Abstract

                                An incubation experiment was conducted to study the transformation of applied phosphorus into various inorganic P fractions in a mixed black calcareous soil. There were three P sources viz, single superphosphate (SSP) diammonium phosphate (DAP) and Mussoorie rock phosphate. Phosphorus was applied at the rate of 60 kg P20s ha' at field capacity moisture level. These were maintained upto 60 days for transformation and inorganic P fractions were determined at 15 days intervel. The concentration of different P froms was higher with DAP followed by SSP. There was continuous increase in the P fractions with advancing incubation time upto 45 days.. However, phosphorus availability was increased upto 60 days irrespective of P source. DAP resulted in highest per cent recovery into inorganic P fractions. Ca-phosphate was the dominant P from followed by RS-P, Fe-P and AI-P in all the P sources. All the P fractions were highly correlated with available P in soil. Ca-phosphate showed highest r value (0.80). The contribution of Ca-P towards P-availability was 64 per cent. The combination of different P fractions were also highly correlated with available P in soil.

Key words : P' Sources, Phosphorus, Transformation, Availabilty, Black Calcareous soil