Thermal conductivity of a Brown Earth soil as affected by biochars derived at different temperatures: Experiment and prediction with the Campbell model

Thermal conductivity is a significant heat transfer property of soil. However, the influence of biochar on this property is not well known. In this research, the influence of corn straw biochars prepared at 300, 500 and 700oC on the thermal conductivity of a Brown Earth (Hapli-Udic Cambisol, FAO) soil and its prediction using a Campbell model was examined. The outcomes revealed that the bulk densities of the soil markedly decreased with increases in the biochar amendment rates of 1, 3, and 5% in linear patterns. The reduction in bulk density was mainly attributed to an increase in soil porosity and organic carbon content. With increasing volumetric water contents (10, 20, 30 and 40%), the thermal conductivity of the soils significantly increased, whereas those of soils with biochar amendment were obviously less than that of the CK and the differences increased with the biochar application rates. The pyrolysis temperature of biochar exhibited a negligible effect on the bulk density and thermal conductivity of soils at large. Combining the linear reduction of bulk density with the biochar amendment rate into the Campbell model, well-fitting results for the variation inthermal conductivity versus volumetric water content were obtained and accurate values could be predicted.