Determination of quantitative pore‐size distribution of soils with ¹H NMR relaxometry

Abstract

Summary The determination of pore‐size distribution (PSD) in soil by conventional methods can be time‐ and effort‐consuming. Therefore, several attempts have been made recently to assess and implement proton nuclear magnetic resonance relaxometry (1H NMR relaxometry) to determine PSDs quantitatively. The 1H NMR relaxometry promises not only to be more time‐ and effort‐saving but also offers a broader range for the estimation of pore size, better resolved results and non‐destructive measurements. To evaluate these possibilities, we tested the extent to which a single calibration curve for the estimation of surface relaxivity of soil, derived from seven soil samples, can be applied to unknown soils. For validation, the quantitative PSDs of seven additional soil samples were determined from the distributions of NMR relaxation times of water saturated samples using this calibration curve; they were compared with their classical water retention curves (WRCs). In general, the quantitative PSDs determined by this approach described the classical WRCs quite well. The best results were obtained for sandy, silty and loam soils. The largest differences were for soils with large clay (47%) and SOM contents (10 and 21%). Our results suggest that these differences derive from swelling processes. Highlights Can NMR relaxometry be used to quantify soil pore‐size distribution without individual calibration? Soil pore size assessment by NMR is fast, detailed and independent of conventional methods NMR method describes the pore‐size distribution of various soil types and soil compositions. NMR method can assess quantitative effects of SOM and swelling of clay in soil.

Water Retention and Pore Size Distribution of a Biopolymeric‐Amended Loam Soil

“…Subject to a later clarification, we will base our work on the definition of Morriss et al (1997) and identify T 2 (1) with clay‐associated water. This is approximately identical to the definition of Meyer et al (2018) of water relaxing faster than 4.5 ms as micro‐ and medium‐pore water. Water fractions relaxing slower are referred to in this scheme as capillary‐pore and macropore water or, in the definition of Meyer et al (2018), as macropore water.…”

“…This is approximately identical to the definition of Meyer et al (2018) of water relaxing faster than 4.5 ms as micro‐ and medium‐pore water. Water fractions relaxing slower are referred to in this scheme as capillary‐pore and macropore water or, in the definition of Meyer et al (2018), as macropore water. The differentiation between capillary pore and macropore water is arbitrary because the boundaries are not clearly defined.…”

“…The direct scaling of NMR relaxation time to pore size was discussed by Jaeger et al (2009), who found better correlation between PSD and T 2 spectra by using a dual‐relaxivity model, which defines separate surface relaxivity parameters for micropores and mesopores. Recently, Meyer et al (2018) confirmed this approach by calibration and validation with 14 different soil materials. They found T 2 surface relaxivities of 551.7 and 9.6 μm s −1 for macro‐ and medium‐sized pores defined by matrix potentials of approximately −32 kPa.…”

Water Retention and Pore Size Distribution of a Biopolymeric-Amended Loam Soil

“…The direct scaling of NMR relaxation time to pore size was discussed by Jaeger et al (2009), who found better correlation between PSD and T 2 spectra by using a dual-relaxivity model, which defines separate surface relaxivity parameters for micropores and mesopores. Recently, Meyer et al (2018) confirmed this approach by calibration and validation with 14 different soil materials. They found T 2 surface relaxivities of 551.7 and 9.6 mm s -1 for macro-and medium-sized pores defined by matrix potentials of approximately -32 kPa.…”

Effects of olive mill wastewater disposal on soil: Interaction mechanisms during different seasons

“…A CarrPurcell-Meiboom-Gill (CPMG) pulse sequence was used to obtain T2 and the corresponding relaxation rates of the water protons in the samples (Jaeger et al, 2009;Meiboom and Gill, 1958). Pore size distribution was determined following the procedure described in Meyer (2015). The pore size distribution was converted into a water retention curve (matric potential as a function of volumetric water content) using Young-LaPlace equation.…”