Spectroscopic analysis of dried manures. Near-versus mid-infrared diffuse reflectance spectroscopy for the analysis of dried dairy manures

The objective was to examine and compare the ability of near- and mid-infrared diffuse reflectance spectroscopy to determine the composition of dried dairy manures. Samples (n = 99) were dried at 60degreesC, ground and scanned in the near-infrared in a rotating sample cup on a Foss-NIRSystems model 6500 scanning monochromator, and in the mid-infrared on a Digilab FTS60 Fourier transform spectrometer using a custom-made sample transport device. While near-infrared calibrations for various measures of fibre composition (neutral detergent fibre etc.) were found to be possible, the results were generally less accurate than found for similar determinations in forages. Results based on mid-infrared spectra were sometimes better, and sometimes worse then near-infrared results, but again were not as accurate as found with forages. Overall, a clear advantage was not demonstrated for either region. Examination of the composition of the dried manures indicated that high ash contents (8-52% of dry matter) might be the cause for the decrease in calibration accuracy. However, a comparison of calibrations based on dry matter to those based on an ash-free basis showed no clear advantage for either means of computation. Accurate determination of minerals such as K or P was not possible using either spectral range (calibrations for K may be useful for gross segregation). In conclusion, while near- and mid-infrared calibrations appear feasible for determining the composition of dried dairy manures, better reference methods appear to be needed.