Changes in pasture and soil properties with liming and superphosphate application on five soils in the Central Tablelands of New South Wales over 12 years

Context: The decision to lime pastures requires understanding of the benefits and their duration. 

Aims: To quantify the effects of contrasting rates of superphosphate and lime on soil chemistry and pasture productivity on five acidic soils over 12 years. 

Methods: The sites were established in 1978 on the Central Tablelands of New South Wales, Australia. Initial treatments of lime were 0, 0.63, 1.25, 2.5 and 5.0 t/ha. Single superphosphate (SSP) was top-dressed annually at 0, 125 and 250 kg/ha. 

Key results: Across the five sites, initial pH increase due to liming was 0.3 units/t. After 12 years, pH declined to 0.1 pH units/t. Without lime, soil pH declined by 0.02 units/year. For all lime treatments and sites, the annual decline averaged 0.07 units/year. Annual applications of SSP were associated with lower soil pH and exchangeable soil K and higher Al saturation, but differences required 2-7 years to emerge. There was an increase in annual dry matter with SSP application. Lime generally increased pasture biomass, with pastures dominated by Trifolium subterraneum. Pasture yields generally increased with exchangeable Ca but yield responses to %Al were more variable. 

Conclusions: A single application of lime had many enduring beneficial effects on soil chemistry, still evident 12 years following application and generally proportional to the quantum of lime initially applied. Ongoing applications of SSP led to cumulative changes in some soil properties and resulted in an increase in pasture productivity. 

Implications: The historical view of lime and SSP being alternative investments is counterproductive. Pasture renovation may be necessary to realise the full benefit of lime and SSP application.