Interactions of silicate and phosphate in a lateritic soil

Abstract

The use of silicates to improve the efficiency of phosphate utilization from a lateritic soil in pots produced only transient effects which, at the best, did not last longer than 1 year. Laboratory investigations with this soil in dilute potassium chloride and calcium chloride systems showed that the proportion of phosphate left in solution increased with the pH and varied as follows for the different treatments: phosphate and silicate added together >phosphate after silicate pretreatment >phosphate alone >silicate after phosphate pretreatment >water after phosphate pretreatment. The levels of phosphate in solution were smaller for the calcium chloride than for the potassium chloride systems but the levels of silicate in solution were similar for the two systems and varied with the pH as found previously. The silicate did not appear to change the type of reaction by which phosphate is fixed but rather altered the equilibrium constants involved.