Soil wetting and texture effects on aggregate stability, seal formation, and erosion

Previous studies about the effect of antecedent moisture content (AMC) on seal formation have shown contradictory results. We hypothesize that this controversy is related to differences in slaking during wetting. The objectives were to analyze the effects of: (i) clay content on aggregate stability and slaking; (ii) clay content and slaking on seal formation and interrill erosion under various wetting rates (WR) and AMC under simulated rain. Aggregate stability was determined on six smectitic soils from Israel with clay content from 80 to 630 g kg^-1. In the rain simulator, soils with 230, 410 and 620 g kg^-1 clay were prewetted with WR = 1 and 5 mm h^-1 to AMC = 0.25 and 0.5 of field capacity (FC), prior to the application of 80 mm of rain. Aggregate stability and slaking by fast WR increased with increase in clay content. In soils with 230 and 410 g kg^-1 clay, raindrop impact was enough to disintegrate the aggregates and sealing was not affected by WR and AMC. Conversely, in the soil with 620 g kg^-1 clay, seal formation increased with slaking caused by fast wetting. Thus, final infiltration rate of the clay soil with AMC = 0.5 FC and WR = 1 mm h^-1 was 11.1 mm h ^-1 compared with 6.0 mm h^-1 in the air-dry soil (fast wetting by rain). The effects of WR and AMC on soil loss were similar to their effect on runoff but more pronounced. The relation between wetting process and clay content should be considered when predicting soil erosion in smectitic soils.