Residual effects of limestone on pasture yields, soil pH and soil aluminium in a krasnozem in north-western Tasmania

Abstract

Residual effects of 15 t/ha of surface applied limestone were evaluated at Elliott in northwestern Tasmania on a clover-based, perennial dryland pasture that was well fertilised and sufficient in molybdenum. The soil was a krasnozem (Gn 4.11) with a mean pH of 5.5. Annual pasture DM increases of 0.5-1.7 t/ha persisted for at least 9 years after the final application of limestone. The largest seasonal DM increases of 0.4-0.7t/ha were recorded in autumn. No decline in the pH of the surface 75 mm of the unlimed plots was detected. However, the pH of the surface 75 mm of the limed plots declined by 0.09 pH units per year from pH 7.0. The decline in surface pH was due to the movement of the zone of maximum limestone effect on pH from the 25-50 mm depth to the 100-125 mm depth, a distance of 75 mm in 8 years. Average soil pH profiles, CaCl2-extractable aluminium and root DM distribution in the surface 300 mm did not indicate that aluminium toxicity was restricting pasture DM production on the unlimed plots. However, toxic concentrations of exchangeable aluminium (extracted with BaCl2) were recorded below 100 mm in the unlimed plots.