Residual Fluometuron Levels in Three Arkansas Soils under Continuous Cotton (Gossypium hirsutum) Production

Abstract

Evidence has shown that fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl]urea} persists beyond the end of the growing season when used in continuous cotton (Gossypium hirsutumL.) production. Samples were taken from three soils following cotton production in 1980, 1981, and 1982. All three soils had been in production under the same herbicide use regime, fluometuron preemergence followed by fluometuron plus MSMA (monosodium methanearsonate), since either 1976 or 1977. The fluometuron remaining in each soil was quantified using a greenhouse bioassay and a chemical extraction technique followed by high-performance liquid chromatography determinations. The fluometuron concentrations determined by bioassay and chemical extraction methods had partial correlation coefficients of 0.62, 0.91, and 0.72 for a Sharkey silty clay, a Dundee silt loam, and a Loring silt loam, respectively. Predictive equations were determined for each soil to relate chemical extraction findings to plant response. Bioassay analysis indicated nearly 2 ppmw of fluometuron in the Sharkey silty clay in October 1980, with 1 ppmw in the Dundee silt loam, and approximately 0.27 ppmw in the Loring silt loam with annual application rates of 4.0, 2.9, and 3.5 kg/ha, respectively. Fluometuron concentrations as determined by chemical analysis were 0.83, 0.34, and 0.14 ppmw, respectively. Fluometuron concentrations declined over the winter in all three soils. Samples taken in March of 1981, 1982, and 1983 showed little difference in carryover levels in the Sharkey silty clay but more yearly variation in the other two soils. Fluometuron was found in all three soils to depths of 60 cm, but more than 55% of the fluometuron was found in the upper 15 cm of each soil. A controlled laboratory study conducted with the three soils showed that both cold and dry conditions reduced fluometuron dissipation rates. In the laboratory under conditions favorable for dissipation, fluometuron had a half-life of 26 days in the Dundee silt loam, 43 days in the Loring silt loam, and 73 days in the Sharkey silty clay. In the field, dissipation was very rapid in the Loring silt loam compared to the Dundee silt loam and the Sharkey silty clay.

Soil pH Effect on Imazaquin Persistence in Soil

“…The degree of herbicide adsorption to soil is one factor that influences the rate of degradation, partly beca.use those herbicide molecules tightly bound to soil col-lOIds are partially unavailable to soil microorganisms for breakdown (I, 2, 6, 16). As a result, herbicides generallỹ ersist longer as soil organic matter and clay content Increase and soil pH decreases, presumably because of greater adsorption (19,21,23). The rate of imazaquin ---lR .…”

Carryover of DPX-PE350 to Grain Sorghum (Sorghum bicolor) and Soybean (Glycine max) on Two Arkansas Soils

“…Soil physical and chemical properties in combination with herbicidal characteristics influence dissipation. Certain herbicides are more persistent in soils with high organic matter and clay content, with increased persist ence attributed to greater adsorption of the herbicide to soil and less availability for degradation (3,5,22,23,24). Chlorsulfuron {2-chloro-AT-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)anMno]carbonyl]benzenesulfonamide} and chlorimuron 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid} are more persistent on soils with high pH (1,28,30).…”

Degradation of Persistent Herbicides in Riparian Wetlands

“…The major mechanisms of disappearance of fluometuron are biological degradation (20) and leaching (10,21). Fluometuron ia a moderately persistent herbicide with reported half-life values from 26 days (22) to twelve weeks after summer field application, and up to 52 weeks upon fall field application (23). One million kilograms of fluometuron were used in the cotton-producing region of the United States in 1993 (9).…”

“…No references were found in the literature to the activity of fluometuron in soil under anaerobic conditions, though one of the laboratory degradation studies was almost certainly carried out under anoxic conditions (23). No influence of organic matter content was found on fluometuron degradation rates (10,22,53) indicating that microorganisms can use fluometuron as a primary substrate rather than relying upon secondary metabolism or cometabolism. Degradation rates decreased with depth in one field study, correlating with microbial biomass decrease (29).…”