Microbial biomass, carbon and nitrogen stocks across land uses and soil types in the Brazilian tropical dry forest region

The Brazilian native dry forest (Caatinga) is used as a natural pasture or converted to unfertilized and overgrazed pastures. We investigated the restoration process, measuring soil attributes after three years of cattle exclusion in four soil types under the most common land covers of the region (dense and open Caatinga and pasture). C and N stocks tended to be higher under the dense Caatingas than under the other vegetation covers, particularly in the Regosol (80 and 8 Mg ha⁻¹), but tended not to significantly differ between the open Caatingas and the pastures. Microbial biomass C had the same trend, higher under dense Caatingas and in the Regosol (553 mg kg⁻¹). Basal soil respiration and C decay constant (0.02 day⁻¹) tended to be lower (thus higher C half-life, 347 days) in the Regosol (higher rainfall sites). The Oxisol (lower fertility soil) separated from the other soils in a Principal Component Analysis, especially from the Luvisol (highest fertility soil). Therefore, studies in the region must consider soil types and rainfall. The differences between open Caatingas and pastures in the dense Caatinga indicate that the period necessary for soil recovery after grazing exclusion is longer than three years, including for the microbial population.