The effect of chemical extractant on the estimation of rock phosphate fertilizer dissolution

Abstract

Rock phosphates have been widely used in the acid soils of the tropics as direct application fertilizers. To estimate their rate and extent of dissolution various chemical extractants have been used. However, the acidic or inadequately buffered nature of these extractants promote extensive dissolution of the apatite and may result in a gross overestimate of the amount of rock phosphate dissolved. To overcome this problem, it is proposed that the soil is shaken for 1 h in 2 M barium chloride buffered at pH 8.1 with triethanolamine (solid : solution ratio of 1:10) and calcium determined in the filtered supernatant. The difference in extractable calcium between fertilized and unfertilized soil is a measure of the dissolution of the rock phosphate.