Impact of Sewage Sludge Application on Soil Fertility, Microbial Population and Enzyme Activities in Soil under Rice-Wheat System

Abstract

A field experiment was conducted at Agricultural Research Farm, Banaras Hindu University, Varanasi, India for two consecutive years taking two crops each of rice and wheat in a sequence to study the effect of one time application of sewage sludge (SS) on soil fertility, microbial population and enzyme activities. Graded levels of SS were applied along with 50 and 100% recommended dose of fertilizers (RDF). The experiment was conducted in randomized block design taking 10 treatments with three replications. The soil pH decreased, while electrical conductivity (EC) and organic carbon (OC) content increased due to addition of SS. Application of SS in first crop and its residual effect in subsequent crops increased the available N, P, K and S content in soil. Higher available P was recorded in the second crop of the experiment, whereas, available K was high in third crop. Microbial colony count (bacterial and fungal) and enzyme activities (urease, phosphatase and dehydrogenase) were significantly increased due to application of SS resulting in higher microbial activity in post-harvest soils with 45 t ha-1 SS. Sewage sludge added during previous years had pronounced residual influence on soil fertility and microbial activity.