Potential of biochar to mitigate methane production in paddy soils—application of a new incubation and modelling approach

Paddy soils are a significant source of methane (CH₄) affecting the global climate. Therefore, it is important to investigate both emission mitigation strategies and the underlying biogeochemical processes. The application of biochar into paddy soils has emerged as a promising measure to mitigate CH₄ emissions. However, it has not yet been clarified why such effects are usually weaker in field studies than in laboratory incubations and which properties of biochar specifically decrease the production of CH₄. We conducted two incubation experiments, one with 1.5% addition of untreated biochars and one with same amounts, but pH-levelled, rinsed biochars. According to the common experimental design of existing incubation studies (experiment 1) biochar addition induced a mean soil pH increase of 0.28 after anaerobic incubation compared to the contro. In these treatments, biochar significantly extended the pre-methanogenic stage (mean 24.23%). However, this effect was weakened or even reversed when pH-levelled, rinsed biochars were amended in experiment 2, which was intended to mimic the persistent long-term effects in the field. This indicated that the provision of electron accepting capacities to suppress methanogenesis may be less important than previously thought. The addition of biochar significantly lowered CH₄ production rates m in both experiments with no significant influence of the pH (mean 25.89%), though. Our study demonstrated that incubation studies on CH₄ production in paddy soils can be improved by separating the pre-methanogenic and the methanogenic stage. This facilitates future research to compare characteristics of biochar, but also combinations of measures to optimise CH₄ mitigation strategies.