Soil Organic Nitrogen Formation Examined by Means of NMR Spectroscopy

NMR spectroscopy has been proven to be a valuable tool for the non-destructive examination of refractory geopolymers. Due to the low sensitivity of the ¹⁵N isotope for an NMR experiment, ¹⁵N NMR spectroscopy has been restricted to the examination of laboratory-derived ¹⁵N enriched material. Recent developments have made it possible to obtain solid-state ¹⁵N NMR spectra of natural soils at natural ¹⁵N abundance. The results of recent ¹⁵N NMR studies obtained from various soil and soil related systems are summarized. These studies indicate that amide functional groups represent the major nitrogen form in many soil systems. The formation of heterocyclic aromatic nitrogen, commonly proposed to be an important mechanism of nitrogen stabilization during humification, was not confirmed by ¹⁵N NMR spectroscopic investigation of natural soils.