Biochar is a fine-grained charcoal high in organic carbon and largely resistant to decomposition. It is produced from pyrolysis of plant and waste feedstocks. As a soil amendment, biochar creates a recalcitrant soil carbon pool that is carbon-negative, serving as a net withdrawal of atmospheric carbon dioxide stored in highly recalcitrant soil carbon stocks. The enhanced nutrient retention capacity of biochar-amended soil not only reduces the total fertilizer requirements but also the climate and environmental impact of croplands. Char-amended soils have shown 50 - 80 percent reductions in nitrous oxide emissions and reduced runoff of phosphorus into surface waters and leaching of nitrogen into groundwater. As a soil amendment, biochar significantly increases the efficiency of and reduces the need for traditional chemical fertilizers, while greatly enhancing crop yields. Renewable oils and gases co-produced in the pyrolysis process can be used as fuel or fuel feedstocks. Biochar thus offers promise for its soil productivity and climate benefits.
How is Biochar carbon-negative?
The overall bio-char process is carbon negative. A carbon neutral process is one that does not add to the climate change problem, but does not actually reverse the problem either. An example of a carbon neutral activity is burning biomass for energy in place of fossil fuel. The bio-char process, by contrast, produces a combination of both bio-energy and carbon-sequestering fertilizer from agricultural waste, which results in a net reduction of carbon dioxide (CO2) from the atmosphere. As a soil amendment, char can sequester or store the carbon in the soil for hundreds and even thousands of years in the stable char matrix. Equally important, the char improves soil fertility, thereby stimulating plant growth, which then consumes more CO2 from the atmosphere. The bio-energy produced as part of the process can be turned into electricity, process heat, ethanol, methanol, or soon, an ultra-clean liquid diesel fuel. The net amount of CO2 in the atmosphere from both these products is thus reduced, making the bio-char process carbon negative and also regenerating soil fertility in the process.
Terra Preta Soils
The biochar process is akin to a process utilized thousands of years ago in the Amazon Basin, where islands of rich, fertile soils called Terra Preta (“dark earth”) soils were created through a process similar to pyrolysis. The high fertility and carbon content of these soils – retained thousands of years later in the absence of additional inputs – is the subject of much research and agricultural interest, and underlies the formation of the International Biochar Initiative. Because the biochar is relatively inert, most of it remains in the soils for orders of magnitude longer than any other organic amendments. This means that biochar might be one of the only tools available in the near future that can actually remove carbon from the atmosphere in a virtually permanent form. |
