Influence of Organic Acids and Wetting-Drying Cycles on the Aggregate Stability and Size Distribution in a Calcareous Soil

Soil structure and aggregate stability are physical characteristics that directly and/or indirectly affect the other soil properties and growth of plants. These soil attributes are influenced by factors such as the type and amount of organic matter and soil water conditions. The effects of 0, 0.05%, 0.5%, and 5% organic acid and 1, 4, 8, and 12 wetting-drying (W-D) cycles of 10 days on the soil aggregate stability and size distribution were evaluated in a factorial experiment arranged in a completely randomized design with three replications. Mean weight diameters (MWD) of aggregates increased significantly (by 22%) as compared to the control when 4 cycles of W-D were applied, whereas geometric mean diameter (GMD) of aggregates was decreased by 27% and 23%, respectively, when 8 and 12 cycles of W-D were applied. Application of 4, 8, and 12 W-D cycles resulted in a significant decrease in D10, and application of 8 and 12 W-D cycles decreased D25, D30, D50, D60, and D75, significantly. The uniformity coefficient of the aggregate size distribution curve increased by 13%, 15%, and 11% when, respectively, 4, 8, and 12 W-D cycles were applied. Also, the curvature coefficient of the aggregate size distribution curve decreased by 6% in response to application of 0.05% organic acids. In general, W-D cycles decreased some indices of aggregate size distribution, while organic acids had no significant effect on aggregate stability. Organic acids could mitigate the adverse effects of W-D cycles. Therefore, their application in the regions with W-D cycles is recommended to reduce the adverse effects of wetting-drying process on the soil structure and aggregate stability, and the negative results of the consequent water and wind erosions.