Studies in biosolids as a fertiliser on acid soils: effects on phosphorus, copper and zinc

This study investigated the P sorption properties of 15 acid soils from Illawarra, and the effects of adding biosolids based on sugarcane P requirements on the chemistry of soil P, Cu and Zn. Three highly weathered soils were treated with biosolids where each soil received 0, 70, 140, 210 kg P/ha i.e. (0, 5, 10, 15 g/ kg) and incubated at 25'C for 90 days at either 80 or 100 % water holding capacity. Subsamples of the incubated soils were periodically extracted for soil solutions and for P sequential fractionation studies. Soil solutions were extracted by centrifugation technique and the concentrations of Al, Ca, Cu, K, Mg, Na, P, S, Zn were determined. Sequential fractionation of solid phase P was conducted to study the changes in inorganic and organic P in the soil components. In order to monitor the contribution of microbial processes to soil solution P, the microbial population activity was monitored by CO2 evolution and by the extraction of microbial biomass. In a subsequent experiment, the distribution of Cu and Zn in the soil components was fractionated from biosolids amended soil samples which had been subjected to 14 wetting and drying cycles.