Soil underpins all life and is the most biodiverse habitat on Earth. One of the key functions of soil is in supplying nutrients such as nitrogen (N) for plants. Recent studies have highlighted that low molecular weight (MW) organic molecules are central to supplying N to plants. This is because low MW organic molecules can be directly taken up by plants and are intermediates in the breakdown of polymers to release inorganic nutrients. Almost nothing is known about the molecules comprising the pool of organic N, yet many questions about N availability require knowledge of molecular composition.

The aim of this study was to develop sampling and analytical procedures for analysing organic N molecules in soil. Studies with CE-MS have overturned the idea that soil is dominated solely by amino acids and their polymers. CE-MS has shown that soil contains a diverse assemblage of >100 organic N monomers, which contrasts with derivatisation-based GC and LC methods reporting occurrence of fewer than 20 organic N monomers. These findings suggest the N cycle may not be dominated by reactions involving condensation and hydrolysis of amino acids. For example, the presence of heterocyclics and osmolytes (e.g. various quaternary ammonium compounds) provides clues as to soil history and function (i.e. fire and abiotic stresses), and direct evidence of a substantial fraction of N being diverted away from amino acids and their polymers.