In this study, a diode array near infrared (NIR) spectrometer that can be mounted on a mobile agricultural machine was tested under lab conditions for its effectiveness as a rapid, on-site hog (Sus domesticus) manure composition sensor. One hundred and sixty nine diverse hog manures, collected from farms in the northern part of Belgium, were assayed by conventional wet chemical analysis and spectroscopy for the following constituents: dry matter content, organic matter content, pH, total Kjeldahl nitrogen, ammonium nitrogen, phosphorus, potash, calcium, sodium and magnesium. Samples were scanned (two fills, three measurements each) on a Zeiss Corona 1.7 VisNIR diode array instrument equipped with an OMK measuring head, ranging between 400 and 1700 nm (five scans per measurement) using a sample cell (50 mm diameter) for diffuse reflectance scanning from the bottom. Based on the absorbance–constituent and constituent–constituent correlations, the constituents were divided into two groups: one for those in the solids (dung) and one for those in the liquid (urine). The pH was not correlated to any other constituent and, therefore, treated separately. Partial least squares calibrations were developed for the constituent groups and for each of the constituents separately using leave-one-out cross-validation, showing a common spectral basis for each constituent group. To investigate the possibility of developing a cost-effective sensor, regression calibrations were developed using a few wavelengths selected based on the partial least squares regression and validated by leave-one-out cross-validation. Results demonstrated that: (1) approximate quantitative predictions can be made for total N, NH4–N and K, (2) a discrimination between high and low values can be made for DM, OM, P and Mg, (3) prediction of Ca, Na and pH are not possible (yet), (4) one measurement and one filling of the cup give a reliable measurement, (5) a cost-effective sensor measuring only a few appropriately selected wavelengths might be able to give comparable results, (6) further work will be necessary to optimise sample presentation and calibration procedures and (7) mounting a diode array instrument on a slurry tanker can make environmentally and economically sound nutrient management possible.
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