Biochar, also known as black carbon, is a product that is derived from organic materials rich in carbon (C) and found in soils in very stable solid forms. It is basically a pyrolysis product of organic residues that has received wide attention to mitigate climate change. Biochars can persist for longer periods of time in the soil at various depths, typically thousands of years. Biochars are well known to improve soil physical and chemical properties, such as increasing soil fertility and productivity. As biochars are acquired through pyrolyzing biomass at temperatures above 300°C in the absence of oxygen, degraded, dry lands and soils with poor fertility as well as low organic matter soils can massively get benefit from biochar amendments. It also has improved nutrient and water-holding capacities that increases fertility and productivity, and improved crop management efficiency. Biochar as a soil amendment can help in sequester the stable carbon in soils and combat climate change. On the other hand, responses to biochars may depend on the type of biochar used and also the specific characteristics of that biochar as its characteristics determine its fitness for specific agronomic or environmental purposes. Additional benefits come from biochars ability to absorb contaminants, including inorganic and organic pollutants in soil and leaching waters, ultimately improving the soil and water quality to improve soil fertility and crop productivity.

Carbon sequestration and greenhouse gas mitigation potential of biochar

Biochar technology has proven the best to achieve carbon sequestration and greenhouse gas mitigation. Biochar potential is determined by several basic factors, including:

tEfficiency of the crop production technology.

Available renewable biomass resource that can be sustainably harvested.

Stability of biochar in the soil for longer period of time.

Adoption and implementation of biochar investment schemes to achieve high yield.

Production and utilization of co-produced bioenergy to replace fossil energy sources

Sustainable biochar can be used now to help combat climate change by holding carbon in soil and by replacing fossil fuel use. Research shows that the stability of biochar in soil significantly exceeds that of un-charred organic matter. Moreover, because biochar retains nitrogen, emissions of nitrous oxide (an effective greenhouse gas) may be reduced. Methane (another strong greenhouse gas) generated by the natural decomposition of the waste can also be reduced by turning agricultural waste into biochar. Biochar as simple but powerful tool can store about 2.2 gigatons of carbon annually by 2050.

Significant reduction of soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions has been observed in short-term laboratory experiments by a number of researchers. However, evidence from long-term field trials has been conflicting. Biochar amendment could suppress soil GHG emissions under field and controlled conditions. In an experiment, biochar amendment suppressed soil CO2 emissions by 33 per cent. Under controlled temperature and equalised gravimetric water content in the laboratory, biochar amendment suppressed soil CO2 emissions by 53 per cent and net soil CO2 eq. emissions by 55 per cent. Research findings also demonstrate that biochar amendment has the potential to suppress the net soil CO2 eq. emissions in bioenergy crop systems for up to one year after addition, mainly through reduced CO2 emissions. We conclude that hardwood biochar has more potential to improve the GHG balance of bioenergy crops through reductions in net soil CO2 eq. emissions.

Our work

Little information exists in Pakistan on the short and longer-term effects of biochar on soil microbial communities and enzyme activities, relative to other organic amendments such as manure, however, energy production from bioenergy crops may significantly reduce greenhouse gas (GHG) emissions through replacing the fossil fuels. It may decrease the net climate forcing of bioenergy crop production although this has not yet been assessed under field conditions. Appropriate technology and policy needs to be executed to deal with environmental issues such as methane emissions that could contribute towards climate change and human health risks. Moreover, socio-economic constraints and benefits are areas for ongoing research. Higher crop yields resulting from biochar applications would be expected to mitigate pressures on land and would also have importance to land restoration and remediation. On the other hand, other environmental benefits may include waste re-use and avoided landfill, offset of fossil fuels through renewable energy production, carbon sequestration, potentially reduced soil emissions of non-CO2 GHGs, improved crop performance and biomass production. In recent years, considerable research has focused on biochar, its nature, and its properties to explore its potential benefits and negative impacts, particularly for applying to agricultural fields as amendments.

The Pakistan Biochar Initiative is the collaborative work started by Dr. Fahd Rasul (Chairperson, Pakistan Biochar Initiative) and Dr. Simon Shackley (Chairperson, British Biochar Foundation) to focus on research for climate change mitigation potential through biochar technology and carbon credits. The prospect of biochar utilization is promising, as biochars may be customized for specific environmental applications. The intended audiences for this factsheet are agricultural producers, crop professionals, state agencies, researchers, resource conservationists, extension educators, high school teachers, students, and the general public.

The writers are associated with the Agro-Climatology Laboratory, Department of Agronomy, University of Agriculture, Faisalabad, Pakistan.

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