Toxic Effects of Distillery Sludge Amendment on Microbiological and Enzymatic Properties of Agricultural Soil in a Tropical City

Distillery sludge application in degraded soils is amongst the most important economical resources for the soil fertility amelioration through improvement in soil water-holding capacity, texture, structure, nutrients retention, roots penetration, and reduction in soil acidity [1-3]. Presently due to the ever increasing number of sugar mills and distillery units in the country, it is now become mandatory to use the distillery sludge as a fertilizer to enhance the fertility levels of the soil. However, its application in soil also results in environmental problems [4] because apart from organic content and nutrients, sludge also includes toxic compounds, heavy metals, coloured compounds i.e., melanoidin, caramel colorants, dissolved inorganic salts, chlorinated lignin, and phenolic derivatives [5]. Thus, soil microorganisms may be affected via variation in soil temperature, pH, nutrient status, heavy metals, oxygen level and which in turn can affect the ecological processes linked with nutrients cycling [6]. Soil microbial activity, often linked with fertility levels, has been found to be indicated by microbial biomass, microbial respiration, hydrolysis of fluorescein diacetate (FDA), and activity of phosphatase and urease [7-9]. Microbial biomass is the 1-5% active fraction of organic matter of the soil, related with the soil fertility and is highly susceptible to soil pollution than the bulk organic matter. It acts as a reservoir of nutrients and gradually releases it into soil with passage of time which influences soil fertility levels. Soil respiration determines the effect of sludge amendment on soil microbial activity terms of carbon dioxide evolution. In this study, we have chosen enzymatic activities representative of main steps of soil biogeochemical nutrient cycles, i.e. C (FDA hydrolytic activity), N (urease), P (phosphatases), and microbial biomass (Dehydrogenase and FDA hydrolytic activity). Fluorescein diacetate has been used to determine amounts active microorganism. Hydrolysation product of FDA by a number of soil enzymes, such as proteases, lipases, and esterases is fluorescein, which can be easily visualized to estimate *Corresponding author: Prof. B. D. Tripathi, Coordinator ,Centre for Environmental Science and Technology, Banaras Hindu University, Varanasi-221005, India, Tel: 0542-2311130; Fax: 2368174; E-mail: [email protected], smriti_envs@ yahoo.co.in