Dear Kaushik Adhikari,

Please have a look at these useful RG links for the answer.

Article Effect of biochar origin and soil pH on greenhouse gas emiss...

Article Biochar for Carbon Sequestration, Reduction of Greenhouse Ga...

Article Biochar as a tool to reduce the agricultural greenhouse-gas ...

Article Mechanisms of biochar decreasing methane emission from Chine...

Book Use of Biochar for Soil Health Management and Greenhouse Gas...

Book Role of Biochar in Mitigation of Climate Change

Good luck!

Biochar amendment to soils is a cost-effective technology and sustainable approach used to mitigate greenhouse gas emissions, improve phytoremediation, and minimize the health risks associated with consumption of PTE-contaminated vegetables.

Biochar converts carbon into a more stable form after pirolysis has been completed. This process takes place in an environment that is oxygen poor therefore retaining its carbon in place. Beside this, the microscopic structure (as revealed by photography through the electron microscope) of biochar shows a plethora of micropores and crevices within its carbon scaffolding that are hospitable to microbial colonization. This combination (biochar and bacteria) at this stage acts as a powerful "sponge" that retains nutrients (including carbon-rich, organic compounds) a step further and also sequesters more carbon from the atmosphere.

The effects of Biochar to reduce greenhouse gas emissions depends on the types and structure of raw material ,Biochar forming process and inherent characteristics of Biochar such as micro-organisms activities because l think they are by deforming nitrogen to another forms (N2O) in the soil.

Biochar is a black carbon generated by pyrolysis of biological materials such as wood, crop residues, poultry litter, cattle manure and municipal wastes. Its application to soil can sequestrate carbon, adsorb inorganic and organic contaminants, improve soil fertility and quality through increases in pH, macronutrients and improved soil water holding capacity. Check the following article:

https://ac.els-cdn.com/S096195341500166X/1-s2.0-S096195341500166X-main.pdf?_tid=21dfbf45-6e27-4020-9676-6b39bf69c20f&acdnat=1531735155_003f75e736aa33c3f0c561592057d2f5

Biochar is supposed to be a chemically inactive material as it is produced by burning. It is thus difficult to understand how it helps in improving C stock in soils and minimizes the emission of CO2. Many research papers are available on this aspect but with little elaboration on the mechanism.

Hi Kaushik,

Several mechanisms have been suggested. See below

(1) biochar improves soil aeration and immobilization of available N in

the soil, resulting in the suppression of denitrifier activities

(2) increases soil pH and the relative abundance of the bacterial N2O reductase nosZ gene that reduces N2O to N2 more efficiently

(3) increases adsorption of organic compounds and microbial inhibiting compounds, such as ethylene

(4) increases adsorption of N2O, NO, and NH3 onto the biochar surface.

The extent of the reduction in emissions is however, dependent on several factors such as biochar type, and soil and environmental conditions.

Hope this is helpful. Thanks, Pranoy

Dear Kaushik, it is a nice question.

It is obvious that agriculture generates around a fifth of the world's greenhouse gas emissions. Studies indicated that soils are the largest carbon reservoir of the terrestrial carbon cycle. The quantity of C stored in soils is highly significant; soils contain about three times more C than vegetation and twice as much as that which is present in the atmosphere.The greenhouse gas mitigation potential from the application of biochar to soils may differ with variation in biomass feedstock types, production technologies, biochar utilization methods and environmental conditions. The stability of organic matter in soils is determined by its ability to resist microbial decomposition through chemical transformations and physical interactions with soil minerals. Biochar, has a predominantly condensed aromatic structure that is known to be highly resistant to microbial decomposition. The priming effect of biochar on organic matter decomposition in soil needs to be accounted for to determine the magnitude of biochar decomposed. Carbon isotope methods (δ13C, or 14C/13C labelling) can be used to identify sources of C decomposed in biochar soil systems.

Biochar is a carbon rich product produced from biomass by controlled pyrolysis; it has been emerged in conjunction with soil management and C-sequestration. For example, Terra Preta soils contain up to 70 times more C than adjacent soils (Lehmann et al. 2009; Glaser et al. 2002). Biochar is a recalcitrant material with half-lives of 100-900 years. According to Haberl (2007), 10.2 Gt C per year fixed by photosynthesis, which is used by humans. The global potential for annual sequestration of atmospheric CO2 through biochar application has been estimated at the billion-ton scale in Gt/year (Laird et al. 2009). So, biochar is C negative, which can reduce greenhouse gas emissions from biomass via C sequestration, with net carbon withdrawal of about 20% from the atmosphere (Glaser et al. 2009; Lehmann and Joseph, 2015). In contrast, despite the application of mulches, composts, and manures having positive effect in enhancing soil fertility, organic matter is usually mineralized very rapidly under tropical conditions (Tiessen, and as a result, only a small portion of the applied organic compounds will be stabilized in the soil in the long term, with most released back to the atmosphere as CO2. Turnover of nitrogen in soils is closely related to carbon; both carbon and nitrogen turnover in the soil are driven by microbial biomass. Thus, biochar contains stable C and after its application to soil, this C remains sequestered for much longer periods than it would in its original organic carbon form.