THE EFFECT OF FURROW LENGTH ON RAIN AND IRRIGATION-INDUCED EROSION ONA VERTISOL IN AUSTRALIA

Runoff and sediment movement were measured from irrigated furrows of d ifferent lengths on a Vertisol in central Queensland. Two farm propert ies (Denaro's and Roberts') were used to compare a short furrow length (SFL) and a long furrow length (LFL). At Denaro's farm, furrows were 241 and 482 m long, and at Roberts' farm they were 151 and 298 m long, with gradients of 1.0% and 1.3% respectively. Runoff and soil loss we re measured from six furrows. At Denaro's farm, soil movement off the farm was measured at a taildrain outlet. Sediment concentration from b oth rainfall and irrigation declined when cultivation had ceased, soil in the furrows had consolidated and when the cotton canopy provided s urface cover. Total soil loss from rainfall and irrigation was approxi mately 4-5 t ha(-1). Rainstorms caused most of the seasonal soil loss, typically 3-4 t ha(-1). The critical soil erosion period was between pre-plant irrigation and canopy closure. Soil surface cover, peak runo ff rate and furrow length explained 97% of variance in soil loss cause d by rainfall. Furrow length was not significant in the soil loss mode l for irrigation (r(2) 0.59).