Effect of Soil Conditions on Persistence of Chlorpyrifos

The persistence of chlorpyrifos in red loam (Oxisol, fine loamy kaolinitic isohyperthermic typic Kandiustult) soil was studied with ten different treatment combinations to assess the effect of a crop individually and in combination with organic matter and lime. At 0–15 cm soil depth, initial deposit of chlorpyrifos when applied @400 g ha⁻¹ was found to vary from 4.0–11.3 µg g⁻¹, which reduced to 1.6–7.3 µg g⁻¹ after 75 days of application, corresponding to a reduction of 60–35.4%. Maximum persistence of chlorpyrifos was observed with the addition of organic manure @ 201 ha⁻¹, witn a half life of 235 days. The half life of chlorpyrifos in cropped condition was only 149 days, while application of organic manure @ 101 ha⁻¹ did not hasten the dissipation of chlorpyrifos and application of lime at recommended dose further lowered it to 67–70 days. Among the different treatments, application of lime was found to have maximum influence on the degradation of chlorpyrifos in soil, followed by organic matter addition at lower rate. The presence of a crop significantly influenced the degradation of chlorpyrifos in soil. Treatment with chlorpyrifos did not affect soil properties