The relationships between reversibly adsorbed ? (Pi) and other soil properties were studied in 39 cultivated mineral soils of Finland. Piwas desorbed by a method, analogous to resin extraction, in which a soil sample is shaken with strips of Fe‐hydroxide impregnated filter paper in a 0.01 M CaCl2solution. The high affinity of Fe hydroxide for ? maintains a low ? concentration in the solution and enhances ? desorption from the soil. At the solution: soil ratio of 40: 1, Piranged from 7.9 mg dm‐3to 64.2 mg dm‐3with a mean of 31.2 mg dm‐3. Soil ? was also extracted with water (Pw) and 0.5 M Acetic acid‐0.5 M Ammonium Acetate at pH 4.65 (PAC). Piwas 1.2 to 8.9 times greater, with a mean of 3.1, than Pw. The ratio of Pito PAcranged from 1.1 to 6.2 with a mean of 2.6 mg dm‐3. In soils of low ? levels the relative difference between Piand Pwand between Piand PAcwas greater than soils rich in P. The molar ratio of ? extracted with NH4F solution ("Al‐P") to oxalate‐extractable Al, together with soil pH, explained 70%, 73% and 74 % of the variation of Pw, PAcand Pi, respectively. The same fractions of ? are extracted by all three methods but the depletion of these reserves is more effective in the Pimethod. The method for determining reversibly adsorbed ? can be a useful tool in assessing the potential of soil to contribute ? to surface waters upon erosion, as well as in studies on the residual effect of. ? fertilization