Proton Nuclear Magnetic Resonance (NMR) Relaxometry in Soil Science Applications

Proton NMR relaxometry is a very powerful tool for investigating porous media and their interaction with water or other liquids and the mobility and interaction of organic molecules in solution. It is commonly used in material science or earth science. However, it is only scarcely applied in soil science although it shows great potential for helping to understand water uptake into the soil matrix and processes occurring at the solid-liquid interface at soil particle surfaces. This review introduces proton NMR relaxometry in the context of soil science and discusses the most important applications of the method in this field. Relevant results from different applications of NMR relaxometry in soils are described and research gaps identified. Some original data is presented concerning biofilm formation in soils, which was investigated using proton NMR relaxometry. NMR relaxometry is a sensitive, informative and promising method to study pore size distribution in soils as well as many kinds of soil physicochemical processes, among which are wetting, swelling or changes in macromolecular status. It is further a very helpful method to study interactions between molecules in soil organic matter and can serve to study the state of binding of water or organic chemicals to soil organic matter. Relaxation times determined by NMR relaxometry are sensitive to various factors that play a role in soil-water interaction which is both an advantage and shortcoming of the method: NMR relaxometry can be applied to numerous investigations in soil science, but at the same time interpretation of the results may be very difficult in such complex and heterogeneous systems like soils.