Phosphorus Adsorption and Movement in Some Sandy Forest Soils

Seven to 11 years after rock or superphosphate was applied to young slash pine ( Pinus elliottii Engelm. var. elliottii ) plantations on seven soils of the Lower Coastal Plains, significant growth responses were evident in five of the seven tests. However, there were indications that the effect of the fertilizer was diminishing in certain soils. Foliage P, soil P intensity measurements, P sorption characteristics, and the Chang and Jackson sequential extraction procedure were used to ascertain the present availability of fertilizer residues at different soil depths. Little or no residual P from superphosphate remained in the top 20 cm of soils with no P sorption or buffering capacity, such as Leon fine sand. However, almost all of the superphosphate remained in an available form in the rooting zone in soils with a low P sorption and buffering capacity. In a soil with a high P sorption and buffering capacity most of the added P was retained in the surface horizon in a poorly available form. Little rock phosphate had been leached from any of the soils. Some transformation of P to adsorbed forms, as with superphosphate, had occurred, but availability was very high in each case. Some observations are made concerning the types and amounts of phosphate fertilizers suitable for these and similar soils.