ENVIRONMENTAL SOIL TESTING FOR PHOSPHORUS

Many soils in the USA have extremely high soil test P levels from long -term fertilization and manuring. Sediment-bound and soluble P in runo ff from these soils may contribute to eutrophication of surface waters . A field rating system, the ''P index,'' has been developed to assess the potential for soil P to contribute to nonpoint source pollution. A critical component in this index is soil test P. The primary objecti ve of this paper is to discuss the roles soil testing programs can pla y in the development of nutrient management strategies, such as the P index, that are needed to minimize nonpoint source pollution by soil P . A survey of soil testing labs participating in four regional soil te sting committees (North Central, Northeast, Mid-Atlantic, Southeast) w as conducted in 1991-1992 to determine current approaches to soil P te sting, the percentage of soils testing in the high or excessive range, and major concerns with high P soils. Results indicated a need for mo re consistency in defining and identifying soils that are excessive in P, from an environmental standpoint, and that P management in animal waste-amended soils was the major environmental issue for most states. Soil P testing for environmental purposes will require a careful re-e valuation of the sampling, analytical, interpretive, and educational r oles of soil testing programs. Alternatives considered in this paper i nclude integration of soil testing databases with land-use planning in formation via geographic information systems, the use of special soil tests for biologically available P, or to estimate P sorption/desorpti on, and expanded educational efforts focused not only on farmers, but on advisory and regulatory agencies and the general public.