SLOPE AND GYPSUM EFFECTS ON INFILTRATION AND ERODIBILITY OF DISPERSIVE AND NONDISPERSIVE SOILS

Water quality and soil chemical properties affect aggregates' stability, seal formation, and infiltration rate (IR). The effect of these factors on soil erosion was the subject of this study. Six different soils were used. The IR and soil losses were measured using a rainfall simulator and soil trays 0.3 by 0.5 m in size. The soils were divided into groups: those that were dispersive and susceptible to seal formation, and those that were nondispersive and maintained high IR. The dispersive soils were more erodible than the nondispersive soils. Spreading 5 Mg ha-1 phosphogypsum (PG) on the soil surface decreased the soil loss sharply from the dispersive soils and moderately from the nondispersive soils. The slope-factor values (the ratio of soil loss per unit area at any slope to soil loss at a standard 9% slope) of the nondispersive soil could be predicted by the Water Erosion Prediction Project (WEPP) model. However, for the dispersive, untreated soils, the equation S = exp(-0.58 + 6.67 sin theta), where theta is the slope angle in degrees, defines the slope factor better than the WEPP model. The interrill erodibility constant (K(i)) values (computed by WEPP) of the dispersive soils were not significantly different from one another, despite the differences in their texture and organic matter content. Additionally, the K(i) values of the dispersive soils were generally higher than the K(i) values of the nondispersive soils and, for both soil groups, the K(i) values for the control treatment were higher than for the PG treatment. The relationship between the K(i) and the final IR was described significantly the equation K(i) = 3.31 (final IR)-0.8.