Antecedent Moisture Content and Aging Duration Effects on Seal Formation and Erosion in Smectitic Soils

Soil susceptibility to seal formation and erosion depends on its inherent properties and surface conditions. Our objective was to study the interaction of two different surface conditions, antecedent moisture content (AMC) and aging duration, on seal formation and erosion in four smectitic soils. Soil samples were packed in trays and wetted with different amounts of water (0, 1, 2, 3, 4, 6, 8, or 16 mm) with a mist type rain. The wetted samples were put in plastic bags and allowed to age for 0.01, 1, 3, or 7 d. The soil trays were exposed to 60 mm of distilled water rain of high energy. At no aging (0.01 d), runoff volume (a measure for seal development) and soil loss increased with an increase in AMC mainly because of enhanced slaking. In general, runoff and soil loss decreased with the increase in aging duration. For instance, in the Clay (Y) soil, to which 3 mm of water was added, as aging increased from 1 to 7 d, runoff decreased from 39 to 28 mm, and soil loss decreased from 660 to 397 g m² For any given aging duration, the smallest runoff volume and soil loss were obtained at the intermediate AMC levels (2, 3, and 4 mm of water added); at this AMC range, increasing aging time resulted in up to 40% decrease in runoff or soil loss. The effects of aging at these AMC levels (generally between wilting point and field capacity [i.e., pF 4.1–2.4]) were significantly more pronounced for clay soils probably because at these AMCs water-filled pores in the clay fabric were considered active in the stabilization process and the development of cohesive bonds between and within particles during the aging period. Soil erosion changed with the increase in aging duration in a manner similar to runoff, suggesting that runoff was the main precursor to erosion under these conditions.