Bladeploughing and exclosure influence soil properties in a semi-arid Australian woodland

Abstract

Runoff and sediment yield were evaluated on a sandplain dominated by woody perennial shrubs in north-western NSW, Australia. The site was bladeploughed; and some plots were grazed by sheep and cattle and others exclosed from grazing. Two years after ploughing and exclosure, grazed plots had significantly lower levels of aggregate stability and organic carbon compared with ungrazed plots, but there was no effect of ploughing. Surface pH levels were significantly greater on unploughed plots compared with ploughed plots. Two years after treatment, runoff and sediment yield were greatest on plots with the least disturbance (unploughed and ungrazed) and least on sites with the greatest disturbance (ploughed and grazed). We attribute differences in soil hydrology to the development of a thin physical soil crust on the unploughed-ungrazed plots, which restricted infiltration. On the ungrazed plots, increases in plant cover and biomass, and colonisation of the physical crust by biological elements, are hypothesised to lead to reduced runoff and sediment yield over time.