Influence of an acid soil on the herbage yield and nodulation of five annual pasture legumes

Abstract

Balansa, persian and subterranean clover and barrel and murex medic were grown in acidic sandy loam in pots in a glasshouse. Four lime treatments (0, 1, 2, 3.5 t/ha) resulted in pH levels of 4.2, 4.7, 5.1 and 6.0 (1:5 CaCl2). After addition of plant nutrients, total exchangeable cations in the nil lime treatment averaged 2.197 cmol(+)/kg, increasing to 4.738 cmol(+)/kg at pH 6.0. With increasing pH, aluminium saturation of the soil exchange was 38, 14, 4 and 3%. The effect of soil acidity on dry matter production was compared between legumes by determining relative yield (yield/maximum yield) responses over the pH range. Subterranean clover was the most tolerant legume, followed by murex medic and balansa clover (similar), persian clover and then barrel medic. All legumes except barrel medic produced at least 90% of maximum yield at pH 4.7; only subterranean clover produced more than 90% of maximum yield at pH 4.2. Establishment of nodules was more sensitive to acidity than indicated by relative yields of dry matter, especially in murex medic and persian clover. Average nodule weight usually increased at lower pH. The dry matter yields of murex medic and persian clover at lower pH were probably reliant on compensatory increases in nodule volume as nodule number declined with increasing acidity.