Herbicide
Persistence in Southern Soils: Bioavailable Concentration and
Effect on Sensitive Rotational Crops
Regional
Research Project S-286
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- Project
objective:
- Determine crop injury and/or yield
reduction caused by carryover.
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Abbreviated history, background, and justification:
- Successive cooperative regional projects
have conducted research since 1950 pertaining to weeds and their
control in southern crops; the behavior and action of herbicides
in plants; and the fate, persistence and efficacy of herbicides
in the environment. Under the initial project number, S-18, there
were several revisions in the title and objectives. The initial
title was "Weed Control Investigations in the South,"
1950 to 1954, with the following objectives: (A) to investigate
the physiological action of herbicides, and (B) to make preliminary
evaluations of herbicidal chemicals on soils and on plant successions
following their use. The early emphasis on physiology, soils,
and weeds was strengthened in the 1995 revision when the objectives
became: (A) to study the mechanisms of herbicidal action in plants,
(B) to evaluate the effects of herbicides on plants and soils
under varying environmental conditions, and (C) to study biological
factors affecting weeds. This project was revised to "The
Development of Principles for the Control of Weeds in the South,"
1959 to 1965, with the objectives: (A) to study life cycles of
selected weeds and the relationships of their life histories
to herbicidal susceptibility, (B) to study the physiological
aspects of certain prescribed herbicides, and (C) to investigate
the behavior of herbicides in soils. The next revision involved
more fundamental research and was entitled "Behavior of
Specific Herbicides in Plants and Soils," 1965 to 1971.
The primary concern then was to develop knowledge about herbicides,
specifically their mode of action and the fate in plants and
soils. The project number was changed to S-78 with the next revision
of the project and was entitled "Herbicide Movement from
Application Sites and Effects on Non-Target Species," 1972
to 1976. To help clarify the influence of tillage and to determine
the response of aquatic organisms to herbicides in runoff water,
the next revision, S-110, was entitled "Effects of Minimum
Tillage and Double Cropping on Weed Populations and the Persistence
and Fate of Herbicides", 1976 to 1981. This project was
then revised to "Influence of Crop Herbicide Management
on Weed Population and Dynamics and Subsequent Crop Physiology,"
under the project number, S-159, 1981 to 1986. The next revised
project was S-215, "Behavior and Fate of Selected Sulfonylurea
and Imidazolinone Herbicides in the Southern Environment,"
1987 to1998. The research accomplishments of this Regional Research
Project have been summarized and are available in the following
publications:
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- Frans, R. E., D. E. Davis, and J. B.
Weber. 1972. Behavior of Specific Herbicides in Plants and Soils
(A Summary of Research Accomplishments for Regional Research
Project S-18). Southern Cooperative Bulletin No. 167. Agricultural
Publications, AGRI 110, University of Arkansas, Fayetteville,
AR 72701. 26 pp.
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- Savage, K. E., B. Truelove, and A.
F. Wiese. 1978. Herbicide Movement From Application Sites and
Effects on Non-target Species (A Summary of Research Accomplishments
for Regional Research Project S-78). Southern Cooperative Series
Bulletin 234. Mississippi State University, P. O. Drawer J, Mississippi
State, MS, 39762. 16 pp.
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- Abernathy, J. R. , R. E. Frans, L.
S. Jeffery, B. Truelove, J. B. Weber, A. F. Wiese, and J. M.
Chandler. 1972. Effects of Minimum Tillage and Double Cropping
on Weed Populations and the Persistence and Fate of Herbicides
(A Summary of Research Accomplishments for Regional Research
Project S-110). Southern Cooperative Series Bulletin 302. Mississippi
State University, P. O. Drawer J, Mississippi State, MS, 39762.
27 pp.
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- Wiese, A. F. (ed.). 1990. Integrated
Weed Management Studies on Crop-Weed Dynamics and Physiology
for Optimum Crop Production (A Summary of Research Accomplishments
for Regional Research Project S-159). Southern Cooperative Series
Bulletin 348. Dept. of Agricultural Communications, Texas A&M
University, College Station, TX, 77843. 30 pp.
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- Schroeder, J. (ed.). 1997. S-215 Regional
Research Project Final Report: Behavior and Fate of Selected
Sulfonylurea and Imidazolinone Herbicides in the Southern Environment.
Southern Cooperative Series Bulletin No. 385, Agricultural Publications,
AGRI 110, University of Arkansas, Fayetteville, AR 72701 or via
the Internet, http://www.msstate.edu/org/saaesd.
66 pp.
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- The current project, S-286, will be
conducted over the period of October 1, 1998 to September 30,
2001. Now the group believes that there is a critical need to
determine the effects of herbicides on rotational crops. The
need is enhanced by the greater flexibility in federal government
programs, which had previously tended to discourage the beneficial
practice of crop rotation. Now, farmers are planning weed management
strategies, of which herbicides remain an essential component,
with an eye towards future crops which may be sensitive to some
herbicides. These crop effects the year after herbicide application
may be subtle, and may be confounded by herbicides used in the
rotational crop, soil properties, and environmental conditions.
Based upon the collaboration of scientists with a wealth of knowledge
and expertise in this area, this project will generate knowledge
on herbicide carryover causing injury to rotational crops and
is establishing better methods to determine these effects.
Membership:
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Next meeting date and site:
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- Texas A&M University will host
the 2000 meeting at a date to be announced.
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- Significant changes and accomplishments:
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- 1. S-18 Regional Project, 1950 to
1971.
- Under the humid conditions of the South,
for the most part, that no phytotoxic residues of herbicides,
such as atrazine, chlorpropham, DCPA, diphenamid, diuron, linuron,
prometryne, or trifluralin, persist after one year when they
are applied at recommended rates.
- 2. S-78, 1972 to 1981.
- Less than 1 % to 2 % of the fluometuron
applied was in runoff water from plots.
- Fluometuron concentrations in runoff
water collected was significantly related to slope.
- Flumeturon concentrations declined
with each increase in depth of the sampling of the soil profile,
and there was little evidence that flumeturon leaches progressively
deeper with time.
- Concentrations of various herbicides
required in water to inhibit various aquatic organisms were determined
and ranged from 4.6 X10 -8 M for ametryn to 2.05 X 10 -6
M for fluometuron. MSMA had little on no effect on Chlorella.
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- 3. S-110, 1976 to 1981.
- Weed population changes as affected
by a change over from conventional to minimum tillage were recorded.
- Herbicide runoff was determined to
be less from land under minimum tillage than from land under
conventional tillage.
- The soil half-life of metribuzin at
several geographic locations was established for land under minimum
versus conventional tillage.
- It was determined that the repeated
use of MSMA in a normal cotton production system did not reduce
rotational rice yield or cause straighthead symptoms.
- It was determined that MSMA toxicity
to rice could be induced under hydroponic conditions.
- The phytotoxic levels of glyphosate,
metribuzin and atrazine were determined for selected aquatic
plants.
- The concentrations of herbicides that
would be toxic to potential rotation crops were determined for
several soils.
- 4. S-159, 1981 to 1986.
- Use of sorghum in rotations resulted
in little or no control of johnsongrass.
- Use of sethoxydim or fluazifop for
one or two seasons in soybean or cotton controlled established
johnsongrass.
- Broadleaf weeds, such as devil's claw,
that were not controlled by trifluralin, sethoxydim, or fluazifop
rapidly infested plots where johnsongrass was controlled.
- Johnsongrass was controlled with plowing
at 4-week intervals in one 15-month fallow period in a winter
wheat-fallow rotation.
- n the Southeast, conventional tillage
controlled johnsongrass better than no-tillage and resulted in
higher yields of corn and soybean. If the newest herbicide technology
was used, johnsongrass was controlled with either conventional
or no-tillage. Johnsongrass was more difficult to control in
corn than in soybean.
- During the 10-month fallow period between
the destruction of old sugarcane (November) and replanting (September),
planting soybeans in the spring and plowing them into the soil
just before replanting sugarcane required less herbicide to control
johnsongrass than where fields were fallowed with tillage and
herbicides, or where wheat was planted in December.
- A rice-cotton rotation gave excellent
control of johnsongrass because johnsongrass could not tolerate
flooding.
- In a soybean-rice rotation, preplant
incorporated applications of alachlor, metolachlor, or alachlor
mixed with trifluralin combined with postemergence sprays of
bentazon plus mefluidide, or directed sprays of paraquat, controlled
red rice in soybean and the subsequent rice crop.
- MSMA (monosodium salt of methylarsonic
acid) levels in soil above 6 kg/ha were detrimental to grain
yield of straighthead-susceptible rice cultivars. There was no
clear relationship between straighthead syndrome and concentrations
of ethylene, IAA, or arsenic in leaf tissue of rice.
- Cogongrass and torpedograss are adapted
to and will likely become more widespread in the Southern Coastal
Plains. Because rhizomes of these weeds are not tolerant to prolonged,
excessive cold, these species are unlikely to spread much further
north than their present range.
- Analyses of 19 soils by 11 soil testing
laboratories for soil organic matter content showed substantial
variation, due primarily to differing methods of analysis. Herbicide
bioactivity was highly correlated with humic and organic matter
contents of the soils. Either determination could be used as
a basis for making herbicide rate recommendations.
- 5. S-215, 1987 to 1993.
- Adsorption: Chlorimuron adsorption
was negatively correlated with soil pH and positively correlated
with soil humic matter content. The adsorption coefficient (Kf)
ranged from 0.07 to 1.50 in soils from the region. Within a soil
type, chlorimuron adsorption and hydrolytic degradation increased
as pH decreased, probably due to differences in molecular characteristics
at different pH levels. Imazaquin adsorption was negatively correlated
with soil pH and positively correlated with soil humic matter
and CBD-extractable iron. The adsorption coefficient (Kf) ranged
from 0.02 to 0.51 in soils from the region. Also, within a soil
type, adsorption increased as pH decreased, probably also due
to differences in molecular characteristics at different pH levels.
- Stability on the soil surface: Chlorimuron
neither photodegraded nor volatilized from the soil surface.
However, chemical hydrolysis of chlorimuron was negatively correlated
with soil pH and was faster at 45oC than at 15oC.
Imazaquin did not volatilize from any soil surface; however,
photolysis occurred with an average dissipation of 17% over 14
days.
- Runoff: Imazaquin runoff from soil
ranged from 0 to 10%, depending on year and tillage system. Greater
runoff of water and herbicide occurred in no-till-planted soybeans
with standing wheat stubble than in late-planted, conventionally
tilled soybeans. Foliar runoff studies indicated that a rainfree
period of 30 minutes was required to maximize efficacy of imazaquin
and chlorimuron.
- Soil mobility: Thin layer chromatography
studies showed that the Rf of chlorimuron ranged from 0.18 to
0.89 and was positively correlated with soil pH and negatively
correlated with adsorption. The Rf of imazaquin ranged from 0.45
to 0.95 and was negatively correlated with soil organic matter
content, adsorption, CBD-extractable iron and plate development
time. Column chromatography studies indicated that the Rf of
chlorimuron (0.32) was comparable to that of metolachlor (0.28)
and was significantly lower than that of imazaquin (0.42). All
three herbicides were 43% more mobile through the subsoils than
through the surface soils. Mobility was negatively correlated
with soil organic matter and humic matter contents.
- Soil persistence: Field persistence
of chlorimuron and imazaquin was related to environmental conditions
after application and during the growing season and not to soil
characteristics. Regional and sub-regional studies indicated
that the half life of chlorimuron in soil varied between 5 and
34 days while the half life of imazaquin ranged from 5 to 35
days. In general, half life of both herbicides was greater under
no till conditions compared to conventional tillage. Half life
of imazaquin or chlorimuron determined in persistence studies
under controlled conditions did not correlate well with field
data. Chlorimuron residues reduced cotton yield, and direct application
caused injury and lowered soybean yield in some years in Arkansas;
however, imazaquin had no effect on either crop in Arkansas or
Mississippi.
- Plant response: Corn response to chlorimuron
concentrations was negatively correlated with soil pH. No correlation
was observed between GR50 values and chlorimuron concentration
in the soil water or uptake by the plant. Corn response to imazaquin
concentrations was not correlated with any soil property. GR50
values were positively correlated with imazaquin concentration
in soil water and negatively correlated with uptake by the plant.
The results indicated that the influence of environmental factors
on plant response to the herbicides is unclear.
- Microbial response: Soil microbial
populations were neither stimulated nor inhibited by either imazaquin
or chlorimuron applications in the regional field persistence
studies.
- Bioassay: Bioassay results were highly
variable in these studies. For example, results from the regional
field study indicated that the half life of chlorimuron in the
MS Marietta 1 soil in 1988, 1989 and 1990 was 6, 6 and 5 days,
respectively, and the subregional field study suggested half
lives of 63, 13, and 17 days, respectively, for the same years
and location. The same variability was observed for imazaquin.
Bioassay techniques were evaluated and found to provide differing
results. The results indicate that further work is needed to
determine the influence of soil and environmental factors on
bioavailability of these herbicides and that work on developing
consistent bioassays is needed.
- Minutes of meetings
- Link
to SAAESD home page
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- Link to list of other SAAESD regional and interregional
projects' web sites
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- Link to lists of all SAAESD projects and special
project groups
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- Link to SAAESD
Good Laboratory Practices home page
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Updated January 21,
2000, by Dave Edmark, University of Arkansas: dedmark@comp.uark.edu