Soil surface-seal measurement using high-resolution x-ray computed tomography (HRCT)
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Rainfall on bare soil breaks soil aggregates, detaching particles, plugging pores and decreasing porosity in the top few mm of soil. This reduces hydraulic conductivity and increases runoff through a process known as surface sealing. The objectives of this study are to measure saturated hydraulic conductivity (Ksat) of surface seals developed on bare Mexico silt loam (Aeric Vertic Epiaqualfs) during a simulated rainfall event, to evaluate the effect of anionic polyacrylamide (PAM) for maintaining high Ksat, and to evaluate models of sealing using total porosity, pore-size distribution collected with high-resolution X-ray computed tomography (HRCT). The study used a factorial design. Factors included rainfall duration (0-, 7.5-, 15-, 30-, and 60-min) at 55-mm hr-1 intensity, and an untreated soil or a soil amended with 20-kg ha-1 PAM. Application of PAM for various rainfall durations maintained from 20% to 41% higher Ksat than did untreated soil, for all times tested. Results indicated density ([rho]) increased, and total porosity and pore-size decreased rapidly after a 15-min rainfall. HRCT-[rho] data helped identify the best model selection for characterizing seal [rho] profile. Although the cost is expensive, HRCT image is a valuable tool to measure soil properties by analyzing soil thickness down to 0.015-mm. The study confirms that HRCT-analysis of soil allows accurate and direct measurements of seal effects on water flow and documents the usefulness of PAM for reducing surface sealing.