The Influence of Calcium Chloride Concentration on the Determination of Lime and Phosphate Potentials of Soil

Summary Schofield's lime and phosphate potentials were determined on four soils using CaC1 2 solutions varying in strength from 0.002 to 0.05 M. The lime potential, pH–½pCa, was found to be independent of the CaCl 2 concentration. The phosphate potential, ½pCa+pH 2 PO 4 , of the neutral and alkaline soils decreased when the CaC1 2 molarity was increased from 0.002 to 0.05. When allowance was made for the formation of a soluble calcium phosphate complex, CaHPO 4 , the phosphate potential became independent of the calcium chloride concentration in all four soils.