A Field Study to Evaluate Leaching of Aldicarb, Metolachlor, and Bromide in a Sandy Loam Soil
- Charles N. Smith * and
- Rudolph S. Parrish
Transport and transformation of pesticides used in agricultural situations are subject to variability from several sources that are impossible to simulate in laboratory settings. This study was conducted to characterize pesticide leaching behavior under conventional cropping conditions and to determine the impacts of related sources of variability. An agricultural field site (Ardilla fine sandy loam, Clarendon loamy sand, Tifton loamy sand, and Lucy loamy sand) located within the Dougherty Plain region of southwest Georgia was used to study pesticide movement in unsaturated and saturated soil zones from 1984 through 1988. A granular formulation of aldicarb [2-methyl-2-(methylthio) propionaldehyde O-(methylcarbamoyl) oxime], an emulsifiable concentrate of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], and a bromide (Br−) tracer were applied on peanut (Arachis hypogea L.) crops under modified conventional tillage practices. Postapplication vertical movement was monitored for periods of up to 111 d for pesticides and 1307 d for Br−. Application distributions for aldicarb showed measured coefficients of variation ranging from 42 to 72, and for metolachlor from 23 to 44. Spatial variability analyses indicated the existence of small-scale correlation for both pesticides upon initial application, and some large-scale trending was observed for metolachlor. Field-based transformation rates of aldicarb were up to three times higher than laboratory-based values. There was no evidence of migration of any of the pesticides into the saturated zone during the study, although Br− was observed at less than 1 mg kg−1 in well-water samples. Aldicarb degraded almost completely within 90 d each year, and it was not observed below 1.2 m. Metolachlor profiles always showed concentrations decreasing with increasing depth, and there was no significant movement below 0.3 m. Bromide was observed in soil samples as deep as 3 m only on the 1307th d, and the profiles showed peak concentrations no lower than 1.5 m with relative vertical dispersion increasing continuously.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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