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PHOSPHORUS SUPPLY TO PLANTS BY SOILS WITH VARIABLE PHOSPHORUS EXCHANGE

Soil phosphorus (P) supply to plants increases with concurrent increases in both soil solution P (CP) and P exchanged between the solution and the soil solid phase that rapidly equilibrates with CP. For many temperate region soils, the amount of P isotopically exchanged in 1 min (E1) acts as an immediate source of replenishment for CP. Relationships between E1 and CP were investigated to characterize the Intensity (CP), Quantity (E1) and Capacity (d E1/d CP) factors of soil P supply to plants. Soil (Alfisol) samples were collected from seven P fertilization field experiments conducted in France over a period of 4 to 32 years. The E1/CP curves are described by the same equation for the seven experiments: E1=vCP0.78, where v is the E1 value at 1 mg P L−1. The v constant is soil dependent and ranged from 14.7 to 28.3 mg P kg−1. The above equation was validated by testing a previous published data set. The buffer power of P in solution controlled by E1 (d E1/d CP) decreased when CP increased. At a given CP level, d E1/d CP increased when v constant increased. The E1/CP curves might be used as a basis for transferring information on soil P supply from one soil to another. The present work proposed an equation based on the use of E1/CP curves to predict the CP value associated with an optimum crop yield in different soils (opt CP). The opt CP value is inversely related to the v value, indicating that the lower the P buffer power of soils, the higher the opt CP value.