Studies of surface applied phosphates in field plots of a loam soil show that biennial applications of superphosphate penetrate not more than 2-3 in., perhaps much less, in 16 yrs.; rock phosphate, penetrated more than 7 in. Eight yrs. after the last application of rock phosphate and 3 yrs. after the last superphosphate application, the rock phosphate pasture contained 188 lbs. per acre of available P, and the superphosphate plat 18 lbs. per acre. Laboratory percolation studies show that more P is available in rock phosphate and N treated soils, of wide pH range, than in the same soils treated with superphosphate. Rock phosphate penetrated more rapidly than superphosphate in an acid soil, but the reverse was true in alkaline soils. (NH4)2SO4 or NaNO3 speeded the penetration of rock phosphate more than that of superphosphate, especially in acid soil. Field and laboratory penetration studies all show more soluble P in rock phosphate treated soils than in superphosphate treated soils. In most field tests in which a comparison has been made of superphosphate and rock phosphate, however, superphosphate has proved the better P fertilizer.