Cooling potentials of growing substrates amended with bamboo biochar

Abstract

Addition of bamboo biochar to growing substrate's can enhance substrates' cooling potentials by increasing water holding capacity and surface evaporation rates, which could contribute to the mitigation of urban heat island effect. However, little research has determined the optimum mixing ratio of bamboo biochar for each type of substrate enhancing the substrate's cooling potential. In this study, we added bamboo biochar or coconuts coir (0, 20, and 40％ by volume) to 4 growing substrates used in urban greening (commercial mix using expanded shale for stormwater management, mineral soil sampled from a vacant lot, commercial garden mix using organic materials, coconut coir), and then these substrate samples were potted and heated by using LED lights for 14 days. We found that, among the treatments using bamboo biochar, the blend of 60％ coconut coir and 40％ bamboo biochar showed the best performance for lowering substrate temperature. Additionally, application of bamboo biochar to coconut coir increased water holding capacity and evaporation rates. However, the addition of 40％ bamboo biochar to the commercial mix using expanded shale reduced evapotranspiration rates and increased the substrate temperature. Further research is needed for determining the optimum mixing ratio of bamboo biochar specific to substrate materials, by incorporating varying particle size distributions to treatments.