Comparison of colorimetric and ICP determination of P in Mehlich III extracts of Kentucky soils.
(S08-sikora967333-oral)
Authors:
F.J. Sikora* - Univ. of Kentucky P. Howe - Univ. of Kentucky E. Hill - Univ. of Kentucky
Abstract:
Soil test laboratories are moving away from colorimetry to inductively coupled plasma (ICP)
spectroscopy to quantify phosphorus (P) is soil test extracts. The use of ICP has advantages of being quicker and provides the ability to quantify P and other plant nutrients in one analytical process. The adoption of ICP for P analysis has come with some controversy since the P value with ICP is not always comparable with the colorimetric P value that has been historically used to set up fertilizer P recommendations. Soil testing laboratories at the University of Kentucky in Lexington and Princeton received ICP spectrometers for soil testing. Data is presented on the comparison of Mehlich3 soil test P using ICP versus colorimetry. The overall comparison of the two analytical techniques resulted in a linear slope of 1.02 and R2 of 0.987 in Lexington for 1118 samples and a linear slope of 0.968 and R2 of 0.978 in Princeton for 418 samples. The scatter of the data around a 1:1 line was compared to normal laboratory error. In the agronomically significant range from 0 to 30 mg dm-3, 5.5% of all the data showed ICP greater than colorimetry above a 4 x standard deviation (4xsd) limit and 0.2%
showed ICP less than colorimetry below the limit. Further research is needed to determine if the higher ICP results in 5.5% of the data is due to factors related to higher P bioavailability.
Speaker Information: Frank Sikora, Univ. of Kentucky, University of Kentucky 103 Regulatory Service Bld, Lexington, KY 40546; Phone: 859-257-2785; E-mail: [email protected]
Session Information: Monday, November 3, 2003, 1:10 PM-2:45 PM Presentation Start: 2:00 PM
Keywords: phosphorus; inductively coupled plasma; colorimetry; soil testing