Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Near and Mid-Infrared Spectroscopy for the Determination of Carbon and Other Analytes in Soil

Authors
item Reeves Iii, James
item McCarty, Gregory

Submitted to: The Soil and Plant Analyst
Publication Type: Popular Publication
Publication Acceptance Date: July 1, 2002
Publication Date: August 1, 2002
Citation: Reeves III, J.B., Mccarty, G.W. 2002. Near- and mid-infrared spectroscopy for the determination of carbon and other analytes in soil. The Soil and Plant Analyst.

Interpretive Summary: Spectroscopy uses the interaction of light with materials to determine their composition. With the increasing need for rapid and inexpensive methods for determining soil carbon, near- and mid-infrared spectroscopy have increasingly become of interest for such analysis especially for on-site analysis. While results have demonstrated that both organic and inorganic carbon can be determined in the laboratory using either the near- or mid-infrared spectral range, results have shown the mid-infrared to be more accurate and less affected by variations in soil type. However, for in situ determinations, samples would not be ground or dry as done for laboratory analysis, and the instrumentation will need to be portable, preferably inexpensive and more rugged than the laboratory spectrometers used to date, all of which are more problematic for the mid-infrared. For example, while the particle size of samples can have an effect on accuracy, efforts with other materials such as forages, silages and grains have demonstrated that the scanning of larger samples can overcome these problems. But while sampling devices exist in the near-infrared for scanning the required sample, they do not exist at present in the mid-infrared and will need to be developed. Finally, while under in situ conditions, carbon distribution and sample heterogeneity are a problem for any analytical method, the rapid analysis possible with spectroscopic techniques will allow many more samples to be analyzed thus reducing the errors induced by these factors.

Technical Abstract: Results with some 1100+ soil samples have demonstrated that accurate calibrations can be developed using either the near- or mid-infrared spectral range to determine soil C with the mid-infrared being more accurate. Efforts have also demonstrated that both near- (NIRS) and mid-infrared (mid-IR spectroscopy can differentiate between organic and inorganic C in soils, and that mid-IR again produces more accurate calibrations. The greatest benefit from NIRS or mid-IR would come with in situ determinations. For such determinations, samples would not be ground or dry, and instrumentation will need to be portable, preferably inexpensive and more rugged than the laboratory spectrometers used to date. While the particle size of samples can have an effect on calibration accuracy, efforts with other materials such as forages, silages and grains have demonstrated that the scanning of larger samples can overcome these problems. While sampling devices exist in NIRS for scanning the required sample, such devices do not exist at present in the mid-IR and will need to be developed. While under in situ conditions, C distribution and sample heterogeneity are a problem for any analytical method, the rapid analysis possible with spectroscopic techniques will allow many more samples to be analyzed thus reducing the errors induced by these factors.

Last Modified: 9/20/2014
Footer Content Back to Top of Page