School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom.
Environ Sci Technol. 2011 Nov 15;45(22):9666-70. doi: 10.1021/es202319a. Epub 2011 Oct 27.
The wettability of soil is of great importance for plants and soil biota, and in determining the risk for preferential flow, surface runoff, flooding,and soil erosion. The molarity of ethanol droplet (MED) test is widely used for quantifying the severity of water repellency in soils that show reduced wettability and is assumed to be independent of soil particle size. The minimum ethanol concentration at which droplet penetration occurs within a short time (≤ 10 s) provides an estimate of the initial advancing contact angle at which spontaneous wetting is expected. In this study, we test the assumption of particle size independence using a simple model of soil, represented by layers of small (~0.2-2 mm) diameter beads that predict the effect of changing bead radius in the top layer on capillary driven imbibition. Experimental results using a three-layer bead system show broad agreement with the model and demonstrate a dependence of the MED test on particle size. The results show that the critical initial advancing contact angle for penetration can be considerably less than 90° and varies with particle size, demonstrating that a key assumption currently used in the MED testing of soil is not necessarily valid.
土壤的润湿性对植物和土壤生物群系非常重要，并且会影响优先流、地表径流、洪水和土壤侵蚀的风险。乙醇液滴摩尔浓度（MED）测试广泛用于量化表现出润湿性降低的土壤的水斥强度，并且假定其与土壤颗粒大小无关。在短时间（≤ 10 秒）内发生液滴渗透的最小乙醇浓度提供了对自发润湿时预计初始前进接触角的估计。在这项研究中，我们使用简单的土壤模型来测试颗粒大小独立性的假设，该模型由小直径（约 0.2-2 毫米）的珠子层表示，预测了顶层珠子半径变化对毛管驱动吸入的影响。使用三层珠系统的实验结果与模型吻合良好，并证明 MED 测试对颗粒大小的依赖性。结果表明，穿透的临界初始前进接触角可能远小于 90°，并且随颗粒大小而变化，这表明当前在土壤 MED 测试中使用的一个关键假设不一定有效。
