ABSTRACT
The use of natural forms of minerals such as rock phosphate as an alternative source to synthetic fertilizers partially or totally is receiving renewed attention worldwide. Apart from nutritional effects, application of such minerals is effective in reducing the cost of crop production and maintaining the natural fertility of soil. Since the solubility of rock phosphate is generally low, it does not always give satisfactory results when directly applied. The present study was therefore, undertaken to explore the possibility of increasing the release of P from rock phosphate at different rates through composting using rice straw and the effect of P-charged compost on the yield and P uptake by corn plants. The concentration of total P significantly enhanced in the final product with all treatments as organic materials decreased during composting compared to control where no P was added. Phosphorus from rock phosphate was solubilized and transformed into available forms during composting. Application of rock phosphate had no effect on degradation of rice straw up to 20% but at higher rates, the degradation decreased. The water soluble P decreased with the addition of rock phosphate to composted materials. The soluble P in 2% citric acid increased dramatically on composting with rock phosphate and the maximum increase was observed with 30% rock phosphate. This fraction is presumed to be available to plant uptake. Release of P from rock phosphate was decreased by addition of [NH[4]] [2] SO[4], but increased by the addition of urea. It is concluded that urea hydrolyzes the organic matter within the period of composting and that the products of hydrolysis chelate Ca[2]+ ions and so increased the release of P from the rock phosphate. The response of corn plants to addition of compost that included rock phosphate was considerable when added in sandy soil. The P-charged compost containing 6.75% total P was comparable to super phosphate or better when combined with phosphate dissolving bacteria in increasing dry matter yield and P uptake. Rice straw compost prepared without rock phosphate did not give significant increase in corn yield