Describes why the degree of P saturation ratio (DPS) is used and how to calculate it, including the extractants that can be used for DPS calculations. Explains the P saturation ratio (PSR), the preferred extractants, and molar calculations. Describes the change point concept and the difference between soil test phosphorus (STP) and PSR.
Gives examples from the literature of reported change points, including those for Florida soils, for the spodic horizon and for wetland soils, and summarizes threshold PSR values from the literature for soils globally and in Florida.
Reviews isotherm models and their components, including equilibrium P concentration and Smax under aerobic and anaerobic conditions, and relates isotherm parameters to soil test data.
Describes the soil P storage capacity (SPSC), a new indicator for evaluating P release from soils, how it is used, how to calculate it for A and E horizons, for the Bh horizon and for the spodic horizon, discusses the relationship between SPSC and WSP for wetland soils, and explains the application of PSR and SPSC in risk assessment of soils.
Reviews the QPT procedure and the relationship between QPT and Mehlich 1-P and PSR, discusses the effects of biochar application to a low-P retentive soil and a high-P retentive soil using SPSC, and describes how to use the recently developed technique to explain the Florida-P index, with suggested modifications to the Florida-P index based on the SPSC.