Soil management systems, with different degrees of soil mobilization and different plant residue composition, alter soil biological properties, with consequences in soil quality and in plant productivity. In order to measure such alterations, soil microbial biomass and its activity were evaluated in a Paleudult soil, in the Central Depression of Rio Grande do Sul state, Brazil, conducted under different soil management systems, in a long-term experiment, for 12 years. Soil samples were collected in four different times, during 12 months, from three tillage (conventional, reduced and direct drilling) and two crop systems (oats (Avena strigosa) + vetch (Vicia sativa)/corn (Zea mays) + cowpea (Vigna sinensis) and oats/corn), in two depths (0-5 and 5-15 cm). Microbial biomass C was estimated using the chloroform fumigation-incubation method. Microbial activity was estimated through C-CO2 release and mineral N production after 60 days of incubation. Soil microbial biomass and activity were greater in the surface 0-5 cm under direct drilling and oats + vetch/corn + cowpea systems. Nitrogen mineralization was the most sensitive parameter evaluated, since it was influenced by tillage systems, crop systems and depth.
microbial biomass carbon; microbial activity; soil tillage; crop systems