Biochar as a negative emission technology: A synthesis of field research on greenhouse gas emissions

Abstract

Biochar is one of the few nature‐based technologies with potential to help achieve net‐zero emissions agriculture. Such an outcome would involve the mitigation of greenhouse gas (GHG) emission from agroecosystems and optimization of soil organic carbon sequestration. Interest in biochar application is heightened by its several co‐benefits. Several reviews summarized past investigations on biochar, but these reviews mostly included laboratory, greenhouse, and mesocosm experiments. A synthesis of field studies is lacking, especially from a climate change mitigation standpoint. Our objectives are to (1) synthesize advances in field‐based studies that have examined the GHG mitigation capacity of soil application of biochar and (2) identify limitations of the technology and research priorities. Field studies, published before 2022, were reviewed. Biochar has variable effects on GHG emissions, ranging from decrease, increase, to no change. Across studies, biochar reduced emissions of nitrous oxide (N2O) by 18% and methane (CH4) by 3% but increased carbon dioxide (CO2) by 1.9%. When biochar was combined with N‐fertilizer, it reduced CO2, CH4, and N2O emissions in 61%, 64%, and 84% of the observations, and biochar plus other amendments reduced emissions in 78%, 92%, and 85% of the observations, respectively. Biochar has shown potential to reduce GHG emissions from soils, but long‐term studies are needed to address discrepancies in emissions and identify best practices (rate, depth, and frequency) of biochar application to agricultural soils.

Sustainable Technological Applications of Green Carbon Materials

“…Biochar, a persistent form of solid carbon produced from biomass at high temperatures under reduced oxygen conditions, is considered a carbon dioxide removal technology that can be deployed at scale [13][14][15][16][17][18][59][60][61]. Indeed, a net emission reduction in Research in carbon nanoparticles to be used in high-performance rechargeable batteries is increasing due to their supreme conductivity values and excellent mechanical stability [58].…”

“…Biochar, a persistent form of solid carbon produced from biomass at high temperatures under reduced oxygen conditions, is considered a carbon dioxide removal technology that can be deployed at scale [13][14][15][16][17][18][59][60][61]. Indeed, a net emission reduction in the range of 0.4-1.2 Mg CO 2 equivalents per Mg of dry feedstock, through carbon persistence, avoided non-CO 2 emissions and decreased native soil organic carbon mineralization [13,18].…”

“…Green nanomaterials/materials are being proposed to mitigate sustainability problems associated with using natural resources and/or production processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. To reduce the environmental impacts related to natural resources and toxicity, carbon-based nanomaterials and/or carbonaceous carbon are being suggested as alternatives, together with the utilization of renewable biomass as a carbon source, and named green carbon nanomaterials (GCN) and/or green carbonous materials (GCM) [7][8][9][10][11][12].…”

“…GCN/GCM appear as sustainable alternatives for several applications: agriculture [12][13][14][15][16][17][18], water treatment [1], sensors [2,7], biomedical applications [4,10,11], and carbon dioxide sequestration [12][13][14][15][16][17][18]. GCNs are usually synthesized by hydrothermal methods directly from the powered carbon source or, when a specific functionality requires improved performance, by mixing with specific reagents (Figure 1).…”

Biochar and greenhouse gas emissions: Comment on “Biochar as a negative emission technology: A synthesis of field research on greenhouse gas emissions”

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Shrestha et al (2023) provide a useful compilation of controlled field experiments using biochar applications to examine subsequent changes in the emission of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O) from agricultural soils. Lower emissions of CH 4 and N 2 O speak to the efficacy of this soil amendment as a contribution to reducing greenhouse gas emissions.

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