Due to the gradual increase of intensive livestock farming in the Netherlands, the amount of nutrients in animal manure exceeds the demand for nutrients on arable land at the national level. In order to account for total amounts of nutrient inputs and outputs on farm level by manure, sampling and laboratory analysis is nowadays a major instrument within the Dutch Fertilizer Law. The major disadvantage of the system the delay between sampling during transport and the moment the laboratory results about the manure composition become available. In recent decades miniaturized techniques, such as Near-Infrared Spectroscopy (NIRS) have become available to perform in situ fertiliser analysis, allowing direct availability of the measurement. The use of these techniques instead of the current system of sampling and analysis could solve the issue related to the time gap between sampling and the availability of the results and enables more precise application of slurry based on actual nutrient content. Over the past decade research has been performed to evaluate NIRS as a potential technique. In close collaboration with all parties involved, the Ministry of Agriculture designed a strategy for the gradual introduction of on board NIRS measurements at slurry transport vehicles for the determination of the total nitrogen and phosphorus content. This plan foresees an improvement of accuracy of NIRS systems over time to eventually meet the performance requirements of the fertilizer legislation. The aim of the NIMACO research project was to gather more information from scientific based research on the performance of NIRS systems for the estimating nutrient content in animal slurry. More specifically for the application of NIRS on board of transport vehicles, estimating the nitrogen (N) and phosphorus (expressed as P2O5) content. For this purpose, two protocols were established for the performance assessment of the NIRS systems. One to perform a Proof of Principle (POP), to evaluate the performance of the NIRS systems under laboratory conditions and one to perform a Proof of Application (POA), to evaluate the performance of the NIRS systems under field conditions. Furthermore, preparations were made to perform a comparison study where NIRS will be applied to monitor slurry data related to commercial transports that are carried out in the conventional way. The research on the latter topic will be addressed in a separate project directly following the NIMACO project. The performance of NIRS systems from three different manufactures have been evaluated according the POP. To date, the results of these tests do not show that the equipment has the accuracy deemed necessary to start a pilot where NIRS is used for the legal determination of the nitrogen and phosphorus content of slurry. Nonetheless, the observed accuracy of the equipment did increase over time by adjustments made by the suppliers to improve the systems.