Abstract
Incorporation of biochar, i.e. charcoal pro-duced by the pyrolysis of biomass, into agricultural soils affects the physical properties of the soils, and thus may alter moisture and heat conditions in agricul-tural soils. However, the effects of biochar incorpora-tion on the thermal properties of soils have yet to be investigated. Therefore, we investigated the influence of biochar incorporation on the thermal conductivity of Shimajiri Maji soil and Toyoura sand. Sugarcane ba-gasse, i.e. the residue obtained by pressing sugarcane stalks to extract juice, was air-dried and heated in a batch-type carbonization furnace at three different py-rolysis temperatures （400, 600 and 800 ℃） with a hold-ing time of 2 h. Incorporation of the biochar decreased the thermal conductivity at a given volumetric water content of each soil. It decreased the estimated ther-mal conductivity of the solid phase and the volumetric solid content of soils, and increased the porosity of soils. Calculation results using the de Vries model sug-gested that the thermal conductivity of the Shimajiri Maji soil is affected by decreasing volumetric solid con-tent and increasing porosity regardless of soil water content, and by decreasing thermal conductivity of the solid phase only at higher soil water content. In addi-tion, the calculation results suggested that the thermal conductivity of the Toyoura sand was mostly influ-enced by decreases in the volumetric solid content and increases in porosity, and to a small extent by decreas-es in the thermal conductivity of the solid phase. These results showed that the thermal conductivity of agricultural soils is affected by rates of changes in the thermal conductivity of solid phase, the volumetric sol-id content and the porosity, when the biochar is incor-porated into the soils.
