The aim of this experiment was to evaluate the nitrogen of the microbial biomass under different soil management systems by the fumigation-incubation (FI) and fumigation-extraction (FE) methods. Soil samples were collected in four seasons, during one year, from a Paleudult soil in the Central Depression of Rio Grande do Sul State, Brazil. Soil microbial biomass N was analyzed in soil under three tillages systems (conventional, reduced and direct drilling) and two crop systems: oats (Avena strigosa) + vetch (Vicia sativa)/corn (Zea mays) + cowpea (Vigna sinensis) and oats/corn), at two depths (0-5 cm e 5-15 cm). The FE procedure was used in the last two evaluations, after soil tillage. The greatest values of microbial biomass N were found in soil from direct drilling and oats + vetch /corn + cowpea, in the upper 0-5 cm. The analyses by the fumigation-incubation method presented the lowest variation, showing that the method is useful in evaluations of soil management systems.
fumigation-incubation; fumigation-extraction; soil tillage; crop systems