The invention concerns a method for quantitative determination of nitrogen present in the form of one or more nitrogen containing compounds and/or ions thereof in an aqueous fluid, the method includes subjecting at least a part of the aqueous fluid to an NMR reading including generating a 14N data having a 14N NMR data spectra and correlating the 14N NMR data to calibration data. A system suitable for carrying out the method as well as a moveable manure spreader including a system is also described.
