原状土与装填土热特性的比较

土壤热特性是研究土壤—植物—大气系统中能量传输的必要参数。目前的研究集中在室内装填土柱上热特性与含水率、质地、温度和体积质量(容重)等因素的关系,田间条件下土壤结构对热特性影响的报道很少。该研究通过比较2种质地土壤田间原状土和室内装填土热特性的差异,初步探讨了不同含水率范围内结构形成对土壤热特性的影响。采集田间原状土,在室内利用热脉冲技术测定其热容量、热导率和热扩散率;然后将样品磨碎、过2mm土筛,填装后得到相同体积质量和含水率的装填土壤样品,并测定其热特性。结果表明,装填土和原状土的热容量基本一致;在中等含水率区域(砂壤土:0.07～0.24m3/m3;壤土:0.15～0.31m3/m3),重新装填后砂壤土和壤土的热导率分别降低了9.7%和9.8%。另外,结构形成增加了土壤热扩散率,在中等含水率区域尤其明显;在接近饱和区域,原状土与装填土的热扩散率趋于一致。因此,土壤结构形成对土壤热容量没有显著影响,但提高了中等含水率区域土壤的热导率和热扩散率。

Comparative study on thermal properties of intact andrepacked soil samples

Soil thermal properties are essential for studying energy transport in the Soil-Plant- Atmosphere-Continuum. Many laboratory studies have been conducted to investigate the influences of water content, texture, temperature and bulk density on soil thermal properties using repacked soil columns. There are few reports about soil structure effects on thermal properties of intact soil samples. The objective of this study is to examine the influences of soil structure on thermal properties at different water content ranges by comparing thermal properties of intact and repacked soil samples for sandy loam soil and loam soil. Intact soil samples were collected from field and volumetric heat capacity, thermal conductivity, and thermal diffusivity were measured with the heat pulse technique. Subsequently the intact samples were air-dried, crushed, sieved through a 2 mm screen, and repacked into the same cores with identical water content and bulk density. Thermal properties of the repacked samples were then measured following the same procedure. Finally soil water content and bulk density were determined using the gravimetric method. Similar heat capacity values were obtained for repacked and intact soils. For the repacked samples, thermal conductivity of the sandy loam and loam was 9.7% and 9.8%, lower than that of their intact counterparts at intermediate water contents (0.07-0.24 m3/m3 for sandy loam, 0.15-0.31 m3/m3 for loam). Soil thermal diffusivity was increased by the formation of soil structure at intermediate water contents. At the water content near saturation, the intact and repacked samples had similar thermal diffusivity values. In summary, soil structure formation does not significantly affect heat capacity, but increases thermal conductivity and thermal diffusivity, especially at intermediate water contents.