Low-Field NMR of Water in Model Soils

The evolution of water contained in soils is a physical phenomenon of importance in soil science and climatology. This work presents preliminary results from the use of mobile NMR to measure moisture in soil columns. To demonstrate the ability of the NMR technique to follow the drainage process of water in model soils, moisture measurements were performed at a certain depth with a mobile NMR sensor during an one-step outflow experiment. The NMR sensor exhibits a cylindrical geometry incorporating the principle of the u-shaped NMR-MOUSE. It could be raised and lowered inside a plastic tube in the soil column similar to a wire-line logging tool. Working with a frequency of 8.8 MHz, the sensitive volume lies 3 mm deep into the soil and 2 mm away from the tube walls, making the technique truly non-invasive. For the purpose of quantitative analysis, the temporal evolution of moisture (described by the Richards Equation) was modelled with the Hydrus1D Program. Out of these simulations, an assessment of the hydraulic parameters (Ks, α, n of the Van Genuchten model) of the soil was achieved.

O. Sucre, F. Casanova, A. Pohlmeier, B. Blümich, Open Magn. Reson. J. 3 (2010) 63-68, DOI: 10.2174/1874769801003010063