N-modified organic matter for soil improvement: State of research on nitrogen binding in ammonoxidised lignins
Oxidative ammonolysis of lignin under mild conditions is considered to be a suitable reaction to mimic the natural humification process. The products obtained can potentially be used as soil-improving materials as they share structural similarities with stable terrestrial humic substances. In addition they release nitrogen slowly to the soil over a long term. Based on studies using model compounds we have acquired clear evidence that the majority of nitrogen in natural and artificial humic substances - the latter obtained by ammonoxidation of ligneous substrates - is bound in similar structural moieties. Furthermore, the results obtained strongly support the idea of the formation of low molecular phenolic and quinoid intermediates for both natural humification and ammonoxidation of ligneous matter.