耕作层土壤热特性的时空变异特征研究

Soil thermal properties, including thermal conductivity, volumetric heat capacity, and thermal diffusivity, are important in studying surface energy balance, heat and water transport in soils, and soil evaporation. Many factors, including soil texture, water content, bulk density, and structure, affect soil thermal properties. However, existing experimental and modeling researches focus on the relationship between soil thermal properties and a single soil or environmental factor. Especially few reports consider the changes of soil thermal properties as related to soil structural variation. The objective of this research is to investigate the spatial and temporal characteristics of soil thermal properties in the tilled soil layer, where soil water content and bulk density vary continuously as a result of age hardening and wet/dry cycle. Soil temperature, water content, bulk density, and thermal properties at four depths of the tilled layer will be monitored continuously after planting. A model will be established to represent the dynamics of soil bulk density with time, which will then be combined with current models that describe the relationship between soil thermal conductivity with water content, and volumetric heat capacity with water content. Thus soil bulk density, in addition to water content, will be used as a new variable to predict the changes of soil thermal conductivity and heat capacity under field condition. Our measurements and models are useful in understanding the spatial and temporal characteristics of soil structure and thermal properties, and can improve current models for coupled heat and water flow near soil surface.

土壤热特性是研究地表能量平衡、土壤中水热过程以及土壤蒸发的基础参数。土壤热特性的大小受质地、含水量、容重和结构等因素影响，具有很大的时空变异性。然而，目前的实验和模型研究往往只关注土壤热特性与单一因子的关系，很少考虑结构变化下土壤热特性的变异特征。本项目拟以土壤耕作层为研究对象，通过动态监测翻耕后不同质地土壤耕作层含水量、温度、热特性和容重的变化规律，探讨干湿交替过程中耕层土壤热特性随含水量和容重的时空变化特征，建立耕层土壤容重的动态变化模型，以及包含土壤质地、含水量和容重的土壤热特性模型，充实非稳态结构下土壤水热耦合传输的理论和研究方法。研究结果不仅有助于深入认识田间条件下土壤热特性的变异特征，而且对探讨土壤水分运动、溶质运移、水热耦合机理以及其它土壤物理过程都具有重要的理论意义和应用价值。

土壤热特性是研究地表能量平衡、土壤中水热过程以及土壤蒸发的基础参数。土壤热特性的大小受质地、含水量、容重和结构等因素影响，具有很大的时空变异性。然而，目前的实验和模型研究往往只关注土壤热特性与单一因子的关系，很少考虑结构变化下土壤热特性的变异特征。本项目通过四年的实验和模拟研究，系统地研究了耕作层土壤热特性的时空变异特征，在以下几个研究方面取得了进展：（1）通过田间定位实验，揭示了耕作后土壤表层热特性、水分特征曲线和孔隙分布的变化规律，初步明确了干湿交替过程中土壤耕层结构的时空变化特征；（2）建立了土壤质地、容重和水分共同作用下的土壤热导率模型；（3）改进了thermo-TDR技术测定土壤容重的理论和技术；（4）完成了田间近地表热特性、含水量和热通量的观测和模拟。研究结果不仅有助于深入认识田间条件下土壤热特性的变异特征，而且对探讨土壤水分运动、溶质运移、水热耦合机理以及其它土壤物理过程都具有重要的理论意义和应用价值。