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Comparison of Two Spectrometers for Profile Soil Carbon Sensing

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2012 Dallas, Texas, July 29 - August 1, 2012  121338240.(doi:10.13031/2013.41892)
Authors:   Anna Maria Hodge, Kenneth A Sudduth
Keywords:   NIR, soil carbon, precision agriculture, spectral reflectance, soil sensing

Visible and near-infrared reflectance spectroscopy satisfies the need for speed and precision in estimation of soil carbon and other soil properties. Previous work has established accuracy of the method, with much of the reported research done using bench spectrometers from a single manufacturer. However, other equipment is now available, capable of both bench and in-situ field operation. Therefore, the objective of this research was to compare two spectrometers, with emphasis on the consistency of soil carbon detection across instruments and determination of the impact wavelength range has on carbon detection. Additionally, the impact of bench versus in-situ probe data acquisition was examined. The spectrometers used were the ASD FieldSpec Pro FR operated as a bench model and the Veris P4000 VIS-NIR-EC-Force Probe operated as both a bench instrument and as a profiling device used in the field. At field sites in Missouri, Nebraska and Pennsylvania, probe spectrometer data were collected, followed by the removal of soil cores at each probe scanning site. The cores were then scanned with each bench top spectrometer. Partial least squares regression was used for statistical analysis and model development. Results showed that C estimation accuracy was very similar for the two spectrometers in bench mode, and that good C estimates were maintained with in-situ operation of the Veris instrument. Wavelength analysis confirmed that the visible spectral range had a negligible effect on C estimation accuracy. These results further validate the effectiveness of reflectance spectroscopy, including in-situ scanning with probe-style devices, for estimation of soil carbon.

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