EVALUATION OF THE CS-137 TECHNIQUES FOR ESTIMATING WIND EROSION LOSSES FOR SOME SANDY WESTERN-AUSTRALIAN SOILS

The utility of the caesium-137 (Cs-137) technique, for estimating the effects of wind erosion, was evaluated on the soils of a semi-arid agricultural area near Jerramungup, Western Australia. The past incidence of wind erosion was estimated from field observations of soil profile morphology and an existing remote sensing study. Erosion was limited to sandy surfaced soils (0-4% clay), with a highly significant difference (P < 0.0001) in Cs-137 values between eroded and non-eroded sandy soils, with mean values of 243+/-17 and 386+/-13 Bq m-2 respectively. Non-eroded soils, with larger clay contents, had a mean Cs-137 content of 421+/-26 Bq m-2, however, due to considerable variation between replicate samples, this value was not significantly different from that of the non-eroded sands. Hence, although the technique discriminates between eroded and non-eroded areas, the large variation in Cs-137 values means that from 27 to 96 replicate samples are required to provide statistically valid estimates of Cs-137 loss. The occurrence of around 18% of the total Cs-137 between 10 and 20 cm depth in these soils, despite cultivation being confined to the surface 9 cm, suggests that leaching of Cs-137 occurs in the sandy soils, although there was no relationship between clay content and Cs-137 value for either eroded or non-eroded soils. In a multiple linear regression, organic carbon content and the mean grain size of the eroded soils explained 35% of the variation in Cs-137 content. This relationship suggests that both organic carbon and Cs-137 are removed by erosion, with erosion being more prevalent on soils with a finer sand fraction. Clay and silt contents do not vary with depth in the near-surface horizons of the eroded sandy soils, hence it is likely that wind erosion strips the entire surface horizon with its Cs-137 content, rather than selectively winnowing fine material.