Agriculture accounts for a substantial portion of global greenhouse gas (GHG) emissions, contributing approximately 25-30% of worldwide land biogenic nitrous oxide (N2​O) emissions and 35-50% of methane (CH4​) emissions. Fertilizers play a role in these emissions, and the application of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More has the potential to significantly alter this scenario. However, the efficiency of biochar in reducing GHGs and enhancing crop productivity, especially when combined with organic and chemical fertilizers, has yielded contradictory reports. To address this, Elnaz Amirahmadi, Mohammad Ghorbani, and Fabrizio Adani conducted a comprehensive meta-analysis, published in Field Crops Research, evaluating the effects of biochar utilization strategies and key variables on GHG emissions and crop productivity.

The meta-analysis examined six groups of variables: biochar utilization strategies (sole biochar (B), biochar with chemical fertilizers (BCF), biochar with organic fertilizers (BOF)), feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More type, pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature, application rate, soil texture, and plant types. Various GHG emission factors (N2​O, CH4​, CO2​, Global Warming Potential (GWP), and Greenhouse Gas Intensity (GHGI)) and crop yield were considered as affected factors. The study included 54 field-based studies, with 27 reporting only crop yield, 9 reporting only GHG emissions, and 18 reporting both.

The findings reveal that the sole application of biochar (B strategy) effectively reduced N2​O emissions by 16.3% and CH4​ emissions by 10.1%. In contrast, BCF and BOF strategies led to increases in N2​O emissions by 62.9% and 11.3%, respectively. Although all biochar application strategies increased CO2​ emissions, the B strategy showed the lowest increase at 1.4%, compared to 27.1% for BCF and 13.9% for BOF. The highest GWP was observed with the BCF strategy, increasing by 35.4%. However, both B and BOF strategies were effective in lowering GHGI, showing 11.4% and 12.1% decreases, respectively.

Feedstock type played a significant role in GHG emissions. Biochar derived from unstable feedstocks (e.g., manure, sewage sludge) considerably increased N2​O emissions by 83.7%. Conversely, degradable and recalcitrant feedstocks reduced N2​O emissions by 43.7% and 9.7%, respectively. The highest CO2​ emission (12.1% increase) was associated with degradable feedstock.

Pyrolysis temperature notably influenced gas emissions. Moderate pyrolysis temperatures (400-550°C) resulted in the highest N2​O increase (27.1%) but the lowest CH4​ decrease (12.5%). This temperature range also showed the best efficiency in reducing overall carbon intensity per crop yield (GHGI) with a 14.9% decrease. This is likely due to the optimal formation of micropores at moderate temperatures, which are unfavorable for anaerobic methanogenic bacteria.

Increasing biochar application rates generally led to increased GHG emissions. The highest application rate ( > 20 t ha−1) resulted in increases of 20.3% for N2​O, 8.8% for CH4​, 17.4% for CO2​, and 26.6% for GWP. However, medium application rates (10-20 t ha−1) decreased CH4​ by 5.3%.

Soil texture also impacted gas emissions. Applying biochar to sandy soil led to a notable 22.1% increase in CO2​ emissions. Clay-textured soil, however, resulted in negative effects on both GWP (3.9% decrease) and GHGI (28.9% decrease).

Regarding crop types, biochar use in vegetable cultivation showed a 59.3% increase in N2​O emissions but a 22.5% decrease in CH4​ emissions. Vegetable cultivation also showed the highest GWP, with a 20.8% increase. Overall, biochar application positively increased crop yield across all utilization strategies, with BOF showing the highest increase at 35.1%.

In conclusion, the study emphasizes that soil texture and pyrolysis processing significantly impact soil GHG emissions when biochar is applied with fertilizers. Expanding the understanding of the relationships among soil GHG emissions, organic fertilizers, and biochar can aid in increasing plant yield and achieving net-zero amending approaches.

Source: Amirahmadi, E., Ghorbani, M., & Adani, F. (2025). Biochar contribution in greenhouse gas mitigation and crop yield considering pyrolysis conditionsThe conditions under which pyrolysis takes place, such as temperature, heating rate, and residence time, can significantly affect the properties of the biochar produced.   More, utilization strategies and plant type – A meta-analysis. Field Crops Research, 333, 110040.