Rosolem, Ciro A., et al. “Soybean Potassic Fertilization in a Dark-Red Latosol Sandy Loam”. Pesquisa Agropecuaria Brasileira, vol. 19, no. 11, Apr. 2014, pp. l319-26, doi:10.1590/S1678-3921.pab1984.v19.16149.