| Biochar as a carbon-rich coproduct of pyrolyzing biomass has been advocated as a potential strategy to enrich soil carbon(C)sequestration.Updated data derived from 50 papers with 395 paired observations were reviewed using meta-analysis procedures to examine the responses of soil respiration,soil organic carbon(SOC)and soil microbial biomass carbon(MBC)contents to biochar amendment.When averaged across all studies,biochar amendment had no significant effect on soil CO2 fluxes,but significantly enhanced SOC content by 40%and MBC content by 18%.A positive response of soil CO2 fluxes to biochar amendment was pronounced only in rice paddies,laboratory incubation studies,soils without vegetation presence and unfertilized soils.Biochar amendment significantly increased soil MBC content in field studies,N-fertilized soils and soils with vegetation presence.The enhancement of SOC content following biochar amendment was the greatest in rice paddies among the different land-use types.Responses of soil CO2 fluxes and MBC to biochar amendment varied with soil texture and pH.The combined use of biochar with synthetic N-fertilizer and waste compost fertilizer led to the greatest increases in soil CO2 fluxes and MBC content,respectively.Both soil CO2 fluxes and MBC responses to biochar amendment decreased with biochar applied rate,pyrolysis temperature or C/N ratio of biochar,while SOC content enhancement increased with them.Among different biochar feedstock sources,positive responses of soil CO2 fluxes and MBC were the highest for manure and crop residue feedstock sources,respectively.Soil CO2 fluxes response to biochar amendment decreased with pH of biochar,while biochar with pH range of 8.1-9.0 showed the highest enhancement of SOC and MBC contents.Therefore,soil properties,land-use type,agricultural practice and biochar characteristics should be taken into account in order to assess the practical potential of biochar for mitigating climate change. |
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