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Biochar has gained significant attention in agricultural and environmental research over the last two decades. This comprehensive review evaluates the effects of biochar on soil organic carbon (SOC), emission of non-CO2 greenhouse gases, and crop yield, including related mechanisms and major influencing factors. The impacts of biochar on SOC, methane and nitrous oxide emissions, and crop yield are controlled by biochar and soil properties and management practices. High-temperature biochar produced from lignin-rich feedstocks may decrease methane and nitrous oxide emissions in acidic soils and strengthen long-term carbon sequestration due to its stable aromatic structure. In contrast, low-temperature biochar from manure may increase crop yield in low-fertility soils. Applying biochar to farmlands in China can increase SOC content by 1.9 Pg C and reduce methane and nitrous oxide emissions by 25 and 20 Mt CO2-eq year−1, respectively, while increasing crop yields by 19%. Despite the increasing evidence of the positive effects of biochar, future research needs to explore the potential factors that could weaken or hinder its capacity to address climate change and secure crop production. We conclude that biochar is not a universal solution for global cropland; however, targeted applications in fields, landscapes, or regional scales, especially in low fertility and sandy soils, could realize the benefits of biochar as a climate-smart measure. Highlights The findings of research on biochar's effects on soil C sequestration, GHG mitigation, and crop production were summarized. The factors influencing the impact of biochar on soil functioning were reviewed. The effects of biochar on soil C sequestration and GHG mitigation in farmlands of China were quantified. [ABSTRACT FROM AUTHOR]

Aims: A field experiment was conducted to quantify annual nitrous oxide (NO) fluxes from control and fertilized plots under open-air and greenhouse vegetable cropping systems in southeast China. We compiled the reported global field annual NO flux measurements to estimate the emission factor of N fertilizer for NO and its background emissions from vegetable fields. Methods: Fluxes of NO were measured using static chamber-GC techniques over the 2010-2011 annual cycle with multiple cropping seasons. Results: The mean annual NO fluxes from the controls were 46.1 ± 2.3 μg NO-N m hr and 68.3 ± 4.1 μg NO-N m hr in the open-air and greenhouse vegetable systems, respectively. For the plots receiving 900 kg N ha, annual NO emissions averaged 90.6 ± 8.9 μg NO-N m hr and 106.4 ± 6.6 μg NO-N m hr in the open-air and greenhouse vegetable systems, respectively. By pooling published field NO flux measurements taken over or close to a full year, the NO emission factor for N fertilizer averaged 0.63 ± 0.09 %, with a background emission of 2.67 ± 0.80 kg NO-N ha in Chinese vegetable fields. Annual NO emissions from Chinese vegetable systems were estimated to be 84.7 Gg NO-N yr, consisting of 72.5 Gg NO-N yr and 12.2 Gg NO-N yr in the open-air and greenhouse vegetable systems, respectively. Conclusions: While NO emissions from the greenhouse vegetable cropping system tended to be slightly higher compared to the open-air system in our experiment, the synthesis of literature data suggests that NO emissions would be greater at low N-rates but smaller at high N-rates in greenhouse systems than in open-air vegetable cropping systems. The estimates of this study suggest that vegetable cropping systems covering 11.4 % in national total cropping area, contributed 21-25 % to the total NO emission from Chinese croplands. [ABSTRACT FROM AUTHOR]