Use of Equilibrium Phosphate Potential as a Measure of Available Soil Phosphorus for Alluvial Soils of Western Uttar Pradesh

Comparison of equilibrium phosphate potential as a measure of available soil phosphorus was made with two conventional soil test methods, such as Bray's P and Olsen's P. The percentage yield and percentage response of wheat obtained from field experiments carried out in fifty five locations of western Uttar Pradesh were correlated with soil test values. The results suggested that the equilibrium phosphate potential could be considered as a reliable index of available soil phosphorus as compared to Olsen's or Bray's P. The limit for sufficiency of soil phosphorus above which no response could be expected was found to be rather high when calculated from linear regression equations. This was due to curvilinear relationship between the percentage yield and the soil test values. The curvilinearity was more in case of Olsen's P and Bray's P as compared to equilibrium phosphate potential. The relationship between the percentage yield and Olsen's P or Bray's P followed the Mitscherlich-Baule type of curve and the Baule units were 12 and 14 kg P₂O₅ per hectare for Olsen's P and Bray's P respectively.