Near-infrared spectroscopic determination of carbon, total nitrogen, and ammonium-N in dairy manures

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 2498 nm 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 NIPS can accurately determine the moisture (r(2) = 0.945, root mean squared deviation or RMSD = 1.0%), total C (r(2) = 0.950, RMSD = 0.40%), total N (r(2) = 0.956, RMSD = 0.030%), and NH3-N (r(2) = 0.967, RMSD = 0.013%) concentrations, but not P or K concentrations in dairy manures. In conclusion, NIPS 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.