Transformation of Applied Phosphorus under Simulated Conditions of Growing Rice and Wheat in a Sequence

Transformation of applied phosphorus was studied at various levels of P on four major Indian soils, namely, alluvial, black, red and laterite under laboratory conditions over a period of 122 days under waterlogging and for 105 days under unsaturated soil-moisture conditions. These periods corresponded to the growing of a rice crop and a wheat crop respectively under greenhouse conditions.

The results showed that the total P extracted by the fractionation procedure was more at the end of 122 days of waterlogging than that could be extracted in the beginning of the experiment. With P application Al-P and Fe-P increased in all the soils while reductant soluble-P (R-P) increased in all but the laterite one and Ca-P increased in black and laterite soils only.

Even after the lapse of another 105 days of incubation under simulated conditions of wheat growing, the P treatments maintained their significant effect particularly on Al-P and Fe-P in all the soils, but on R-P and Ca-P only in black and laterite soils. When the soils were incubated under unsaturated moisture conditions there was a tendency for the P fractions to revert to the initial values, thus nullifying the changes brought about by waterlogging.