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United States Department of Agriculture

Agricultural Research Service

Title: Estimating Soil Phosphorus Sorption Saturation from Mehlich-3 Data

Authors
item Kleinman, Peter
item Sharpley, Andrew

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2002
Publication Date: July 8, 2002
Citation: KLEINMAN, P.J., SHARPLEY, A.N. ESTIMATING SOIL PHOSPHORUS SORPTION SATURATION FROM MEHLICH-3 DATA. COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS. 2002. V. 33. P. 1825-1839.

Interpretive Summary: The transfer of phosphorus from agricultural lands to surface water has been implicated in eutrophication, one of the most pervasive water quality problems in the U.S. This study examines the use of readily available soil testing information in estimating one of the best predictors of P loss from soil: soil P sorption saturation. Drs. Kleinman and Sharpley, Soil Scientists with the Pasture Systems and Watershed Management Research Unit show that Mehlich-3 soil test data can be used to estimate P sorption saturation in a wide range of soils. Their approach overcomes the constraints of traditional methods of estimating P sorption saturation, which were not easily adopted by soil testing laboratories and were generally limited to soils with specific properties, helping to expand the relevance of soil test information from agronomic to environmental realms.

Technical Abstract: Soil phosphorus sorption saturation (Psat) measures the degree to which soi P sorption sites have been filled and has been found to be a good indicator of P availability to runoff and leachate. At present, analytical methods required to estimate Psat are generally not offered by soil testing laboratories. We evaluated the use of Mehlich-3 data in estimating Psat in na wide range of soils. In acidic soils (pH = 4.1-5.9), Psat estimated fro Mehlich-3 P, Fe, and Al was highly correlated with Psat estimated from ammonium oxalate data (r = 0.94) as well as with a reference Psat estimated from bicarbonate P and the Langmuir sorption maximum (r = 0.89). In alkaline soils (pH = 7.3-8.4), Psat estimated with Mehlich-3 P and Ca was highly correlated with the reference Psat (r = 0.84), and the strength of that correlation improved only slightly by factoring in soil clay content (r = 0.86). Results indicate that Psat may be effectively estimated from Mehlich-3 data across a wide range of soils. This study confirms that Psa may be readily estimated by soil testing laboratories that routinely measure Mehlich-3 P, Al, Fe, and Ca.

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