Ask Dr. Mike: How Does Biochar Restore Soil Productivity?

By Mike Amaranthus Ph.D and Paul Hepperly Ph.D

Professor Johannes Lehmann of Cornell University (right) is a soil scientist who became familiar with biochar or “terra preta do indio” as a visiting scholar in Brazil. He has been one of the principal proponents of the value of extending the ancient work of using carbon for restoring soil productivity. Now he is working with teams of interested collaborators to extend this truth into an energy system which can counteract issues related to global climate change from greenhouse gases both as renewable energy and for its soil sequestration potential. Although terra preta goes back to ancient roots, he is envisioning modern comprehensive systems which produce food and fiber and soil improvement for the soils most in need.

Making Soil More Fertile

Biochar is a powerhouse example of the potential of transforming soils. This potential was manifested in the terra preta soils of Brazil. Literally translated, these are the dark soils of the Indians. According to investigators these soils were generated from 450 years BC to 950 years BC. Yet some researchers suggest they may be dated at over 5,000 years old. These pre-Colombian soils developed on depleted oxisols sometimes called latosols with extremely low carbon content of less than 10,000 kg/ha C. Under the recycling of organic wastes and chars around these villages soil became deep and fertile with estimates reaching over 300,000 kg/ha C.

Doris Hamil from NASA Langley is passionate about using biochar as a technology to combat global issues. She touts its multiple benefits from sequestering carbon, counteracting global climate change, removing toxic heavy metals from contaminated soils, enriching farm soils, filtering groundwater as well as ability to foster outer space production of food (Dietrich, 2018).

The top A horizon of terra preta have soil organic matter levels at 13-14%. These elevated carbon and mineral contents are far above anything in the surrounding non-biochar transformed oxisols in this southern American region. These Indian created soils were the focus for food production and the retention of nutrients in these tropical and heavily leached soils. Earthworms might have played a critical role in the transformation. Ponge et al (2006) has demonstrated the Amazonian earth worm, Pontoscolex corethrurus, has the ability to ingest charcoal, moving it into deep profiles within the soil mass. These workers took nontransformed soils and, by adding manioc or cassava peels and charcoal, produced a soil with similar appearance and structure as the terra preta. These researchers suggest earthworms are major drivers of the development of terra preta.

The terra preta effect represents an increase of 290,000 kg/ha C potentially. The terra preta soils of Brazil have been discovered on an area superior to modern country of France indicating the potential of extensive modification without any modern technology at all. Soil scientists were encouraged as the soils in some of the poorest areas of South America took on highly productive and sustainable characteristics based on this Indian transformation. People suggest we cannot transform and improve the carbon content and productive potential of our soils on a mass scale. Indeed, it has already been done successfully on a mass scale millennia ago in South America.

Biochar Meets Mycorrhizae

Biochar and mycorrhizae – two “hot” research trends among agronomy scientists – are beginning to converge in an effort to help address the various challenges posed by global warming and modern non-sustainable agricultural practices.

Conventional farming practices are major producers of carbon dioxide emissions and carbon losses from the soil are a major issue worldwide. Soil can also be a powerful means by which to accumulate carbon reserves in the form of organic matter. Land management practices such as no-till, winter cover crops, biological inoculants, perennial pastures, and manure and compost inputs are all methods known for their ability to increase soil-stored carbon. Over time, if farming activities result in soil carbon loss exceeding replacement by the natural rhythms of root and mycorrhizal activity, decay and recycling, production will likely decline.

Mycorrhizal fungi and their activities represent an enormous opportunity to increase soil-stored carbon. Mycorrhizal fungi form a symbiotic relationship with approximately 80-90% of the world’s plant species and have thrived on planet Earth for approximately 460 million years. Mycorrhizal filaments create an extensive network of filaments in the soil (see figure to the left). The soil colonized by mycorrhizal fungi rapidly accumulates soil glomalin, thus sequestering air-derived organic carbon and stimulating soil productivity. Technically a glyco-protein, the relatively stable glomalin molecule is made up of 30-40% carbon, resists decomposition for up to 42 years and can comprise up to 40% of the total carbon found in soil. It has been estimated that all the soil on Earth contains about 1.58 trillion metric tons of carbon; therefore, the contribution of soil carbon to this total by mycorrhizal fungi could be as much as 630 billion metric tons. This exceeds the 611 billion metric tons estimate for all the carbon stored in the entire world’s terrestrial vegetation.

Mycorrhizal fungi’s significant role in long-term CO2 sequestration is an ongoing research endeavor. The many soil health and plant growth benefits from these ubiquitous plant symbionts are already well-documented. We are seeing burgeoning knowledge related to the glycoprotein glomalin. The United States Department of Energy is currently funding studies to determine glomalin’s promising potential to offset atmospheric CO2.

Compounding Cumulative Soil Benefits

So where is the convergence? Biochar and mycorrhizae both augment soil sustainability and they both implement substantial long-term carbon sequestration. The bonus is that combining these two remedial agents apparently compounds their cumulative beneficial properties into a powerful “2 + 2 = 5” soil scenario. In other words, the sum of the benefits exceeds that of each of the contributors.

Researchers say biochar contributes to pro-mycorrhizal soil environments via multiple mechanisms:

• The myriad, tiny pores on biochar particles may serve as physical “shelters” for mycorrhizal hyphae and various symbiotic bacteria, protecting them from damage and microbial predators. Biochar might be envisioned as a soil apartment complex with biochar forming the living space. Mycorrhizal filaments aggressively colonize bits of biochar in soils. See photo at right.
• Biochar appears to modify soil pH, cation exchange capacity (CEC) and waterholding capacity, creating a more favorable environment for mycorrhizal activity.
• Biochar seems to promote microbial populations, which further stimulate mycorrhizal performance.

So far, the majority of studies indicate that mycorrhizae- colonized plants grown in biochar-treated soils significantly out-perform non-biochar controls.

Much more research is needed but perhaps the soil management tools of the future will include both mycorrhizal inoculants and biochar amendments – a combination simultaneously addressing two vital global issues: agricultural sustainability and atmospheric CO2 mitigation.

Our approach is an organic, biologically based strategy for managing soils. It is an approach that improves rather than degrades the productive capital of soil. This is exactly why the soil and its creatures need to be seen as our allies and not as our enemies. The potential of biochar, mycorrhizae and a living soil are enormous and key to a sustainable future for generations to come.