Active Forms of Phosphorus in Some Alluvial Soils

Abstract

The content and distribution pattern of various forms of soil phosphorus in alluvial soils of Uttar Pradesh were examined. Total P content ranged from 405 to 530 ppm in the surface soil samples and decreases progressively with depth. Organic P constituted 11.5 to 23.7 per cent of total P in the surface samples and its' content decreased progressively with depth synchroniSing with organic carbon (r=0.886**). Fractionation of inorganic P indicated that Ca-P was the dominant P fraction constituting about half of the total P. Fe-P was the second most abundant P fraction followed by AI-P. The ratio of Ca-p, Fe-P and AI-P in the surface soil samples .. was on the average 4.0: ].\ : 1.0 and their distribution pattern with depth was similar to total P. The amount of reductant soluble P was very low ranging from 8 to 32 ppm. Stepwise regression analysis indicated that AI-P explained most of the variation in available P followed in order by Ca-P and adsorbed P. The contribution of Fe-P was very little while reductant soluble P was not related to available P.