CLAY MINERALOGY EFFECT ON RAIN INFILTRATION, SEAL FORMATION AND SOIL LOSSES

The effect of clay mineralogy on seal formation, infiltration rate (IR) and soil loss was studied on 19 cultivated soils from South Africa (SA) using a laboratory rainfall simulator. Two soil treatments were applied: control and spreading phosphogypsum (PG) at the rate of 5 mg ha-1. The IR and soil losses were compared with the same parameters of smectitic soils from Israel. Based on the final IR values the SA soils were divided into two groups: (1) stable soils, in which the final IRs of untreated and PG treated soils were > 8 and > 18 mm h-1, respectively; and (2) dispersive soils, in which the final IRs were < 4.5 and > 12.5 mm h-1, respectively. The final IRs of the SA dispersive soils were similar to those of the smectitic soils from Israel. The soil loss rates of the SA dispersive soils were higher than those of the stable soils. However, the soil loss rates of the smectitic soils from Israel were significantly higher than those of the SA dispersive soils. It was suggested that soils in which either kaolinite or illite clay predominated, but that contained small amounts of smectite, were dispersive and as susceptible to seal formation as smectitic soils. However, the smectitic soils were more erodible than the soils that contained only small amounts of smectites. Conversely, soils that do not contain smectite are more stable, less crodible, and less susceptible to seal formation.