de Mendonça, Marcio Mattos, et al. “Genotypic Variability of Maize for Nitrogen Accumulation and Contribution of Biological Nitrogen Fixation”. Pesquisa Agropecuaria Brasileira, vol. 41, no. 11, Nov. 2006, pp. 1681-5, doi:10.1590/S1678-3921.pab2006.v41.7332.