Persistence and Movement of Chlorpyrifos in Sprinkler-Irrigated Soil1

Abstract

The chemical persistence and vertical movement of chloropyrifos 4EC in a loam soil were compared with respect to time of posttreatment sprinkler irrigation. Irrigation intervals of 0, 2, and 6 days posttreatment, together with a nonirrigated control, were assessed. Sprinkler irrigation (2 ha-cm of water) immediately after insecticide treatment reduced the dissipation rate of chlorpyrifos compared with delayed irrigation or no irrigation. Chemical persistence was least in nonirrigated plots. Chlorpyrifos dissipation rates were rapid during the 2 weeks after treatment. Thereafter, chlorpyrifos dissipation proceeded more slowly in all plots but relative rates were greater in nonirrigated plots. Vertical movement of the insecticide in the soil after sprinkler irrigation was minimal; greater than 99% of the total chlorpyrifos residue were found in the top 2.5-cm layer.