Soil P fractions have been estimated in a 30‐year‐old replicated superphosphate experiment established inPinus radiata.The treatments were 0, 25, 50, 75 and 100 kg.P ha‐lbroadcast applied and the timber productivity was increased from 144 m3ha‐lto 396 m3ha‐1merchantable volume over 30 years. The soil P fractions were basically as in the Chang and Jackson 7 p fractionation procedure, except each fraction was further separated into organic and inorganic components. The total organic P fractions accounted for more than 55% of the total P and were correlated with changes in organic matter. The results indicated an equilibrium situation had developed between the various components and that, based on correlations with tree growth, the readily soluble organic fractions could be the most important P forms for long term forest productivity.