Soil chemical and physical attributes associated with Rhizoctonia root rot of soybean in southern Brazil.

Background and aims: There are controversies in the literature regarding the edaphic factors that may interfere with the occurrence of Rhizoctonia root rot in soybean, a disease caused by the soilborne fungus Rhizoctonia solani. The objective of this study was to determine which chemical and physical soil attributes are associated with the occurrence of Rhizoctonia root rot in soybean grown in a subtropical environment. Methods: Four fields with history of disease occurrence were selected, according to their soil class variability (Acrisol, Cambiol Ta, Cambisol Tb and Nitisol), in the municipality of Soledade, Rio Grande do Sul, Brazil. In each field, soil samples were collected in the 0–10 cm layer, inside and outside the bare patch with Rhizoctonia root rot, and in four repetitions for analysis of chemical and physical attributes. Results: The exchangeable contents and the saturation by aluminum and the extractable copper content were higher in the patch with the disease. On the other hand, the indicators of lower soil acidity (higher exchangeable calcium and magnesium content, pH value and base saturation) were the ones most associated with the area outside the patch. There was some association with soil texture regarding high clay content where the disease has been observed. Conclusion: Chemical attributes related to acidic soils are the ones most associated to the incidence of Rhizoctonia root rot in soybean grown in a subtropical environment in southern Brazil. [ABSTRACT FROM AUTHOR]