Industrial-scale continuous on-line analysis of liquid hog manure by NIRS

Abstract

The objective of the work was to use near-infrared spectroscopy (NIRS) to identify the pattern of distribution of the manure nutrients onto a field. The paper describes what is believed to be the first application of NIRS to continuous analysis of liquid manure on an industrial scale. The on-line analysis is accomplished without the need for a sample cell to scan the sample, or the need for sampling during manure application to the land, because the entire amount of the material is analyzed. Diode array instruments were used for continuous scanning of the manure as it was being applied. Because of differences among the instruments in spectral data, four instruments were set up in line for the development of the industrial-level calibration. Spectral data were recorded as direct reflectance over the range of 11,100 cm−1 to 5,900 cm−1. Calibrations for total solids, nitrogen, phosphorus, and potassium were developed using the Unscrambler, with a data pre-treatment of first derivative. No outliers were removed. Values of the RPD (ratio of SD of reference data to SEP) of between 3.1 and 4 were attained for all constituents. Interpolation of blind duplicates revealed that reproducibility of NIRS predictions for all constituents was significantly superior to that of laboratory analysis by certified laboratories. This was attributed to the enormous differences in the volume of manure scanned by the NIRS instruments, relative to the volumes used in laboratory analysis. Continuous scanning and analysis of liquid manures enable mapping of nutrients as they are being applied to the land, which provides valuable information to farmers as to the purchase, and efficiency of use of fertilizers.