PHOSPHATE SOLUBILITY IN DANISH SOILS EQUILIBRATED WITH SOLUTIONS OF DIFFERING PHOSPHATE CONCENTRATIONS

Summary In four out of ten Danish soils, varying in texture, pH, and forms of inorganic phosphate, phosphate solubility in dilute CaCl 2 solution corresponded to the solubility of one or other of six phosphate minerals presumed to exist in soils. On adding moderate rates of phosphate, only one of the soils sustained phosphate activities corresponding to such a mineral (octocalcium phosphate). Consequently, removal of added phosphate from solution, as in the determination of the differential phosphate potential buffering capacity was the result of an adsorption type of mechanism rather than precipitation of crystalline phosphate compounds.