A Simplified Soil and Plant Phosphorus Model: III. Testing

Testing of a simplified soil phosphorus model is described. Changes in organic P content of the surface soil due to cultivation are simulated relatively accurately for periods of up to 40 years at several locations in the Great Plains. Simulated changes in organic P contents of the subsoil are smaller than those of the topsoil. Concentrations of soil test P are accurately simulated over periods of up to 20 years with and without fertilizer P applications in several soils. Simulated responses of maize ( Zea mays L.) and wheat ( Triticum aestivum L.) to soil test P concentrations are similar to those found in three published studies. Fertilizer P required to maintain adequate P fertility is accurately simulated for maize and wheat at several locations in the U.S.