Abstract:In order to reveal the influence of biochar on soil thermal properties, the farmland soils with different biochar contents were studied in northern cold regions. Soil moisture levels were set at 0%, 8%, 16%, 24%, 32% and 40%, respectively. The variation characteristics of soil thermal conductivity, thermal diffusivity and thermal capacity within the temperature range of 15~-15℃ were measured by ISOMET2114, and the response mechanism of soil thermal characteristic parameters to soil hydrothermal regime was investigated with different biochar contents. Results showed that with the increase of soil moisture, the soil thermal properties had increasing trend while freezing and nonfreezing. Under the condition of 3℃ and biochar content of 0t/hm2, the soil thermal conductivity was increased by 0.1414W/(m·K) and 0.5805W/(m·K), respectively, with the soil moisture content at 24% and 32%, compared with that at 16%. With the increase of biochar, the soil thermal conductivity and thermal diffusivity were decreased, and the thermal capacity was decreased while nonfreezing and increased while freezing. Under the condition of -3℃ and moisture content of 32%, the soil thermal capacity was increased by 0.16J/(cm3·K) and 0.20J/(cm3·K), respectively, with the biochar content of 4t/hm2 and 6t/hm2, compared with that of 0t/hm2. There was a logarithmic relationship between soil thermal conductivity and moisture content, a linear relationship between thermal capacity and moisture content, and a quadratic relationship between thermal diffusivity and moisture content. The effects of biochar on thermal properties of frozen and nonfrozen soils were studied with different soil moisture contents, and the influence of biochar on the thermal properties of frozen soils was firstly analyzed using freezing characteristic curve, which provided theoretical basis for accurately describing the soil thermal condition and applying biochar to improve the soil in northern cold region.
