Benefits and limitations of biochar for climate-smart agriculture:a review and case study from China

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-CO_(2) 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 CO_(2)-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.

Divergent effects of biochar amendment and replacing mineral fertilizer with manure on soil respiration in a subtropical tea plantation

Applying biochar amendment and manure in tea plantation ecosystems can diminish soil acidification and degradation.However,the impact of these practices on soil respiration and associated mechanisms remains unclear.In this study,we combined a two-year field experiment and laboratory analyses based on soil properties,functional genes,and microbial co-occurrence networks to explore the determinants of soil respiration intensity in a subtropical tea plantation with biochar amendment and manure application.The results showed that the effect of biochar amendment on soil respiration was unconspicuous.Although biochar amendment increased bacterial richness and Shannon index,biochar amendment did not alter the abundance of species associated with C-cycling functional genes.Besides directly adding recalcitrant C to the soil,biochar also indirectly enhanced C sequestration by weakly increasing soil carbon dioxide(CO_(2))emissions.However,replacing mineral fertilizer with manure significantly stimulated soil respiration in the tea plantation,resulting in a 36%increase in CO_(2) emissions over two years.The increase in CO_(2) emissions under the manure treatment was mainly attributed to the increased soil labile C pool,the activity of hydrolytic enzymes(e.g.,cellobiohydrolase and acetylglucosaminidase),and the relative abundance of functional genes associated with the C-cycle.This may also be related to the application of manure that increased the abundance of Gemmatimonadetes and altered ecological clusters in bacterial co-occurrence networks.Our correlation network analysis suggested that Gemmatimonadetes might be the potential hosts for C-cycling genes due to their strong positive correlation with the abundance of C-cycling genes.Overall,these findings provide new insights into soil respiration under biochar amendment and manure application in tea plantations and broaden the options for carbon sequestration in soils.