Effect of long-term irrigation of treated distillery waste water on microbial activity and heavy metals content in a Vertosol under sugarcane cropping system

Abstract

A field experiment was conducted to evaluate the effect of long-term application of spentwash on heavy metals content in soil and sugarcane crop in Northern Dry Zone of Karnataka. The distillery effluent was characterized by neutral pH (7.37), high EC (17.32 dS m-1), high biological oxygen demand (7200 mg L-1), and chemical oxygen demand (18032 mg L-1). The application of spentwash significantly increased the microbial activity in the soil; among different periods of spentwash irrigation dehydrogenase activity ranged between 51.77 to 43.77 μg TPF g-1 of soil day-1, phosphates activity 105.22 to 88.24 μg PNP g-1 of soil hr-1 and urease activity 141.7 to 107.5 μg NH4- N g-1soil hr-1. Distillery effluent application for 5-10 years recorded the higher dehydrogenase (51.77 μg TPF g-1 of soil day-1) and urease activity (141.7 μg NH4- N g-1soil hr-1) while higher phosphates activity (105.22 μg PNP g-1 of soil hr-1) in 10-15 years spentwash irrigated treatment. The distillery effluent application appeared to have promoted the enzymatic activities in soil as lower microbial activity was observed in the control treatment. The present study has shown that sugarcane distillery effluent had slightly elevated levels of toxic heavy metals like cadmium (Cd), arsenic (Ar), and chromium (Cr) therefore seemed not fit for long-term irrigation or disposal without applying proper remedial measures.