SOIL-EROSION OF AGRICULTURAL LAND IN WESTERN AUSTRALIA ESTIMATED BY CESIUM-137

The caesium-137 technique was used to estimate net soil loss from 10 hillslopes in the agricultural area of Western Australia. The gravel fraction of the soil was found to have approximately 56% of the total Cs-137 activity found on the <2 mm fraction of the soil on three slopes where it was measured. In the lower rainfall zones, Cs-137 appeared not to have uniformly labelled the soils in uncleared areas, possibly due to the redistribution of rainfall in the canopy and above the soil surface, and the water repellence of some soils. A previously established calibration curve was used to calculate net soil losses from the 10 hillslopes. Potato-growing land and slopes below rock outcrops in the Wheatbelt appear to have experienced the most severe erosion since the soils were first labelled with Cs-137 in the mid 1950s (19-27 t ha-1 yr-1). Hillslopes below rock outcrops had appreciably less Cs-137 than those below lateritic breakaways, indicating the presence of sheet erosion.