Ethion degradation and its correlation with microbial and biochemical parameters of tea soils

Ethion, a highly persistent insecticide in soil, is extensively used in tea cultivation in the tropics. The studies on the environmental impact of ethion in tea soil ecosystems are scanty. Silty loam and sandy loam soils from tea fields of Dooars (Typic Uderthents) and Hill (Typic Dystrudepts), respectively, were investigated for the degradation and effect of ethion application on soil microbial and biochemical variables under controlled laboratory conditions. Ethion degraded faster in the Hill soil than in the Dooars soil. Higher temperature (30A degrees C) aided in faster degradation due to the increased microbial activity in the soils. Ethion application at field rate (FR) had lower half-lives (70 days at 20A degrees C and 42.3 days at 30A degrees C for Dooars soil; 65.4 days at 20A degrees C and 39 days at 30A degrees C for Hill soil) than at ten times FR (10FR; 75.2 days at 20A degrees C and 44.2 days at 30A degrees C for Dooars soil; 70 days at 20A degrees C and 41.8 days at 30A degrees C for Hill soil). Soil microbial biomass carbon, ergosterol content, fluorescein diacetate hydrolyzing and beta-glucosidase activities declined in all the treatment combinations up to day 60 for both FR and 10FR doses at 20A degrees C, irrespective of the soil types. At 30A degrees C, the decreasing trend was observed up to day 30 for both the soils. The toxicological effect of ethion on microbiological and biochemical parameters persisted till their corresponding half-lives. The microbial metabolic quotient and microbial respiration quotient were altered, but was short-lived, indicating ethion induced disturbances. The recovery of the depressive action at 10FR ethion spiking on the studied variables was of slightly longer duration than noticed at FR application, although the depressive effect was overcoming after the respective half-lives of ethion. The microbial and biochemical soil parameters were negatively correlated with application of ethion up to day 60 of incubation.