To close the nutrient cycle, the nutrients in animal manure need to be valorized in plant production. However, due to its heterogeneity, the fertiliser value of animal manure can vary significantly between farms, and even between different loads obtained from the same farm. This means that the use of animal manure often increases the variability in soil fertility within a field, rather than reducing it.
In the context of precision fertilisation, one could try to compensate for this variation based on crop measurements. However, it would be far better if the nutrient content of the manure was known at the time of application. This would enable the application rate to be adjusted to allow for both the nutrient content of the manure and the needs of the crop. NIR spectroscopy has the potential to bridge this gap, through online measurement of the manure composition. In this paper, our experiences with the calibration of NIRS systems for online measurement of manure composition in slurry tankers will be presented. Some interesting observations on the variation in manure composition between different loads from the same storage facility, and even within a load, will be discussed, together with scenarios on how this information could be used efficiently in practice.