Phosphorus Intensity, Quantity, and Capacity Factors of Representative Alfisols of Greece

A number of phosphorus intensity indices, including P concentration, activity of the H 2 PO 4 ion, and certain chemical potentials, were found to satisfactorily predict P uptake by ryegrass from 14 representative Alfisols of northern Greece, both initially and also upon prolonged cropping. Simple intensity indices, such as P concentration in either CaCl 2 or H 2 O extracts, proved as good as more elaborate ones. Activity of phosphate on the solid phase correlated most closely when expressed as a molar fraction. The two common P quantity indices, E‐value and Resin‐P, also proved satisfactory predictors. Bray 1, Olsen, and Colwell tests were equally effective to more complicated and tedious indices. Phosphorus capacity indices were generally found ineffective as predictors, though “ultimate” P capacities as determined from cumulative P uptake were similar for all soils studied.