Relationship of chemical fractions of heavy metals with microbial and enzyme activities in sludge and ash-amended acid lateritic soil from India D. Chaudhuri Æ S. Tripathy Æ H. Veeresh Æ M. A. Powell Æ B. R. Hart Abstract The influence of metals, Cd, Cr, Cu, Ni, Pb and Zn, on the microbial biomass and enzyme activities of an amended acid lateritic soil were investigated under field conditions receiving a one- time application of 52 t ha )1 of sludge, coal ash and their mixtures at 1:3, 1:1 and 3:1 proportions, and including control and chemical fertilizer treatment at crop-specific recommended doses. Paddies and peanuts were grown in the experimental plots and soil was sampled twice after 6 months and 1 year after amendment application. The heavy metals in the soil were fractionated using sequential extraction and the increments in their concentrations in amended soil with respect to the control were determined. Concentrations of Cd, Ni and Zn were determined to have increased in their mobile fractions and were more pronounced in soil collected during the second sampling, which was associated with a decrease in soil organic carbon. The size of the microbial biomass carbon and the soil enzyme activities increased with the addition of an amendment and was highest at equal proportions of coal ash and sludge. Further increase in the proportion of sludge resulted in a significant decrease in biomass carbon. Simple correlation revealed significant and strong negative relations of mobile fractions of Cd and Ni with the ratio between microbial biomass C and organic carbon in soil, while the organic carbon content and the pH were positively correlated. The microbial activities were determined to be sensitive to the concentrations of some heavy metals in mobile fractions and therefore indicated possibilities of being useful as indicators for evaluation of toxic effects of sludge-borne metals on soil organisms. Keywords Coal fly ash Æ Sewage sludge Æ Heavy metals Æ Soil enzymes Æ Microbial biomass Æ India Introduction Agricultural use of coal ash and sewage sludge is gaining practice and is being considered as one of the alternative avenues for gainful utilization as opposed to disposal in water bodies or land/lagoons. Coal ash and sewage sludge contain essential micro- and macronutrients beneficial for plant growth and improved physicochemical properties of soil. Mixtures of coal ash and sludge provide a more nutritionally balanced soil amendment as application of sludge alone tends to increase acidity in soil due to proton release from organic matter decomposition, while ash alone is a poor source of N and P. Associated with their utilization, however, is the environmental risk of potential buildup of toxic elements in soil leading to the deteriora- tion of the overall soil microbial health. Repeated appli- cation of sludge may lead to the accumulation of trace metals in soils, causing adverse effects on its microbial activity and also crop productivity (Baath 1989; McGrath and others 1994, 1995; McBride 1998; Giller and others 1998). The accumulated trace metals may reduce the amount of microbial biomass (Brookes and McGrath 1984; Chander and others 1995) and various enzyme activities (Mathur and Sanderson 1980; Kandeler and others 1996). In contrast, there are also reports of beneficial effects of low-sludge application rates on microbial biomass carbon and enzyme activities (Fliessbach and others 1994; Kunito and others 2001). Further, there are conflicting reports on the effect of ash on soil microbial activities. Lai and others Received: 30 September 2002 / Accepted: 10 June 2003 Published online: 22 August 2003 ª Springer-Verlag 2003 D. Chaudhuri Æ S. Tripathy (&) Æ H. Veeresh Department of Geology and Geophysics, Indian Institute of Technology, 721302 Kharagpur, India E-mail: trip@gg.iitkgp.ernet.in Tel.: +91-3222-283384 or 277194 Fax: +91-3222-277194 or 255303 M. A. Powell Æ B. R. Hart Department of Earth Sciences, University of Western Ontario, London, Ontario, N6A 5B7, Canada DOI 10.1007/s00254-003-0864-4 Environmental Geology (2003) 45:115–123 115 Original article