On-line measurement of animal and bio slurry quality variations with near infrared spectroscopy

There is a very large variation in dry matter and content of various plant nutrients in animal slurry and digestate from biogas production. For more precise fertilization application, quantification and monitoring of available plant nutrients prior to spreading at the farm would be advantageous. Near infrared reflectance (NIR) spectroscopy is suitable for on-line analyses and is a potential technology for such monitoring. In this study, 73 dairy, pig and bio slurries were analyzed in a test rig simulating a real spreader. Calibrations were made with partial least squared (PLS) regression. Calibrations worked best for dry matter content and, in general, calibrations for dairy slurry worked better than those for pig and bio slurries. In addition, 13 real bio slurry loads were analyzed during spreading. Spectral variation between loads was slightly larger than within loads. Compared to the variation between bio slurry plants, the variation between loads was very small.