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Group Title: Agronomy research report - University of Florida Institute of Food and Agricultural Sciences ; AY-86-07
Title: Studies of chemical combinations and rates used to convert a living crimson clover cover crop to a mulch for no-tillage planting of summer crops
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Permanent Link: http://ufdc.ufl.edu/UF00056055/00001
 Material Information
Title: Studies of chemical combinations and rates used to convert a living crimson clover cover crop to a mulch for no-tillage planting of summer crops
Physical Description: 11 leaves : ; 28 cm.
Language: English
Creator: Gallaher, Raymond N
University of Florida -- Agronomy Dept
Publisher: Institute of Food and Agricultural Sciences, University of Florida, Agronomy Research Lab
Place of Publication: Gainesville, Fla.
Publication Date: 1986?
 Subjects
Subject: Crimson clover -- Florida   ( lcsh )
Cover crops -- Florida   ( lcsh )
Soil fertility -- Florida   ( lcsh )
Genre: non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Raymond N. Gallaher.
General Note: Caption title.
General Note: gronomy research report - University of Florida Institute of Food and Agricultural Sciences ; AY-86-07
 Record Information
Bibliographic ID: UF00056055
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 62557744

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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










Agronomy Research Report AY-86-07


Studies of Chemical Combinations and Rates Used to Convert a Living Crimson Clover

Cover Crop to a Mulch for No-Tillage Planting of Summer Crops


BY


Raymond N. Gallaher, Professor of Agronomy, Institute of Food and Agricultural

Sciences, University of Florida, Agronomy Research Lab, 631 Wallace Building,

Gainesville, FL 32611.
Liyrar] !

INTRODUCTION FFE3 2 '


Winter cover crops of small grains or legugS7hFave historically been used-for

soil conservation. Properly established cover crops can effectively reduce wind

and/or water erosion to within tolerance levels. Historically these cover crops

were called green manure corps and were plowed down at some point in time before

planting the succeeding summer crop. Using conventional tillage to prepare the

seedbed for the summer crop was also an effective treatment to kill the winter

cover crop or green manure crop.

In recent years no-tillage farming provides excellent conservation management

of cropland. This method or direct seeding without prior land preparation does

not allow the traditional plow down of cover crops. Because of this the cover

crop must be killed prior to or at the planting time of the succeeding summer
crop. Not only have studies shown that cover crops provide soil conservation but

they have also shown that when converted to a dead mulch, soil water is conserved.

Legumes also provide N from the decaying residue to, the succeeding crop. Recent









No-tillage studies have shown that when the legume crop is effectively converted

to a mulch in no-tillage systems the N is still available and may be better

utilized because of beneficial moisture conservation and weed control from the

mulch.

As mention earlier, in-no-tillage the cover crop must be killed chemically.

Cover crops are difficult to kill during their vegetative stage of growth. For

example, the application of paraquat on small grain prior to heading will

desiccate the above ground plant but food reserves and tillering ability will

result in regrowth soon after paraquat treatment. This principal is similar to a

ruminant animal eating the top out of the cover crop and the crop growing back.

In order to kill the crop with paraquat alone during vegetative growth, split

applications may be necessary with the second application administered soon after

regrowth has occurred when food reserves in the root system are bdpleted or low.

Single applications have worked well to kill small grain if applied after heading

or flowering has occurred. In the latter case the vegetative stage is complete

and the plant is in the reproductive stage of growth.

Winter cover crops may have to be killed during vegetative stages of growth

because of timing necessary in the planting of the succeeding summer crop. If

irrigation is not available the cover crop can obplete soil water reserves unless

killed at some time prior to planting the summer crop to allow time for natural

rainfall to recharge the soil profile. Because of the importance in timing for

planting succeeding crops and the potential for depletion of soil water needed by

the succeeding crop killing the cover crop with chemicals becomes an important

problem to solve. The objective of this research was to evaluate chemical

desiccants in combination with other chemicals and rates of application to

effectively kill a winter cover crop of crimson clover in a single application.









MATERIALS AND METHODS


Crimson clover ('Tibbie') was planted into residue or no-tillage corn with a

"Tye" drill in the fall of 1984. *Chemical desiccation experiments were initiated

during vegetative growth on 9 April, 1985. The three experiments were all split

plot designs with four replications.

Plot size was 5 feet by 10 feet in all three experiments. Chemicals were

measured with graduated cylinders, mixed with water, and sprayed with a hand

applicator. Fan tips (8004) were used and application was at 30 psi at a boom

width and speed to give an output of 46 gallons of liquid/a. Treatments were

applied in bright sunlight from about 9 am to 2 pm and low wind conditions.

Clover control ratings were made on 15 May, 1985. A rating of 0 was

considered no control of clover while a rating of 10 represented complete control

or death of the clover. On the same day control ratings were made soil samples

were take from the surface to a depth of 12 inches for total soil water

determination using standard gravimetric procedures.

Data was statistically analyzed using a TRS-80 Tandy Corporation

microcomputer and a program for analyzing a split plot written for use on the

microcomputer. Differences among means were tested by use of LSD. Correlation

coefficients were determined on clover control ratings and soil water content

using standard statistical procedures.


Paraquat Experiment


Whole plots were five rates of 24-D at 0.0, 0.25. 0.50. 0.75, and 1.00 lb

active ingredient (ai)/acre (a). Paraquat rates of 0.0, 0.12, 0.25. 0.37, and

0.50 lb ai/a were split plots randomized within each of the 24-D whole plots.










Diquat Experiment


Whole plots were five rates of 24-D at 0.0, 0.25, 0.50, 0.75, and 1.00 lb

ai/a. Diquat rates of 0.0, 0.12, '0.25, 0.37, and 0.50 lb al/a were split plots

randomized within each of the 24-D whole plots.


Glyphosate Experiment


Whole plots were five rates of 24-D at 0.0, 0.25, 0.50, 0.75, and 1.00 lb

ai/a. Glyphosate rates of 0.0, 0.25, 0.50, 0.75, and 1.00 lb ai/a were split

plots randomized within each of the 24-D whole plots.


RESULTS



Data means are tabulated in two way tables (Tables 1-6) for all experiments.


Paraquat Experiment


A minimum of 0.37 lb al paraquat/a was necessary to give complete obsiccation

of the crimson clover top growth. It was observed that some rates of paraquat and

combinations with 24-D resulted in complete desiccation of top growth. Plants

were completely white within 7 days of application but new growth soon appeared

apparently due to tillering ability and food reserves in the roots and crowns.
The use of 24-D alone seemed to twist, reduce growth and otherwise kill some

of the weaker clover plants as indicated from clover control ratings (Table 1).

Paraquat alone turned the tops completely white as mentioned earlier at the higher









two rates. It appeared that mixing 24-D and paraquat together was ineffective

over using paraquat alone in this one year study. In fact it was suspected that

paraquat may have worked to quickly for 24-D to have any effect when the two were
mixed together.

Soil water levels (Table 2) were better correlated with paraquat rates than

with 24-D rates. This indicate that the quick action of paraquat may have stopped

plant water use quicker than 24-D so that more water was retained in the soil. On

the other hand the lower water levels under 24-D may also indicate that our visual

control ratings for 24-D when used alone without paraquat were not as good as the

ratings from paraquat used alone without 24-D

Note that soil water content increased by 1.1% from the application of 0.37

lb paraquat/a over the control when sprayed without 24-D in the mixture. Each 1 %

change in soil water content represents about 1/4 acre inch of water available in

the top 12 inches of soil. Agricultural engineers at the University of Florida

indicate that cost of application of 1 acre inch of irrigation water may cost from

$12 to $18 per acre. The savings of 1/4 acre inch or more in the case discussed

here (Table 2) would have a value of about $3 to $5/a if replace by irrigation.
Of course it could be worth much more if needed by the succeeding no-tillage crop
during a critical drought period. The correlation coefficient between average

means of paraquat over all 24-D levels for clover control ratings and soil water

content was 0.90 indicating that use of paraquat as a desiccant and conservation
of soil water are highly correlated when controlling crimson clover in this study.
This same correlation combination among means at 0.0 level of 24-D was 0.80.


Diquat Experiment


Diquat was less effective than paraquat was in the paraquat experiment in








killing crimson clover whether used alone or in mixtures with 24-D (Taole 3). The

maximum control occurred with 0.50 lb ai/a with a control rating of about 5.

Diquat did an excellent job in killing winter broadleaf weeds in crimson clover,

caused relatively quick obsiccation of clover top growth, but resulted in

relatively quick regrowth of clover in this experiment.

The limited control of clover using diquat was reflected in the limited soil

water conservation from its use compared to the control plots that received no

diquat or 24-0 (Table 4). There appeared to be no benefit in mixing 24-D with

diquat in the control of clover for either clover control or water conservation.

Higher rates of diquat than were used in this study may be necessary to

obtain clover control equal to paraquat. This study pointed out a possible

benefit for the use of diquat on crimson clover. Since diquat killed most of the

winter broadleaf weeds it may be useful as an over the top weed control practice

for this'legume, especially when the clover is to be harvested for seed. This was

an observation that was not planned for in this experiment and further testing

would be necessary to confirm this benefit. It appeared that diquat killed the

weeds, caused slight injury to clover which quickly gained regrowth, and resulted
in a clean clover stand with continued soil water use (Table 4).


Glyphosate Experiment


The glyphosate experiment was located in the field where the clover stand was

good but growth was not as vigorous as in the paraquat and diquat studies. Data

shows that glyphosate either alone or in mixtures with 24-0 were extremely
effective in complete control of crimson clover (Table 5). Best control of the

clover when using glyphosate alone without 24-D was at the 0.75 to 1.00 lb ai/a

rates. On the other hand equally good control of clover was found with mixtures









of 0.25 to 0.50 lb ai glyphosate/a plus 0.50 to 0.75 lb 24-D/a. In this case the

24-D had a positive benefit on the effectiveness of glyphosate in control of

crimson clover.

Soil water measurements confirmed that glyphosate with or without 24-0 was

effective in eliminating the clover plants and thus the use of stored soil water.

From 1/4 to 1/3 acre inch of water was retained in the soil from use of these

treatments over control plots without chemical sprays.

As in the paraquat experiment, glyphosate and/or glyphosate plus 24-0

mixtures were highly correlated with conserved soil water. The correlation

coefficient (r) for average means of glyphosate over all 24-0 rates for clover

control ratings and soil water content ratings was 0.91. This same correlation

between means of glyphosate without 24-D addition was 0.93.


CONCLUSIONS


Single application of paraquat was relatively effective in control of crimson

clover cover crop at the 0.37 Ib ai/a rate. Paraquat combined with 24-D did not

seem to be beneficial over the use of paraquat alone. The 0.37 lb ai paraquat/a

treatment resulted in conservation of about 1/4 acres inch of soil water that

would cost about $3 to $5 to replace with irrigation. The use of paraquat was

highly positively correlated with soil water conservation.

Diquat appeared to have potential as an over the top broadleaf weed control

treatment for crimson clover at the rates used in this study. Regrowth of clover

was rather quick giving a healthy clean weed free cover crop. Diquat did not

conserve soil water further indicating limited effect on the growth of crimson

clover.

Glyphosate was effective in control of crimson clover either when used alone









or when mixed with 24-D. Treatment with glyphosate used alone or in mixtures

conserved and average of 1/4 to 1/3 acre inch of soil water. Glyphosate

treatments either used alone or mixed with 24-D was highly positively correlated

with soil water conservation.

THESE DATA AND CONCLUSIONS ARE-BASED ON ONLY ONE YEARS DATA. FURTHER TESTING

OF THESE TREATMENTS AND OTHERS MAY RESULT IN DIFFERENT CONCLUSIONS FROM WHICH

RECOMMENDATIONS CAN EVENTUALLY BE OBTAINED.


ACKNOWLEDGEMENT


The author gratefully acknowledges the technical assistance of Mr. Scott

Taylor, Agricultural Technician III.






Use of trade names in this publication is solely for the purpose of providing

specific information. It is not a guarantee or warranty of products named and

does not signify approval to the exclusion of others of suitable composition.








Table 1. Crimson clover cover crop desiccation control ratings as affected by
rate and combination of paraquat and 24-D herbicides at the Green Acre Agronomy
Farm in 1985, Gainesville, FL.
24-0 Rate (lb al/a)
Paraquat
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb al/a- -------------- Rating -------------- -----

0.00 0.0 0.5 3.0 5.9 6.8 3.2

0.125 3.0 4.9 6.1 6.9 6.1 5.4

0.25 3.5 3.5 5.8 6.6 6.0 5.1

0.375 6.8 5.3 5.5 7.4 5.4 6.1

0.50 5.5 7.0 6.8 6.4 5.3 6.2

Average 3.8 4.2 5.4 6.6 5.9
Interaction Significant; LSD @ .05 P among interaction means = 2.45


ai = active ingredient. A rating
10 is complete control of crimson
and ratings were made 5/15/85.


of 0 = no control of crimson clover, a rating of
clover. Chemical treatments were applied 4/9/85


Table 2. Soil water content in crimson clover treated plots as affected by -rate
and combination of paraquat and 24-0 herbicides at the Green Acre Agronomy Farm in
1985, Gainesville, FL.
24-0 Rate (lb ai/a)
Paraquat
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb ai/a- ------------------------- % soil water ---------------------

0.00 2.0 1.7 .2.0 2.1 2.5 2.06

0.125 2.1 2.5 2.1 2.7 2.2 2.32

0.25 3.0 2.6 2.2 2.7 2.5 2.60

0.375 3.1 2.6 2.5 2.9 2.7 2.76

0.50 2.7 2.6 2.8 2.6 2.8 2.70

Average 2.58 2.40 2.32 2.60 2.54
Significant among average means for paraquat only; LSD @ .05 P = 0.28


active ingredient. Chemical treatments
5/15/85. Moisture was determined from
by the gravimetric method. Chemical
moisture samples were taken on 5/16/85.


were applied 4/9/85 and ratings were
samples taken in the top 12 inches of
treatments were imposed on 4/9/85 and


ai =
made
soil
soil







Crimson clover cover crop desiccation control ratings as
combination of diquat and 24-D herbicides at the Green Acre
Gainesville, FL.


affected by
Agronomy Farm


24-0 Rate (lb ai/a)
Diquat
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb ai/a- --------------------------- Rating -------------------..---...

0.00 0.0 0.5 3.0 5.9 6.8 3.2

0.125 4.0 4.8 5.0 5.5 5.9 5.0

0.25 3.3 3.8 4.8 3.8 4.8 4.1

0.375 3.3 4.3 5.5 4.3 4.3 4.3

0.50 5.5 4.9 4.0 4.5 6.3 5.0

Average 5.3 4.6 4.5 4.8 5.6
Significant interaction; LSD @ .05 P among interaction means = 2.38


ai = active ingredient. A rating of 0 = no
10 is complete control of crimson clover.
and ratings were made 5/15/85.


control of crimson clover, a rating of
Chemical treatments were applied 4/9/85


Table 4. Soil water content in crimson clover treated plots as affected by--rate
and combination of diquat and 24-0 herbicides at the Green Acre Agronomy Farm in
1985, Gainesville, FL.

24-D Rate (Ib al/a)
Diquat
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb ai/a- ----------------------- % soil water ---------------------

0.00 2.0 1.7 2.0 2.1 2.5 2.06

0.125 2.24 1.17 2.11 1.82 1.82 1.83

0.25 2.12 2.07 2.26 1.92 2.18 2.11

0.375 2.27 2.42 2.31 2.33 2.03 2.27

0.50 3.03 2.51 2.34 2.40 2.73 2.60

Average 2.33 1.97 2.20 2.11 2.25
Interaction not significant @ .05 P.
Significant among average means for 24-0; LSD @ .05 P = .29
Significant among average means for Diquat; LSD @ .05 P = .27


ai =
made
soil
soil


active ingredient. Chemical treatments were applied 4/9/85 and ratings were
5/15/85. Moisture was determined from samples taken in the top 12 inches of
by the gravimetric method. Chemical treatments were imposed on 4/9/85 and
moisture samples were taken on 5/16/85.


Table 3.
rate and
in 1985,








Table 5.
rate and
Agronomy


Crimson clover cover crop desiccation control ratings as affected by
combination of glyphosate (Roundup) and 24-D herbiciabs at the Green Acre
Farm in 1985, Gainesville, FL.


24-D Rate (lb ai/a)
Glyphosate
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb ai/a- --------------------------- Rating -------------------------

0.00 0.0 0.5 3.0 5.9 6.8 3.2

0.25 6.9 8.3 9.6 9.6 10.0 8.9

0.50 7.8 9.0 9.6 9.8 9.9 9.2

0.75 8.5 9.3 9.5 10.0 10.0 9.5

1.00 9.1 9.6 9.5 9.8 9.9 9.6

Average 6.5 8.2 8.2 9.0 9.3
Significant interaction; LSD @ .05 P among interaction means = 1.41


ai = active ingredient. A rating of 0 = no
10 is complete control of crimson clover.
and ratings were made 5/15/85.


control of crimson clover, a rating of
Chemical treatments were applied 4/9/85


Table 6. Soil water content in crimson clover treated plots as affected by- -Xate
and combination of glyphosate (Roundup) and 24-0 herbicides at the Green Acre
Agronomy Farm in 1985, Gainesville, FL.

24-D Rate (lb ai/a)
Glyphosate
Rate 0.00 0.25 0.50 0.75 1.00 Average

- lb ai/a- --------------------- % soil water ---------------------

0.00 2.0 1.7 2.0 2.1 2.5 2.06

0.25 2.64 2.39 3.03 2.77 3.01 2.77

0.50 3.01 2.70 2.53 3.09 2.87 2.84

0.75 3.33 3.25 2.84 3.59 3.61 3.32

1.00 3.21 3.69 2.68 3.33 3.60 3.30

Average 2.84 2.75 2.62 2.97 3.12
Interaction not significant @ .05 P.
Significant among average means for 24-0; LSD @ .05 P = .31
Significant among average means for Glyphosate; LSD @ .05 = .32


ai =
mach
soil
soil


active ingredient. Chemical treatments were applied 4/9/85 and ratings were
5/15/85. Moisture was determined from samples taken in the top 12 inches of
by the gravimetric method. Chemical treatments were imposed on 4/9/85 and
moisture samples were taken on 5/16/85.




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