地表覆盖对土壤热参数变化的影响

Study of effects of the surface mulch on soil thermal properties using heat pulse technology

摘要:

覆盖条件下土壤热性质的研究对于包气带水热运移及覆盖技术的应用均有重要意义。使用11针热脉冲探头对沙黄土不同深度（6 mm、18 mm、30 mm）的土壤热扩散率、热容量和热导率三个热参数进行测定，并进行地表覆盖（石子覆盖、秸秆覆盖）处理，旨在探究覆盖条件下表层土壤热性质动态变化过程及土壤热参数与水分的内在联系。结果表明：（1）相对于裸土，石子和秸秆覆盖条件下土壤热参数增大，且覆盖对于靠近表层土壤热参数的影响更加明显；（2）随降雨的发生，土壤热参数均增大，在两次降雨期间，土壤热参数逐渐减小，覆盖与裸土热参数差异逐渐增大；（3）三个热参数随降雨的发生，其动态变化过程表现不同，热容量对降雨的响应最为敏感，热导率次之，热扩散率开始减小的时间较热导率和热容量滞后，三个深度滞后时间均在48 h以上，而且覆盖以后热扩散开始减小的时间较裸土推迟（48 h以上）。土壤容重不变的情况下，在频繁干湿交替的过程中土壤水分为土壤热参数变化的最主要影响因素。覆盖条件下土壤热参数与土壤含水量关系研究表明：石子和秸秆覆盖条件下土壤热参数与土壤含水量的变化关系与裸土条件下一致，热导率与含水量呈幂函数增加的趋势，热容量随含水量线性增加，热扩散率随含水量增加先增后减，本研究所用沙黄土热扩散率峰值对应的含水量在0.20 cm³ cm^-3左右。由以上结果可以发现覆盖对近表层土壤热参数的动态变化有显著的影响，覆盖的保水效应直接影响土壤热参数的变化。

Abstract:

The study on thermal properties of mulched soil is of some great significance to the study of water and heat transfer in the vadose zone and application of the mulching technology. A 11-needle heat-pulse probe was used to measure soil thermal diffusivity, thermal capacity and thermal conductivity at different depths, 6 mm, 18 mm and 30 mm in sandy yellow earth under different mulches, no mulch, straw and gravel, so as to explore dynamic variation of the soil thermal properties and inner relationship between the soil thermal parameters and soil moisture in mulched soils. Results show that (1) mulching increased the soil thermal parameters and the more significant the effects, the closer to the soil surface; (2) rainfall also increased the soil thermal parameters, which decreased between two rainfall events and the difference increased between the bare soil and the mulched soils in the thermal parameters; (3) after a rainfall event, the three thermal parameters differed in dynamic variation process, with thermal capacity being the most sensitive in response to rainfall, and followed by thermal conductivity, and with thermal diffusivity starting to decline later than the other two, over 48 hours later at all the three soil layers, and in the mulched soils than in the bare soil. In soils constant in soil bulk density, soil water content was the most important factor affecting the soil thermal parameters in the process of frequent alternation of wetting and drying. Analysis of the relationships between the soil thermal parameters and soil water content in mulched soils showed that the relationship in soils mulched with either gravels or straw was similar to that in the bare soil, and that thermal conductivity increased as an exponential function of soil water content, soil thermal capacity did linearly with soil water content and soil thermal diffusivity increased first and then decreased with increasing water content. The peak of soil heat diffusion rate occurred in the sandy yellow earth, 0.20 cm³ cm^-3 in water content. Besides, from these above findings, it can be concluded that surface mulch had a significant impact on dynamic variation of the thermal properties and the water conservation effect of mulch would directly affect variation of the soil thermal properties.