Abstract Soil thermal conductivity is an important parameter for estimating soil heat flux and soil thermal regime. Knowledge on the components of apparent soil thermal conductivity (λ) across various water contents (θ) and temperatures is important to accurately understand soil heat transfer mechanisms. In this study, soil thermal conductivity was measured for sandy loam and silty clay soils at various temperatures and air pressures using a transient method. Four components of λ, namely, heat conduction, latent heat transfer by water vapor diffusion, sensible heat transfer by liquid water, and sensible heat transfer by water vapor diffusion were quantified. Results showed that in uniform soils, the magnitudes of sensible heat transfers by liquid water and water vapor were negligible during these transient measurements. The contribution of latent heat transfer through vapor diffusion to total heat transfer increased as temperature increased, and the peak value occurred at an intermediate water content. The water content at which the maximum vapor diffusion occurred varied with soil texture. In addition to the four calculated components, a significant residual contribution to λ caused by an unidentified vapor transfer mechanism was observed between 3.5°C and 81°C. For example, calculations indicated that approximately 66% of the sandy loam λ at θ=0.11 m3 m−3 was caused by an unidentified vapor transfer mechanism at 81°C. This extra contribution by vapor transfer could be explained either as enhanced vapor diffusion or by an advection mechanism. Further investigation is needed to clarify whether enhanced diffusion or advection is occurring in unsaturated soils.

中文翻译：

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估算不同含水量和温度下土壤表观热导率的组成部分

摘要 土壤热导率是估算土壤热通量和土壤热态的重要参数。了解不同含水量 (θ) 和温度下表观土壤热导率 (λ) 的分量对于准确理解土壤传热机制非常重要。在这项研究中，使用瞬态方法在不同温度和气压下测量了砂质壤土和粉质粘土的土壤热导率。λ的四个分量，即热传导、水蒸气扩散潜热、液态水显热传递和水蒸气扩散显热被量化。结果表明，在均匀土壤中，液态水和水蒸气的显热传递幅度在这些瞬态测量期间可以忽略不计。通过蒸汽扩散的潜热传递对总热传递的贡献随着温度的升高而增加，并且峰值出现在中间水含量处。发生最大蒸汽扩散时的含水量随土壤质地而变化。除了计算出的四个分量外，在 3.5°C 和 81°C 之间还观察到由不明蒸汽转移机制引起的对 λ 的显着残余贡献。例如，计算表明，在 θ=0.11 m3 m-3 处，大约 66% 的砂质壤土 λ 是由 81°C 时不明的蒸汽传递机制引起的。蒸汽转移的这种额外贡献可以解释为增强的蒸汽扩散或平流机制。需要进一步调查以澄清在非饱和土壤中是否发生了增强的扩散或平流。