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ARS Home » Research » Publications at this Location » Publication #204419

Title: Fractionation of Soil Phosphorus

item Kovar, John

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 6/13/2007
Publication Date: N/A
Citation: N/A

Interpretive Summary: Non-point phosphorus (P) loss from agricultural sources has affected surface water quality and created a need for more and better information on methods of P analysis for soil, water, and residual materials. Cycling of inorganic and organic P in soils is very complicated, so this chapter was developed to provide a standard set of soil P analytical methods that will enable uniform comparison of soil P forms across county, state, regional, and even national boundaries. The qualitative and quantitative information provided by fractionation data is useful for addressing both agronomic and water quality issues. The methods presented in this chapter will be a valuable reference for any private or public laboratory that analyzes soil for P content.

Technical Abstract: An understanding of the qualitative and quantitative information provided by soil phosphorus (P) fractionation methods is important for addressing agronomic and water quality problems, as well as evaluating P biogeochemistry in extreme environments. This chapter provides a schematic overview of and specific methods for fractionation of inorganic (Pi) and organic (Po) soil phosphorus. Methods of soil P fractionation and improvements on the original 1957 Chang and Jackson procedure are briefly summarized. Basic principles and detailed procedures for fractionation of inorganic and organic soil P are provided. Phosphorus biogeochemistry is complicated because Pi can react with calcium (Ca), iron (Fe) and aluminum (Al) to form discrete phosphates. Fractionation procedures are based on the differential solubility of the various Pi forms in various extracts. Organic phosphorus also occurs in forms with varying resistance to microbial degradation. The method for characterizing soil Po fractions involves the use of acid and alkaline extracting solutions that separate the various fractions based on the type and strength of Po physicochemical interactions with other soil components. The fractionation scheme involves a sequence of extractions that separates soil Po into labile, moderately labile, and non-labile fractions. The qualitative and quantitative information provided by fractionation data is useful for addressing agronomic (e.g. availability and positioning of fertilizer P), water quality, and P biogeochemistry issues.