de Azevedo, Watson Rogério, et al. “Boron Effects on Nodule Development in Pea Plants Cultivated in Lowland Soils”. Pesquisa Agropecuaria Brasileira, vol. 37, no. 8, Aug. 2002, pp. 1137-43, doi:10.1590/S1678-3921.pab2002.v37.6447.