Soil temperature, composition, and structure directly affect the heat transfer mechanisms in soil. Understanding the thermal behavior of soil is fundamental for describing the processes of mass and energy exchange in the soil-plant-atmosphere system. In addition, estimating thermal property values is necessary to determine the amount of heat transferred, stored, or transmitted by conduction and convection between the soil surface and deeper layers. This study used two soil heat transfer models (the conduction and conduction-convection methods) to estimate soil thermal properties. Soil data were collected in a natural pasture area in the Pampa biome in southern Brazil over 1.5 years. The results showed that soil thermal diffusivity (k) has an inverse seasonal variation with soil temperature (T_s). The k and soil thermal conductivity (λ) values are higher as the soil depth and soil moisture ($\theta$) increase, confirming the vertical variation of thermal properties. The liquid water flux density (W) represents the vertical movement of water in the soil and decreases in periods of higher T_s. Increasing values of W led to an increase in the variability of k with depth. The conduction–convection method provides the best estimates for T_s with R² = 0.99 for deeper layers compared to the conduction method. However, we found that both models gave similar results for near-surface layers since, in this case, the conduction process was responsible for most of the heat transfer from the surface to the ground. The results obtained here allowed us to evaluate heat transfer at different depths and estimate thermal properties as a function of soil moisture in a natural pasture area in the Brazilian Pampa biome. Furthermore, the results can be integrated into global land surface models intended to represent the behavior of the energy exchange between soil, surface, and atmosphere.

土壤温度、成分和结构直接影响土壤中的传热机制。了解土壤的热行为是描述土壤-植物-大气系统中质量和能量交换过程的基础。此外，估算热属性值对于确定通过土壤表面和深层之间的传导和对流传递、存储或传输的热量是必要的。本研究使用两种土壤传热模型（传导和传导-对流方法）来估算土壤热特性。土壤数据是在巴西南部潘帕生物群系的一个天然牧场地区收集的，历时 1.5 年。结果表明，土壤热扩散系数( k )与土壤温度( T_秒）。k和土壤热导率 ( λ ) 值随着土壤深度和土壤水分($\theta$）增加，证实了热性能的垂直变化。液态水通量密度 ( W ) 代表水在土壤中的垂直运动，并在较高的T _s期间降低。W值的增加导致k随深度的变化增加。传导-对流方法提供了T _s和R ²的最佳估计 = 0.99 对于较深的层与传导方法相比。然而，我们发现这两个模型对近地表层给出了相似的结果，因为在这种情况下，传导过程负责从地表到地面的大部分热传递。此处获得的结果使我们能够评估不同深度的热传递，并估计热特性作为巴西潘帕生物群落天然牧场区域土壤水分的函数。此外，结果可以整合到全球陆地表面模型中，以表示土壤、地表和大气之间的能量交换行为。