Degradation of imazethapyr in soil: impact of application rate, soil physicochemical properties and temperature

A dissipation study of pesticides in soil is essential as it is a major sink for bulk of globally used pesticides. Soil properties, temperature and application rate play important role in its degradation. Laboratory studies were carried out in order to assess the degradation dynamics of imazethapyr under subtropical conditions. In all soils, at all studied temperatures dissipation followed single first-order kinetics at lower application rates (0.0375 and 0.187 µg g−1) with half-life varying from 30.15 to 52.16 days. However, at higher application rate (0.8 and 1.5 µg g−1), dissipation followed biphasic first-order kinetics and half-life varied from 6.57 to 7.79 days (p > 0.05) during initial phase and 93.74–152.83 days (p < 0.05) during final phase. Dissipation rate was fastest in alkaline soils (pH = 8.0–8.8) followed by neutral soil (pH = 7.4) and acidic soil (pH = 5.0). Amendment of soil with farmyard manure and increase in temperature enhanced the dissipation of imazethapyr. Application of imazethapyr at low rate has nonsignificant effect on dehydrogenase and alkaline phosphates activity, whereas short and momentary toxic effect was observed at 0.8 and 1.5 µg g−1. These findings indicate that soil physicochemical parameters especially pH, OM content and temperature should be considered in combination along with the application rate of imazethapyr for achieving satisfactory weed control and reducing environmental risk associated with the use of imazethapyr in different crops.