Nuclear magnetic resonance (NMR) relaxation time (T2) distributions are well known to be linked to the pore size distribution and show promise as a method of estimating soil texture. As traditional laboratory methods used for soil texture estimates in soil science are generally time consuming, in this study, we explore an alternative approach based on NMR T2 distributions to estimate the soil texture of water‐saturated soil samples collected from three field sites. Using two T2 cut‐off times, T2a and T2b, the T2 distribution of a soil was partitioned into three regions, short, intermediate and long relaxation times, each of which represents the fraction of clay, silt and sand, respectively. Two approaches for determining the cut‐off times were used: the first used T2 cut‐off times determined from the data from all sites and the second used site‐specific T2 cut‐off times. The NMR estimates of soil texture were compared to measurements of soil texture made using the sieve–pipette method and laser diffraction particle size analysis (LDPSA). The results show that there is no universal cut‐off time for estimating the clay, silt and sand fractions based on the NMR T2 distributions. The accuracy of NMR measurements to estimate the soil texture depends on the magnetic susceptibility of the measured material. For soils with low magnetic susceptibility (<2 × 10−4 SI) using site‐specific cut‐off times, the NMR‐derived soil texture (root mean squared error [RMSE] = 9.43%) more closely matches the soil texture measured from the sieve–pipette method than the soil texture determined using LDPSA (RMSE = 11.88%). However, the NMR estimate of soil texture breaks down for soils with high magnetic susceptibility (>4 × 10−4 SI). These results suggest that the NMR method can provide reasonable estimates of the soil texture for soils with low magnetic susceptibility. Highlights No universal cut‐off time exists for estimating the clay, silt and sand fraction based on the NMR T2 distributions. NMR can provide better estimates of clay, silt and sand fractions for soils with low magnetic susceptibility than LDPSA. Site‐specific cut‐off times are determined through comparison between NMR data and sieve–pipette measurements. NMR yields reasonable estimates of the soil texture for soils with low magnetic susceptibility.

We have developed a laboratory nuclear magnetic resonance (NMR) study to investigate the effect of clay, silt, and sand content on the NMR relaxation time distribution. Transverse NMR relaxation times ( T2) were determined for water-saturated unconsolidated sediment mixtures of 1%–60% kaolinite clay, 5%–85% silt-size glass beads, and 8%–94% quartz sand by mass. Nearly all of the mixtures were characterized by a unimodal T2 distribution. When clay is present in quantities greater than 10%, the clay content dominates the response. For these samples, the mean-log relaxation times ( T2ML) range from 0.03 to 0.06 s, regardless of silt or sand content. For mixtures with <10% clay, T2ML decreases with increasing clay content. When the clay content is kept the same, T2ML decreases with increasing silt content and increases with the increasing sand content. The strong effect of the clay content on the NMR response is due to the high specific surface area of the clay and the distribution of clay throughout the samples. These results will help improve the interpretation of NMR field data in soils and unconsolidated sediments.

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