The least limiting water range (LLWR) is considered a modern indicator of soil physical quality for plant growth. The aim of this study was to determine the LLWR for assessing the soil physical quality of a dystroferric Red Latosol (Oxisol) under no-tillage in a crop-livestock integration system. In the crop-livestock integration system of the study area, soybean was planted in the summer and oat (Avena strigosa Schreb) plus ryegrass (Lolium multiflorum Lam) in the winter with different pasture heights during grazing: 7, 14, 21, and 28 cm, and an ungrazed control. Undisturbed soils samples were taken from the layers 0-7.5 and 7.5-15 cm, in which the soil bulk density (Bd), soil water retention and soil resistance to penetration curves were determined, to then calculate the LLWR. The critical soil bulk density (Bdc) was determined for LLWR=0. Regardless of the treatments, it was found that an increase of the soil bulk density requires an increase of soil water contents to maintain soil penetration resistance below 2.5 MPa and a decrease in soil water to ensure adequate soil aeration, mainly in the 0-7.5 cm layer. In the treatments with grazing heights of 21 and 28 cm, the magnitude of LLWR was greater than in the control, suggesting that crop-livestock integration creates a positive soil physical environment, provided that an appropriate stocking is maintained to prevent overgrazing. In the 7 cm treatment, the soil physical degradation was very high in the 0-7.5 cm layer, and certainly predisposes the crops to stress resistance to soil drying and to reduced aeration under prolonged conditions of high soil moisture. A progressive reduction in the proportion of samples with greater bulk density values than the critical density of the 7 cm treatment toward the control was verified, indicating that the treatment effect of excessive animal trampling resulted in a loss of soil physical quality in the 0-7.5 cm soil layer. The grazing height of oat and ryegrass pasture should be maintained above 21 cm to ensure adequate physical soil quality in the 0-7.5 cm soil layer.
soil physical quality; bulk density; penetration resistance; soil structure; available water
