Leaching of phosphorus from the organic soils of the Holland Marsh

The extensive leaching experiment on organic soils of the Holland Marsh has revealed that substantial amounts of P have been retained in the soils as a result of previous cultural practices. The phosphorus so retained is identified by the higher P content near the surface of the soil. The leaching of the organic soils at an accelerated rate in the laboratory removed some of the accumulated P. It was estimated that approximately 340 kg/ha was removed during leaching. Such a result has important implications for the future. The results suggest that P will continually leach from the soils of the Holland Marsh for many years. Changes in current agronomic practices would not likely change the problem. The rate of such P loss will be contingent on the hydrologic characteristics of the Marsh and the net leaching that will occur. A major unknown factor is the fate of P in the soils as the organic soils continue to subside. It should be anticipated that as the soils become shallower, the concentration of P will become closer to the depth of drainage tile and the future rate of leaching of P may accelerate.