Perez, Kátia Sueli Sivek, et al. “Microbial Biomass Nitrogen in Soil Cultivated With Soybean, under Different Management Systems, in the Cerrado”. Pesquisa Agropecuaria Brasileira, vol. 40, no. 2, Feb. 2005, pp. 137-44, doi:10.1590/S1678-3921.pab2005.v40.6934.