The water potential in drying soils, comprising both matric potential and osmotic potential components, can be measured using the dew point method (DPM). By combining DPM data with retention curve data acquired from techniques such as the suction plate method or the simplified evaporation method (SEM), it becomes possible to determine the soil water retention curve across the entire moisture spectrum. However, as the latter methods only determine the matric potential, the osmotic potential component in DPM data must either be negligible or known so that osmotic and matric potential components can be separated. This study aims to critically analyse common approaches for calculating the osmotic potential. To achieve this, we measured the water retention properties of a silt loam, a sandy loam and a sand across the entire moisture range by combining SEM and DPM. By using almost salt‐free soil material, we characterized reference water retention curves with negligible osmotic potential components. The impact of salt on water potential was analysed by conditioning soils with MgCl2 solutions of different concentrations, drying them, and measuring the water potential at different water contents using the DPM. The resulting water potentials were compared to the reference potentials and differences were interpreted as the osmotic potential component. The DPM‐measured water potentials in drying soils can be significantly affected by osmotic potential, especially at higher matric potentials (low suctions). Two models accounting for ideal and one model accounting for non‐ideal electrolyte behaviour were used to compare osmotic potential predictions with measurements. At low to medium salt concentrations, all models performed fairly well. At high concentrations, only the model accounting for non‐ideal behaviour predicted the osmotic potential satisfactorily, whereas at very high concentrations, all models underestimated the impact of osmotic potential on water potential. This suggests that the surface properties of the soil matrix, such as the specific surface area and surface charges, may lead to a decrease in osmotic potential beyond what is expected in pure solutions.

中文翻译：

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盐浓度对干燥土壤渗透电位的影响 - 测量和模型


干燥土壤中的水势，包括基质电位和渗透电位成分，可以使用露点法 （DPM） 进行测量。通过将 DPM 数据与从吸盘法或简化蒸发法 （SEM） 等技术中获得的保留曲线数据相结合，可以确定整个水分光谱的土壤保水曲线。然而，由于后一种方法只能确定矩阵电位，因此 DPM 数据中的渗透电位分量必须可以忽略不计或已知，以便可以分离渗透电位分量和矩阵电位分量。本研究旨在批判性地分析计算渗透电位的常用方法。为了实现这一目标，我们通过结合 SEM 和 DPM 测量了淤泥壤土、砂壤土和沙子在整个水分范围内的保水性能。通过使用几乎无盐的土壤材料，我们表征了渗透电位成分可忽略不计的参考保水曲线。通过用不同浓度的 MgCl2 溶液调节土壤，将其干燥，并使用 DPM 测量不同含水量下的水势，分析盐对水势的影响。将所得水势与参考电位进行比较，并将差异解释为渗透电位分量。干燥土壤中 DPM 测得的水势会受到渗透势的显着影响，尤其是在较高的基质电位（低吸力）下。两个解释理想模型的和一个解释非理想电解质行为的模型用于将渗透电位预测与测量值进行比较。在低到中等盐浓度下，所有模型的表现都相当不错。 在高浓度下，只有考虑非理想行为的模型才能令人满意地预测渗透电位，而在非常高的浓度下，所有模型都低估了渗透电位对水势的影响。这表明土壤基质的表面特性，例如比表面积和表面电荷，可能会导致渗透电位降低，超出纯溶液的预期水平。