Role of Soil Amendments in Dissipation of Chlorpyriphos in Mollisols

The potential of some soil amendments namely, gypsum (5 t ha⁻¹), pyrite (5 t ha⁻¹), farmyard manure (FYM, 5 t ha⁻¹) and fresh cow-dung slurry (FCD, 0.5 t ha⁻¹) were evaluated for studying dissipation of chlorpyriphos (0,0-diethyl-O-3,5,6-trichloro-2-pyridinyl phosphorothioate), an organophosphate insecticide in mollisols under laboratory conditions. The data obtained in dissipation of chlorpyriphos in soil (0–15 cm) were evaluated after eight consecutive samplings (0, 1, 3, 5, 7, 10, 15 and 30 d). The results indicate that the degradation of chlorpyriphos was at faster rate during the first 7 days but thereafter became slower upto 30 days. Dissipation studies could be better accounted by biphasic pattern involving an initial faster and a later slower phase. The kinetics of dissipation of chlorpyriphos from soil could be accounted by two component (1 +1) first order kinetics. The half life of chlorpyriphos in control (without amendment) soil was 9.82 d in initial phase and 37.03 d in later phase which was reduced to 7.64 d in initial phase and 22.41 d in latter phase by treatment of FCD@ 0.5 t ha⁻¹ while FYM @5 t ha⁻¹ and gypsum @ 5 t ha⁻¹ showed no significant effect in the initial phase but their effect on dissipation of chlorpyriphos was better observed in later phase. A comparison of kinetic parameters among different treatments also revealed that faster dissipation fraction of applied chlorpyriphos from mollisols was significant under FCD treatments.