The effect of different phosphate fertilisers on soil pH and the consequent effect on phosphate retention

Abstract

Summary A comparison has been made of the degree of phosphate retention by yellow-brown loam of different phosphate fertilisers—superphosphate, double superphosphate, potassium dihydrogen phosphate and diarn-monium phosphate. The soils used were of low, medium and high phosphorus status. The addition of the phosphate to the soil suspension alters the pH, and the differences between the pH values of the suspensions are sufficient to account for the differences in phosphate retention. To determine how long these differences in pH persist, a low and a high phosphorus status soil were topdressed in a laboratory experiment at 90 lb P/acre and the pH of the surface soil measured over a period of three months. Changes of over one pH unit were recorded after topdressing, and it is considered that, even under light topdressing in the field, these pH changes would occur in the immediate vicinity of the phosphate particles and affect the concentration of phosphate in the soil solution and the utilisation of the appl...