Review and Measurement of Thermal Properties of Soil Amended with Different Biochar Types Considering Unsaturated Soil Perspective

The role of biochar (a carbon negative material) in modifying soil thermal properties, a critical aspect in advancing soil management and geotechnical engineering practices have been studied in literature. However, its understanding with respect to unsaturated soil perspective and also from production of biochar (i.e., feedstock type) is rare. This is crucial for advancing the basic understanding of soil-biochar-water-atmospheric interactions. The objective of this study is to critically analyze the influence of biochar on unsaturated soil thermal properties and also to conduct an experiment to verify biochar type's (produced from different feedstocks) effect on the thermal conductivity of biochar-amended soil. The analysis indicates that biochar typically reduces soil thermal conductivity and diffusivity. However, its impact on soil heat capacity remains ambiguous, with studies showing contrasting results. This study attributes these discrepancies to variations in biochar type, content, and soil type. Based on the review, it was found that the gas phase demonstrates the most substantial impact on soil thermal properties. In contrast, the liquid phase primarily affects variations in soil heat capacity. Inconsistencies in understanding influence of biochar on soil thermal properties have been observed in this review. Based on the experiments, it was found that more porous structure of peach pit biochar enhances thermal conductivity of kaolin clay at near degree of saturation followed by that of Reed and Apple wood. Future research should focus on the differential impacts of various biochar and soil types, emphasizing controlled laboratory studies to unravel the complex interactions between biochar, soil heat capacity, and moisture content. This approach is crucial for resolving ongoing debates and harnessing biochar's full potential in soil thermal management.