STRENGTH CHARACTERISTICS OF A POTENTIALLY HARDSETTING SOIL UNDER PASTURE AND CONVENTIONAL TILLAGE IN THE SEMIARID REGION OF AUSTRALIA

Strength characteristics of a potentially hardsetting soil near Trangie, N.S.W., Australia was investigated under native permanent pasture as well as cultivated conditions. Field results indicated that while the cultivated soil exhibited the characteristic increases in strength on drying, soil strength of the 0-30-mm layer of the permanent pasture soil did not vary significantly with water content. Laboratory results using repacked soil disks suggested that for the permanent pasture soil, the potential to hardset increased markedly with depth over the top 150-mm layer, from non-hardsetting to more hardsetting than the 0-100-mm layer of the cultivated soil. The tendency to hardset was significantly related to the soil organic carbon concentration which decreased rapidly with depth. Results highlight the exacerbation of the hardsetting problem under the existing cropping regimes and the current tillage practice as the cause of soil degradation. There is an urgent need to devise suitable alternative tillage techniques which can take into account the inherent soil profile variation with depth of these structurally fragile soils.