Effects of biochar on soil chemical properties: A global meta-analysis of agricultural soil

Improved soil properties are commonly reported benefits of adding biochar to agriculture soils. To investigate the range of biochar’s effects on soil chemical properties (e.g., soil pH, electrical conductivity (EC), cation exchange capacity (CEC), soil organic carbon (SOC), soil total carbon (TC), and soil carbon-nitrogen ratio (C : N ratio)) in response to varied experimental conditions, a meta-analysis was conducted on previously published results. The results showed that the effect of biochar on soil chemical properties varied depending on management conditions, soil properties, biochar pyrolysis conditions, and biochar properties. The effect size (Hedges’d) of the biochar was greatest for SOC (0.50), the C : N ratio of soil (0.44), soil pH (0.39), TC (0.35), EC (0.21), and CEC (0.20). Among the various factors examined by aggregated boosted tree analysis, the effects of biochar on soil chemical properties were largely explained by the biochar application rate, initial soil pH, and soil sand content. In conclusion, our study suggests that improving soil chemical properties by adding biochar not only requires consideration of biochar application rates and chemical properties but also the local soil environmental factors, especially soil initial pH and sand content of the soil, should be considered.