Soil-Aggregate Stability Under Conservation Tillage and Sod-Based Crop Rotations.

A desire for healthy food and environmentally friendly farming systems has made sod-based rotations desirable in conservation agriculture. Integrating perennial grasses, such as bahiagrass (Paspalum notatum Flugge) in a rotation generally increases soil organic matter and plant nutrients for following row crops, while the quantification of aggregate stability depend on internal soil properties and external factors such as tillage and crop rotation management.

The objectives of this study were to: (i) determine aggregate size distribution in sod-based and non-sod/row-crop rotations, and (ii) assess the effect of system-management on aggregate stability.

Perennial sod has an effect on soil aggregation, but the proportion of the sod in a crop rotation may affect the quantification of aggregate size distribution. In an 8-year sod-based rotation study with different row-crop and grass-sod sequences the aggregate separation was made from 0 to 20-cm depths with a 5-cm increment in a range (0-100%) of sod-based crop rotations. Aggregates separated by dry and wet sieving methods were compared. Five aggregate-size ranges (2, 2-1, 1-0.5, 0.5-0.25, and 0.25-0.053 mm) were obtained by sieving. The mean weight diameter (MWD) of the aggregates was calculated and correlated with the soil properties. The smaller the aggregate, the higher was the aggregate stability according to MWD. The aggregate-size status differed between crop-rotation systems as well as between the depths within a system. In spite of conservation tillage the permanent sod and the rotations without sod decreased in aggregate stability compared with the sod-based rotations.