Borkert, Clóvis Manuel, et al. “Soybean Response to Fertilization and Potassium Availability in Latossolo Roxo álico (Oxisol)”. Pesquisa Agropecuaria Brasileira, vol. 32, no. 11, Nov. 1997, pp. 1119-2, doi:10.1590/S1678-3921.pab1997.v32.4768.