Modeling Soil and Plant Phosphorus Dynamics in Calcareous and Highly Weathered Soils

Labile and organic phosphorus (P) and sorbed P are required as the minimum data set to run a soil‐plant P cycling model recently developed for continental U.S. soils. Labile and organic P and P sorption index were related to physical and chemical properties of 23 calcareous (>50 g kg −1 CaCO 3 content) and 32 highly weathered soils (>30% Al saturation), to allow estimation of these P forms from readily available soil data. The P sorption or fertilizer availability index was estimated as the fraction of fertilizer P remaining as labile (resin extractable) P following incubation of soil and fertilizer. Labile P was linearly related ( R 2 = 0.71–0.90) to soil test P measured by Olsen (calcarous soils) and by Bray, Colwell, Mehlich III, and Truog methods (highly weathered soils). Organic P was also linearly related to organic C ( R 2 = 0.87) and total N ( R 2 = 0.89) content of all soils. Fertilizer P availability index decreased with increased incubation time from 30 to 180 d, with the decrease related to CaCO 3 and extractable Fe and Al contents of calcareous and highly weathered soils, respectively. At the present time, the model uses a 180‐d incubation value of fertilizer P availability index, which can be estimated from CaCO 3 and clay contents of the calcareous and highly weathered soils, respectively. Using these relationships, accurate simulations were obtained of P transformations during 60‐yr cultivation of calcareous Houston Black clay and yield of maize ( Zea mays L.) on two highly weathered Hawaiian soils receiving varying amounts of fertilizer P.