Phosphorus characterization and correlation with properties of selected benchmark soils of the United States

Twenty-one benchmark soils of the United States, including surface and subsurface horizons and satellites, from the Water Erosion Prediction Project (WEPP) were analyzed for phosphorus (P), using methods that include total (TP), water-soluble (WP), Bray 1 (BP), Mehlich No. 3 (MP), Olsen (OLP), New Zealand P Retention (NZP), organic (OP), anion exchange resin (AEP), and acid oxalate (P-o). Objectives of this study were to determine relationships among soil P test values and other soil properties. Knowledge and understanding of these relationships are important to researchers when evaluating soil P data sets for use in predictive models for agronomic, soil genesis, or environmental purposes. Important relationships that were developed, using simple or multiple linear regression models, among P methods and other soil properties, e.g., organic carbon (OC), total N (TN), dithionite-citrate extractable iron and aluminum (Fe-d, Al-d), and clay are as follows: TP (mg/kg) = 229.02 + 27.76 Al-d (g/kg) + 27.44 OC (g/kg) + 4.14 Fe-d (g/kg), r(2) = 0.89, p < 0.01, n = 263 (all soils) OP (mg/kg) = 114.07 + 38.07 TN (g/kg) - 14.74 pH + 6.94 OC (g/kg), r(2) = 0.80, p < 0.01, n = 262 (all soils) BP (mg/kg) = -1.82 + 1.11 MP (mg/kg), r(2) = 0.96, p < 0.01, n = 268 (all soils) P-o (mg/kg) = 16.02 - 24.27 Al-o (g/kg) + 25.59 Fe-o (g/kg) + 19.33 OC (g/kg)r(2) = 0.79, p < 0.01, n = 203 (non-calcareous) NZP (%) = 16.92 + 1.37 Al-d (g/kg) + 0.28 clay (%), r(2) = 0.91, p < 0.01, n = 203 (non-calcareous).