Transformation of Fixed Phosphorus in Soils under Waterlogged Condition

Sixty to seventy-five per cent of the amount of the applied phosphate was found to remain in soil in the fixed form as Al-, Fe- and Ca- phosphates after the harvest of rice plants. Experiment was conducted to study the transformation of such fixed Pin soil during the period when the soils art re-waterlogged in the following cropping season after an intervening dry fallow period for about 5 months. The overall results indicated that the applied P which was left in the soil in the fixed from after the crop harvest could significantly contribute to the pool of avail. P in the succeeding season during the initial period of plant growth. The amount of fixed Al-P did not practically record any change on re-waterlogging the soil in the next season, particularly during the initial period. The fixed Fe-P recorded a decrease immediately after re-waterlogging the soils having high P-fixing capacity, whereas in low fixing soil it remained practically unchanged. The fixed Ca-P recorded a gradual increase in the soil rich in native Ca-P but showed a slow decrease in the soil comparatively poor in this fraction of P.