Basic principles of solid state nuclear magnetic resonance (NMR) spectroscopy relevant to the study of the structure of organic matter of whole soils or solid fractions of soils are outlined. These include cross polarization, magic angle spinning, relaxation phenomena, and decoupling. There are problems in obtaining quantitative data by cross polarization techniques since there is more than one spin lattice relaxation time in the rotating frame. Selective relaxation can be used, however, to identify specific functional groups in soil. Spectra of wood, cellulose, lignin, and their decomposition products can be related to spectra obtained from soil organic matter. The most notable feature about 13C-NMR spectra of whole soils is their variability, and it is shown that this is due to soil-forming factors such as climate and vegetation. The isotopes 31P and 15N in soils can also be studied by NMR spectroscopy and can be used to trace the incorporation of these elements into soils.
Nuclear magnetic resonance spectroscopy (NMR) is a nondestructive technique which can provide information about the types of forms of C, P, N, and other elements in materials and hence has great potential in soil science. The application of some aspects of NMR spectroscopy to the analysis of soil organic matter is the subject of this chapter. A full description of the NMR technique is beyond the scope of this chapter and the reader is referred elsewhere for a more detailed treatment (Becker, 1980; Fukushima & Roeder, 1981; Fyfe, 1983; Shaw, 1984), in particular to the text specifically written for geochemists (Wilson, 1987). However, a fairly lengthy description is necessary here in order that the reader who has little NMR background can follow the text. Thus, the chapter has a secondary function: that is to act as an NMR spectroscopy primer for the practicing scientist. A list of symbols and definitions is shown in the Appendix.