to velvet beans in 1924. A satisfactory growth was
obtained and this cover crop was plowed under in the fall. Pine-
apple oranges budded on rough lemon stock were set in January,
1925. The trees were set in squares 25 by 25 feet. The grove
was divided into plots of 16 trees each to be planted to the differ-
ent cover crops. A diagram showing the arrangement of the plots
in the grove is given in Figure 1. In the beginning, each cover














Citrus Grove


CH()-us Gr-ove


2' 3* .. 6. ^


.* /


r3or1 r Ro4/


. . . . .. .. o T rees


FIG. 1.-Diagram of summer cover crop plots, Citrus Experiment Station, Lake Alfred, Florida. Pineapple orange
trees on rough lemon stock were planted 25x25 feet in January, 1925. There were 16 trees per plot. Cover crops were
grown on the. various plots as follows:
1. Natal grass (volunteer cover crop).
2. Cowpeas (in rows).
3. Beggarweed (broadcast).
4. Velvet beans (in rows).
5. Crotalaria striata (broadcast).
6. Natal grass.
7. Natal grass in 1925-26, cowpeas 1927, velvet beans 1928, beggarweed and C. striata 1929; C. striata 1930, natal
grass and C. striata 1931.
8. Cowpeas (in rows) 1925-28, inclusive; mulch 1929-31.
9. Beggarweed (broadcast).
10. Velvet beans (in rows).
11. Crotalaria striata (broadcast).
12. Clean culture.
13. Clean culture.


* .1.


'3


.... t







Bulletin 253, Studies on Summer Cover Crops


crop plot was duplicated except the one planted to a rotation of the
cover crops. In 1928 one of the cowpea plots was mulched heavily
with hay made of a mixture of grasses and Crotalaria striata.
The results obtained on this block of trees will not be discussed
in this report. A row of trees was set in February, 1925, between
the plots and a grove roadway to eliminate possible border effects.
The general system of cultivation for this grove was to disc in
the spring to prepare a seedbed and cover the seeds of the planted
cover crops, and to plow or disc in the fall to incorporate the cover
crops with the soil. In addition, a strip of land on each side of
the tree rows was kept clean cultivated during the fall and spring
months, thus preventing direct competition of the cover crops
and the trees for moisture and fertilizer. A summarized state-
ment of the handling of the plots up to the present is given in
the record of the handling of this grove for the past seven years.

'Record of Cultivation of Summer Cover Crop-Experimental Grove
1924
Feb ........... Land broken with 2-horse plow
April 15 ........ Sowed velvet beans
Oct. 25 ........ Plowed in velvet beans
1925
Jan. 9 .......... Harrowed new land
Jan. 23, 24 ...... Planted trees on summer cover crop plots
April 28 ....... Watered trees
-May 6 .......... Prepared soil for cover crops
May 8 .......... Sowed cover crop seed-cowpeas and velvet beans in rows,
other cover crops broadcast
June 9 ......... Cultivated cowpeas and velvet beans and hoed trees
July 29 ......... Plowed and harrowed clean culture plots
July31 .........Harrowed other plots
August 20 ...... Cut and weighed cover crops
December 2 .....Plowed in cover crops
December 16 .... Banked trees
1926
March 2 ........ Unbanked trees
April 24 ....... Disked plots
April 25 ....... Harrowed plots
May 14 ......... Sowed cover crop seed
Aug. 7 .........Weighed cover crops
Sept. 22 ........ Hoed trees
Oct. 19 ......... Weighed cover crops
Dec. 16 ........Banked trees
Dec. 22 ......... Plowed plots

1Compiled from a diary recording the handling of a 60-acre grove, of
which the cover crop plots were a part.







Florida Agricultural Experiment Station


1927
Feb. 24 ......... Unbanked trees
March 4 ........Plowed
March 28 .......Harrowed
April 21 .......
April 28 ........Sowed cover crop seed
May 11 ......... Dug out Bermuda grass
May 26 .........Hoed trees
June 15 ........Harrowed trees
June 29 ........Hoed trees
Oct. 3 ..........Mowed cover crops
Nov. 17 ........ Plowed under cover crops
Dec. 12 ........ Banked trees

1928
March 12 ....... Unbanked trees
March 26 ....... Harrowed
May 26 .........Plowed
May 28 ........ Harrowed
June 6 .........Sowed cover crop seed
June 20 ........ Hoed trees
June 21 ........ Replanted cover crop seed
Oct. 3 ..........Hoed
Oct. 6 .......... Plowed
Nov. 26 ........ Harrowed
Nov. 29 ........Banked trees
Dec. 6 .......... Plowed

1929
Feb. 20 ........ Harrowed
Feb. 22 ......... Unbanked trees
March 13 ....... Harrowed
April 20 ........ Harrowed
May 8 ......... Disked for cover crops
May 9 .......... Sowed cover crop seed
May 23 ........Hoed
June 1 .......... Destroyed cowpeas on account of federal ruling in regard
to Mediterranean fruit fly, planted soy beans instead
Sept. 10 ........ Mowed cover crops
Oct. 9 ..........Disked in cover crops

1930
Feb. 20 ........ Unbanked trees
March 28 .......Harrowed
May 1 ..........Sowed cover crop seed in plots and harrowed
May 2 .......... Hoed
May 29 ......... Hoed clean culture plots
Aug. 2 ......... "
Aug. 22 ........ Mowed
Dec. 11 ........ Disked







Bulletin 253, Studies on Summer Cover Crops


1931
March 13 ....... Harrowed
March 23 ....... Sowed cover crop seed
March 24 ....... Harrowed in cover crop seed
June 30 ........ Hoed clean culture plots
June 26 ........ Cultivation
Oct. 5 ..........Cut cover crops
Oct. 6 .......... Hoed and mowed
Oct. 7 .......... Hoed
Oct. 9 .......... Disked
Oct. 12 ......... Mowed
Oct. 30 ......... Hoed
Nov. 3 ......... "
Nov. 5 ......... "

The necessary spraying and pruning for the control of citrus
insects and diseases were done under the direction of the ento-
mologist and plant pathologist at the Citrus Experiment Station.
A ready mixed commercial fertilizer was used, the quantities
and analyses of which are given in Table I. The application of
the fertilizer was made under competent supervision and all plots
were fertilized alike with a single minor exception with reference
to the clean culture plots 12 and 13 in the fall fertilizer applica-
tion of 1930, as noted in Table I.
In this experiment the grove plots planted to cowpeas, beggar-
weed and velvet beans gave very poor yields after the fourth
year and were more or less overrun by a volunteer growth of
natal grass, thus voiding any true comparison of these crops with
crotalaria and natal grass. In view of this fact, it is thought
best to rearrange the original experiment, discontinuing the use
of cowpeas, beggarweed and velvet beans as summer cover crops
but making continued use of crotalaria, natal grass and mulch in
future studies on this particular experimental grove area.

SUMMER COVER CROP YIELDS
The cover crop yields were obtained by cutting and weighing
the green cover crop from a 64 square-foot area in each plot. This
was done when the cover crops had reached maximum growth.
The weighed sample of green material from the 64 square-foot
area was then air-dried to about 8% moisture. The yield of the
cover crops per actual acre (not grove acre) was calculated from
the dry weights of the crops from the 64 square-foot areas. The
average yield per actual acre of the duplicate plots of the different
summer cover crops for each of the years 1925 to 1931 inclusive,








8 Florida Agricultural Experiment Station

TABLE I.-AMOUNTS AND ANALYSIS OF FERTILIZERS APPLIED PER TREE DURING
THE SEVEN-YEAR PERIOD, 1925-1931.


Application per tree
Year Spring Summer Fall

Amount Analysis Amount Analysis Amount Analysis
NH3-P20-K20 NH3-P205-K20 NHa-P20s-K20

Pounds Percent Pounds Percent Pounds Percent
1925. 3-8-4 1 3-8-5 1 3-8- 5

1926.. 1 3-8-4 1 3-8-5 12 3-8- 8

1927.. 2 4-8-5 2 3-8-5 2Y2 3-8- 5

1928.. 3 3-8-5 3 3-8-5 3 3-8-10

1929.. 4 4-8-4 5 3-8-5 5 3-8- 8

1930.. 6 4-8-5 6 4-8-5 6* 3-8- 5

1931.. 7 3-8-5 8 4-8-5 54 3-6- 5


*Two pounds less on clean culture plots 12 and 13.

TABLE II.-AVERAGE YIELDS OF SUMMER COVER CROPS FROM DUPLICATE PLOTS.


Pounds per acre of air-dried top growth
Cover crop ----
1925 1926 1927 1928 1929 1930 1931 7-year
average
Crotalaria striata.. 7,656 4,835 2,401 4,080 5,750 2,613 7,448 4,969

Velvet beans..... 2,212 2,526 2,295 2,380 1,873 435 2,003 1,960
4 grass
Beggarweed...... 3,062 2,178 failure 3,400 3,398 1,742 3,397 2,453
Yi grass grass 4 grass
Cowpeas ....... 2,211 1,350 1,147 3,400 1,001* 1,306* 4,051* 2,066
soybeans 4 grass

Natal grass...... ..... 3,060 4,292 3,400 3,398 3,049 3,223 3,403A

Rotated to above
crops*......... .... 3,400 1,360 2,040 3,703 2,613 4,051 2,861A
Natal cowpeas velvet beggar- C. striata Natal
grass beans weed grass
C. striata C. striata


*Single plot. A6-year average.







Bulletin 253, Studies on Summer Cover Crops


as well as the seven-year average, is given in Table II. The yield
of cover crops on the grove-acre basis have not been calculated
for this experiment due to a failure to record the tree spread or
the width of the middle given over to the cover crops during each
of the seven years of the experiment. Yields on the basis of the
grove acre may be calculated by properly evaluating the cultivated
strip which, as a rule, is determined by the tree spread, and of
course, varies with the age and size of trees. This factor should
be kept in mind in estimating the quantity of organic matter
returned to the soil by cover crops. The results of this experi-
ment are most applicable to groves on Norfolk deep sands.
The yearly yield results given in Table II show that crotalaria
was the highest yielding cover crop for five years out of seven,
while natal grass was the highest yielding cover crop for the
other two years. The plot rotated to the different cover crops
outyielded the natal grass plots in 1926, 1929 and 1931. How-
ever, since the rotated block was not duplicated, too much sig-
nificance should not be attached to a single plot record. Consid-
ering the other cover crops, beggarweed gave higher yields than
cowpeas and velvet beans for four years out of the seven. One
year cowpeas outyielded the beggarweed and velvet beans. How-
ever, that year the cover crop from the cowpea plots was esti-
mated to be made up of three-fourths natal grass. Velvet beans
out-yielded cowpeas and beggarweed for two years (1926 and
1927).
The seven-year average yields of the cover crops, together with
the nitrogen content of the crops, are shown in Table III. The
average yields per actual acre of cover crops calculated from the
air-dry weights of top growth of duplicate plots show that cro-
talaria yielded 1,566 pounds more dry material per acre than did
natal grass, while velvet beans yielded 1,443 pounds per acre
less than the natal grass plots, and beggarweed and cowpeas
yielded 950 pounds and 1,337 pounds per acre, respectively, less
than the natal grass. In attempting to establish a cover crop of
beggarweed, velvet beans and cowpeas on this type of soil, lower
yields of these crops are obtained than of the volunteer cover
crop of natal grass.
The nitrogen percentages were obtained on similar cover crops
grown at Gainesville. They should approach the percentages of
the Lake Alfred crops as they were grown under similar condi-
tions and during the same years. The percentages of nitrogen
were as follows: crotalaria 2.177, velvet beans 1.998, beggarweed







Florida Agricultural Experiment Station


TABLE III.-AVERAGE ANNUAL YIELD AND AVERAGE NITROGEN CONTENT OF
DIFFERENT CROPS USED IN SUMMER COVER CROP EXPERIMENTS FOR THE SEVEN-
YEAR PERIOD 1925-1931.

7-year average yield of Nitrogen content
air-dried top growth (8 percent moisture basis)
Cover crop Yield Increase Nitrogen Increase
per over returned over
actual Natal IPercent per actual Natal
acre grass acre grass
Pounds Pounds Percent Pounds Pounds
Crotalaria striata .......... 4,969 1,566 2.177 108 72
Velvet beans.............. 1,960 -1,443 1.998 39 3
Beggarweed............... 2,453 950 1.207 29 7
Cowpeas.................. 2,066 -1,337 1.662 34 2
Natal Grass............... 3,403 ...... 1.081 36 ...

1These nitrogen percentages were obtained on material grown at Gaines-
ville.


1.207, cowpeas 1.662 and natal grass 1.081 percent. The average
results show that 72 pounds more nitrogen per actual acre was
returned by the crotalaria tops than by natal grass. Despite a
higher percentage of nitrogen in the tops of cowpeas, velvet beans
and beggarweed as compared with natal grass, these leguminous
plants returned only insignificant increases or actual decreases
of nitrogen to the soil in comparison with the amounts returned
by natal grass. This was largely due to comparatively low yields
of cowpeas, velvet beans and beggarweed as contrasted with the
relatively high yields of natal grass.


TREE GROWTH

The cross-section area of the tree trunk at a definitely marked
height above the ground was used as an index of tree growth.
Individual tree records were kept. The diameter of the tree
trunk was measured for the first five years of the experi-
ment, after which circumference measurements were taken,
since this measurement is considered more accurate for calcu-
lating the cross-section area when the tree trunks become large
and more or less irregular in diameter. The measurements were
made the first part of August each year. From these measure-







Bulletin 253, Studies on Summer Cover Crops


ments the average cross-section areas were calculated to square
inches.
Table IV gives the average cross-section areas of the tree
trunks of the differently handled plots for the seven years of the
experiment. The average cross-section areas of the tree trunks
expressed in square inches as obtained for the crotalaria, natal
grass and clean culture plots are shown graphically in Fig. 2.

22



--- Natal grass
16 --- .----- Clean culture



1, 12
o










1925 1926 1927 192s 1929 1970 1931
Year
FIG. 2.-Graphical presentation of average cross-section areas (in square
inches) of tree trunks on Crotalaria striata, natal grass and clean culture
plots.

There are small and perhaps insignificant differences in the
average cross-section areas of the tree trunks for the first four
years of the experiment. After that time, when undoubtedly the
tree roots were reaching into the area where cover crops had
been grown and turned under, differences begin to appear in the
cross-section areas, showing that greatest growth has been made
by the trees of the crotalaria plots while the trees of the natal
grass plots are second largest and the trees of the clean culture
plots are the smallest. The average cross-section areas of the
tree trunks of the other cover crop plots, as a rule, ranged between
the clean culture and the natal grass plots.








Florida Agricultural Experiment Station


TABLE IV.-YEARLY AVERAGE CROSS-SECTION AREA OF TREE TRUNKS ON THE
PLOTS IN THE GROVE USED FOR SUMMER COVER CROP STUDIES.


Cover crop


Crotalaria striata .
Velvet beans. ... .
Beggarweed ........
Cowpeas...........
Natal grass........
Rotated cover crops*
Clean culture.......

*Single plot.


1925
sq. in.

0.60
0.59
0.58
0.59
0.59
0.61
0.64


Average cross section area of tree trunks
1926 1927 1928 1929 1930
sq. in. sq. in. sq. in. sq. in. sq. in.

1.84 3.91 5.89 8.07 14.94
1.70 3.77 5.46 7.17 12.78
1.91 3.84 5.60 7.34 13.13
1.69 3.32 5.36 6.79* 13.13*
1.71 3.74 5.99 7.22 13.70
1.81 3.84 5.90 7.31 12.43
1.85 3.54 5.68 6.55 9.55


The top growth of the trees was uniform and normal on all the
plots for the first three years of the experiment. After that time
the general condition and appearance of the trees on all the cover
crop plots were better than that on the clean culture plots. At
the end of the seventh year many of the trees of the clean culture
plots were in a very unthrifty condition.


FRUIT YIELDS

The percentages of the trees under the various cover-cropping
systems which bore measurable quantities of fruit have been
calculated from the individual tree records for the years 1928 to
1931, inclusive, and are given in Table V. Only one outstanding
fact is brought out in these data and this is that clean culture is
evidently not a desirable method for bringing the maximum
number of Pineapple orange trees (on rough lemon stock) into
bearing on this type of soil. Otherwise there is no specific corre-
lation between the numbers of trees brought into measurable
bearing and any system of cover-cropping.
Fruit yields for the years 1928 to 1931, inclusive, have been
calculated from the individual tree yield records for the different
cover crop plots, allowing 80 pounds of fruit per box. The average
yearly fruit yields and the average total fruit yields in boxes per
acre obtained from the trees of the various cover crop plots during


1931
sq. in.

19.49
16.17
17.48
16.33*
18.37
16.12
13.93








Bulletin 253, Studies on Summer Cover Crops 13


FIG. 3.-The natal grass plot as it appeared shortly after the experiment
was started.


""A' -



.7


FIG. 4.-Crotalaria striata plot on left, clean culture plot on right, in the
cover crops experiments.







Florida Agricultural Experiment Station


their fourth,, fifth, sixth and seventh years of age as well as
increases or decreases over or under the natal grass plots are
given in Table VI. Considering the average total yields for the
four years, the trees of the rotated cover crop plot yielded great-
est; however, these yields represent a single plot and results from
duplicate plots would be more desirable. The average total yield
of the duplicated crotalaria plots ranks second. For the four-year
period they outyielded the natal grass plots, which were third,
by 12.3 boxes per acre. The plots which were either planted to
the other leguminous cover crops or kept in clean culture, show a

TABLE V.-PERCENT OF CITRUS TREES IN PLOTS GROWN TO DIFFERENT SUMMER
COVER CROPS WHICH BORE MEASURABLE QUANTITIES OF FRUIT.
1928-'31 INCLUSIVE.


Cover crop

Crotalaria striata .............
Velvet beans ..................
Beggarweed ..................
Cowpeas* ....................
Natal grass ..................
Rotated cover crops* ..........
Clean culture .................
*Single plot.


Percent of trees bearing
1928 1929 1930 1931
4th 5th 6th 7th
year year year year


78.1
31.3
53.1
56.3
68.8
81.3
9.4


75.0
71.9
78.1
81.3
78.1
81.3
43.8


93.8
96.9
84.4
87.5
84.4
81.3
43.8


90.6
96.9
100.0
87.5
87.5
100.0
28.1


distinct decrease in fruit yield as compared to the natal grass
plots. The clean culture plots yielded 117 boxes per acre less than
the natal grass plots for the four years of measurable fruit yields.
Table VII summarizes the results of the seven years' observa-
tions on cover crop yields and tree growth (as measured by in-
crease in cross-section area of the tree trunks) and gives the total

TABLE VI.-YEARLY FRUIT YIELDS IN BOXES PER ACRE OBTAINED FROM TREES
OF COVER CROP PLOTS DURING THEIR FOURTH, FIFTH, SIXTH AND SEVENTH
YEARS OF AGE.
Boxes of oranges per acre of 70 trees
('25 ft. by 25 ft.)
Cover crop Increase
1928 1929 1930 1931 Total over
natal grass
Crotalaria striata... 4.5 5 .6 76.1 83.3 169.5 +12.3
Velvet beans ........ 0.8 2.1 40.3 71.5 114.7 -42.5
Beggarweed ........ 3.9 7.4 24.3 99.8 135.4 -21.8
Cowpeas* ........... 3.0 3.7 43.5 41.1 91.3 -65.9
Natal grass ......... 3.8 7.7 49.3 96.4 157.2
Rotated cover crops* 6.1 7.9 57.2 100.6 171.8 +14.6
Clean culture ....... 0.2 1.4 28.8 9.6 40.0 -117.2
*Single plot. 80 lbs. allowed per box of oranges.







Bulletin 253, Studies on Summer Cover Crops


fruit yields for the years 1928 to 1931, inclusive. Only the cover
crop plots which were duplicated were used in preparing the data
of the table. These summarized results show that the grove plots
on which crotalaria grew ranked first in cover crop yields, tree
growth and fruit yields. The natal grass plots ranked second, the
beggarweed third, the velvet bean fourth and the clean culture
fifth. The increases in cross-section areas of the tree trunks and
the total yields of fruit are correlated directly with the yields of
air-dry material of the cover crops returned to the soil. Larger
cover crop yields have meant a faster tree growth and larger fruit
yields for the duration of the experiment. Clean culture has little
or nothing to recommend it as a grove practice on this type of soil.

SOIL ORGANIC MATTER STUDIES
Soil organic matter includes all organic materials in the soil.
These organic materials may be arbitrarily divided into the "de-
composed organic matter" or soil "humus", and the "rough or
decomposing organic matter." The "decomposed organic matter"
or soil "humus" is made up of plant and animal materials which
have undergone a rotting process in the soil. They are the re-

TABLE VII.-SEVEN-YEAR AVERAGE YIELD PER ACRE OF TOP GROWTH OF COVER
CROPS, INCREASE IN CROSS SECTION AREA OF TREE TRUNKS AND TOTAL YIELD
OF FRUIT PER ACRE IN SUMMER COVER CROP EXPERIMENT.
Cover crop Increase in cross Total yield of
Cover crop (air-dried section area of fruit for
top growth) trees in 7 years four years
lbs. per Square Boxes
actual Rank chuare Rank per Rank
acre chesacrel
Crotalaria 1
striata ........ 4969 1 18.89 1 169.5 1
Velvet beans .... 1960 4 15.58 4 114.7 4
Beggarweed ..... 2453 3 16.90 3 135.4 3
Natal grass...... 3403 2 17.78 2 157.2 2
Clean culture .... ... 13.29 5 40.0 5
10n basis of 70 trees per acre.

sistant materials and have in the process of rotting lost their
structure. This "decomposed organic matter" or soil "humus"
influences the color, the water-holding capacity and other soil
properties. It is the seat of the continuance of the life of the
soil, since it furnishes a food supply for the soil microorganisms.
In following the effects of any system of soil management on soil
organic matter, the "decomposed organic matter" or soil "humus"
is usually estimated. The separation of the organic matter into






Florida Agricultural Experiment Station


"decomposed organic matter" and "rough organic matter" is arbi-
trary, but if followed on a series of samples over a number of
years gives comparable results of the effect of any soil manage-
ment system on potential soil fertility.
The "rough or decomposing organic matter" is the plant and
animal materials which are undergoing decomposition in the soil.
These materials have not lost their structure and are in a state
of active decomposition. It is difficult to estimate this type of
organic matter. The course of the decomposition of such materi-
als is usually followed by making periodic determinations of
simple products of the rotting process, such as carbon dioxide
and nitrates.
Soil samples were taken from each of the cover crop plots in
February, 1925, in March, 1929, and in March, 1932. Sub-samples
were taken from three depths in the middle of the squares between
the trees. Nine sub-samples were composite to make the samples
used for analyses. The depths sampled were 0-8 inches, 8-16
inches and 16-24 inches. The samples were taken where the
maximum effects of the cover crop could be detected. Approxi-
mately the same place was sampled in 1925, 1929 and 1932.
The soil samples were air-dried and put through a 2 mm. sieve
to remove large lumps of charcoal and "rough or decomposing
organic matter" such as roots, pieces of undecomposed cover crop,
etc. This is an arbitrary separation but material which will pass
through a 2 mm. sieve is usually well decomposed and has for the
most part lost its structure.
The loss on ignition and the nitrogen content may be used as
measures of the "decomposed organic matter" content. The loss
on ignition gives a satisfactory measure of the organic matter of
sandy soils. The determinations have been carried out by stand-
ard methods. The results are given in Table VIII.
The results indicate a slight decrease in the "decomposed soil
organic matter" of the surface 8 inches of soil from 1925 to 1932,
despite the return of large quantities of rough organic matter in
the form of summer cover crops. However, the clean culture plot
is the only one where the decrease is significant and progressive.
The content of "decomposed organic matter" of the soil of the
cover crop plots is not being decreased to the extent of the clean
culture plot. The nitrogen content of the surface soil is evidently
being maintained by the cover crops. Clean culture has decreased
the original nitrogen content of the surface soil as shown by the
samples taken in 1929 and 1932.







Bulletin 253, Studies on Summer Cover Crops


TABLE VIII.--"DECOMPOSED ORGANIC MATTER" AND NITROGEN CONTENT OF
THE SOIL OF THE SUMMER COVER CROP PLOTS.
fLoss on Ignition Nitrogen pH
Cover crop Deptht 1925 1929 1932 1925 I 1929 1932 1932

linchesI % % % % % %

Crotalaria
striata ...... 0-8 1.084 0.888 0.753 0.024 0.020 0.029 5.04
8-16 0.562| 0.555 0.501 0.012 0.012 0.013 5.21
16-24 0.439| 0.4321 0.416 0.009 0.012 0.0101 5.08
Velvet beans.... 0-8 0.8751 0.667 0.767 0.021 0.015 0.019 4.94
8-16 0.5121 0.492 0.437 0.013 0.012 0.011 4.91
16-24 0.409 0.390 0.403 0.008 0.008 0.009 5.02
Beggarweed ... 0-8 0.9331 0.726 0.883 0.021 0.017 0.022 5.02
8-16 0.515| 0.4711 0.493 0.013 0.012 0.0131 4.95
16-241 0.459| 0.3871 0.3831 0.0111 0.009 0.009 5.02
Cowpea ........ 0-8 0.949 0.771 .. 0.020 0.017 .. 5.17
8-16 0.541 0.507 .. 0.013 0.0131 .. 5.17
16-24 0.4151 0.418 0.010 0.0091 .. 5.04
Natal grass.... 0-8 1.058| 0.813 0.817 0.022 0.019 0.020 5.04
8-16 0.507 0.5471 0.468 0.013 0.013 0.012 5.21
16-24 0.427 0.418 0.416 0.009 0.010 0.010 5.08
Rotated* ...... 0-8 0.8881 0.705 0.809 0.017 0.015 0.019 4.95
S8-16 0.4931 0.484 0.470 0.011 0.011 0.010 4.91
I 16-24 0.441 0.475 0.410 0.010 0.013 0.008 5.04
Clean culture*.. 0-8 0.720 0.645 0.486 0.018 0.014 0.013 4.87
I 8-16 0.439 0.441 0.391 0.014 0.011 0.0111 4.91
S16-24 0.3831 0.378 0.348 0.010 0.009 0.009 4.87

*Single plot.
tLoss on ignition is a measure of the "decomposed organic matter" con-
tent of sandy soils.

The consistency of the analyses of the lower depths of soil for
the different years of the experiment indicated that the soil
samples are comparable. The pH values of aqueous suspensions
of the soil show little variation in the different plots and for dif-
ferent depths in 1932. All the values are below pH 7.00, indi-
cating an acid soil condition.


SUMMARY

Crotalaria striata, velvet beans, beggarweed, cowpeas and natal
grass were compared as summer cover crops in a young pineapple
orange grove on a deep phase Norfolk medium fine sand from
1925 to 1931, inclusive. A part of the grove has been rotated to






Florida Agricultural Experiment Station


the different cover crops. Clean culture has been used on two
plots. Cover crop yields have been measured for each year of
the experiment. The growth of the trees as shown in the cross-
section area of the tree trunks has been measured each year.
Fruit yields have been taken for the years 1928 to 1931, inclusive.
Studies of the soil organic matter were made in 1925, 1929 and
1932.
Crotalaria has given a seven-year average yield of 4,969 pounds
of air-dried top growth per actual acre, velvet beans 1,960 pounds,
beggarweed 2,453 pounds, cowpeas 2,061 pounds, natal grass 3,403
pounds and the rotated crops 2,861 pounds. In attempting to
establish velvet beans, beggarweed and cowpeas, lower yields of
these crops have been obtained than of the volunteer natal grass.
Average yields of crotalaria tops returned to the soil 108 pounds
of nitrogen per acre, velvet beans 39 pounds, beggarweed 29
pounds, cowpeas 34 pounds and natal grass 36 pounds.
The cross-section area of the tree trunks varied very little for
the first four years of the experiment (1925 to 1928, inclusive).
After that time, the average cross-section area of the tree trunks
of the crotalaria plots was the largest, that of the natal grass
plots was the second largest, and that of the clean culture plots
was the smallest. Fruit yields have been largest on the rotated
plot and on the crotalaria plots. In general there is a direct corre-
lation between the quantity of cover crop incorporated with the
soil and the growth of the tree and the fruit yield. A higher
yielding cover crop is reflected in a larger tree and a higher fruit
yield. The decomposed organic matter content of the soil both in
1929 and 1932 was slightly less than that of the virgin soil in 1925.
The nitrogen content of the soil appears to be maintained by the
cover crops. Clean culture has materially reduced the content of
both the decomposed organic matter and nitrogen in the soil.










Summer Cover Crops Studies
are being continued on an enlarged scale at the Citrus Experi-
ment Station, Lake Alfred, Fla. The enlarged experiments
include four varieties of grapefruit, as well as orange trees.
Crotalaria striata is being compared with Crotalaria spec-
tabilis and natal grass. The question of mulching is coming
into prominence throughout the citrus belt. A more exten-
sive mulching test is being included in these revised studies.
Also, variations are being made in the fertilization of the
different blocks.

Every Interested Citrus Grower is Invited to

Visit the Citrus Experiment

Station
at Lake Alfred, Fla.
and see for himself these test plots, as well as numerous
other plots in which are running tests of various fertilizers
and rates of application, rootstocks, cultural methods, disease
and insect control, and other features of interest regarding
citrus. Visitors will be welcome singly or in groups, at
any time.

AGRICULTURAL EXPERIMENT STATIONS
OF THE
UNIVERSITY OF FLORIDA
GAINESVILLE, FLORIDA
WILMON NEWELL, Director

(These Experiment Stations are a part of the College of Agriculture.
The College includes also the Division of Resident Teaching and the
Agricultural Extension Service.)




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