Phosphate fractions as influenced by long-term phosphorus fertiuzation

A long-term field experiment on pearl millet-wheat cropping sequence initiated during rabi 1968 using split plot design was selected for present investigation at Soil Research Farm, CCSHAU, Hisar, Haryana. There were eleven treatment combinations related to sources (rock phosphate, nitrophosphate, SSp, DAP and UAP) and levels of P (60 and 120 kg PPs ha⁻¹), including one control which were in main plots and three modes of P application were in sub-plots. Continuous application of different phosphatic fertilizers increased Olsen's available P in soil. The maximum increase of available P was found with DAP (18.0 ppm) and minimum with RP (6.7 ppm). The available P content of the soil in control plot decreased from its original level of 6.6 ppm to 2.7 ppm. Inorganic P fractions revealed that Ca-P was the dominant fraction (78.7%) followed by A1-P (10.1%), Fe-P (7.9%) and saloid-P (3.3%). Increasing levels of P application increased significantly saloid-P, A1-P, Fe-P and Ca-P over lower levels of P application. Saloid-p, A1-P and Fe-P fractions were highly interrelated and they all were significantly correlated with Olsen's available P in soil.