Soil wettability as determined from using low-field nuclear magnetic resonance

Area of Science:

• Soil Science
• Geophysics
• Materials Science

Background:

• Traditional soil wettability tests like ethanol droplet and water drop penetration time are quick but lack reproducibility.
• Reproducible soil wettability assessment is crucial for understanding soil-water interactions and environmental processes.

Purpose of the Study:

• To introduce low-field nuclear magnetic resonance (NMR) as a reproducible and accurate method for determining soil wettability.
• To establish NMR-based criteria for differentiating between wettable and water-repellent soils.

Main Methods:

• Utilized low-field nuclear magnetic resonance (NMR) to analyze the transverse relaxation times (T2) of water in soil samples.
• Compared NMR-derived T2 values and the geometric mean of T2 (T(2gm)) for wettable and water-repellent soil samples.
• Investigated the dynamic changes in T2 values over time upon water addition to assess sample wettability evolution.

Main Results:

• Wettable soils exhibited predominant NMR peaks at T2 values ≤ 100 ms, while water-repellent soils showed peaks near 1000 ms.
• The geometric mean of T2 (T(2gm)) was > 1000 ms for water-repellent soils and < 1000 ms for wettable soils immediately after water addition.
• NMR measurements indicated that water-repellent soils eventually reach equilibrium with wettable soils upon continuous water exposure.

Conclusions:

• Low-field NMR provides a reproducible and reliable method for assessing soil wettability.
• NMR can be used to formulate a screening criterion for rapid soil wettability determination.
• NMR offers a significant advantage over traditional methods due to its high reproducibility and accuracy.