Silva Júnior, Elson Barbosa da, et al. “Cowpea Nodulation and Production in Response to Inoculation With Different Rhizobia Densities”. Pesquisa Agropecuaria Brasileira, vol. 49, no. 10, Nov. 2014, pp. 804-12, doi:10.1590/S1678-3921.pab2014.v49.19103.