[The following is an excerpt taken from my book, 'A New Vision for Iowa Food and Agriculture'.]
Chapter 23. Biochar
As mentioned above, one of the products of pyrolysis is biochar, a charcoal-like substance. In fast pyrolysis, which optimizes for bio-oil production, biochar comprises 12 to 15 percent of the end product. In slow pyrolysis, the biochar yield can be 50 percent or more.
Biochar has many potential uses. It can be burned as a fuel, and it has many potential commercial and industrial uses. But, probably the most important potential use for biochar is as a soil amendment. When added to soils, biochar increases the water-holding and nutrient-holding capacity of soils, thereby reducing the need for irrigation and fertilizers. Biochar has a very long residence time – hundreds or even thousands of years – in soils before being degraded. That makes biochar an ideal soil amendment for long-term carbon sequestration. In other words, biochar additions to soils could make an important contribution to carbon sequestration to reduce the amount of greenhouse gases in the atmosphere.
The Amazon Basin contains areas of deep, rich, dark soils which local people call terra preta (black earth). Those black earth soils are known to have almost magical qualities of rejuvenation and nearly inexhaustible fertility. The soil in that area of Brazil is otherwise thin, red and infertile. For many years, the origin of the terra preta soils befuddled archeologists and anthropologists. Only in the late 20th Century was the idea of the human origin of those soils accepted. It is now widely believed that terra preta soils were created by an indigenous population between 450 BC and AD 950 by amending the soils with a charcoal substance created by a form of pyrolysis. The resiliency and productivity of terra preta soils indicate that adding biochar from pyrolysis to soils today could contribute greatly to soil fertility and food production as well as sequester large amounts of carbon into soils.
The world’s soils contain about twice as much carbon as is in the atmosphere. That means that the soil has a very large capacity to serve as a carbon sink to help mitigate climate change. However, carbon can also be lost from soils when they are farmed. Much of the organic carbon of virgin soils was lost when they were put under crop production. For example, Midwestern prairie soils have lost about half of their original carbon in 150 years of crop production. Biochar additions to those soils could not only rebuild soil organic matter levels by sequestering carbon but also increase soil productivity.
It is exciting to think about the many potential benefits of pyrolysis, particularly if the technology can be developed to produce green diesel and gasoline on a farm scale: 1) It would allow farmers to produce fuel on the farm to power the farm, allowing farmers to reduce or eliminate fossil fuel purchases. 2) For farmers who produced more fuel than needed on the farm, it would provide a higher-value product to sell compared to raw materials like corn or other biomass. 3) Regular biochar additions to soils would increase soil organic carbon, improving soil productivity and drought tolerance, and reducing irrigation and fertilizer costs. 4) Soil biochar additions would sequester carbon, reducing agriculture’s carbon footprint and helping mitigate climate change. 5) Emissions of the greenhouse gases methane and nitrous oxide from soils are reduced when biochar is added to soils. 6) Perennial crops could be used as the biomass source for pyrolysis, helping to protect the soil from erosion and nutrient loss, and reducing the amount of fossil-fuel-inputs – such as fuel, fertilizers and pesticides – needed to grow annual crops. 7) Yard wastes and many household, commercial and industrial organic wastes could be diverted from landfills to transformation into fuel and biochar through pyrolysis, reducing waste streams to landfills, and methane (a potent greenhouse gas) production in landfills.
[Stay tuned to this blog: I will be posting all the chapters from my book, 'A New Vision For Iowa Food And Agriculture' to this blog during the final weeks before the election on November 2nd. I look forward to any comments or questions you have.]