Too much biochar is not better than nothing

This study investigated the benefits and potential risks of biochar application using literature data on CH 4 emission from paddy fields (n = 107) and N 2 O from upland fields (n = 174).Literature data indicated that biochar application decreases a substantial amount of CH 4 (by 14.4%) from paddy and N 2 O (by 22.9%) from upland fields.However, the regression analysis between biochar application and greenhouse gas (GHG) mitigation was not significant, suggesting that the performance of biochar on GHG reduction is not additive due to the diminished capacity of unit-weight biochar to mitigate GHG with increased biochar application rate.Besides, it is also warned that heavy application of biochar may cause soil and food contamination and ecological toxicity because of toxic compounds such as polycyclic aromatic hydrocarbon and heavy metals contained in biochar.An optimal biochar application rate by considering these potential risks of biochar needs to be established to take full advantage of biochar to mitigate GHG and enhance soil carbon sequestration.