Souza, Rosinei Aparecida de, et al. “Minimal Set of Parameters for Evaluation Soil Microbiota and Biological Nitrogen Fixation in Soybean”. Pesquisa Agropecuaria Brasileira, vol. 43, no. 1, Jan. 2008, pp. 83-91, doi:10.1590/S1678-3921.pab2008.v43.7963.