Inorganic soil phosphorus: II. Changes in monocalcium phosphate and lime potentials on mixing and liming soils

Mixtures of Woburn (non‐calcareous) and Barnfield (calcareous) soils, with and without added monocalcium phosphate, and of Woburn soil with added CaCO3, were stored moist in an incubator at 25 ± 2 °C. Equilibrium phosphate concentrations in 0·01M CaCl2 and pH were measured on moist soils and mono‐calcium phosphate (½pCa+pH2PO4) and lime (pH–½pCa) potentials were calculated at intervals up to 670 days. Most of the mixtures remained under‐saturated with respect to CaCO3; values of ½pCa+pH2PO4 and pH–½pCa changed during storage but remained close to the solubility isotherm for octacalcium phosphate (OCP). Mixtures which reached equilibrium with CaCO, remained undersaturated with respect to OCP.