Effect of foliar spray of different doses of selected insecticides on soil enzyme activity under brinjal cultivation

Abstract

A field experiment was conducted at the PG Research Block, College of Agriculture, KSNUAHS, Navile, Shivamogga to study the effect of foliar spray of different doses of acephate and lambda-cyhalothrin on soil enzyme activity under brinjal cultivation. The experiment was laid out in a randomized complete block design with seven treatments and three replications. The treatments consisted of different doses of acephate 75 SP and lambda-cyhalothrin 5% EC along with an absolute control (water spray). Soil enzyme activities such as dehydrogenase, acid phosphatase and urease were assessed at 0, 8 and 15 days after spray (DAS) during two consecutive insecticide applications using standard procedures. The results revealed that enzyme activities were significantly influenced by insecticide type, concentration and duration after spray. Initially, at 0th day (2 hours after spray), enzyme activities showed non-significant differences among treatments. However, a significant reduction in enzyme activities was observed at 8 DAS in insecticide treated soils compared to the control. The reduction was more pronounced with increasing dose of acephate, particularly at 1120 g a.i. ha-1, whereas lambda-cyhalothrin treated soils recorded comparatively higher enzyme activity. Partial recovery of enzyme activity was observed at 15 DAS in all treatments, indicating microbial adaptation and degradation of insecticide residues over time. During the second spray, enzyme inhibition was relatively greater, suggesting the cumulative effect of repeated insecticide application. Overall, acephate exerted stronger inhibitory effects on soil enzymatic activities than lambda-cyhalothrin. The study indicated that higher doses of insecticides can temporarily suppress soil biological activity, while lower doses cause comparatively lesser impact, emphasizing the need for judicious use of insecticides to maintain soil health and microbial functioning in brinjal cultivation.