Near-Infrared Spectroscopic Determination of Carbon, Total Nitrogen, and Ammonium-N in Dairy Manures

Abstract

The objective of this study was to investigate the feasibility of using near-infrared reflectance spectroscopy (NIRS) to determine nutrient concentrations in dairy manures. We assayed diverse dairy manures (n=107) collected from dairy farms in the northeastern United States (CT, MD, NY, PA, and VA) by conventional means and NIRS for total C, total N, NH3-N, moisture, P, K, and pH. Samples were scanned from 400 to 2498nm in polyethylene bags on a FOSS-NIR-Systems Model 6500 scanning monochromator equipped with a sample transport device. We developed calibrations using a one-out cross validation procedure under partial least-squares regression. Preliminary results showed that eight samples were outliers either because of inaccurate conventional analysis or because they were uncharacteristic (i.e., two samples had moisture content below 72%, while all others were above 78%). These outliers were removed from further consideration. Final calibration results with the remaining 99 samples demonstrated that NIRS can accurately determine the moisture (r2=0.945, root mean squared deviation or RMSD=1.0%), total C (r2=0.950, RMSD=0.40%), total N (r2=0.956, RMSD=0.030%), and NH3-N (r2=0.967, RMSD=0.013%) concentrations, but not P or K concentrations in dairy manures. In conclusion, NIRS was shown to be a viable alternative to conventional analysis procedures for determining moisture, total C, total N, and NH3-N in a very diverse set of dairy manures.