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Title: NEAR-INFRARED REFLECTANCE SPECTROSCOPIC ANALYSIS OF SOIL C AND N

Author
item CHANG, CHEN-WEN - IOWA STATE UNIVERSITY
item Laird, David

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2001
Publication Date: 2/1/2002
Citation: CHANG, C., LAIRD, D.A. NEAR-INFRARED REFLECTANCE SPECTROSCOPIC ANALYSIS OF SOIL C AND N. SOIL SCIENCE. 2002. V. 167. P. 110-116.

Interpretive Summary: Soil analysis is an important component of modern farming systems. However, the use of soil analysis is limited by labor and laboratory costs. Near infrared reflectance spectroscopy (NIRS) is an analytical technique that is widely used in industry for quality control and has the potential to be a simple and inexpensive means of analyzing soils. Our data shows that NIRS analysis can be used to distinguish between organic carbon, primarily humus, and inorganic carbon, primarily carbonates, in soils. The study also demonstrates that NIRS independently responds to nitrogen which is bound in soil organic matter. Much work is still needed, but this study provides critical information needed for the development of soil analysis using NIRS. This research benefits farmers, agricultural extension agents, agricultural consultants, the Natural Resources Conservation Service, and environmentalists by advancing the development of the cost effective NIRS method for soil analysis.

Technical Abstract: Near-infrared reflectance spectroscopy (NIRS) is a rapid and nondestructive analytical technique that can be used to quantify various soil properties. The objective of this study was to evaluate the ability of NIRS to independently evaluate organic C, inorganic C, and total N content of diverse soil materials. Samples (n=108) were prepared by mixing soil with CaCO3, humic acid, and/or compost materials. About 30% of the samples were randomly selected for the "validation set", and the rest of the samples were assigned to the "calibration set". NIR spectra of these samples were correlated with measured values of organic C, inorganic C, total C, total N, and C:N ratios using partial least squares regression. Leave-one-out cross-validation analysis yielded r**2 values between the measured and predicted soil properties higher than 0.86 for all tested properties. Similar results were obtained from analysis of the validation set (r**2 greater than 0.85). The successful prediction of total N and C:N ratios for the studied samples indicates that NIRS predictions of total N for soils is not based on the strong correlation between levels of C and N, rather to an independent response to soil N. The results indicate that NIRS can be used to independently and simultaneously quantify organic C, inorganic C and total N for soils with diverse C and N compositions.