Palhano, João Baptista, et al. “The Use of Phosphate and Potassium Fertilizers in Soybean Culture in the State of Paraná, Brazil”. Pesquisa Agropecuaria Brasileira, vol. 18, no. 4, Apr. 2014, pp. 357-62, doi:10.1590/S1678-3921.pab1983.v18.15241.