Effect of rainfall electrolyte concentration and slope on infiltration and erosion

The quality of water used for irrigation and rainfall simulation studies may affect infiltration and soil erosion rates significantly due to the effect of dissolved salts on flocculation of soil clays. While these effects have been documented on smectitic soils, less information is available for kaolinitic soils, especially as a function of slope gradient. A small runoff pan (0.4 × 0.2 m) study was carried out to evaluate the effect of solution electrolyte content (CaSO₄ · 2H₂O added to give electrical conductivities (EC) = 0, 50, 100, and 200 mS m⁻¹) and slope (9%, 18%, 30%) on runoff, infiltration, and interrill erosion under a rainfall simulator at an intensity of 41 mm h⁻¹. For cultivated topsoils of Appling sandy loam and Davidson clay loam, increasing the EC to 50 mS m⁻¹ decreased the runoff percentage and decreased soil loss, but further increases in EC up to 200 mS m⁻¹ had little effect for either soil. The amount of soil loss reduction due to increased EC was greater at higher slopes for both soils. Soil loss increased significantly as the slope gradient increased at all EC values for both soils. Increasing EC to 50 mS m⁻¹ resulted in elimination of primary clay in sediment for both soils at all slopes, suggesting flocculation of clay was responsible for decreases in runoff and erosion with salt treatment. Flocculation tests on the soils showed 50 mS m⁻¹ as CaSO₄ was sufficient to flocculate the soils, suggesting such a test might predict EC values likely to affect the field behavior of the soils under rainfall.