Extracting representative plant-available phosphorus (P) from P-rich soils has always been a challenging task given the variability that exists in soils and the dynamic nature of the P. Selecting the best method for soil-P extraction while accounting for soil variability would provide a strong analytical tool for research projects and experiments. The present study was initiated to compare the efficiency and suitability of Olsen and Mehlich III reagents for P extraction and analysis from manure-amended P-rich soils on North Central Texas dairies and to develop a relational model between Mehlich III or Olsen P with water-soluble P (also called environmental P or runoff P). Surface soil samples were collected from dairy pastures which were subjected to historical manure application. Samples represented 15 soil series with wide variations in clay and calcium carbonate contents. Samples were analyzed for pH, organic carbon %, clay % and CaCO3 %. Agronomic P was extracted separately from Mehlich III and Olsen reagents. Water-soluble P was also analyzed in all the samples. The Mehlich III procedure was more stable in varying levels of pH, clay and organic carbon content. Olsen reagent extracted more available P when CaCO3 levels were greater (>3.5 %) but failed to maintain stability with varying pH, OC and clay content of soil. Regression models between Mehlich III P and water soluble P were more consistent with greater r2 values