Changes in Soil Microbial Functioning Associated With the Removal of Increasing Amounts of Trash in Areas of Green Sugarcane in Northeastern Brazil.

The use of sugarcane trash as a source of energy is appealing both economically and environmentally, if one considers its renewable nature. However, removing trash from soil surface in areas under green sugarcane may affect soil quality. Microbial variables have been long proposed as sensitive indicators to monitor changes in soil quality. The aim of this study was to evaluate the response of soil microbial functioning (SMF) to the amount of trash left in areas of green sugar cane, as to indicate the minimal amount of trash to be kept in the field for soil protection purposes. SMF was analyzed as the response of ten pooled microbial variables using multivariate techniques. The experiment was conducted at Usina Coruripe (Alagoas State) in an Ultisol, and was arranged in a randomized block design, with five treatments representing the proportions (0, 25, 50, 75 and 100%) of straw kept on soil surface relative to the maximum quantity produced and four replications. After the second harvest, soil samples were collected from a depth of 0-10 cm and analyzed for the following variables: microbial biomass C (MBC), basal respiration (BR), metabolic quotient (qCO2), acid phosphatase, β-glucosidase, aryl sulfatase, cellulase, invertase, laccase and total enzymatic activity expressed by the hydrolysis of fluorescein diacetate (FDA). The removal of trash from soil surface reduced MBC, BR, FDA and the activity of many enzymes related with the cycles of C, P and S. However, this response was not linear, since the SMF did not differ between 75 and 100% remaining straw. The SMF decreases with the removal of trash from the soil surface, but did not differ between the levels of 75% and 100% of remaining residues. Financial support: Petrobras S.A.