Changes in Solubility of Phosphorus and its Availability to Rice Plant in the Waterlogged Soils

In an experiment conducted on two soils, one slightly acidic (pH 6.6) red soil of Mirzapur and the other weakly alkaline (pH 7.4) Karail soil of Azamgarh districts of Eastern U.P., with four treatments, viz., (i) control, (ii) added P, (iii) added farmyard manure, and (iv) farmyard manure with P, avail. P increased during the tillering stage of rice, then it tended to decrease. The increase in avail. P in the red soil was related mainly to decrease in Fe-P and Ca-P concentrations while in Karail soil it was related to decrease in Al-P and Ca-P. The decrease in avail. P was due to reformation of insoluble Fe-P and Ca-P in red soil and Ca-P and Al-P in Karail soil. Addition of FYM increased the availability of native Fe-P and Ca-P in red and Karail soils, respectively. Added P mostly remained in the form of Ca-P and Fe-P. The maximum P uptake was observed when it was applied with FYM and it was highly pronounced in the case of red soil.