Measurement and prediction of permethrin persistence in six Malaysian agricultural soils

The effect of soil types, soil temperature, and soil moisture content on the degradation of permethrin was studied under controlled greenhouse conditions. Six soils were used in the study: Soil 1 (Teringkap series), Soil 2 (Ringlet series), Soil 3 (Teringkap 2), Soil 4 (Teringkap 3), Soil 5 (Gunung Berinchang), and Soil 6 (Lating series). Observed data showed that permethrin was more persistent in Soil 1 (23.3 days) and less persistent in Soil 5 (16.7 days). Similarly, the degradation rate coefficient (k) was greater in Soil 5 than Soil 1. The half-life and the dissipation patterns of permethrin between the observed and predicted data were not much different in all 6 soils studied, even though the predicted data were slightly higher. The half-life of permethrin in Soil 6 decreased as the temperature increased from 20degreesC (36.1 days) to 35degreesC (13.9 days). The degradation rate coefficient increased as the temperature increased. The predicted data derived from the model showed greater values than the observed data. The half-life of permethrin in Soil 6 decreased as the soil moisture increased from 30% (26.8 days) to 80% (20.1 days). The dissipation rate was not very different between the predicted and the observed data at 80% field capacity and at the temperature of 35degreesC, and it consequently became closer when the incubation period was prolonged.