N-15 and C-13 CPMAS and solution NMR studies of N-15 enriched plant material during 600 days of microbial degradation

Nitrogen-15 enriched plants (Lolium perenne (rye grass) and Triticum sativum (wheat)) have been composted under controlled conditions up to 630 days. The composts were characterized by C-13 and N-15 CPMAS spectra. For some composts N-15 HR NMR solution spectra of the NaOH extracts were studied. The composts were characterized by weight loss and elementary analysis. Most of the nitrogen detectable is assigned to amide/peptide structures (80–90%), the remaining intensities being found in the chemical shift region of amino- and ammonium groups. Signals for nitrogen-containing heterocycles were not observed. Less than 5% of the intensity of the low field side of the main peptide/amide signal might be ascribed to indole/imidazole/uric acid derivatives. Combined analysis of C-13 CPMAS spectra, the elemental analysis and mass balance, yield the result that all chemical structures visible in the C-13 spectra are altered in the composting process, although at different rates.