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Title: Mid- Versus Near-Infrared Reflectance Spectroscopy for On-Site Determination of Soil Carbon

Author
item Reeves Iii, James
item McCarty, Gregory
item Hively, Wells - Dean

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2008
Publication Date: 2/5/2008
Citation: Reeves III, J.B., Mccarty, G.W., Hively, W.D. 2008. Mid- Versus Near-Infrared Reflectance Spectroscopy for On-Site Determination of Soil Carbon. Meeting Proceedings. vol. 2, chapter 17.

Interpretive Summary: Near-infrared spectroscopic (NIRS) methods using light beyond the range of human site has been used for the last several decades to rapidly determine the composition of a wide range of agricultural products. More recently, research has demonstrated that for the determination of soil C diffuse such methods (Diffuse reflectance Fourier transform spectroscopy or DRIFTS) using mid-infrared radiation is often more accurate and produces more robust (better able to predict future samples) calibrations (equation relating spectral data to composition) than NIRS when analyzing ground, dry soils. However, DRIFTS is not considered to be feasible on samples containing high levels of moisture due to the strong water absorptions in the mid-infrared, although water is also known to degrade even NIR spectra and calibrations. While DRIFTS has been shown to be advantageous in the laboratory, if samples need to be ground and dried and instruments purged with dry air to obtain useable data, it may not be practical for on-site use. The objective of this research was to determine the effect of ambient atmospheric conditions and soil state (ground, dried, etc.) on DRIFTS and NIRS calibrations for soil C. Results using a portable DRIFTS spectrometer over a wide range of ambient temperatures and humidity levels have demonstrated that purging is not necessary to obtain calibrations for C in soils equal to those obtained in the lab with dry or dried-ground samples. Efforts with field moist samples has demonstrated that while calibrations using DRIFTS can be developed with an accuracy equal to those obtained using NIRS, the calibrations may not be as robust.

Technical Abstract: Research has demonstrated that the determination of soil C diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is often more accurate and produces more robust calibrations than near-infrared (NIR) reflectance spectroscopy (NIRS) when analyzing ground, dry soils. DRIFTS is also not considered to be feasible on samples containing high levels of moisture due to the strong water absorptions in the mid-infrared water (also known to degrade even NIR spectra and calibrations). While DRIFTS has been shown to be advantageous in the laboratory, if samples need to be ground and dried and instruments purged to obtain useable data, it may not be practical for on-site use. The objective of this research was to determine the effect of ambient atmospheric conditions and soil state (ground, dried, etc.) on DRIFTS and NIRS calibrations for soil C. Results using a portable DRIFTS spectrometer over a wide range of ambient temperatures and humidity levels have demonstrated that purging is not necessary to obtain calibrations for C in soils equal to those obtained in the lab with dry or dried-ground samples. Efforts with field moist samples has demonstrated that while calibrations using DRIFTS can be developed with an accuracy equal to those obtained using NIRS, the calibrations may not be as robust.