Surface runoff, soil and nutrient losses from farming systems in the Australian semi-arid tropics

Abstract

Most soils suitable for dryland agriculture in north-west Australia occur in the Daly Basin. These are sesquioxidic soils which include red, yellow and grey earths, and soils related to yellow and red earths. The potential, for these arable soils to be degraded by highly erosive rainfalls, common to the region, is high. Farming practices strongly influence the soil surface characteristics (vegetation cover, roughness, soil strength), which in turn control surface runoff, and sediment detachment and transport. In studies conducted during 1984-89 in the Daly Basin, conventionally tilled catchments, produced 1.5-2 times more runoff and lost 1.5-6 times more soil than their no-tillage counterparts (all catchments were within soil conservation banks). In these conventionally tilled catchments, soil loss was <8.1 t/ha.year. Other studies in the region have shown that, without soil conservation banks, soil loss can be around 100/ha.year under conventional tillage. Little work, however, has been undertaken on farms in the Australian semi-arid tropics to study the movement of nutrients and herbicides (in ionic and adsorbed forms) and further research is warranted.