Residual benefits of limestone and superphosphate on barley yields and soil-water deficits on a krasnozem in north-western Tasmania

Abstract

Twelve years after the last application of limestone, the residual benefits of 15 t/ha of surface applied limestone were measured on barley grown on a krasnozem [Gn4.11, pH 5.5 (1:5 soil:water)] at Elliott in north-western Tasmania. Liming increased grain yield by 77% (1.9 t/ha) when phosphorus (P), sulfur (S), potassium (K), and molybdenum (Mo) were non-limiting. An increase in the number of ears per m2 accounted for 73% of the yield increase, number of seeds per ear 20%, and slightly larger grains 7%. The soil-water deficit on the limed plots at the end of the growing season did not exceed that on the unlimed plots. We suggest that the crop responses to liming were due not to an increase in the potential soil-water available for extraction by the crop but to increased levels of available nitrogen on the limed plots, which increased tillering before the onset of water stress. Termination of superphosphate applications 20 years before reduced yield by 1.18 t/ha, to 59% of the yield obtained with superphosphate applied at 500 kg/ha.year. By comparison, the liming effect was 1.6 times larger. The barley crop responded equally to both the P and S components of the superphosphate, but did not respond to K or Mo fertilisers.