SUMMARYThe effect of limestone application on the ~P supplying power of Davidson clay loam, a soil high in free iron, was investigated by laboratory and greenhouse procedures. The soff under study did not receive fertilization for a 17-year period prior to the investigation. Application of dolomitic limestone to the soil increased both yield and P uptake of 3 successive cuttings of alfalfa. A comparison of inorganic P fractions in the soil before and after growth of each alfalfa crop showed that mineralized organic P and Ca-P supplied P to the first cutting of alfalfa and that Fe-P supplied P to the second and third cuttings. Application of limestone increased the availability of the Fe-P fraction to the secortd and third crops of alfalfa. The P availability of the inorganic P fractions was explained on the basis of chemical properties of the soil.