## 4 \({}^{13}\)C Solid-State NMR Applications to Vermicomposting  
Several studies applied \({}^{13}\)C CP-MAS NMR to characterize vermicomposts obtained from different substrates [106; 107; 108; 109; 110; 111]; the relative areas of the spectral regions of the vermicomposts together with details on the feedstocks and on the process are reported in Table 4. The hydrophobic index _HB/HI_ is also reported, when available. Most of the studies used feedstocks containing cattle manure (CM), either alone or mixed with other organic wastes, like flock cotton residues, garden green wastes, sugar cane bagasse, and sunflower cake. In fact, CM has been demonstrated to be a good habitat for earthworms. Only in two cases the feedstock did not contain CM, but it was either a mixture of lettuces, apples, residual maize, ground spent coffee and pieces of cardboard [106], or it was made of map pruning wastes [111]. In two independent studies [108; 110], CM alone was vermicomposted in apparently very similar conditions (5 kg of worms per m\({}^{3}\) of organic residue, precomposing time of 1 month, vermicomposting time of 4 months), but the \({}^{13}\)C CP-MAS NMR spectra of vermicomposts were quite dissimilar, displaying different integral intensities especially for alkyl C and O-aryl C. The areas of the spectral regions, taken from Table 4, are shown in Figure 4, where data on humic extracts are also shown. The observed variability in the compost composition can be due to differences in unstated process parameters or, more probably, to the different origin of the feedstock. In fact, the data of Table 4 indicate that vermicomposts tend to inherit the molecular features of the starting feedstocks. For example, when CM is progressively replaced with lignocellulosic residues from cotton [108], the integral intensities of the O-alkyl C and aromatic C regions tend to increase, whereas the area of the alkyl C region decreases. Indeed, the fractions of O-alkyl C and aromatic C show values of about 44% and 18% in vermicompost entirely produced from cotton, whereas they are 37% and 14% in CM vermicompost; on the other hand, the fraction of alkyl carbons is about 19% in the first case and about 28% in the second one. The \({}^{13}\)C CP-MAS NMR spectra of vermicomposts containing CM and different amounts of cotton residues are shown in Figure 5.  
Figure 4: Relative areas of the \({}^{13}\)C NMR spectral regions recorded for CM vermicomposts (squares) and humic extracts of CM vermicomposts (circles) in the following studies: (\(\bullet\),\(\square\)) [108], (\(\bullet\)) [110], (\(\bullet\)) [110], (\(\bullet\)) [112], (\(\bullet\)) [113], (\(\bullet\)) [114], (\(\square\)) [115]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Ref. \({}^{*}\)** & **Feedback.\({}^{*}\)** & **Sample.\({}^{*}\)** & **Alkyl C** & **O-Alkyl C** & **Avromatic C** & **Carbony/C** & **mm** \\  & & & & & **CH\({}_{0}\)OCHEN** & **O-Alkyl C** & **Di-O-Alkyl C** & **Ayl C** & **  
The effect of vermicomposting time on the composition of the resulting vermicompost was studied by [PERSON] et al. [110] and [PERSON] et al. [111]. [PERSON] et al. monitored vermicomposts produced from different substrates (i.e., CM; CM and sugar cane bagasse; CM and sunflower cake; CM, sugar cane bagasse and sunflower cake) and observed a decrease in carbohydrates after 120 days of vermicomposting together with an increase in aryl and O-aryl groups. The decrease was larger when sugar cane bagasse was used. The intensities of the spectral regions for the feedstocks and vermicomposts after 120 days of treatment are reported in Table 4. The described trends resulted in an increase in the hydrophobic index in the mature vermicomposts compared to the starting materials and suggested the mineralization of carbohydrates and the selective preservation of the aromatic components. The carboxyl C fraction tended to increase for vermicomposts obtained from CM and from CM and sugar cane bagasse, whereas no significant changes were reported for vermicompost from the other feedstocks.