The agricultural use of biosolids has been stimulated, however, as the chemical composition of these residues is varied, the agronomic value and effects on soil quality characteristics need to be individually assessed in order to establish safety norms for their application. The present work evaluated biological characteristics after the application for two consecutive years of increasing doses (0, 6, 12, 18 and 24 t ha-1 dry matter) of biosolid generated by a PET fiber and resin industry. There was also a complete mineral fertilizer treatment in corn cultivation in a Cambisol, compared to an adjacent area under Brachiaria sp. without cultivation for the last ten years. The microbial biomass C and N, basal respiration and urease, beta-glucosidase and fluorescein diacetate hydrolysis activities were increased, while the acid phosphatase activity was reduced with the increase of biosolid rates. The different biosolid doses had no effect on the microbial metabolic quotient (qCO2). The decrease in phosphatase activity was related to the increase in phosphorus availability in soil rather than representing an adverse effect to biosolid application. With the application of 12 Mg ha-1 biosolid (agronomic recommendation), the basal respiration and fluorescein diacetate hydrolysis were higher and the phosphatase activity lower than in the soil that received mineral fertilizer, while the other parameters were not affected by these treatments. The mycorrhizal colonization of Brachiaria sp. did not differ among spontaneously growing plants in plots previously cultivated with corn and those of adjacent area. In spite of the lower spore number, an enrichment in the arbuscular mycorrhizal fungi species was observed in the cultivated plots. Organic carbon and microbial biomass were highly correlated with the other characteristics. This indicates that the changes in the amount and quality of soil organic matter, as a result of biosolid application, altered microbial dynamics and influenced the biological parameters of soil quality positively.
sewage sludge; microbial biomass; soil respiration; microbial metabolic quotient (qCO2); microbial activity; soil enzymes; fluorescein diacetate (FDA); beta-glucosidase; urease; phosphatase; arbuscular mycorrhizal fungi
