Escalante, Gladys, et al. “Nitrogen Fixation in Shade Trees (<i>Erythrina poeppigiana< I>) in Cacao Plantations in North Venezuela”. Pesquisa Agropecuaria Brasileira, vol. 19, no. 13, July 2013, pp. 223-30, doi:10.1590/S1678-3921.pab1984.v19.17535.