Forms of P and Efficacy of Different Soil Tests for P Extractability in Calcareous Soils

A greenhouse study was conducted with winter maize on ten calcareous soils collected from nine well established soil series of Punjab to evaluate the efficacy of various soil tests for available P. Crop responded to both native and applied P. Calcium-P was the dominant inorganic P fraction (92.8%) followed by At-P (5.4%), Fe-P (1.4%) and saloid-P (0.4%). Among different indices of P availability, Olsen's soil test method was found to be the most snitable. Olsen-P had a sigoificant negative relationship with CaCO₃ and clay content. Olsen's P showed sigoificant relationship with Fe-P and this relation improved by 7 per cent on inclusion of saloid-P along with Fe-P. Both Fe-P and saloid-P controlled P availability to maize in these soils. These two fractions of soil-P seemed to be important as these correlated sigoificantly with Olsen's P and various yield and P uptake parameters of winter maize grown on calcareous soils.