• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Introduction
 Description of lysimeters
 Preliminary experimental proce...
 Experimental results
 Experiments with the decomposition...
 Experimental procedure
 Experimental results
 Summary






Group Title: Bulletin - University of Florida. Agricultural Experiment Station - no. 327
Title: Lysimeter studies with the decomposition of summer cover crops
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027519/00001
 Material Information
Title: Lysimeter studies with the decomposition of summer cover crops
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 44 p. : ill., charts ; 23 cm.
Language: English
Creator: Barnette, R. M
Jones, H. W
Hester, J. B ( Jackson Boling ), 1904-
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1938
 Subjects
Subject: Lysimeter   ( lcsh )
Cover crops -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references.
Statement of Responsibility: by R.M. Barnette, H.W. Jones, and J.B. Hester.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027519
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: aleph - 000924555
oclc - 18214197
notis - AEN5182

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page 1
        Page 2
    Introduction
        Page 3
    Description of lysimeters
        Page 4
    Preliminary experimental procedure
        Page 5
        Page 6
    Experimental results
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
    Experiments with the decomposition of crotalaria striata and natal grass
        Page 14
    Experimental procedure
        Page 14
        Page 15
        Page 16
    Experimental results
        Page 17
        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
    Summary
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






October, 1938


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
WILMON NEWELL, Director





LYSIMETER STUDIES WITH THE

DECOMPOSITION OF

SUMMER COVER CROPS

By
R. M. BARNETTE, H. W. JONES AND J. B. HESTER











,J"


I-7




Fig. 1.-Rougl lemon seedling roots growing in partially decomposed Crotalaria striata stems.


Bulletins will be sent free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


Bulletin 327








EXECUTIVE STAFF

John J. Tigert, M.A., LL.D., President of
the University
Wilmon Newell, D.Sc., Director
Harold Mowry, M.S.A., Asst. Dir., Research
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Editor
Clyde Beale, A.B.J., 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. Ritehey, M.S., Associate2
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant
Roy E. Blaser, M.S., Assistant
ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman'
R. B. Becker, Ph.D., Dairy Husbandman
L. M. Thurston, Ph.D., Dairy Technologist
W. M. Neal, Ph.D., Asso. in Dairy Nutrition
D. A. Sanders. D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
O. W. Anderson, M.S., Asst. Poultry Husb.
W. G. Kirk, Ph.D., Asst, An. Husbandman
R. M. Crown, B.S.A., Asst. An. Husbandman
P. T. Dix Arnold, M.S.A., Assistant Dairy
Husbandman
L. L. Rusoff, M.S., Asst. in An. Nutrition
CHEMISTRY AND SOILS
R. V. Allison, Ph.D.. Chemist'
R. M. Barnette, Ph.D., Chemist
F. B. Smith, Ph.D., Soil Microbiologist
C. E. Bell, Ph.D., Associate
R. B. French, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
J. Russell Henderson, M.S.A., Assistant
L. W. Gaddum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst'
Richard A. Carrigan, B.S., Asst. Chemist
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist'
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist'
Ruth Overstreet, R.N., Assistant
ENTOMOLOGY
J. R. Watson, A.M., Entomologist'
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Spec. Fumigation Res.
R. D. Dickey, B.S.A., Assistant Horticulturist
J. Carlton Cain, B.S.A., Asst. Horticulturist
Victor F. Nettles, M.S.A., Asst. Hort.
PLANT PATHOLOGY
W. B. Tisdale, Ph.D.. Plant Pathologist'
George F. Weber, Ph. D., Plant Pathologist
R. K. Voorhees, M.S., Assistants
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist


BOARD OF CONTROL

R. P. Terry, Chairman, Miami
Thomas W. Bryant, Lakeland
W. M. Palmer, Ocala
H. P. Adair, Jacksonville
Chas. P. Helfenstein, Live Oak
J. T. Diamond, Secretary, Tallahassee

BRANCH STATIONS

NORTH FLORIDA STATION, QUINCY
L. O. Gratz, Ph.D., Plant Path. in Charge
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
Michael Peech, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
W. W. Lawless, B.S., Asst. Horticulturist
EVERGLADES STATION, BELLE GLADE
J. R. Neller, Ph.D., Biochemist in Charge
J. W. Wilson, Sc.D., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane
Physiologist
Jos. R. Beckenbach, Ph.D., Asso. Horticul.
Frederick Boyd, Ph.D., Asst. Agronomist
G. R. Townsend, Ph.D., Asso. Plant Path.
R. W. Kidder, B.S., Animal Husbandman
W. T. Foresee, Ph.D., Asst. Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer2
SUB-TROPICAL STATION, HOMESTEAD
W. M. Fifield, M.S., Asst. Horticulturist
S. J. Lynch, B.S.A., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Asso. Plant Pathologist
W. CENTRAL FLA. STA., BROOKSVILLE
W. F. Ward, M.S., Asst. An. Husbandman
in Charges

FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
K. W. Loucks, M.S., Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
R. N. Lobdell, M.S., Asst. Entomologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
Monticello
Samuel O. Hill, B.S., Asst. Entomologist'
Bradenton
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in Charge,
Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant Pathologist
Lakeland
E. S. Ellison, Meteorologist2
B. H. Moore, A.B., Asst. Meteorologist2

'Head of Department.
'In cooperation with U.S.D.A.
'On leave.









LYSIMETER STUDIES WITH THE DECOMPOSITION

OF SUMMER COVER CROPS

By
R. M. BARNETTE, H. W. JONES' AND J. B. HESTER1

CONTENTS
PAGE
D ESCRIPTION OF LYSIMETERS ...... ..................................... ........................ 4
PRELIMINARY E XPERIMENTAL PROCEDURE ...... .. ......................................................... ...... ...........
E XPERIM EN TAL R ESU LTS ............ .................... ............................... ................. ................... .......... 7
EXPERIMENTS WITH THE DECOMPOSITION OF Crotaaria striata AND NATAL GRASS ................ 14
EXPERIMENTAL PROCEDURE ........................ .................. .. .. .................... .....-....... 14
E XPERIM ENTAL R ESULTS ........................ ... .. ............ ................ .... ............................ ... 17
SU M M ARY ...................................... ..... .............................................. ........................ ........... 38

An adequate summer cover crop is considered essential for an
economical citrus grove management program in Florida. Here,
as a rule, in the summer months there is an abundant supply of
rainfall. Therefore this season is an excellent time for growing
a cover crop without serious competition with the tree for mois-
ture as would be the case in the drier spring, fall and winter
months. The summer cover crops are usually incorporated with
the soil in the late fall months or when the harvest of the citrus
fruits begins.
The many obvious effects of the growing summer cover crop
are fully appreciated by the citrus grower. Thus, the lowering
of the temperature of the soil during the summer months, the
protective action against blowing of the soil and the prevention
of leaching of plant nutrients are recognized generally as benefi-
cial effects. However, the more intricate processes involved in

NOTE: The authors have purposely avoided a review of the extensive
literature on the effects of cover crops and green manuring crops on the
soil and on plant growth. This has been done to keep the bulletin as brief
and clear as possible and thus of more value to the agriculturist. Excellent
and thorough reviews of this extensive literature may be found in "Prin-
ciples of Soil Microbiology," S. A. Waksman: The Williams and Wilkins
Co., 1937; and "Humus: Origin, Chemical Composition and Importance in
Nature." S. A. Waksman: The Williams and Wilkins Co., 1938. Some of
the more practical applications of cover cropping and green manuring are
discussed in "Green Manuring: Principles and Practice." A. J. Pieters:
John Wiley and Sons, Inc., 1927, and in numerous bulletins from the Bureau
of Plant Industry and Soil Conservation Service, U.S.D.A., and the South-
eastern agricultural experiment stations.
IFormerly Assistant Chemists, University of Florida Agricultural Ex-
periment Station, now Assistant Soil Surveyor, Soil Conservation Service,
and Soil Technologist, Campbell Soup Company, respectively.






Florida Agricultural Experiment Station


the decomposition of the cover crops in the soil and their effect
on plant growth are not understood so completely and for this
reason they are especially interesting to the horticulturist.
In this work, small soil tanks or lysimeters have been used to
study the decomposition of cover crops. This method permits
the collection and chemical analyses of the water leaching
through the soil as well as the sampling and chemical analyses
of the soil, cover crops and citrus seedlings grown in the presence
of decomposing cover crops.

DESCRIPTION OF LYSIMETERS
The soil tanks or lysimeters were constructed as shown in
Figure 2. The arrangement of the small tanks, 171/2 inches in
diameter and 26 inches tall, permitted the collection of the leach-
ings in the five gallon carboys below. Small, clean, smooth rocks
prevented the soil from washing from the tanks and no difficulty
was experienced in obtaining clear leachings. The tanks were
placed in the open and, therefore, received the natural rainfall
of this area.


Fig. 2.-Diagram showing arrangement of small lysimeters.






Lysimeter Studies of Summer Cover Crops


The arrangement as shown in the diagram proved to be a very
satisfactory temporary setup for carrying on experiments for a
short period. Two series of studies have been made using this
equipment. The first experiment was an orienting study of the
decomposition of Crotalaria striata and velvet beans. This study
served as a basis for planning the more comprehensive second
experiment on the decomposition of Crotalaria striata and Natal
grass. These experiments will be reported separately.

PRELIMINARY EXPERIMENTAL PROCEDURE
The purpose of the preliminary experiment was to study the
effect of different methods of handling Crotalaria striata and
velvet beans upon their decomposition in the soil, upon the
leachings of rain water, upon the growth of rough lemon seed-
lings, and upon the soil itself. On December 8, 150 pounds of
a well mixed subsoil of a Norfolk medium fine sand were placed
in each of 18 lysimeters. Fifty pounds of surface soil of a Nor-
folk medium fine sand were placed upon this subsoil, filling the
tanks to within about four inches of the top. On December 9,
and on subsequent dates Crotalaria striata and velvet beans were
added to the soil of the tanks in the same manner indicated in
Table 1. Five pounds of the green material were chopped into
small pieces approximately four inches in length and added to
each of the treated tanks. The Crotalaria striata carried 35.5
percent dry matter, and analyzed 2.02 percent nitrogen on the
dry basis. The velvet beans were 32.5 percent dry matter, and
2.86 percent nitrogen on the dry basis. No commercial fer-
tilizing materials were added to the soils at any time during
the experiment.
In lysimeters 3, 4, 11 and 12 the plant materials were allowed
to remain undisturbed on top of the soil during the course of the
experiment. In lysimeters 5, 6, 13 and 14, the fresh materials
were incorporated with the surface six inches of soil. In lysim-
eters 7, 8, 15 and 16 the materials were allowed to lie on top
of the soil from December 9 until January 23, when they were
incorporated 1 to 15 inches deep with a layer of soil over them.
This simulated deep plowing of dry materials. In lysimeters 9,
10, 17 and 18, the materials were allowed to lie on top of the soil
from December 9 until March 2, when they were incorporated
with the six inches of surface soil. This procedure simulated
the incorporation of dry materials in the spring.







Florida Agricultural Experiment Station


TABLE 1.-OUTLINE OF METHODS OF HANDLING COVER CROPS IN
PRELIMINARY LYSIMETER EXPERIMENTS.


Cover
Crop

None





Mature
Crotalaria
striata


Method of Handling Cover Crop

No cover crop or fertilizer
material

Material used as mulch
December 9
Green material incorporated
with surface soil December 9
Dry material incorporated
10 to 15 in. deep January 23
Dry material incorporated
with surface soil March 2


Tank No. Tree Treatment'


3
4
5
6
7
8
9
10


with tree
without tree

with tree
without tree
with tree
without tree
with tree
without tree
with tree
without tree


Material used as mulch 11 with tree
December 9 12 without tree
Green material incorporated 13 with tree
Mature with surface soil December 9 14 without tree
velvet
beans Dry material incorporated 15 with tree
10 to 15 in. deep January 23 16 without tree
Dry material incorporated 17 with tree
with surface soil March 2 18 without tree
'One rough lemon seedling was planted in each alternate lysimeter on March 2.

On March 2 one rough lemon seedling was planted in each al-
ternate lysimeter. Therefore, for each method of handling the
cover crop material there was a lysimeter with a tree and one
without a tree. The rough lemon seedlings were selected for
uniformity and were approximately 18 inches from root tip to
stem tip. There had been no leaching rains up to this time-and
the seedlings were watered well and the tanks leached artificially
but uniformly at this time. All the rough lemon seedlings lived
and made satisfactory growth. The experiment was discon-
tinued 595 days after the addition of the cover crops to the
soils and 512 days after setting the seedlings (July 26).
Whenever a leaching occurred the quantity of water leached
was measured and the nitrates in the leaching were determined
by the phenoldisulphonic colorimetric method.
At the close of the experiment the mulch materials were re-
moved from the surface of the soil, washed and dried at 100 de-
grees Centigrade; the 0 to 9 inch and 9 to 18 inch depths of the


1
2






Lysimeter Studies of Summer Cover Crops


soils were sampled and the rough lemon seedlings were washed
from the soils, dried at 100 degrees Centigrade, and weighed.

EXPERIMENTAL RESULTS
EFFECT OF COVER CROPS AND METHOD OF THEIR INCORPORA-
TION WITH THE SOIL UPON GROWTH OF
ROUGH LEMON SEEDLINGS
The dry weights of the rough lemon seedlings, the percentages
of nitrogen in their leaves and combined stems and roots, and the
total quantities of nitrogen recovered in the seedlings are given
in Table 2.
As may be seen from the data of this table, the addition of
Crotalaria striata and velvet beans greatly increased the dry
weight produced by the rough lemon seedlings. The average dry
weight of all the plants grown with additions of Crotalaria
striata was 273.6 grams, while that of the seedlings grown with
velvet beans was 288.9 grams. These weights are, respectively,
2.73 and 2.88 times the weight of the plants produced in the
absence of the cover crop materials.
The method of handling the cover crop apparently had some
effect on the response of the rough lemon seedlings. Averaging
the weights of the seedlings where the two cover crops were
handled differently gives the following results: cover crops used
as a mulch, 336.7 grams; green cover crops incorporated with the
surface soil, 279.9 grams; dry cover crops incorporated 10 to 15
inches deep, 222.1 grams; dry cover crops incorporated with the
surface soil in the spring, 286.4 grams. Thus the average re-
sults show that the mulching process has produced the largest
plants; deep incorporation of the dry materials, the smallest
plants; and incorporation of the green and dry materials with
the surface soil, intermediate plants.
Percentages of nitrogen in the leaves and in the combined
stems and roots of the rough lemon seedlings do not vary in any
consistent manner with the cover crop treatments. However,
the total nitrogen contained in the seedlings was lowest in the
absence of cover crops. There were also appreciably lower re-
coveries of nitrogen in the case of the deep incorporation of
Crotalaria striata and velvet beans than with the other methods
of handling. There were no consistent variations in the recovery
of nitrogen in the seedlings where other methods of handling
cover crops were used.









TABLE 2.-DRY WEIGHTS AND NITROGEN CONTENT OF ROUGH LEMON SEEDLINGS GROWN WITH Crotalaria striata AND
VELVET BEANS ADDED TO THE SOIL.


Cover Crop



None




Mature
Crotalaria
striata








Mature
velvet
beans


Dry Matter
Roots
Leaves and I Total
Stems I


24.0 76.4 100.4


65.5 293.0 385.5

84.9 201.8 286.7

76.4 125.0 201.4

76.7 170.8 247.5


Method of Handling






Material used as mulch December 9 ....

Green material incorporated with
surface soil December 9 ....................

Dry material incorporated 10 to 15 in.
deep January 23 ..............................

Dry material incorporated with
surface soil March 2 ....................


Material used as mulch December 9 ....

Green material incorporated with
surface soil December 9 ......................

Dry material incorporated 10 to 15 in.
deep January 23 .................. ............

Dry material incorporated with
surface soil March 2 ........................


314.9

273.1

242.7

325.2


Nitrogen
Roots
Leaves and
Stems


Total Nitrogen
Roots
Leaves and Total
Stems
g g g
0.29 0.46 0.75


1.00 1.41 2.41

1.29 1.45 2.74

1.01 0.73 1.74

1.00 1.29 2.29


224.0

181.8

165.0

231.2







Lysimeter Studies of Summer Cover Crops


EFFECT OF METHOD OF INCORPORATION OF Crotalaria striata AND
VELVET BEANS WITH THE SOIL UPON THE
LEACHING OF WATER

The drainage water percolating through each lysimeter after
a heavy rain was measured carefully. Total amounts of rain
water that leached are given in Table 3.
TABLE 3.-TOTAL QUANTITY OF WATER AND PERCENTAGE OF TOTAL RAIN-
FALL LEACHING THROUGH LYSIMETERS WITH Crotalaria striata AND
VELVER BEANS HANDLED BY DIFFERENT METHODS.

Total Percentage of
Cover Method of Handling -- Leaching Total Rain
Crop No No
Tree Tree Tree Tree
L. L. % %
None 152.7 174.7 39.4 45.1

Material used as mulch
December 9 .................................. 165.9 202.0 42.8 52.1
Green material incorporated
Mature with surface soil December 9.... 145.5 184.1 37.5 47.5
Cratalaria
striata Dry material incorporated
10 to 15 in. deep January 23 .... 134.7 180.5 34.8 46.6
Dry material incorporated
with surface soil March 2 ........ 139.8 174.5 36.1 45.0

Material used as mulch
December 9 ................................ 145.1 214.9 37.4 55.5
Green material incorporated
Mature with surface soil December 9.... 148.9 190.1 38.4 49.1
velvet
beans Dry material incorporated
10 to 15 in. deep January 23 .... 133.9 192.3 34.6 49.6
Dry material incorporated
with surface soil March 2 ........ 129.0 167.5 33.3 43.2
Total rain falling on tank was 387.5 liters or 98.27 inches.

In the series of lysimeters with trees there was no consistent
variation in the leaching which could be attributed to the differ-
ent methods of handling the cover crops. The percentage of the
total rainfall which leached in the tree series varied from 33.3
percent to 42.8 percent in the different lysimeters.
In the series without trees, the use of Crotalaria striata and
velvet beans as mulches increased materially the quantity of
water leached over that obtained from the soil without additions
of cover crop materials. The incorporation of the green mate-






Florida Agricultural Experiment Station


rials and the deep incorporation of the dry materials increased
the leaching of water somewhat but not nearly to the extent of
their use as mulches. The incorporation of the dry materials
with the surface soil had little or no effect on the leaching of
rain water. The larger quantities of water leached from the
mulched tanks with trees indicated a conservation of water in
the soils due to decreased surface evaporation.
RATE OF NITRATE FORMATION FROM Crotalaria striata AND VEL-
VET BEANS AS MEASURED BY LEACHING OF NITRATES
FROM THE SOILS WITHOUT TREES
The lysimeters without rough lemon seedlings served as a
basis for arriving at the rate of nitrate formation from Crota-
laria striata and velvet beans as measured by the leachings of
nitrates during the months subsequent to treatment of the soils
with cover crops. The cumulative monthly leachings of nitrates
from the lysimeters without trees are shown graphically in Fig-
ure 3. The results are expressed in grams of nitrate nitrogen
leached by months from March to July 29, the quantity leached
each month being added to the previous quantities leached.
There was no leaching of nitrates from December until March.
Leachings of nitrates subsequent to March increased rapidly
from all the lysimeters having cover crops. Leachings of nitro-
gen as nitrates from the soils to which cover crop materials had
been added were very much larger than from the soil without
cover crop materials. The incorporation of green cover crops
with the surface soil and the deep incorporation of the dry mate-
rial showed a larger leaching of the nitrates during the months
immediately following March than did the use of the cover crops
as mulch or the surface incorporation of dry materials. That
the differences in the quantities of nitrates leached is not due to
the quantity of water leached but to the actual quantities of ni-
trate formed from the cover crops may be seen in Table 3, in
which the amounts of leachings are given. Thus the time for
maximum rate of nitrification of the nitrogenous compounds of
the cover crops is extended approximately two months by the
use of the materials as a mulch or by the incorporation of the
dry materials with the surface soil. Under the conditions of this
experiment, this extended period of formation of nitrates evi-
dently has reacted favorably on tree growth, as the soils which
were mulched and those which had the dry material incorporated
with the surface soil in the spring produced the largest seed-
lings.







Lysimeter Studies of Summer Cover Crops


6 0 '- >z 'd a > z

Fig. 3.-Graphs showing the accumulative monthly leaching of nitrogen as nitrates
from Norfolk fine sand used in lysimeter studies with the decomposition of velvet beans and
Crotalaria striata.

EFFECT OF COVER CROPS UPON LOSS ON IGNITION AND
NITROGEN CONTENT OF THE SOIL
In this paper the term "organic matter" is understood to mean
all plant and animal parts found in the soil regardless of their
stage of decomposition. This organic matter includes both the
plant and animal parts in the process of decomposition in the
soil as well as the more decay-resistant materials which have lost
their original structure and have become intimately admixed
with the soil. It is easy to understand that the transition of the






Florida Agricultural Experiment Station


plant and animal parts from their original forms to well decom-
posed materials without recognizable structure is so gradual in
a soil that any method of separation is more or less arbitrary.
However, such a separation even though arbitrary is desirable
in certain studies with the soil.
In this study the separation was made mechanically by screen-
ing the soil through a 2 mm. round hole sieve. The sand and the
small particles of well decomposed organic matter of most Flor-
ida soils are sufficiently fine to pass very readily through this
sieve. The portion remaining on the sieve is made up of coarse
materials in the process of decomposition, and of debris. These
include plant roots, cover crop parts and other crude organic
materials in the soil. If the cover crop residues are to be studied
under these conditions they must be separated from the roots of
the recently grown plants, from large lumps of charcoal and
from small pebbles and stones which are sometimes present in
the soil. This portion of the soil organic matter may be desig-
nated as the "rough organic matter" or the "organic matter in
an active stage of decomposition."
In this preliminary study the soil to which the cover crops
had been added was carefully sampled at the 0 to 9 inch and the
9 to 18 inch depths. The samples were air-dried and screened
through a 2 mm. round-hole sieve. The residues on the sieve
were discarded and analyses were confined to the soil passing
through the sieve. The soil samples were carefully pulverized in
an agate mortar and pestle power mill before analysis.
The loss on ignition is considered a reliable measure of the
quantity of organic matter present in sandy soils. Loss on igni-
tion and total nitrogen content of the soil samples were de-
termined. Averaged results of duplicate determinations on the
soils of the lysimeters are given in Table 4.
The total organic matter content of both depths of soil was
very slightly increased by the addition of the large quantities of
Crotalaria striata and velvet beans. The nitrogen content of the
soil was not materially affected by the addition of the cover crops.
When it is considered that Crotalaria striata was added at the
rate of approximately 23 tons of dry material per acre and the
velvet beans at the rate of 21 tons per acre, it is surprising that
there was so little effect upon the well decomposed organic mat-
ter content of the soil. The method of incorporation of the
cover crops with the soil apparently has had no definite effect on
the organic matter content of the soil.







Lysimeter Studies of Summer Cover Crops


TABLE 4.-Loss ON IGNITION AND NITROGEN CONTENTS OF SOILS TO WHICH
COVER CROPS HAD BEEN ADDED.

Loss on Nitrogen
Cover Method of Handling Ignition
Crop 0-9 9-18 I 0-9 9-18
inches inches I inches inches
% % % %
None 1.871 1.384 0.038 0.026

Material used as mulch
December 9 .................................. 1.979 1.432 0.039 0.028
Green material incorporated
Mature with surface soil December 9..- 1.885 1.719 0.036 0.031
Crotalaria
striata Dry material incorporated
10 to 15 in. deep January 23 .. 1.941 1.738 0.037 0.029
Dry material incorporated
with surface soil March 2 ........ 2.062 1.724 0.042 0.022

Material used as mulch
December 9 ............-- ................. 1.960 1.679 0.043 0.022
Green material incorporated
Mature with surface soil December 9.. 2.162 1.846 0.044 0.029
velvet
beans Dry material incorporated
10 to 15 in. deep January 23 .... 1.898 1.618 0.033 0.029
Dry material incorporated
__ with surface soil March 2 .... 2.051 1.758 0.044 0.031

The Crotalaria striata and velvet beans used as a mulch were
carefully collected from the surface soil, washed, dried, and
analyzed for nitrogen. The results of the analyses are given
in Table 5.
These results emphasize the rapidity of decay of cover crops
even when used as a mulch on Florida soils. The period of de-
composition of the mulches was approximately 1 year and 8
months. During this period 78.0 percent of the dry matter of
Crotalaria striata and 74.2 percent of the dry matter of velvet
beans had undergone decomposition. This decomposition had
been accompanied by a transfer of 84.7 and 78.2 percent of the
nitrogen of crotalaria and of the velvet beans, respectively. The
nitrogen compounds had for the most part been washed into the
soil underneath the mulch and either used by the rough lemon
seedlings or leached from the soil. Prevailing high temperatures,
favorable moisture conditions, and thorough aeration of the well
drained soils in Florida are contributing factors to the rapid de-
composition of organic materials added to the soils.






Florida Agricultural Experiment Station


TABLE 5.-QUANTITIES AND NITROGEN CONTENT OF COVER CROPS
REMAINING AS MULCH AFTER DECOMPOSITION PERIOD.

Original Residue Percentage
Material Used Material Liberated
as Mulch Dry DryI Dry
Matter N Matter N Matter N
g. % g. % % %
805 2.02 197 1.48 75.5 82.1
Crotalaria striata 157 1.31 80.5 87.4
Average ........... 177 1.39 78.0 84.7
737 2.86 171 2.09 76.8 83.1
Velvet beans 209 2.69 71.7 73.3
Average............ 190 2.39 74.2 78.2

EXPERIMENTS WITH THE DECOMPOSITION OF
Crotalaria striata AND NATAL GRASS

From the preliminary experiment it is evident that the in-
corporation of the cover crop with the surface soil or the use of
the cover crop as a mulch offers some advantages. The light in-
corporation with the surface soil is by far the most generally
used method of handling cover crops in Florida. The practice of
mulching offers the disadvantage of a fire hazard and is, there-
fore, used to a limited extent only. However, considerable inter-
est is manifested in this system of management of the cover
crop. For this reason these two systems have been compared
more extensively.
The soil tanks described previously were used to study the de-
composition of Crotalaria striata and Natal grass. Large appli-
cations of these two cover crops were used so that sufficient
materials might be available for chemical analyses. For this
reason the results of the experiment may not be applied directly
to grove conditions, but at the same time many apparently very
fundamental relationships between cover crop decomposition,
tree growth and leaching of plant nutrients were studied.

EXPERIMENTAL PROCEDURE
Each lysimeter was filled with 250 pounds of moist Norfolk
fine sand on October 23. The soil in the tanks was allowed to
stand undisturbed, leach, and become settled until February 27
of the following year, when 10 of the tanks were set to rough
lemon seedlings of uniform size with an average green weight of






Florida Agricultural Experiment Station


TABLE 5.-QUANTITIES AND NITROGEN CONTENT OF COVER CROPS
REMAINING AS MULCH AFTER DECOMPOSITION PERIOD.

Original Residue Percentage
Material Used Material Liberated
as Mulch Dry DryI Dry
Matter N Matter N Matter N
g. % g. % % %
805 2.02 197 1.48 75.5 82.1
Crotalaria striata 157 1.31 80.5 87.4
Average ........... 177 1.39 78.0 84.7
737 2.86 171 2.09 76.8 83.1
Velvet beans 209 2.69 71.7 73.3
Average............ 190 2.39 74.2 78.2

EXPERIMENTS WITH THE DECOMPOSITION OF
Crotalaria striata AND NATAL GRASS

From the preliminary experiment it is evident that the in-
corporation of the cover crop with the surface soil or the use of
the cover crop as a mulch offers some advantages. The light in-
corporation with the surface soil is by far the most generally
used method of handling cover crops in Florida. The practice of
mulching offers the disadvantage of a fire hazard and is, there-
fore, used to a limited extent only. However, considerable inter-
est is manifested in this system of management of the cover
crop. For this reason these two systems have been compared
more extensively.
The soil tanks described previously were used to study the de-
composition of Crotalaria striata and Natal grass. Large appli-
cations of these two cover crops were used so that sufficient
materials might be available for chemical analyses. For this
reason the results of the experiment may not be applied directly
to grove conditions, but at the same time many apparently very
fundamental relationships between cover crop decomposition,
tree growth and leaching of plant nutrients were studied.

EXPERIMENTAL PROCEDURE
Each lysimeter was filled with 250 pounds of moist Norfolk
fine sand on October 23. The soil in the tanks was allowed to
stand undisturbed, leach, and become settled until February 27
of the following year, when 10 of the tanks were set to rough
lemon seedlings of uniform size with an average green weight of







Lysimeter Studies of Summer Cover Crops


14.5 grams each. Five grams of commercial nitrate of soda
were applied to each tank previous to setting the seedlings. On
May 15 each tank received 5 grams of nitrate of soda, 8 grams
of diammonium phosphate and 5 grams of potassium sulfate.
The seedlings were allowed to grow until February 9 following,
when the cover crop experiment was started. The soil of the
tanks without trees was undisturbed but received the same
fertilizer treatments. The leachings were collected and meas-
ured after each rain during this period, and the nitrate nitrogen
content of each was determined.
On February 9 additions of the cover crop and fertilizer mate-
rials as indicated in Table 6 were made to the soil in the various
tanks. The Crotalaria striata and Natal grass used were mature,
air-dried plants. The dried materials were cut into approxi-
mately 4-inch lengths before being incorporated with the soil
or used as a mulch on the surface of the soil.

TABLE 6.-COVER CROP MATERIALS AND FERTILIZERS ADDED TO THE SOILS
OF THE SMALL LYSIMETERS.


Amount and
Handling of
Cover Crop

2 lbs. incorporated
with surface soil


2 lbs. used as mulch
on surface


1 lb. incorporated
with surface soil


1 lb. used as mulch
on surface


Tank
No.

1
2
3
4

5
6
7
8

9
10
11
12

13
14
15
16

17
18
19
20


Fertilizer Treatment

10 g. superphosphate
2 g. potassium sulfate


10 g. superphosphate
2 g. potassium sulfate


5 g. sodium nitrate
10 g. superphosphate
2 g. potassium sulfate

5 g. sodium nitrate
10 g. superphosphate
2 g. potassium sulfate

5 g. sodium nitrate
10 g. superphosphate
2 g. potassium sulfate


Cover
Crop


Dry
mature
Crotalaria
striata






Dry
mature
Natal
grass


No
cover
crop


Following addition of the cover crop materials to the soil, the
leachings after each rain were carefully measured and the nitrate
nitrogen was determined by the phenoldisulphonic acid colori-






Florida Agricultural Experiment Station


metric method and the potassium by the cobaltic nitrite method.
One hundredth part of each leaching was saved for a composite
sample for more detailed analyses.
Nitrate of soda at the rate of 2.5 grams per tank was added to
the soil of all tanks on April 2 and June 8 of the following year.
On August 31 the experiment was discontinued, after having
run more than 18 months. At this time, samples of the rough
lemon seedlings, the residues of the cover crops, of soils and
leachings were collected for partial chemical analyses.
Tops of the rough lemon seedlings were removed at the soil
level and leaves were stripped from stems and branches. The
larger roots were collected and later when the soil was screened
the smaller roots were separated from the residue on the screen
and combined with the larger roots. The roots were washed as
free as possible from adhering sand. The plant parts were dried
at 100 degrees Centigrade and the dry weights obtained. The
entire sample of the plant parts was ground for analyses. Stand-
ard methods for plant analyses were used.
The residues of the cover crops used as a mulch on the sur-
face of the soil were carefully removed, dried and weighed. Resi-
dues of the cover crops which had been incorporated with the
surface soil were collected by screening the entire soil mass of
the 0 to 6 inch depth through a 2 mm. round-hole sieve. The
residues consisted of the larger pieces of the undecomposed cov-
er crops, the small roots of the rough lemon seedlings, the larger
lumps of charcoal and the undecomposed organic materials of the
original soil with small pebbles. The larger pebbles were re-
moved and the conglomerate mixture washed three times by
flotation on a 1 mm. round-hole screen placed in a large porcelain
dish of such size as to permit the lighter material to float around
in the screen but not to be carried off by the water. Most of the
fine sand adhering to the cover crop residues was removed in
this manner. The materials were removed from the screen and
dried in the air. The cover crop residues were separated from
the small roots, charcoal and other materials. A small paint
brush was used in this separation. The separated residues of
the cover crops were dried at 100 degrees Centigrade, weighed
and prepared for analyses.
The air-dried soil which had been screened through the 2 mm.
round-hole sieve was thoroughly mixed, quartered, and sampled.
The 6 to 13 and 13 to 20 inch depths were also removed separ-
ately, screened and sampled.






Lysimeter Studies of Summer Cover Crops


A composite sample of the leachings from each of the lysim-
eters was obtained by taking one hundredth part by volume
of the individual leachings.
Very few modifications of the standard methods for making
the chemical analyses were used. The wet combustion method
developed by Adams1 was used for the carbon determinations.

EXPERIMENTAL RESULTS
EFFECT OF COVER CROPS ON GROWTH AND COMPOSITION OF
ROUGH LEMON SEEDLINGS
The dry weight of the leaves, stems, branches and roots of the
rough lemon seedlings grown in the lysimeters are given in Table
7. The incorporation of the Crotalaria striata with the surface
soil produced the largest seedlings while the use of this material
as a mulch produced the second largest. The use of the large ap-
plication of Natal grass both incorporated with the surface soil
and as a mulch produced smaller seedlings than the use of no
cover crop material. The smaller growth of the seedlings in the
presence of large quantities of a decomposing non-leguminous
cover crop is in keeping with experimental and practical obser-
vations on the use of such materials.
The detrimental influence of the mature non-leguminous Natal
grass on the plant growth may be attributed to competition of
the soil microorganisms for nitrogen in the early stages of de-
composition. The Natal grass used in this experiment had 0.749
percent nitrogen and 39.000 percent carbon, or a ratio of nitro-
gen to carbon of 1:52.87. During the early stages of decompo-
sition of such material, nitrogen compounds are not released to
the growing plants, as the microorganisms are successful com-
petitors for the nitrogen of the soil since they require more
nitrogen for their metabolic processes than is available in the
materials.
The leaves of the rough lemon seedlings growing in the pres-
ence of decomposing Natal grass turned yellow at times, necessi-
tating the application of nitrate of soda. The superior growth of
the rough lemon seedlings in the presence of the decomposing
Crotalaria striata may be attributed partially to a larger supply
of nitrogen. Nitrates were formed from the crotalaria soon after
its addition to the soil, as shown by the analysis of the leachings.
The nitrates formed from the crotalaria became available to the
'Adams, J. E., "Determinatiou of the total carbon in soils by the wet
oxidation method," Industrial and Engineering Chemistry, Analytical
Edition: 6: 277-279. 1934.







Florida Agricultural Experiment Station


rough lemon seedlings over an extended period. Comparison of
analyses of leachings from lysimeters with and without seed-
lings showed that these nitrates were readily taken up by the
young trees.
TABLE 7.-DRY WEIGHTS OF ROUGH LEMON SEEDLINGS GROWN WITH Cro-


talaria striata AND NATAL GRASS
SOIL AND USED AS A MULCH.


Cover
Crop




Dry
mature
Crotalaria
striata




Dry
mature
Natal
grass


No
cover
crop


Method of
Handling
Cover Crop

Incorporated
with
surface soil


Mulch


Incorporated
with
surface soil


Mulch


Tank
No.


1
2
Average

5
6
Average

9
10
Average

14

17
18
Average


INCORPORATED WITH THE SURFACE


Dry Weight of Plant Part
Stem and I
Leaves Branches Roots Total
g. g. g. g.
64 216 120 400
69 227 135 431
66 222 128 416

45 154 91 290
66 192 114 372
56 173 102 331

38 122 74 234
32 139 70 241
35 131 72 238

27 115 64 206

41 152 86 279
44 158 111 313
43 155 98 296


Percentages of nitrogen, potassium, phosphorus and calcium in
the leaves, stems and roots of the rough lemon seedlings grown
in the lysimeters are given in Table 8.
Average percentages of nitrogen in the dry matter of the rough
lemon seedlings were 1.794, 0.895, and 0.547 for the leaves, roots,
and stems, respectively. All plant parts had a higher percentage
of nitrogen when grown with the cover crops. The higher per-
centages of nitrogen in the seedlings grown with crotalaria may
be attributed to the greater supply of nitrogen added as crota-
laria. The higher percentages in the seedlings of the Natal grass
cultures may be attributed to the availability of nitrogen during
the late stages of decomposition of the grass.
The average percentages of phosphorus in the dry matter of
the rough lemon seedlings were 0.289, 0.196, and 0.111 for leaves,
roots and stems, respectively. Variations in the percentages of











TABLE 8.-PERCENTAGES OF NITROGEN, PHOSPHORUS, POTASSIUM AND CALCIUM IN THE LEAVES, STEMS AND ROOTS OF ROUGH
LEMON SEEDLINGS GROWN IN SMALL LYSIMETERS.


Cover Crop and
Method of Nitrogen
Handling Leaves Stems I
% %
Crotalaria striata 1.847 0.580
incorporated

Crotalaria striata 1.777 0.575
mulch

Natal grass 1.897 0.555
incorporated

Natal grass 1.861 0.560
mulch

No cover crop 1.588 0.465


Average 1.794 0.547


Phosphorus Potassium Calcium
Roots Leaves Stems I Roots ILeaves Stems Roots ILeaves I Stems
% 0 % % % % % % %
0.973 0.275 0.113 0.129 1.425 0.491 0.282 2.964 0.761


0.889 0.286 0.123 0.169 1.512 0.574 0.278 2.701 0.651


0.909 0.292 0.109 0.238 2.366 0.933 0.379 1.859 0.507


0.868 0.312 0.106 0.249 2.421 0.935 0.383 2.113 0.543


0.835 0.278 0.104 0.196 1.205 0.446 0.227 3.609 0.833


0.895 0.289 0.111 0.196 1.786 0.676 0.309 2.649 0.659


Roots
%
0.782


0.733


0.867


1.015


0.945


0.868


----






Florida Agricultural Experiment Station


phosphorus in the leaves and stems of the seedlings were not sig-
nificant. The highest percentage of phosphorus in the roots was
found in the seedlings grown with Natal grass, the lowest in the
roots of plants grown with crotalaria, while the roots of the
plants without cover crop additions occupied an intermediate po-
sition.
Average percentages of potassium in the dry matter of the
rough lemon seedlings were 1.786, 0.676, and 0.309 for the leaves,
roots and stems, respectively. Seedlings grown with Natal grass
had much higher percentages of potassium in all plant parts
than those grown with Crotalaria striata or without the addition
of cover crop materials.
Likewise, the percentages of potassium in various parts of the
seedlings of the crotalaria cultures were higher than those in the
seedlings grown without the addition of cover crop materials.
Average percentages of calcium in the dry matter of the rough
lemon seedlings were 2.649, 0.868, and 0.659 for leaves, roots
and stems, respectively. The highest percentages of calcium
were found in the seedlings without cover crop additions, with
the exception of the roots of plants grown with the Natal grass
mulch. Percentages of calcium in leaves and stems of plants
grown with Crotalaria striata were substantially higher than
those grown with Natal grass.
PERCENTAGE OF ORGANIC MATTER, NITROGEN AND CARBON
IN COVER CROPS BEFORE AND AFTER DECOMPOSITION
Organic matter, nitrogen and carbon contents of samples of
the original cover crop materials, and of residues at the end of
the experiment, were determined. Percentages of these plant
constituents liberated from the original cover crops were calcu-
lated from the weights and analyses of the materials. Results
of the analyses and calculations are given in Table 9. The chemi-
cal analyses were calculated on a silicon dioxide and sand free
basis because of the very great variability of the sand content in
the materials used as a mulch or incorporated with the soil. The
period of decomposition which the cover crops underwent was
from February 9 one year to August 31 of the next, or 569 days.
The change in composition of the cover crops after their addi-
tion to the soil is interesting. The percentage of organic mat-
ter in the residues of the cover crops, whether incorporated with
the soil or used as a mulch, was slightly lower than that of the
original materials, but hardly significant. Residues of both
Crotalaria striata and Natal grass increased in percentage of






Lysimeter Studies of Summer Cover Crops


nitrogen over the original materials. At the end of the period
of decomposition these residues had a practically constant per-
centage of nitrogen of approximately 1.8 percent, regardless of
the original material and the method of handling. The percent-
age of carbon in the original crotalaria sample was 41.210 and in
the Natal grass 39.000. These percentages remained virtually
unchanged in the residues of these materials after decomposi-
tion in the soil or use as a mulch.
The carbon-nitrogen ratio of the original Crotalaria striata
was 31.030 and that of Natal grass was 52.870. After decom-
posing in the soil or as a mulch, residues of these two cover crops
had a practically constant carbon-nitrogen ratio varying only
from 22.010 to 23.610. Thus, through decomposition processes
taking place in the soil these two materials with a widely diver-
gent carbon-nitrogen ratio, were brought to practically the same
percentage composition with regard to nitrogen and carbon.
However, during this period of decomposition a very large
part of the organic material added to the soil in the form of
cover crops had been oxidized. For Crotalaria striata incor-
porated with the surface soil, 87.550 percent of the organic mat-
ter, 82.537 percent of the nitrogen and 87.450 percent of the car-
bon applied in the material had been oxidized. The values of
the Crotalaria striata used as a mulch were lower, being 72.200
percent for the organic matter, 63.064 for the nitrogen and 72.350
percent for the carbon. The corresponding values for the Natal
grass incorporated with the soil were 95.930 percent for the or-
ganic matter, 91.626 for the nitrogen, and 96.260 percent for the
carbon; and for the Natal grass used as a mulch, 74.880 percent
for the organic matter, 36.597 for the nitrogen, and 73.936 for
the carbon. Thus, the use of Crotalaria striata and Natal grass
as a mulch has definitely decreased the rates of decomposition
of the organic constituents of these materials. However, the
analyses show that the residues had about the same percentages
of organic matter, nitrogen and carbon regardless of the method
of handling.
PERCENTAGE OF CALCIUM, PHOSPHORUS AND POTASSIUM IN
COVER CROPS BEFORE AND AFTER DECOMPOSITION
Calcium, phosphorus and potassium in the cover crops and in
their residues were determined by standard methods for plant
analysis. From these analyses and from weights of cover crops
added to the soil, and of residues in the soil at the end of the
period of decomposition, percentages of these elements which













TABLE 9.-PERCENTAGES OF ORGANIC MATTER, NITROGEN AND CARBON IN ORIGINAL COVER CROP MATERIALS AND IN THEIR
RESIDUES AFTER PARTIAL DECOMPOSITION.
____________________---- ---------------------.------------------------ 0.
Percentage Composition' Percentage Liberated' s
Crotalaria striata Natal Grass
Constituent I I Crotalaria striata Natal Grass
Original Residue Original Residue I
Material Incor- Material Incor- Incor- Incor- c
porated 1 Mulch porated Mulch porated Mulch porated Mulch


Organic matter 96.694 94.264 95.189 96.068 91.890 87.550 72.200 95.930 74.880


Nitrogen 1.328 1.864 1.765 0.749 1.540 1.891 82.537 63.064 91.626 36.597 ,


Carbon 41.210 41.560 41.000 39.000 36.360 41.620 87.452 72.350 96.260 73.936


C/N ratio 31.030 22.300 23.230 52.870 23.610 22.010

2Average of quadruplicate samples calculated on SiO2 and sand free basis except for incorporated Natal grass.
2Determined from weight of materials and percentage composition, on a dry basis.






Lysimeter Studies of Summer Cover Crops


had been removed from the cover crops during the period of de-
composition were calculated. Results of chemical analyses and
of calculations are given in Table 10. The results were calcu-
lated on a silicon dioxide and sand free basis because of the great
variation in the sand content of the residues.
Percentages of calcium in the residues of both Crotalaria stri-
ata and Natal grass were very substantially higher than those in
the undecomposed plants. Percentages of phosphorus in the
residues of crotalaria were lower than in the original material
while the residue of the Natal grass mulch had a higher percent-
age of phosphorus than the original material. Percentages of
potassium in the residues were much lower than percentages
found in the original plant materials.
Of the calcium contained in the original sample of Crotalaria
striata, 75.421 percent was liberated by incorporation with soil
and 51.248 percent by mulching; of the phosphorus, 93.539 per-
cent by incorporation with the soil and 88.625 percent by mulch-
ing; of the potassium 96.188 percent by incorporation with the
soil, and 90.840 percent by mulching. Thus, the use of Crotalaria
striata as a mulch has materially decreased the rate of liberation
of calcium, phosphorus and potassium in comparison with the
incorporation of the material with the soil. There was not
enough residue of the Natal grass incorporated with the soil to
make the partial analysis; however, the Natal grass used as a
mulch showed a slight gain in calcium, a liberation of 47.502
percent of the phosphorus, and 96.107 percent of the potassium
contained in the undecomposed material.
It is evident that the oxidation of such large quantities of
organic matter and the liberation of the mineral constituents
from the organic matter must exert a definite influence not
only upon tree growth but also upon the leaching of plant
nutrients from the soil.
TOTAL QUANTITIES OF WATER AND CONCENTRATION OF
NITROGEN, POTASSIUM AND CALCIUM IN WATER
LEACHED FROM SOILS
Total quantities of water leaching through the lysimeters were
determined by adding together the volumes of the individual
leachings. Total nitrogen leached as nitrates was determined
by adding the grams of nitrogen removed by the individual per-
colates; amounts of potassium and calcium by analysis of com-
posite samples of the leachings.















TABLE 10.-PERCENTAGES OF CALCIUM, PHOSPHORUS AND POTASSIUM IN COVER CROPS BEFORE AND AFTER DECOMPOSITION
AND PERCENTAGE LIBERATED BY DECOMPOSITION.


Percentage Composition' Percentage Liberated'
Crotalaria striata Natal Grass
SR Crotalaria striata Natal Grass
Original Residue Original Residue
Material Incor- Material Incor- Incor- Incor-
poratedI Mulch porated Mulch porated Mulch porated Mulch
% % % % % % % % % %
0.759 1.499 1.331 0.339 1.657 75.421 51.248 Gain


0.489 0.254 0.200 0.212 0.444 93.539 88.625 -47.502


0.297 0.093 0.098 0.728 -- 0.112 96.188 90.840 96.107


'Average of quadruplicate samples calculated on Si02 and sand free basis.
2Determined from weight of materials and percentage composition.


Constituent




Calcium


Phosphorus


Potassium






Lysimeter Studies of Summer Cover Crops


Total volume of water leached and concentrations of nitrogen,
potassium and calcium in the leachings, expressed as parts per
million, are tabulated in Table 11.
In these experiments the air-dried Crotalaria striata was ap-
plied at the rate of approximately 26 tons per acre, and Natal
grass at 13 tons per acre. As may be seen from the volumes of
water leached from the tanks, these amounts of rough organic
matter have influenced definitely the water relationships in the
soil. The leachings from the tanks without trees show that in
every instance the incorporation or use as a mulch of such large
quantities of organic matter increased very materially the vol-
ume of water leached. The smaller application of Natal grass in-
creased the volume of leaching more than Crotalaria striata.
This may be attributed to the physical properties of the Natal
grass; for example, its fine, easily matted leaves and stems form
a more effective mulch in comparison with the easily decomposed
leaves and large woody stems of the crotalaria.
The use of Crotalaria striata as a mulch did not increase the
volume of water leached more than its incorporation with the
surface soil. Leaves and small stems of crotalaria decomposed
rapidly and soon left only the larger, more decay-resistant,
woody stems on the soil surface. These were not effective in re-
ducing evaporation from the surface of the soil. On the other
hand, the interlacing of the fine stems and leaves of the Natal
grass formed an excellent mulch on the surface of the soil and
materially reduced evaporation.
That this change in the water relationships in the soil may
have been a contributing factor in the influence exerted by the
cover crop materials on plant growth is indicated by the data
obtained from the cultures growing seedlings. Crotalaria striata,
incorporated with the surface soil or used as a mulch, produced
the largest seedlings of the experiment. The vigorous seedlings
in these cultures had a greater supply of available moisture than
those growing without the addition of cover crops as shown by
the leachings from the lysimeters without seedlings. That the
seedlings in the crotalaria treated soil used this moisture is
shown by the volumes of leachings which were not significantly
greater from these tanks than from the tanks without cover
crops. On the other hand, the poor growth conditions in the
soils treated with Natal grass resulted in small plants and a poor
utilization of the conserved water, with a greater leaching of
water in these tanks as compared to that obtained from the cul-
tures without cover crops.













TABLE 11.-ToTAL QUANTITIES OF WATER LEACHED AND THE CONCENTRATIONS OF NITROGEN AS NITRATES, POTASSIUM AND
CALCIUM IN LEACHINGS OF SOILS WITH Crotalaria striata AND NATAL GRASS INCORPORATED WITH THE SURFACE SOIL AND
USED AS A MULCH.

Liters of Water p.p.m. of N as p.p.m. of K p.pm. of Ca
Cover Crop Method of Leached Nitrate in Leaching in Leaching in Leaching
Handling Without With Without With Without With Without I With
S_ _Seedling Seedling Seedling Seedling Seedling Seedling Seedling I Seedling

Dry Incorporated with 121.6 62.8 38.5 5.2 11.4 1.3 53.4 31.2
mature surface soil
Crotalaria
strata Used as mulch 120.9 67.6 30.8 1.9 13.9 1.2 43.2 23.9


Dry Incorporated with 138.8 76.4 19.6 6.1 14.8 1.7 29.8 23.8
mature surface soil
Natal
grass Used as mulch 145.3 108.8 16.8 6.4 11.6 1.0 27.0 21.8

No cover crop 86.7 64.4 27.6 7.5 6.4 0.6 40.4 25.0






Lysimeter Studies of Summer Cover Crops


If the rough lemon seedlings had been without effect upon the
concentration of plant nutrients in the leachings, the smaller
leachings from the cultures with seedlings would have contained
higher concentrations of these nutrient elements for any given
cover crop treatment. However, the results obtained show that
this has not been the case. In every instance the concentrations
of nitrate nitrogen, potassium and calcium were very much
larger in the leachings from the cultures without seedlings. This
indicates a very definite absorption and utilization of these nu-
trient elements by the seedlings.
Concentration of the nitrate nitrogen in leachings from the
lysimeters without trees was highest from the soils in which
Crotalaria striata had been incorporated and next highest where
it had been used as a mulch. The concentration of nitrate nitro-
gen from the soil without any cover crop additions was substan-
tially higher than that from the soil to which Natal grass had
been added. This lower concentration of nitrate nitrogen from
the Natal grass cultures resulted partially from the larger vol-
umes of water leached through these tanks and partially from
a transitional fixation of nitrogen during the early decomposition
of the non-leguminous grass with a low nitrogen content.
The concentration of nitrate nitrogen in leachings from tanks
with seedlings was highest from soils without cover crop addi-
tions and lowest in leachings from tanks where Crotalaria stri-
ata was used and where the trees were making the most vigorous
growth. Very low concentrations of nitrate nitrogen in leach-
ings from soils with rough lemon seedlings in comparison with
those from soils without seedlings indicate a relatively efficient
utilization of the nitrates by the seedlings.
The concentration of potassium in leachings from soils to
which mature Crotalaria striata and Natal grass had been added
and without rough lemon seedlings was approximately twice
that from soil without cover crops. There were no significant
differences in concentration of potassium in leachings from
soil in which Crotalaria striata and Natal grass had been in-
corporated or used as a mulch.
The concentration of potassium in leachings from soils to
which cover crops had been added and in which rough lemon
seedlings had grown was higher than that to which no cover crops
had been added. The very low concentration of potassium in
the leachings from the soils with rough lemon seedlings in com-
parison with those from the soils without rough lemon seedlings
indicates a very efficient utilization by the seedlings of the po-






Florida Agricultural Experiment Station


tassium added as potassium sulfate and liberated from the cover
crops by decomposition processes.
The concentration of calcium in leachings from soils without
rough lemon seedlings was 53.4 p.p.m. where Crotalaria striata
had been incorporated with the soil; 43.2 p.p.m. where it was
used as a mulch; and 40.4 p.p.m. where no cover crops were used.
Where Natal grass was incorporated with the surface soil the
concentration was 29.8 p.p.m. in the leachings, and where it was
used as a mulch 27.0 p.p.m. The lower concentration of calcium
in the leachings from the soil to which Natal grass had been
added may be attributed partly to the greater volume of water
leached from these lysimeters.
The concentrations of calcium in leachings from soils with
seedlings were all lower than from those without seedlings but
show no definite correlation with the various cover crop treat-
ments. However, these lower concentrations of calcium in the
leachings from the soils with trees do indicate an absorption of
the calcium by the seedlings. The smaller, slower growing seed-
lings of the Natal grass lysimeters evidently absorbed much less
calcium than the more vigorous plants in the other cultures.
Average parts per million of potassium in the leachings for
each month during which water percolated through the lysimet-
ers are given in Table 12. Results from lysimeters without trees
indicate that a higher concentration of potassium was soluble
in soils to which Crotalaria striata and Natal grass had been
added than in soil without additions of cover crops. The com-
paratively low concentrations of potassium in leachings from
tanks with seedlings indicate an effective utilization of potassium
by rough lemon seedlings during all months when leachings were
collected, including periods of both high and low temperatures.
DISTRIBUTION OF NITROGEN, PHOSPHORUS, POTASSIUM AND
CALCIUM IN LEACHINGS, IN ROUGH LEMON SEEDLINGS
AND IN COVER CROP RESIDUES
From results of analyses given in the preceding tables it is
evident that the nitrogen, phosphorus and potassium, and in most
instances the calcium of the cover crop materials, were made
soluble and mobile through the decomposition of organic mate-
rials in the soils and by rain. Also the growth and percentage
composition of rough lemon seedlings indicate a direct influence
of these cover crops on the seedlings. Thus the distribution of
nitrogen, phosphorus, potassium and calcium in the leachings,
rough lemon seedlings and cover crop residues is of interest.









TABLE 12.-AVERAGE MONTHLY CONCENTRATION OF POTASSIUM IN THE LEACHINGS FROM THE SOIL WITH AND WITHOUT
COVER CROP ADDITIONS.


Cover Crop




Mature
Crotalaria
striata





Mature
Natal
grass




No cover
crop


Method of
Handling


Incorporated with Tree
surface soil No Tree


Mulch Tree
No Tree


Incorporated with Tree
surface soil No Tree


Mulch Tree
No Tree


Tree
No Tree


Feb. I March
ppm. ppm.
0.73 1.26
4.52 8.35


1.43 2.25
3.20 5.66


0.86 2.76
4.60 6.90


1.00 1.80
2.79 6.90


1.35 1.73
3.40 5.98


April
ppm.

1.80
12.80


4.26
12.80


2.80
10.00


1.60
7.80


1.84
6.13


1931- 1932
July Aug.
ppm. ppm.
1.63 1.40
8.03 4.89


0.80 2.10
5.66 7.21


1.34 2.91
5.42 10.00


0.65 1.60
3.93 7.78


1.27 0.79
0.98 4.27


March
ppm.
0.55
8.60


0.67
12.30


1.03
12.00


0.92
9.35


0.42
5.95


June
ppm.
0.43
8.90


0.54
14.10


1.21
20.60


0.92
16.00


0.84
4.50


Aug.
ppm.

5.20



8.65



9.60



8.30



4.00






Florida Agricultural Experiment Station


Nitrogen.-The quantities of nitrogen added in the form of
fertilizer salts and cover crop materials and the quantities found
in the leachings, rough lemon seedlings and cover crop residues
are given in Table 13.
All rough lemon seedlings were given the same fertilizer treat-
ment from the time they were transplanted on February 27 until
February 9 of the following year, when the cover crop materials
were added to the soils. During this period of establishment of
the seedlings, 3.225 grams of nitrogen in the form of diammon-
ium phosphate and nitrate of soda were added to each culture.
The nitrogen leached during this period was determined sep-
arately and the quantities are given in the columns of Table 13,
headed, "In first leaching." The quantities of nitrogen leached
from the lysimeters with seedlings amounted to approximately
50 percent of the quantity applied. An average of 81 percent was
leached from the lysimeters without seedlings.
Nitrogen added as Crotalaria striata amounted to 11.421
grams, while only 3.310 grams were added as Natal grass. With
applications of nitrate of soda, total quantities of nitrogen ap-
plied to Crotalaria striata cultures was 15.411 grams, to Natal
grass cultures 8.065 grams and to cultures without cover crops
4.755 grams.
Leachings of nitrogen compounds from the soil after the ad-
dition of cover crop materials was very small for the lysimeters
with seedlings. This indicates a very effective utilization of
both nitrogen and water by the rough lemon seedlings during
this period. Relatively large quantities of nitrogen were
leached as nitrates from the lysimeters without seedlings.
Larger quantities of nitrate nitrogen were leached from the
soils in which Crotalaria striata had been incorporated than
from those where this leguminous cover crop had been used as
a mulch. On the other hand, residues of crotalaria used as a
mulch contained over twice as much nitrogen as those of the
same material incorporated with the surface soil. The same
general relationships were found to hold for the non-leguminous
Natal grass, though the quantities of nitrogen added and found
in the leachings and cover crop residues were correspondingly
smaller. These larger quantities of nitrogen, found in residues
of cover crops used as mulches, indicate a definitely slower de-
composition of cover crop materials when they were used as
mulches.
It is interesting to note that in cultures without cover crop
materials there was practically total recovery of the nitrogen










TABLE 13.-DISTRIBUTION OF NITROGEN ADDED TO NORFOLK FINE SAND AS FERTILIZERS AND COVER CROP MATERIALS IN
LEACHINGS, ROUGH LEMON SEEDLINGS AND COVER CROP RESIDUES.

Added Seedling No Seedling
Added Added with In I In
Cover Method of Before as or Total In In Cover In In In Cover
Crop Handling Cover Cover After First Second Crop Seed- Total First I Second Crop Total
Crop Crop Cover I Leach- Leach- Resi- ling Leach- Leach- Resi-
SCrop | ing ing'2_ due I ing' ing' due
g. g. g. g. g. g. g. g. g. g. g. g. g.
Incorporated 1 1
Mature with surface 3.225 11.421 0.765 15.411 1.899 0.330 1.994 3.752 7.975 2.874 4.680 1.994 9.548 c
Crotalaria soil
stmiata .
Used as mulch 3.225 11.421 0.765 15.411 2.117 0.130 4.218 2.897 9.362 2.748 3.720 4.218 10.686

Incorporated
Mature with surface 3.225 3.310 1.530 8.065 1.624 0.470 0.277 2.045 4.416 2.609 2.720 0.277 5.606
Natal soil
grass -
Used as mulch 3.225 3.310 1.530 8.065 1.707 0.700 2.099 1.701 6.207 2.444 2.440 2.099 6.983 a


No cover 3.225 1.530 4.755 1.584 0.480 -- 2.222 4.286 2.488 2.390 4.874
crop
'Before addition of cover crop materials.
'After addition of cover crop materials.






Florida Agricultural Experiment Station


added as fertilizer salts. The nitrogen was recovered in the
leachings and seedlings in the case of the cultures with rough
lemon seedlings and in the combined leachings in the cultures
without seedlings.
The quantity of nitrogen recovered in the rough lemon seed-
lings was relatively low in comparison with quantities added in
the form of cover crop and nitrogenous fertilizing materials.
Percentages of nitrogen recovered in the rough lemon seedlings
were 24 percent for those grown with Crotalaria striata incor-
porated with the surface soil, 18 percent for seedlings grown with
Crotalaria striata used as a mulch, 25 percent for those grown
with Natal grass incorporated with the surface soil, 21 percent
for those grown with Natal grass used as a mulch and 46 per-
cent for seedlings grown without cover crop additions. The
quantity of nitrogen recovered was definitely correlated with the
size of the seedlings, the higher quantity being recovered in the
larger seedlings grown in the cultures which had additions of
Crotalaria striata and the lower quantities in the smaller plants
of the Natal grass cultures.
The low recovery of nitrogen in seedlings of the Natal grass
cultures may be attributed to competition between microorgan-
isms and the plant for the nitrogen compounds during early
stages of decomposition of the non-leguminous cover crop. This
effect of non-leguminous cover crops on plant growth is some-
times encountered under grove conditions when excessively large
quantities of mature grass or similar materials are incorporated
with the soil and adequate provision for sufficient nitrogen both
to decompose the organic matter and to supply the growing plant
is not made.
Quantities of nitrogen not accounted for by leachings, cover
crop residues and rough lemon seedlings were found in the soil
for the most part. However, it is difficult to make sufficiently
accurate analyses of such a heterogeneous material as the soil
that will detect a few grams of nitrogen in several hundred
thousand grams.
Phosphorus.-The quantities of phosphorus added to the cul-
tures as ammonium phosphate, superphosphate and cover crop
materials, and those found in the cover crop residues and rough
lemon seedlings are given in Table 14. The leachings were tested
at intervals for phosphorus but only traces were found. Resi-
dues of the incorporated cover crop materials and of the mulches
contained small quantities of phosphorus.












TABLE 14.-DISTRIBUTION OF PHOSPHORUS ADDED TO NORFOLK FINE SAND IN THE FORM OF FERTILIZERS AND COVER CROP
MATERIALS, IN COVER CROP RESIDUES AND ROUGH LEMON SEEDLINGS.
Added Added Added In
Cover Method of Before as with Cover In
Crop Handling Cover Cover Cover Total Crop Seedling
S Crop Crop Crop Residue
g. g. g. g. g. g.
Dry -"
mature Incorporated with 1.778 4.205 0.780 6.763 0.272 0.597
Crotalaria surface soil o
striata
Used as mulch 1.778 4.205 0.780 6.763 0.478 0.545


Dry Incorporated with 1.778 0.937 0.780 3.495 0.416
mature surface soil
Natal "
grass Used as mulch 1.778 0.937 0.780 3.495 0.492 0.365


No cover crop 1.778 0.780 2.558 -0.472
l 0






Florida Agricultural Experiment Station


Highest quantities of phosphorus were recovered in the larger
seedlings grown with Crotalaria striata, lowest in the smaller
seedlings of the Natal grass cultures. The percentages of phos-
phorus recovered were small in all cultures. The phosphorus ap-
plied both as fertilizing and cover crop materials evidently was
readily retained by the soil, as only very small quantities were
found in the cover crop residues, seedlings and leachings.
Potassium.-The quantities of potassium added to the cultures
as potassium sulfate and cover crop materials, and those found
in the leachings collected after the addition of cover crop mate-
rials, in the residues and in the rough lemon seedlings, are given
in Table 15.
Due to the much higher percentage of potassium in Natal grass
than in Crotalaria striata, a larger quantity was added to the
grass cultures despite the much smaller quantities of the cover
crop. As noted before, this additional quantity of potassium
was reflected in a higher percentage of potassium in the rough
lemon seedlings grown with Natal grass than those grown in
other cultures. This higher percentage resulted in practically
as large a recovery of potassium in these smaller seedlings as in
the larger seedlings of the Crotalaria striata cultures. There
was a much greater recovery of potassium in seedlings grown
with cover crops than in the cultures without cover crop addi-
tions.
Leachings from cultures with rough lemon seedlings contained
very small quantities of potassium, as did the crop residues.
Leachings from cultures without seedlings contained relatively
large quantities of potassium, especially those from the soils
with addition of cover crop materials. The potassium of the
cover crop materials and of the potassium sulfate evidently had
been readily available to the seedlings and utilized by them.
Calcium.-The quantities of calcium added to the lysimeters
as cover crop materials and superphosphate, and the quantities
found in the leachings, rough lemon seedlings and cover crop
residues are given in Table 16.
Cultures in which Crotalaria striata was used received more
than four times as much calcium in the form of cover crops as
did the Natal grass cultures. The quantity of calcium added as
superphosphate was the same for all cultures. It is impossible
from the analysis to determine how much calcium was taken up
by the rough lemon seedlings in the period of establishment, or
before the cover crop materials were added. The leachings dur-











TABLE 15.-DISTRIBUTION OF POTASSIUM ADDED TO NORFOLK FINE SAND IN THE FORM OF FERTILIZERS AND COVER CROP
MATERIALS IN LEACHINGS, COVER CROP RESIDUES AND ROUGH LEMON SEEDLINGS.

Added Added Added Seedling No Seedling
Cover Method of Before as with Total In In In In In In
Crop Handling Cover Cover Cover First Second Cover In First Second Cover
Crop Crop Crop Leach- Leach- Crop Seed- Leach- Leach- Crop
Sing' ing Residue ling ing' ing Residue
gDr. g. g. g. g. g. g. g. g.
Dry Incorporated
mature with surface 1.990 2.554 0.796 5.340 0.080 0.099 2.391 1.390 0.099
Crotalaria soil
striata I
Used as mulch 1.990 2.554 0.796 5.340 0.080 0.234 2.123 1.680 0.234

Incorporated
Dry with surface 1.990 3.218 0.796 6.004 0.130 2.323 2.050
mature soil
Natal .. ..
grass Used as mulch 1.990 3.218 0.796 6.004 0.110 0.125 1.974 1.680 0.125


No cover 1.990 0.796 2.786 0.040 1.431 0.560
crop


'No analyses made.


____


~~






Florida Agricultural Experiment Station


ing this preliminary period were not analyzed for calcium but
treatments were uniform within the series for cultures with and
without seedlings.
The larger rough lemon seedlings grown in cultures with
Crotalaria striata incorporated with the surface soil contained
by far the larger quantities of calcium. Seedlings grown with-
out the addition of cover crop materials and those grown with
Crotalaria striata used as a mulch contained the second highest
amounts of calcium.' The smaller seedlings grown with Natal
grass contained approximately half as much calcium as the other
seedlings. The percentage of calcium in leaves and stems of
the seedlings grown in the Natal grass cultures was definitely
lower than that in the leaves and stems of the other plants.
Considering the leaching of calcium from both the lysimeters
with seedlings and those without seedlings, there is some evi-
dence that the decomposition of Natal grass has influenced the
absorption of calcium by the seedlings.
Very materially larger quantities of calcium were leached
from the cultures without seedlings than from those with seed-
lings. Residues of the cover crop materials used as mulches con-
tained significantly higher quantities of calcium than the small-
er residues of materials incorporated with the surface soil. Resi-
dues of the Natal grass mulch contained a larger quantity of
calcium than the original material. Without doubt this is due to
the admixture of soil and fertilizer with the Natal grass resi-
dues.
Considering the total quantities of calcium in the leachings,
cover crop residues and seedlings, cultures with Crotalaria stri-
ata showed a slight gain of calcium cover crop residues. There
was a practical balance of calcium in the cultures with Natal
grass incorporated with the surface soil with seedlings, but a
slight loss of calcium without seedlings. Cultures with Natal
grass used as a mulch and those without cover crops indicate a
definite drain on the calcium of the soil.
Analyses of Soils.-The average percentages of nitrogen in
the 0 to 6, 6 to 13, and 13 to 20 inch and of the loss on ignition
(organic matter) in the 0 to 6 and 13 to 20 inch depths of the
soils of the lysimeters after screening through a 2 mm. round-
hole sieve are given in Table 17. The incorporation of Crota-
laria striata with the surface soil (0 to 6 inches) has increased
significantly the nitrogen and organic matter content of the soil.
The other differences in percentages of nitrogen and organic










TABLE 16.-DISTRIBUTION OF CALCIUM ADDED TO NORFOLK FINE SAND IN THE FORM OF FERTILIZERS AND COVER CROP
AM T L. Dr


C7


ATA Ln S lltN AUHINAGSI IOUGH LIIEMOUN EEDjULINGSj ANU OVER CKUROP rlESIDUES.

Seedling No Seedling
Added Added Added In | N S In
Cover Method of Before as with Total In In Cover In In In Cover
Crop Handling Cover Cover Cover First I Second Crop Seed- Total First Second Crop Total Y
Crop Crop Crop Leach- Leach- Resi- ling Leach- Leach- Resi- t.
S ing' ing' due ing' ing2 due
g. g. g. g. g. g. g. g. g. g.
Dry Incorporated
mature with surface None 6.527 2.032 8.559 1.960 1.604 4.646 8.210 6.490 1.604 8.094
rotalaria 1 1L
strata C4
Used as mulch None 6.527 2.032 8.559 1.620 3.181 3.386 8.187 5.230 3.181 8.411

Incorporated
Dry with surface None 1.498 2.032 3.530 1.820 1.939 3.759 -- 4.140 4.140
mature soil
Natal
grass Used as mulch None 1.498 2.032 3.530 2.370 1.839 1.843 6.052 3.930 1.839 5.769


No cover None 2.032 2.032 -- 1.610 3.769 5.379 -- 3.500 -- 3.500
crop
No analyses made.






Florida Agricultural Experiment Station


matter are well within the limits of error of this type of ex-
perimentation.
TABLE 17.-PERCENTAGES OF NITROGEN AND ORGANIC MATTER IN SOIL TO
WHICH Crotalaria striata AND NATAL GRASS HAD BEEN ADDED.

Cover Crop and Nitrogen Loss on Ignition
Method of Handling 0-6 6-13 13-20 0-6 13-20
Inches Inches Inches Inches Inches
I % % % % %
Dry Crotalaria striata
incorporated with 0.057 0.043 0.045 2.211 1.951
surface soil
Dry Crotalaria striata 0.048 0.042 0.042 2.062 1.813
used as mulch
Dry Natal grass
incorporated with 0.046 0.042 0.043 2.013 1.849
surface soil
Dry Natal grass 0.042 0.043 0.041 1.941 1.784
used as mulch
No cover crop 0.043 0.044 0.040 1.985 1.801

SUMMARY

In the preliminary experiment, Crotalaria striata and velvet
beans were added to the soil in lysimeters at the rate of 5
pounds of green material per culture. These cover crop materi-
als were added to the soil on December 8 and rough lemon seed-
lings were set in the soil on March 2 of the following year. Thus
a period of decomposition of approximately three months
elapsed between the addition of cover crop materials to the soil
and the setting of seedlings. In addition, the seedlings required
several weeks to become established and to utilize the plant nu-
trients of the soil and decomposing cover crop materials. No
leaching of rain water occurred between December 8 and March
2, but the soils were artificially leached when the seedlings were
set.
Four methods were used for adding each cover crop to the soil.
They were: (1) green cover crop materials cut into approximate-
ly 4-inch lengths used as a mulch; (2) chopped green materials
incorporated with the surface six inches of soil; (3) chopped
green materials allowed to remain on the surface of the soil
from December 9 until January 23 and then incorporated 10 to
15 inches deep in the soil; (4) chopped green materials remained
on the surface from December 9 to March 2, when they were in-
corporated with the surface six inches of soil. These treatments






Lysimeter Studies of Summer Cover Crops


with a culture using the soil without cover crop additions made
up the experiment. A series of these lysimeters was set with
rough lemon seedlings on March 2. Another series without seed-
lings was maintained for each of the different methods of han-
dling the two cover crops. The experiment was discontinued on
July 26 of the year after the seedlings were set. The results are
summarized as follows:
1. Average dry weight of rough lemon seedlings grown with
Crotalaria striata was 2.73 and with velvet beans 2.88 times the
average weight of seedlings grown without the addition of cover
crop materials.
2. The use of Crotalaria striata and velvet beans as a mulch
produced the largest rough lemon seedlings. The incorporation
of these materials 10 to 15 inches deep in the soil yielded the
smallest seedlings, while the incorporation of green and dry
materials with the surface soil produced plants intermediate in
size.
3. Percentages of nitrogen in the rough lemon seedlings did
not vary in any consistent manner with the method of handling
the cover crops. The total nitrogen recovered in the seedlings
was greatest in those grown with Crotalaria striata and velvet
beans. The cultures with dry Crotalaria striata and velvet beans
incorporated 10 to 15 inches deep in the soil grew seedlings
showing a lower nitrogen recovery than other methods of han-
dling these materials.
4. In the lysimeters with rough lemon seedlings there were
no consistent variations in quantities of water leached which
could be correlated with methods of incorporation of the Crota-
laria striata and velvet beans with the soil. In the cultures
without rough lemon seedlings the use of Crotalaria striata and
velvet beans as mulches materially increased the quantities of
water leached through the lysimeters. Incorporation of green
materials with the surface soil and deep incorporation of dry
materials increased the amount of water percolating through the
lysimeters above that obtained without the addition of these
materials, but not nearly to the extent of their use as mulches,
while the incorporation of dry materials with the surface soil
had very little effect on the quantities of water leached.
5. The use of Crotalaria striata and velvet beans as mulches
and the incorporation of the dry materials with the surface soil
retarded the rate of leaching of nitrate nitrogen in the early
stages of decomposition.






40 Florida Agricultural Experiment Station

6. The content of the well decomposed portion of soil organic
matter was increased slightly for the 0 to 9 and 9 to 18 inch
depths by additions at the rate of approximately 23 tons of dry
Crotalaria striata and 21 tons of dry velvet beans.
7. The residues of the Crotalaria striata and velvet bean
mulches showed that after 20 months, 78 percent of the crota-
laria and 74 percent of the velvet beans were decomposed, re-
sulting in a transfer of 84 percent and 78 percent of the nitro-
gen of crotalaria and velvet beans, respectively, to more soluble
forms.
In the more extensive second series of cultures the lysimeters
were filled with Norfolk fine sand on October 23 and the tanks
were allowed to stand untreated and exposed to the leaching
rains until February 27 of the following year, when 10 of the
tanks were planted to rough lemon seedlings of uniform size.
All the cultures were fertilized with commercial nitrate of soda,
diammonium phosphate and potassium sulfate. On February 9
of the year following the setting of seedlings the experiment with
Crotalaria striata and Natal grass was started. Thus the rough
lemon seedlings were well established in the cultures before the
cover crop materials were added to them.
The cover crop materials were air-dried and cut into approxi-
mately 4-inch lengths for use in the cultures. The dried cover
crop materials were used at the rate of 2 pounds per culture for
the Crotalaria striata and 1 pound for Natal grass. Cultures
were maintained without the addition of cover crop materials
and with the use of cover crop materials as a mulch and incor-
porated with the surface soil. Duplicate cultures in a series
with and without rough lemon seedlings were established for
each method of handling the summer cover crop materials. The
cultures with Crotalaria striata received 10 grams of superphos-
phate and 2 grams of potassium sulfate; the Natal grass cul-
tures and those without additions of summer cover crops re-
ceived 5 grams of commercial nitrate of soda in addition to the
superphosphate and potassium sulfate.
Additional applications of 2.5 grams of commercial nitrate of
soda were made on April 2 and June 8, the second year after
the seedlings were set. The experiment was discontinued on
August 31 of that year, after a period of 568 days, and after
proper collection of samples of the rough lemon seedlings, the
cover crop residues, the water and the soil had been made.
Chemical analyses of these samples were made, using standard
procedures.






Lysimeter Studies of Summer Cover Crops


The result of this experiment may be summarized as follows:
1. The largest rough lemon seedlings were produced by the
incorporation of Crotalaria striata with the surface soil; the
second largest by the use of this summer cover crop as a mulch-
ing material. The heavy application of Natal grass both incor-
porated with the surface soil and used as a mulch produced
smaller seedlings than were produced in cultures without the
addition of cover crop materials. The detrimental influence of
the mature non-leguminous Natal grass on the rough lemon seed-
lings may be attributed to the competition of the soil microor-
ganisms for nitrogen in the early stages of decomposition of
this material.
2. The leaves, stems and roots of the rough lemon seedlings
grown with the decomposing cover crops had a higher percent-
age of nitrogen than those grown without cover crop material.
The higher percentages in the plants grown with Crotalaria
striata may be attributed to the greater supply of nitrogen add-
ed in the cover crop material, while the higher percentages in
the seedlings grown with Natal grass may be attributed to the
increased availability of nitrogen during the late stages of de-
composition of this cover crop material.
3. Variations in percentages of phosphorus in the leaves and
stems of the rough lemon seedlings grown under the different
conditions were not sufficiently large to have any great signifi-
cance. Percentages of phosphorus in the roots were highest in
seedlings grown with Natal grass, lowest in plants grown with
crotalaria, and intermediate in plants grown in Norfolk fine sand
without cover crop additions.
4. Leaves, stems and roots of seedlings grown with Natal
grass had much higher percentages of potassium than those
grown with Crotalaria striata or without the addition of cover
crop materials.
5. Highest percentages of calcium were found in seedlings
without cover crop additions, with the exception of roots of
plants grown with the Natal grass mulch. Percentages of cal-
cium in leaves and stems of plants grown with Crotalaria striata
were substantially higher than those grown with Natal grass.
6. Partial chemical analyses of samples of Crotalaria striata
and Natal grass and of the residues of these cover crop materi-
als after decomposing for 596 days in the surface soil or as a
mulch were made. Eighty-seven percent of the organic matter
of crotalaria decomposed when it was incorporated with the






Florida Agricultural Experiment Station


soil; 72.0 percent when used as a mulch. With Natal grass, 95.9
percent of the organic matter was decomposed when it was in-
corporated with the soil, and 63.0 percent when used as a mulch.
Similar results were obtained for the loss of nitrogen and carbon
from these cover crop materials. The carbon-nitrogen ratio
of the Crotalaria striata was 31.03; this ratio decreased to an
average of 22.76 in the residues. For the Natal grass this ratio
was 52.87 in the undecomposed material and 22.81 for the resi-
dues.
7. The calcium, phosphorus and potassium contents of the
Crotalaria striata and Natal grass and their residues were de-
termined. The calcium content of crotalaria increased from
0.759 percent in the undecomposed material to 1.499 percent in
the incorporated residue and 1.331 percent in the mulch residue.
The calcium content of Natal grass increased from 0.339 percent
in the undecomposed material to 1.657 percent in the mulch resi-
due. The phosphorus content of the crotalaria decreased from
0.489 percent in the undecomposed material to 0.254 percent in
the incorporated residue and 0.200 percent in the mulch residue.
On the other hand, the percentage of phosphorus in the Natal
grass increased from 0.212 percent in the undecomposed mate-
rial to 0.444 percent in the mulch residue. The potassium con-
tent of the crotalaria decreased from 0.297 percent in the unde-
composed material to 0.093 percent in the incorporated residue,
and 0.098 percent in the mulch residue; while the Natal grass
showed a decrease from 0.728 percent in the undecomposed mate-
rial to 0.112 percent in the mulch residue.
However, due to the active decomposition of the cover crops
both incorporated with the surface soil and used as a mulch,
there was a high percentage of the calcium (except for the Natal
grass mulch cultures), phosphorus and potassium liberated from
the decomposing cover crops. During the period of decomposi-
tion, 75 percent of the calcium was released from the incorpo-
rated crotalaria and 51 percent from the crotalaria mulch. The
residue of the Natal grass used as a mulch showed a gain in total
calcium indirectly associated with an increased retention of cal-
cium from the soil and fertilizers by the partly decomposed
grass.
Of phosphorus, 93 percent was released from the incorporated
crotalaria and 89 percent from the mulch of crotalaria and 47
percent from the mulch of Natal grass.






Lysimeter Studies of Summer Cover Crops


8. Both incorporation and use as mulch of large quantities of
Crotalaria striata and Natal grass materially increased the
quantities of water leached through the lysimeters without rough
lemon seedlings. With seedlings the use of the large quantities
of the mature non-leguminous Natal grass materially reduced
growth of the seedlings, resulting in the leaching of larger quan-
tities of water in these cultures than in the lysimeters without
cover crop additions.
9. Average concentrations of nitrogen in the drainage waters
of the lysimeters without seedlings were 27.6 p.p.m. for the cul-
tures without additions of cover crop materials; 34.6 p.p.m. for
those with Crotalaria striata; and 18.2 p.p.m. for those with
Natal grass. Concentrations in the drainage water from the
cultures with seedlings were 7.5 p.p.m., 3.5 p.p.m. and 6.2 p.p.m.
for the corresponding cultures.
Average concentrations of potassium in the drainage waters
of the lysimeters without seedlings were 6.4 p.p.m. for the cul-
tures without the addition of cover crop materials; 12.6 p.p.m.
for those with Crotalaria striata; and 13.3 p.p.m. for those with
Natal grass. The corresponding values for the cultures with
seedlings were 0.6 p.p.m., 1.2 p.p.m. and 1.3 p.p.m., respectively.
Average concentrations of calcium in the drainage waters of
the lysimeters without seedlings were 40.4 p.p.m. for the cul-
tures without the addition of cover crop materials; 48.3 p.p.m.
for those with Crotalaria striata; and 28.4 p.p.m. for those with
Natal grass. The values for the corresponding cultures with
seedlings were 25.0 p.p.m., 27.9 p.p.m. and 22.8 p.p.m., re-
spectively.
Differences in the concentrations of these elements in the
leachings from cultures without seedlings and those with seed-
lings indicate a definite absorption of the respective elements
by the seedlings.
10. Average monthly concentrations of potassium in the drain-
age waters from the lysimeters with and without seedlings show
an absorption of potassium by rough lemon seedlings during all
seasons of the year. The liberation of potassium from the de-
composing cover crop materials maintained the concentration of
potassium in the drainage waters at a substantially higher level
than from the soil without additions of plant materials.
11. A study of the distribution of the nitrogen added as fer-
tilizer and cover crop materials to the cultures shows substan-
tially larger amounts of nitrogen leached from the cultures with-






Florida Agricultural Experiment Station


out rough lemon seedlings. Larger quantities of nitrogen were
recovered by the larger seedlings grown in the crotalaria cul-
tures. The seedlings grown in the cultures without cover crop
additions recovered more nitrogen than was obtained by seed-
lings grown in the cultures receiving large additions of mature
Natal grass. Residues of the cover crop materials used as
mulches contained very much larger quantities of nitrogen than
those of the incorporated materials. The largest gain of nitro-
gen in the soil was in the cultures where Crotalaria striata was
incorporated with the surface soil. Other treatments failed to
show significant gains in soil nitrogen.
12. Additions of phosphorus to the cultures were highest for
the soils with Crotalaria striata incorporated with the surface
soil or used as a mulch and lowest in cultures without cover crop
additions. Largest quantities of phosphorus were recovered in
the seedlings grown with crotalaria and the smallest in seedlings
grown with Natal grass. The seedlings in the cultures with
fertilizers alone were intermediate in phosphorus recovery. Very
small quantities of phosphorus were recovered in the cover crop
residues.
13. Largest quantities of potassium were applied to cultures
having applications of mature Natal grass. Very small quanti-
ties of potassium remained in the cover crop residues. Sub-
stantially larger quantities of potassium were leached from the
cultures without rough lemon seedlings. The recovery of potas-
sium in the seedlings was materially greater for those grown
in the presence of cover crop materials.
14. The quantity of calcium added in the Crotalaria striata
was several times larger than the total added in Natal grass and
in the fertilizers. Less calcium was leached from the cultures
with seedlings than from those without seedlings. By far the
largest quantity of calcium was recovered in the rough lemon
seedlings grown with the crotalaria incorporated with the sur-
face soil and the second largest with the seedlings grown without
cover crop additions. Total calcium content of the seedlings
grown with mulched crotalaria was nearly as great as that with-
out additions of cover crop materials. The content of this ele-
ment in the seedlings grown with Natal grass was approximately
half that of the other seedlings. Approximately half of the
calcium contained in the Crotalaria striata was found in the
mulch residue; approximately one-quarter in the residue of the
crotalaria incorporated with the surface soil.




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