Soil organic matter in physical fractions after intensification of irrigated rice-pasture rotation systems

Abstract Crop-pasture systems improve soil quality, but their intensification through the increase of the frequency of annual crops may reduce it. We evaluated the impacts of six no-till rice rotations systems on soil quality after five years in a field scale long term experiment established on a site with a 30 years old stabilized rice-pasture rotation. Rotations included: continuous rice (ContRc); rice-soybean (Rc-Sy); rice-soybean-rice-sorghum (Rc-Sy-Sg); rice-soybean-pasture (Rc-Sy-Past); and rice-pasture, with short (Rc-SPast) and long-term pastures (Rc-LPast). Cover crops were included in winter between cash crops. All rotation phases coexisted and were replicated three times in space. Soil quality indicators included: soil organic carbon and total nitrogen contents in bulk soil (TSOC and TN, respectively) and in particulate (>53 μm, POM-C and POM-N) and mineral associated soil organic matter fractions (