The effect of the siliceous component of decomposing rice hulls on the solubility of phosphate

Abstract

The effects of decomposing rice hulls on the solubility of sparingly soluble phosphates have been examined. Rice hulls decomposed slowly and increased the solubility of ferric and aluminium phosphates. Phosphate was also released from the rice hulls alone. The increased solubility of the phosphates was shown to be due to greater hydrolysis which occurred when the pH of the cultures rose to 8 and also, in the case of aluminium phosphate, to an interaction with silica. Aluminium phosphate was dissolved in the presence of rice hulls over the pH range 5-8, with a minimum solubility near pH 7. Rice hulls also decreased the amounts of soluble phosphate adsorbed by aluminium and ferric oxides over this range. The response of plants following additions of rice hulls to soil is discussed in the light of these results.