Crop rotation and tillage systems to control root rot and leaf spot diseases of wheat in Brazil

Soil degradation under conventional tillage is a major ecological problem in Brazil. It has been reported that more than 240 million tons of soil were lost every year in the southernmost Brazilian state up to the end of the 1980 decade due to excessive soil cultivation and heavy rainfall. To prevent erosion farmers were recommended to adopt no-till with debris preserving practices. However, the maintenance of crop residues on soil surface promotes a suitable environment for survival and rapid increase of necrotrophyc pathogens. Tests of crop rotation and soil tillage systems were carried out in Passe Fundo, State of Rio Grande do Sul, Brazil, over the past ten years, aiming to control root rot and leaf spot diseases of wheat. The incidence of leaf spot diseases was reduced by crop rotation, but their severity was not. Nevertheless, crop rotation and tillage systems significantly reduced root rots and increased wheat yields. Although chisel plowing was efficient in controlling root rots and increasing wheat yield, the benefits of disease control by incorporating crop residues into the soil by plowing do not justify the high risk of soil erosion losses.