CHANGES TO SOIL PHYSICAL-PROPERTIES AFTER GRAZING EXCLUSION

The potential for degraded physical properties of soil to regenerate n aturally after exclusion of grazing animals was examined at a long-ter m stocking rate trial near Armidale, New South Wales, Australia. Unsat urated hydraulic conductivity was measured before grazing was excluded , and after 7 months and 2.5 years' grazing exclusion. These data were compared with controls grazed at 10, 15 and 20 sheep/ha. After 2.5 ye ars, there were significant increases in unsaturated hydraulic conduct ivity at 5 and 15 mm tension in the ungrazed treatments compared with the grazed controls. The unsaturated hydraulic conductivities and bulk density of surface soils under pasture which had been ungrazed for 2. 5 years were comparable to those where the pasture had been ungrazed f or 27 years. We speculate that the natural amelioration of soil physic al properties in these soils was due to biological activity and wettin g and drying cycles, in the absence of the compactive effect of animal treading.