BLADEPLOUGHING AND EXCLOSURE INFLUENCE SOIL PROPERTIES IN A SEMIARID AUSTRALIAN WOODLAND

Runoff and sediment yield were evaluated on a sandplain dominated by w oody perennial shrubs in north-western NSW, Australia, The site was bl adeploughed; and some plots were grazed by sheep and cattle and others exclosed from grazing, Two years after ploughing and exclosure, graze d plots had significantly lower levels of aggregate stability and orga nic carbon compared with ungrazed plots, but there was no effect of pl oughing, Surface pH levels were significantly greater on unploughed pl ots compared with ploughed plots, Two years after treatment, runoff an d sediment yield were greatest on plots with the least disturbance (un ploughed and ungrazed) and least on sites with the greatest disturbanc e (ploughed and grazed), We attribute differences in soil hydrology to the development of a thin physical soil crust on the unploughed-ungra zed plots, which restricted infiltration, On the ungrazed plots, incre ases in plant cover and biomass, and colonisation of the physical crus t by biological elements, are hypothesised to lead to reduced runoff a nd sediment yield over time.