Changes in the Microbial Metabolism of Agricultural Tropical Soils Amended with Sugarcane Vinasses

Sugarcane vinasse is a liquid waste derived from ethanol production. In Brazil, large amounts of this waste are applied to soil as fertigation. In general, this management seems to be beneficial for soil fertility and for some biological parameters, though the published information about the effects of sugarcane vinasse on the soil biota is controversial and the results may vary according to the vinasses' composition. In this study, we assessed the effects of different sugarcane vinasses on microbial growth and activity indicators to verify their influence on soil microbial metabolism. For this purpose, we used two vinasses from different distillery plants (VA and VB) and a vinasse from a laboratory production (VC). Increasing concentrations of these vinasses were amended on two tropical Oxisols, with 33.6% (RL) and 17.6% (RYL) of clay, in a microcosm experiment with sugarcane plants. Ten, 30 and 60days after application, we assessed the effects of the vinasses on soil microbial biomass carbon (MBC), basal soil respiration (C-CO2), the metabolic quotient (qCO2) and dehydrogenase activity of the soils. We found an increase in MBC, C-CO2, qCO2, as well as in dehydrogenase activity with increasing vinasse concentrations in both soils, when compared to the control. These changes were attributed mainly to the addition of carbon sources (C) of the vinasses to the soils, which improves the general biological activity.