Santos, Henrique Pereira dos, et al. “Risk Analysis of Four Crop Rotation Systems for Wheat, over a Ten-Year Period, in Passo Fundo, RS”. Pesquisa Agropecuaria Brasileira, vol. 34, no. 4, Apr. 1999, pp. 519-26, doi:10.1590/S1678-3921.pab1999.v34.5199.