Use of Mid-infrared and Near-infrared Diffuse Reflectance Spectroscopy for Characterization of Soil Biochemical Parameters.
Gregory McCarty, USDA-ARS-NRI,Bldg.007, Rm. 201, Beltsville, MD 20705-2325, James Reeves, USDA Environmental Management & Byproduct Utilization Laboratory, Building 306 BARC East, Beltsville, MN 20705, and Dean A. Martens, USDA-ARS Southwest Watershed Research Center, 2000 E. Allen Road, Tucson, AZ 85719.
The ability to rapidly characterize the quality of soils within agricultural landscapes is limited by the ability to rapidly measure soil biochemical properties. Diffuse reflectance spectroscopic analysis in the near-infrared (NIR, 400-2500 nm) and mid-infrared (MIR 2500-25000 nm) regions may provide a means for measurement of multiple biochemical parameters such as amino acid composition. The soil samples were collected over a large geographic region in central and western United States. The soils ranged considerably in organic carbon and amino acid contents. Both spectral regions calibrated well to organic carbon and amino acid content. Amino acid contents, however, were generally well correlated to organic carbon content and the ability to calibrate for amino acids was related to the degree to which the parameter correlated to organic carbon. This provided indication that organic carbon was surrogate for amino acid content in these calibration models. This demonstrates a limitation in developing calibrations in systems with highly correlated parameters. Although, surrogate-type calibrations can be used in mapping local and regional variation in soil parameters depending on stability of relationship between parameters.