Distribution and Availability of Phosphates Added to a Lakeland Fine Sand

Analyses of soil samples obtained from the surface 6 inches of experimental plots located on the Citrus Experiment Station at Lake Alfred, Florida, indicated that a high percentage of the phosphorus added as superphosphate was not found in this zone. In order to study the distribution of this “leached” phosphorus, soil samples were obtained at various depths from the surface to 7 feet within the citurs‐root feeding zone. Analyses of these samples for total, adsorbed (NH 4 F extractable) and acid‐soluble (0.1 N HCl extractable) phosphorus indicated the following: Essentially all of the added phosphorus was retained within the citrus‐root feeding zone, even though it may have been leached from the surface 6 inches of soil. The greatest accumulation occurred within the 12‐ to 36‐inch subsoil zone; however, phosphorus had leached to a depth of at least 7 feet in some cases. Separation of the phosphorus into adsorbed and acid‐soluble fractions indicated that the major portion of the added phosphorus was retained in an adsorbed or NH 4 F extractable form. The availability to citrus seedlings of the phosphorus accumulated in both the surface and subsoil was measured by the A value technique utilizing radio‐phosphorus. The data indicated that the phosphorus accumulated in the subsoil was as available as that phosphorus which was retained in the surface 6 inches of soil. A good correlation was obtained between A value phosphorus and the amount of phosphorus extracted from the soils with NH 4 F.