Relative Availability of Neutral Ammonium Citrate Soluble Phosphorus in Nitric Phosphate Fertilizers

Availability coefficients of citrate soluble phosphorus fraction relative to that of water soluble phosphorus fraction were worked out for three nitric phosphate fertilizers of 30, 50 and 70 per cent water solubility, taking urea ammonium phosphate as a standard source, on three soils varying in pH and CaCO3 content, after greenhouse experimentation. Availability coefficient ratios for different nitric phosphates relative to urea ammonium phosphate were also computed. Relative availability coefficient of citrate soluble phosphorus increased as the proportion of citrate soluble phosphorus decreased. Linear regression between the two was significant at 5% level of significance. Magnitude of the relative availability coefficient of citrate soluble phosphorus was more on neutral and non-calcareous soils rather than on alkaline calcareous soils.