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Title: EFFECT OF SAMPLE DIVERSITY ON MID-AND NEAR- INFRARED CALIBRATIONS FOR SOIL C

Author
item Reeves Iii, James
item McCarty, Gregory
item FOLLETT, R - SPNRU
item KIMBLE, J - SPNRU
item REEVES, V - FDA

Submitted to: Agronomy Abstracts
Publication Type: Proceedings
Publication Acceptance Date: 9/8/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Two hundred and thirty-seven soil samples were collected in the western US (area from the Canadian border to Texas and west of the Missouri River to the Rockies), and a sub-sample acidified. Samples were dried (105 C) and ground prior to analysis. Samples were scanned in the mid-infrared (MIDIR) on a Digilab FTS-60 spectrometer equipped with a custom made sample transport (50 by 2 mm area scanned), and in the near-infrared (NIR) on a NIRSystems model 6500 spectrometer (rotating sample cup). Calibrations were developed using partial least squares regression and one-out cross validation. Mean and (STD) values for total-C, inorganic-C and organic-C were 18.3 (15.6), 6.19 (10.8), and 12.1 (13.3), respectively. Final calibrations for organic-C using 237 acidified samples gave r2 of .984 and .854 based on MIDIR and NIR spectra, respectively. For non-acidified samples, final MIDIR calibrations gave r2 of .957, .990 and .971 for organic-, inorganic- and total-C, respectively, while NIR results gave r2 of .890, .965 and .901 for organic-, inorganic- and total-C, respectively. These results demonstrate that while accurate calibrations for organic-, inorganic- and total-C in diverse sets of samples can be developed using either NIR or MIDIR spectra, MIDIR results are more accurate.