Determination of ammonium-N, moisture, total C and total N in dairy manures using a near infrared fibre-optic spectrometer

The objective of this study was to investigate the feasibility of using nea r infrared (400 to 2498 nm or sub-regions thereof) fibre-optic-based spectr oscopy to estimate nutrient concentrations in dairy manures, One hundred an d seven diverse manures, collected from dairy farms in the north-eastern Un ited States (CT, MD, NY, PA, VA) mere assayed by conventional means and spe ctroscopically for total C and N, ammonium-N and moisture. Samples were sca nned (64 coadded scans) on a Foss-NIRSytems Model 6500 scanning monochromat or equipped with a fibre-optic probe from 400 to 2498 nm, and on an Ocean O ptics 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 Re gression, 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 38x200 mm) and vertical cell transport device (non-fibre-optic); 2) limitations th igh noise in the 2000-2498 nm region) in the spectra produced by fibre-opti c 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 determi nations 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 larg er data sets is needed to better determine the feasibility, limitations and requirements for developing accurate and robust calibrations for manure co nstituents using fibre-optic based spectrometers, regardless of the spectra l region used.