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SOIL PHYSICS

Aggregate Stability and Erosion Response to Antecedent Water Content of a Loess Soil

Ghent Univ., Dep. of Soil Management, Coupure links 653, B-9000 Ghent, Belgium

^* Corresponding author (jan.vermang{at}UGent.be).

Soil erosion processes are affected by the erodibility of the soil and by the erosivity of the rain. The effects of rain characteristics and invariant soil properties such as texture and organic matter content on soil erosion processes are well documented. The effect of antecedent soil water content (_a) on aggregate breakdown, seal formation, and subsequent soil erosion is much more disputable, however, as opposing effects have been reported. We conducted lab experiments with a rainfall simulator on a Belgian silt loam soil. The objectives were to determine the effect of _a on seal formation, runoff, and soil loss and to evaluate its effect on an empirical sediment transport equation. Air-dried soil aggregates were subjected to _a of 0.04 (air-dry aggregates), 0.12, and 0.19 m³ m^–3. No runoff occurred on the soils with the highest _a, highest total runoff values were observed for intermediate _a, while intermediate amounts of total runoff were observed for the air-dry aggregates. Soil loss, however, showed a different trend: highest values were found for the lowest _a, intermediate values for the intermediate _a, and no soil loss for the highest _a. We further observed that _a had no influence on the final runoff rates and on the final infiltration rate through the soil surface. In using a water discharge and stream power equation to predict sediment transport, the intercept and exponent of the regression equations were found to be lower for _a of 0.19 than 0.12 m³ m^–3, indicating decreasing erodibility with increasing _a. We therefore suggest including _a as an additional variable to assess soil erodibility in deterministic event-based water erosion models.