Distribution of phosphorus fractions in different soil orders of Indo-Gangetic plains of India

The status and distribution of phosphorus fractions in some soil orders and their relationship with soil characteristics under Indo-Gangetic plains of India was studied at Mohanpur, Nadia (W.B.). Soil samples were collected from three depths (0-15, 15-30 and 30-45 cm) covering Entisols, Inceptisols and Alfisols during 2016. Results revealed that soil pH and clay content increased whereas EC and organic carbon tended to decrease with increasing soil depth. Among different phosphorus fractions, Ca-P was dominant contributing 35% and 20% of total phosphorus content in Entisols and Inceptisols, respectively followed by Fe-P, RS-P and OC-P. In Alfisol, Fe-P fraction constituted 21% of the total soil P followed by Ca-P, RS-P and Al-P. The fractions Al-P, RS-P and Ca-P increased whereas organic P decreased with increasing soil depth. Soil pH was positively correlated with Ca-P and negative with Al-P, Fe-P of all the soil orders. Calcium-P was the highest in Entisols (35%) and Inceptisols (20%) while Fe-P (21%) in Alfisols. Among the inorganic P fractions, Ca-P was the dominant contributor to the availability of phosphorus in Entisols and Inceptisols. The dominant fraction for the release of P in Alfisols was iron phosphate. In general, inorganic P fractions increased while organic available P decreased with soil depth. Various P fractions also had relationships among themselves.