## 3 \({}^{13}\)C Solid-State NMR Applications to Composing
It was hypothesized that the high content of organic C of the composted rice husk and the chemical resistance to microbial decomposition could provide special benefit in sustaining an organic C reserve if used as a soil ameliorant, especially in tropical soils where organic matter decomposes rapidly. [PERSON] et al. [69] examined the composting process of winery-distillery waste, i.e., grape marc (the primary waste of wine production obtained after the pressing process) and exhausted grape marc (the solid waste of alcohol distillation), showing the importance of combining thermal analysis, and FTIR and \({}^{13}\)C SSNMR spectroscopies with classical analytical techniques, the latter being insufficient to study the humification processes of these kinds of feedstocks. Areas of the \({}^{13}\)C CP-MAS NMR spectra, evaluated at the beginning and after two months of composting, showed a relative decrease in the carbohydrates and an increase in the alkyl groups. Interestingly, the obtained compost showed good properties for agronomic uses. [PERSON] et al. [77] used \({}^{13}\)C CP-MAS NMR spectra to characterize the OM composition of eleven different composting obtained from waste derived from aromatic plant production and compared the NMR results with the suppressive properties against _Rhizoctonia solani_ and _Sclerotinia scleroorum_ on garden cress, a vegetable crop appreciated for its nutraceutical and taste-giving components, but threatened by soil-borne pathologies due to its very short life-cycle. The study demonstrated good potential for several of the investigated composts as sustainable remedies, substituting for synthetic chemicals. The analysis of \({}^{13}\)C CP-MAS NMR spectra showed correlations between the best performing composts and the higher humification level. In particular, the removal of essential oils resulted in an improved humification, a preservation of apolar compounds, and a decrease in _LigR_. This beneficial effect was attributed to the known antioxidant and antimicrobial properties of essential oils, which could have hampered the microbial activity in the processed biomass. [PERSON] et al. [60] investigated the effect on soil fertility and crop yields in a volcanic Mediterranean soil of two different composts, one made from olive mill waste and orchard pruning residues, and one from olive mill waste, animal manure and wool residues, as well as of a biochar and of mixtures of the biochar and the composts. \({}^{13}\)C CP-MAS NMR spectra were recorded for the two composts and the biochar, and the areas of the characteristic spectral regions showed that biochar had the lowest content of O-alkyl, methoxyl and alkyl C and the highest content of aromatic species. Overall, the authors concluded that the effects of these organic amendments on crop yield are largely variable and influenced by the interaction with soil chemistry. \({}^{13}\)C SSNMR has been applied in a few cases to study compost from MSW [42; 79; 80], which generally has a large organic fraction (40%), but, due to its origin, can also show peculiar spectral features. In particular, [PERSON] et al. [42] applied a complete set of quantitative and selective \({}^{13}\)C SSNMR experiments to MSW after various composting times and, besides observing the expected decomposition of carbohydrates, the presence of plastics (especially polystyrene, but also polyethylene and polypropylene) was recognized from characteristic signals in both the aliphatic and aromatic regions. Both aromatic and aliphatic signals increased with composting time because of an accumulation of these non-biodegradable materials. The effect of composting on plastics was also investigated by [PERSON] et al. [70] by means of different \({}^{13}\)C SSNMR measurements. In this case the decomposition of a bio-degradable starch-based thermoplastic mulching film for horticultural crops was followed in a real on-farm composting process.