Olivia Campbell1 and Brendan Torpy1
Soil acidity is a soil condition where there are excess hydrogen ions present due to the removal of alkaline nutrients in plant and animal products; addition and leaching of nitrogen from fertilisers and legumes and the build-up of organic matter. Soil pH(CaCl₂) levels of 5.2 to 8.0 provide optimum conditions for most agricultural plants. All agricultural plants are affected by the extremes of pH, however different plant species have significant variation in their acidity and alkalinity tolerance. Lime (calcium carbonate) and other liming materials (dolomite, lime sand) reduce soil acidity via neutralising the acid reaction within the soil.
Traditionally lime has been applied at standard blanket rates of between 1 – 2.5 t/ha. Grid soil pH mapping enables measurement of spatial pH variation within a paddock. Analysis of over 19,000 ha of mapping in Victoria has demonstrated that 33% of this area would not receive an optimum lime rate (outside of 1 -2.5 t/ha) for a target pH(CaCl₂) 5.2 scenario. Ten percent of this area required more lime than 2.5 t/ha to achieve the target pH level while 23% did not require any lime.