SOIL-PH CHANGES UNDER VICTORIAN PASTURES

The severity and extent of surface soil acidification was assessed at 107 pasture sites across Victoria. At each site, soil samples (0.20 cm depth) were taken from the pasture area and an adjacent reference (undisturbed) area for analysis of soil pH (1:5 0.01 m CaCl2 or water). Acidification was evident in the 0.10 cm depth of sites with moderately and slightly acid (pH [water] 5.5-7) reference soils, while alkalinization was evident in the 0.20 cm depth of sites with strongly acid (pH [water] <5.5) reference soils. Causes of pH changes were not clearly evident from the relationships between site factors and changes in soil. It was evident that site factors were confounded since sites that had acidified often supported subterranean clover and had slightly to moderately acid reference soils, while sites which had alkalinized often supported white clover-based pastures under higher rainfall and had more acidic reference soils. An understanding of the causes of acidification in pasture-based agricultural ecosystems will only be gained through more fundamental studies at individual sites.