In arid regions, severe salinization can commonly result in the formation of a salt crust layer that covers the soil surface. The salt crust, composed of salt crystals, has significantly different physical properties compared to its matrix soil. It can alter the energy budget in soil, thus affecting soil temperature. However, the effect of salt crust on soil temperature remains unclear. To address this, we conducted an experiment comparing soil temperatures between salt-free and saline soils. The two soils were initially saturated with fresh water and a saline solution (∼25%, NaCl), respectively, with a fixed shallow groundwater table. Salt precipitation was induced by evaporation using a halogen lamp (600 W m-2). Moreover, we measured the dynamic variation of evaporative water loss, salt cover fraction, and temperature (surface, 5 cm, and 15 cm). We developed a numerical model involving the variation of cover fraction and thickness of the salt crust, as well as the exothermic enthalpy of salt precipitation. The experimental results revealed that salt crust can significantly increase soil temperature. The variation of saline soil temperature was dominated by the evolution of the salt crust. The model accurately described soil temperature changes with the evolution of the salt crust and found that the higher temperature in saline soil than that in salt-free soil was attributed to lower heat loss due to greater evaporation resistance and lower surface emissivity by the salt crust, very small thermal resistance of the salt crust, the unique heat released during the crystallization of saline solution, and lower soil heat capacity. Higher temperatures in saline soil were also observed under various radiation intensities (200–1000 W m-2). Our findings help improve understanding of the energy balance in saline soil and provide new insights into quantitatively describing soil temperature variation with evolving salt crust.

中文翻译：

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盐壳对湿沙质土壤温度的影响


在干旱地区，严重的盐碱化通常会导致形成覆盖土壤表面的盐壳层。由盐晶体组成的盐壳与其基质土壤相比具有明显不同的物理性质。它可以改变土壤中的能量收支，从而影响土壤温度。然而，盐壳对土壤温度的影响仍不清楚。为了解决这个问题，我们进行了一项实验，比较了无盐土壤和盐碱土壤的土壤温度。这两种土壤最初分别用淡水和盐溶液（∼25%，NaCl）饱和，具有固定的浅层地下水位。使用卤素灯 （600 W m-2） 蒸发诱导盐沉淀。此外，我们测量了蒸发水分损失、盐覆盖分数和温度（表面、5 cm 和 15 cm）的动态变化。我们开发了一个数值模型，涉及盐壳覆盖分数和厚度的变化，以及盐沉淀的放热焓。试验结果表明，盐壳可以显著提高土壤温度。盐渍土温度的变化受盐壳演化的影响。该模型准确描述了土壤温度随盐壳演变的变化，发现盐渍土的温度高于无盐土，这是由于盐壳的蒸发阻力较大，表面发射率较低，盐壳的热阻非常小，盐溶液结晶过程中释放的独特热量较低， 以及降低土壤热容量。在各种辐射强度 （200–1000 W m-2） 下，盐渍土壤中也观察到更高的温度。 我们的发现有助于提高对盐渍土壤能量平衡的理解，并为定量描述土壤温度随盐壳变化提供新的见解。