Effects of Copper Sulphate Application on Microbial Numbers and Respiration, Nitrifier and Urease Activities, and Nitrogen and Phosphorus Mineralization in an Alfisol

Abstract

ABSTRACT Fresh topsoil samples of an alfisol (Oxic Tropudalf) were moistened to 70% field capacity with CuSO4 solution to give varying concentrations of Cu; 0, 87, 174, 348 and 676 mg kg−1. The treated samples and the untreated controls were incubated at 30°C in a static microcosm for 8 weeks. The microbial respiration, and N and P mineralization were determined fortnightly. At the end of the experiment, total microbial counts, extractable Cu, pH, short-term nitrifier (SNA) and urease (UA) activities were also determined. Copper sulphate treatments significantly acidified the soil and reduced bacterial counts, microbial respiration, N and P mineralization, SNA and UA. Fungal counts, on the other hand, were significantly increased at the highest rates. The ratio of bacterial to fungal populations decreased from 2352:1 in the control to 2.5:1 in soil that received the highest concentration of Cu. Hence, fungi exhibited greater tolerance of high extractable Cu contents than bacteria. Nitrifier activity was significantly reduced by a lower Cu content than was UA. This study shows that repeated applications of CuSO4 could have detrimental effects on ecosystem functioning in terms of microbial numbers and composition, and nutrient cycling.