生物质炭添加对旱地红壤热性质的影响机理研究

Soil thermal properties are important factors governing the exchange of water and heat between the soil and atmosphere. Soil thermal properties are not constant but vary with soil structure and the contents of soil water and soil organic matter. Recently, biochar produced from agricultural waste and its application to the soils has drawn much attention as an effective way of soil carbon sequestration to mitigate global climate change. Notably, the input of considerable amount of recalcitrant organic matter into the soils should affect soil thermal properties by alter soil substance composition, soil structure and water holding capacity. However, the mechanism of the effects of biochar application on soil thermal properties remains unclear. Thus, the objects of the proposed project are to 1) quantify the changes of soil thermal properties (soil thermal capacity, soil thermal conductivity and soil thermal diffusivity) affected by different amounts and durations of biochar application; 2) to clarify the mechanism of the effects of biochar application on soil thermal properties by investigating its direct and indirect influences on relevant soil properties; 3) to depict the soil temperature and water dynamics influenced by the alteration of soil thermal properties due to biochar application. The results of this project will improve our knowledge of the relationships between soil organic matter and soil thermal properties, and provide an insight into the feedback of artificial soil carbon sequestration on the exchange of water and heat exchange between soil and atmosphere.

土壤热性质是影响土壤-大气间水热交换的重要因素，其随土壤结构、含水量及土壤有机质含量的变化而变化。近年来，农业废弃物生物质炭转化与还田被认为是实现土壤固碳以应对全球气候变化的重要手段之一。然而，生物质炭作为人为输入的稳定有机物在迅速提高土壤有机质含量并改变土壤结构和持水性能的同时必然对土壤热性质产生综合影响。但由于相关研究较少，生物质炭添加对土壤热性质的影响及其机理尚不清楚。本研究拟结合室内模拟及田间定位试验，明确旱地红壤热性质（热容量、导热率和热扩散系数）随生物质炭添加量及添加时间的变化规律；阐明生物质炭通过影响土壤有机质、孔隙状况、持水性能等对土壤热性质产生直接或间接作用机理；揭示生物质炭添加引起土壤热性质变化后土壤温度和水分动态响应特征。本课题研究成果将丰富土壤热性质影响因素的认识，为研究人为固碳对土壤-大气间水热交换过程的影响提供科学依据。

土壤的热性质是影响土壤中的热量储存和传递的关键性因素，因而也可以通过决定土壤中的微气候来影响土壤中的各种过程。长久以来，施用生物质炭由于可以作为一种提升土壤一系列理化与生物性质的处理方式而受到广泛关注。然而，几乎没有关于生物质炭处理对于土壤热性质影响的资料可供参考。本次试验分为室内与田间两部分。在室内试验中，使用红壤与小麦秸秆生物质炭填装扰动土柱，容重均为1.3 g cm-3，生物质炭处理分别占质量分数为0%, 0.5%, 1.0%, 1.5%, 2.0%与2.5%。与此同时，本研究也在红壤地区的表土层（0~20cm）进行了同样处理的田间试验。所得的扰动土柱与原状土样品的热性质测量方法为热脉冲法，土壤的含水量处理由0%至40%以5%的间隔递增。同时，在田间自然状态下也原位测量了土壤的热性质。在扰动土柱实验中，因为容重一定，所以在大多数含水量下土壤的热容量，导热率和热扩散系数均不受影响。这表明即使施用量达到2.5%，生物质炭对于土壤热性质的影响也并不能通过改变土壤的物质组成直接实现。而田间原状土样品的测得的结果显示，在大多数含水量的水平下，土壤的热容量和热扩散系数均有显著的下降趋势。同时，田间直接测量的结果显示生物质炭的施用对于土壤的热容量、导热率和热扩散系数均有显著下降的作用。现认为生物质炭有两种影响土壤热性质的机理。其一是通过增多土壤中的中空隙和大孔隙从而使土壤的总孔隙度增加，这对于热容量与导热率有负面影响。另一种则是使土壤的保水能力增强从而导致土壤含水量增加，这对于土壤的热性质有正面影响。其中第一种影响，即为由其对于土壤结构影响而产生的负面影响则为田间环境下的主要影响因素。此外，生物质炭自身所具有疏水性，会使土壤的疏水性增加，这也对土壤导热率和热扩散系数的降低具有潜在影响。