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Water films and scaling of soil characteristic curves at low water contents

机译：低水含量下水膜和土壤特性曲线的变化

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摘要

Individual contributions of capillarity and adsorptive surface forces to the matric potential are seldom differentiated in determination of soil water characteristic (SWC) curves. Typically, capillary forces dominate at the wet end, whereas adsorptive surface forces dominate at the dry end of a SWC where water is held as thin liquid films. The amount of adsorbed soil water is intimately linked to soil specific surface area (SA) and plays an important role in various biological and transport processes in arid environments. Dominated by van der Waals adsorptive forces, surface-water interactions give rise to a nearly universal scaling relationship for SWC curves at low water contents. We demonstrate that scaling measured water content at the dry end by soil specific surface area yields remarkable similarity across a range of soil textures and is in good agreement with theoretical predictions based on van der Waals interactions. These scaling relationships are important for accurate description of SWC curves in dry soils and may provide rapid and reliable estimates of soil specific surface area from SWC measurements for matric potentials below -10 MPa conveniently measured with the chilled-mirror dew point technique. Surface area estimates acquired by fitting the scaling relationship to measured SWC data were in good agreement with SA data measured by standard methods. Preliminary results suggest that the proposed method could provide reliable SA estimates for natural soils with hydratable surface areas smaller than 200 m~2/g.
机译：在确定土壤水分特征（SWC）曲线时，很少区分毛细管作用和吸附表面力对基质势的贡献。通常，毛细力在湿端占主导地位，而吸附表面力在SWC干端占主导地位，在SWC中，水以液态薄膜形式存在。吸附的土壤水的量与土壤的比表面积（SA）密切相关，并且在干旱环境中的各种生物和运输过程中起着重要的作用。在范德华吸附力的支配下，地表水相互作用在低水含量下对SWC曲线产生了几乎普遍的比例关系。我们证明按比例缩放在干燥端通过土壤比表面积测量的水含量会在各种土壤质地上产生显着的相似性，并且与基于范德华相互作用的理论预测非常吻合。这些比例关系对于准确描述干燥土壤中的SWC曲线非常重要，并且可以通过使用冷镜露点技术方便地测量的-10 MPa以下的基质电势从SWC测量中快速，可靠地估算土壤比表面积。通过将比例关系与测量的SWC数据拟合而获得的表面积估算值与通过标准方法测量的SA数据非常吻合。初步结果表明，该方法可以为水合表面积小于200 m〜2 / g的天然土壤提供可靠的SA估计值。

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