Uso agrícola de lodo do tratamento de resíduos industriais e sanitários: impactos agronômicos na cultura do milho e nos indicadores microbiológicos de qualidade de solo

Abstract

Approximately four thousand tons of sewage sludge are produced daily in Brazil, so the application of this waste in agricultural areas has been identified as the most economical and environmentally viable condition of final disposal. The present work aimed to evaluate the agronomic impacts on the soil microbial community and its influence on the availability of nutrients from the sludge submitted about two forms of stabilization into maize soils. We assessed two forms of stabilization, is a chemical (LEQ) and a thermal (LET). The experiment was set up in a field experiment with the randomized block design, where doses of 0, 10, 20, 30, and 40 t ha-1 of sludge were applied in each form of stabilization. The maize was grown for three cycles, and at each of them, the plant's nutrition, dry matter production, grain yield, and soil chemical attributes at 0 to 20 cm depth layer were assessed. In the first crop of maize, soil microbiological parameters were investigated to determine the influence of microorganisms on the nutrients availability and the impact of sludge on the microbial community. Maize productivity increased due to the sludge doses increasing. Sludge doses had a residual effect (i.e., higher productivity than the control) until the third crop for 20 t ha-1. The highest doses of sludge (30 and 40 t ha-1) were more efficient than mineral fertilization, probably due to the content of micronutrients added by the sludge and the effects of organic matter on physical, chemical, and biological soil properties. The two forms of sludge application determine an increase in the enzymatic activity of β-glucosidase and dehydrogenase, while urease was reduced. LEQ addition promoted the highest abundance of bacteria and total fungi, while the functional gene abundance was favored by LET application. The application of treated sewage sludge under different forms of stabilization had a positive impact on the soil microbial community, inducing lower C-CO2 emissions due to the efficiency of existing microorganisms capacity in degrading the organic matter added in the soil, resulting in N release in the form of ammonium and nitrate besides P available to the soil.