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Abstract
Calcium (Ca) plays a vital role in the structural integrity of soils, plants, and animals. This review considers the Ca status of New Zealand pastoral soils and examines the Ca requirements of pastures and animals. Against this background the diagnostic criteria used to assess Ca requirements for pastures are reviewed. It is concluded that the current Ca concentrations in New Zealand topsoils are more than adequate for optimal pasture and animal production and that this situation is sustainable, based on Ca budgets, given a continuance of the traditional fertiliser practices of superphosphate and liming. For a set of 97 pastoral topsoils, covering all the major soil groups in New Zealand, it was found that soil pH was not related to either exchangeable Ca or Ca saturation (exchangeable Ca/CEC at pH 7). In addition it was found that Ca saturation based on CEC underestimated the Ca saturation calculated from the effective CEC (ECEC). It is likely therefore that soil Ca requirements based on the former would be overestimated. From this and other evidence it is concluded that soil pH should be used as the sole criterion for determining lime requirements.