Abstract

The objective of this study was to investigate the feasibility of using near infrared (400 to 2498 nm or sub-regions thereof) fibre-optic-based spectroscopy to estimate nutrient concentrations in dairy manures. One hundred and seven diverse manures, collected from dairy farms in the north-eastern United States (CT, MD, NY, PA, VA) were assayed by conventional means and spectroscopically for total C and N, ammonium-N and moisture. Samples were scanned (64 co-added scans) on a Foss-NIRSystems Model 6500 scanning monochromator equipped with a fibre-optic probe from 400 to 2498 nm, and on an Ocean Optics model S2000 CCD, fibre-optic probe spectrometer from 430 to 1100 nm (1000 scans/sample, integration time of 41 ms). Calibrations were developed using the one-out cross-validation procedure using Partial Least Squares Regression. Results demonstrated the following: 1) calibrations for ammonium-N, moisture and total C and N can be developed, but are not as accurate as those previously developed using a large sample cell (approximately 38 × 200mm) and vertical cell transport device (non-fibre-optic); 2) limitations (high noise in the 2000–2498 nm region) in the spectra produced by fibre-optic bundles are at least partially responsible for the reduced accuracy found with fibre-optic systems when compared to non-fibre-optic means of sample presentation; 3) spectra produced by fibre-optic systems appear to be more spectrally diverse than those for non-fibre-optic systems; 4) while determinations based on spectra covering the region from 400 to 2300 nm appear to be a viable alternative to manure Quick Tests already on the market, those using only the 400 to 1098 nm region are not; and 5) further work with larger data sets is needed to better determine the feasibility, limitations and requirements for developing accurate and robust calibrations for manure constituents using fibre-optic based spectrometers, regardless of the spectral region used.

© 2000 NIR Publications

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