Effects of Soil Water Content on Pendimethalin Dissipation
1983
Barrett, Michael R. | Lavy, Terry L.
Laboratory and field studies were conducted to evaluate pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitroaniline] dissipation over time in a Crowley silt loam (Typic Albaqualfs). In the laboratory, dissipation rates approximately followed pseudo first-order kinetics over a 56-d period, except in air-dried soil that had no significant loss of pendimethalin detected after 56 d. Half-lives for 30 kPa, continuous flood, and alternately flooded and dried treatments averaged 59, 63, and 30 d, respectively, under laboratory conditions. Application rates of 0.5, 1.0, and 2.0 µg/g of soil did not have a significant influence on the half-lives. The ratio of pendimethalin residues in laboratory systems detected by a root bioassay with grain sorghum [Sorghum bicolor (L.) Moench.] to those detected with gas-liquid chromatography (GLC) declined by 17% from 0 to 56 d after treatment. Dissipation in the field in each of 2 y was studied with lowland rice (Oryza sativa L.) (flush irrigated then flooded 2–3 weeks after application), upland rice (flush irrigated throughout the season), and soybean [Glycine max (L.) Merr.] (furrow irrigated as needed) management systems. Soil water content had a strong influence on the amount of pendimethalin that dissipated, especially for about the first 2 weeks after herbicide application. Half-lives in the field were much shorter during the initial 2 weeks than after 2 weeks, with >50% of the applied herbicide having disappeared in 1 week for all treatments except in soybeans the first year. Soil persistence of pendimethalin was greater under soybean culture (soil-incorporated herbicide, low irrigation frequency) than under rice culture (surface-applied herbicide, high irrigation frequency, and/or flooded conditions).
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