Santos, Henrique Pereira dos, et al. “Crop Rotation in Guarapuava. X. Effects of Winter Crops on Some Agronomic Characteristics of Soybean Plants under Direct Drilling”. Pesquisa Agropecuaria Brasileira, vol. 26, no. 9, Sept. 1991, pp. 1551-6, doi:10.1590/S1678-3921.pab1991.v26.3497.