Slope and Phosphogypsum's Effects on Runoff and Erosion

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Abstract
The effect of slope on runoff and erosion has been studied mainly in stable soils. Loamy soils from semiarid regions have unstable structures and tend to seal during a rainstorm. The permeability of the seal is sensitive to water quality. The effect of slope angle (5–30%) and addition of phosphogypsum (PG), which changes the water quality, on the infiltration rate (IR), runoff and erosion from an unstable sandy loam soil material (Typic Rhodoxeralf) was studied using a rain simulator. Increasing the slope slightly reduced the amount of runoff and increased the final infiltration rate. The increase in final IR was due to seal erosion. The PG application increased the permeability of the seal, tripled the final IR of the soil sample and decreased the volume of runoff by 50%. Phosphogypsum application also reduced erosion by 60% at the gentlest slope angle. Change in slope angle from 5 to 25% doubled soil loss in the PG‐treated soil samples but increased by seven‐fold soil loss from the untreated soil samples. Gypsum treatment releases electrolytes into the percolating and runoff water. Its effect on soil erosion is due to decreasing the fraction of runoff water, stabilizing the soil structure at the soil surface, and increasing the rate of sediment deposition. The dramatic effect of PG in reducing erosion from steep slopes may be used in stabilizing soil structures on steep slopes.