Biochar amendment pyrolysed with rice straw increases rice production and mitigates methane emission over successive three years.

A sustainable biochar strategies on increasing crop yield and mitigating CH emissions over successive years is unknown. Thus, on-site equivalent rice straw biochar-returning (ERSC, biochar at 2.8 t ha annual) were compared with on-site equivalent rice straw- returning (RS, rice straw at 8 t ha annual) and high application rate biochar-returning (RSCH, biochar at 22.5 t ha only in the first year). The RS and RSCH treatments increased rice production by 10.1% and 11.8% on average, respectively. The ERSC treatment continually increased rice production by 8.0%, 1.6% and 7.3% in three successive years. The ERSC treatment had a cumulative effect on the soil nutrients phosphorus (P), potassium (K), and magnesium (Mg), as well as increasing total carbon (TC) and total nitrogen (TN) and continuously reducing the effect of soil available aluminum (Al). The RS treatment significantly promoted CH emissions while the ERSC treatment reduced methane emissions by 43%, 31% and 30% and the RSCH treatment reduced methane emissions by 52%, 22% and14% in three successive years. Compared with RSCH, ERSC showed the best long-term stable effect on methane emission mitigation in three successive years. This might result from the fact that fresh biochar promoted anaerobic oxidation of methane. This research gives us scientific evidence that an on-site equivalent rice straw biochar-returning strategy may be a promising method for sustaining rice production and mitigating methane emissions.