Effect of Cultivation and Soil Tillage Systems on the Microbial Biomass in Castor Bean Crop at the Irecê Plateau, Bahia

Inadequate soil management alters the microbiological attributes of the soil, causing reduction in microbial biomass and activity. Microbial biomass is the living and active part of the soil and can serve as an indicator of changes in the quantity of due to changes in land use. This study aimed to evaluate the effect of intercropping and soil tillage systems on the microbial biomass in castor bean-based crop in the Irecê Plateau, Bahia, Brazil. The experiment was carried out on an eutrophic Haplic Cambisol with clay texture in the Mata Verde Farm of Alto do Quindinho, municipality of São Gabriel, Irecê Plateau, Bahia, Brazil. Six intercropping systems were evaluated including solely castor bean (control) and castor bean intercropped with each of the castor bean cake, common bean, pigeon pea, corn, and gliricidia. Plowing + harrowing and subsoiling were the two soil tillage techniques associated to the intercropping systems. C and N contents in microbial biomass (Cmic and Nmic), soil basal respiration and metabolic quotient were determined in soil samples collected from the 0-10 and 10-30 cm layers. The different soil management systems influenced microbial biomass and activity, and the most suitable conditions for soil microbiota occurred in the soil tillage system with subsoiling. In the semi - arid condition, at 0-10 cm depth, the castor bean + castor bean cake crop system promoted an increase of Cmic content, and the castor + gliricidia system increased Nmic content, both under soil tillage with subsoiling.