A comparison of dicalcium phosphate and single superphosphate as phosphate sources for pasture

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Abstract
The effect of commercially available dicalcium phosphate (DCP) and single superphosphate on pasture production was evaluated in glasshouse and field trials. When compared on a unit-P basis, DCP (5.6% P) was slightly inferior (up to 10%) to superphosphate (8.6% P) in a glasshouse trial with ryegrass as the indicator plant; on a unit weight basis, DCP was only 60–70% as effective as superphosphate. No differences were obtained in the P concentration of the herbage obtained using the two materials. In a field trial on a P-responsive site, DCP and superphosphate gave similar increases in pasture production. Marked treatment differences were obtained for the P concentrations in ryegrass and clover in the field trial, particularly in the first harvest and with ryegrass. No difference was obtained in the short-term residual effect of the two materials. The data obtained are interpreted in terms of the chemical and mineralogical composition, and water solubility of DCP.