In the Amazon basin, where the Amazon River and its tributaries drain into the forests of South America, patches of dark, charcoal-rich soil called terra preta exist. This “black earth” is found where ancient cultures lived, many years before the arrival of Europeans. Unlike the other red and yellow weathered soils typical of the region, terra preta is highly fertile. Why? Human-made additives were incorporated more than 2,500 years ago to develop land that would otherwise have proved difficult to cultivate. For thousands of years, this soil has retained its fertility and is well-known for its productivity.
Inspired by the legacy left by the earliest residents of the Amazon basin, the idea of adding carbon-rich charcoal to soil is now being applied in urban and suburban tree care in the form of biochar.
While the concept of using charred matter as a soil amendment is centuries old, the creation and use of biochar as we now know it is a relatively new idea in tree care. As a soil additive, it has unique characteristics that improve the condition of the soil, creating a better environment for growing trees and shrubs.
Biochar is a carbon-rich material made from waste organic debris. Due to its porous nature and high surface area, the addition of biochar improves the soil’s ability to retain water. This reduces the need for watering, helps regulate soil temperature and improves a plant’s ability to grow.
Use of biochar also reduces nutrient leaching, the loss of water-soluble nutrients from the soil. Critical macronutrients like nitrogen, phosphorous and potassium and micronutrients remain in the soil for plant use. Keep in mind that biochar is not a fertilizer. Its addition does not alter the nutrients in the soil. Rather, it creates more favorable soil conditions so that nutrients remain present and can be used as needed by the plant.
Beneficial microorganisms like Trichoderma and mycorrhizal fungi thrive in soil amended with biochar. Mycorrhizal fungi have a symbiotic relationship with plants. They live on or in the roots of a host plant, promoting efficient root function and offering the plant protection from soil-borne pathogens. The increase in the presence of these microorganisms resulting from use of biochar means better growth and improved resistance to insects and disease.
Once added, biochar, and its benefits, persist in the soil for years – similar to the fertile terra preta that remains in the Amazon basin today.
Ancient made modern.
While much is still unknown about exactly how ancient cultures created charcoal for the purpose of adding it to soil, the process called pyrolysis was the same then as it is now. During pyrolysis, plant waste is heated at high temperatures in the presence of little or no oxygen. The result is a highly porous charcoal (biochar) that can be tilled into the soil of a tree or shrub’s root zone or introduced by liquid injection.
To be clear, biochar is not just any charcoal. Its ingredients and the way it is produced yield a charcoal specifically suited to soil incorporation. What’s more, not all biochar is created equal and landscapers should be aware of the differences.
Biochar can be created from almost any discarded organic waste; however chars made from woody biomass typically yield a superior product for most landscapes. Knowing and understanding the water content, bulk density, ash percentage and adsorption capacity of the biochar is also key.
If you are considering offering biochar as a soil amendment, it is important to do your research and look for a quality product from a seller that has experience and case studies as well as positive lab results from third-party testing. Here at Bartlett, we have worked extensively with a provider to create our own Premium Landscape Biochar made solely from woodchips. We are continually reviewing progress and results and tracking data to ensure effectiveness and client satisfaction.
Roots in research. The decision to offer a new service or even an addition to existing services is not one to be taken lightly. Though modern biochar had been studied for many years in agriculture, until about five years ago it had been largely untested in the tree care industry.
Working with The Morton Arboretum outside of Chicago, Illinois, The Bartlett Tree Research Laboratories began investigating biochar’s impact on landscape plants in 2008. Comprehensive research is ongoing and involves over a dozen studies in greenhouses as well as nursery, field plot and street settings under a variety of soil conditions.
To date, the findings indicate that adding biochar has a measurable positive impact on soil quality and plant growth. Some of the most promising results have been seen when biochar is used in conjunction with compost. This combination packs a one-two punch with nutrients made available by compost demonstrating better adsorption thanks to biochar. It yields an expedited improvement in plant appearance and health.
A sustainable future.
As more clients opt for a natural-based approach to the care of their landscape, biochar is a great organic option for healthier trees and shrubs. In fact, Bartlett’s Premium Landscape Biochar is certified organic by the Organic Materials Review Institute (OMRI). However the contributions of biochar production to environmental sustainability have the potential to go even further.
Pyrolysis converts what would otherwise be waste biomass into a valuable product. While so doing, the process retains carbon in a stable form (biochar) and produces capturable heat energy and synthesis gas. Essentially, pyrolysis is a carbon-negative process, locking up carbon instead of releasing it into the atmosphere.
While research into the impact that the production of biochar can have on the environment is in its infancy, what we know now is the efficacy of this soil additive in helping to grow lush, healthy plants as part of a sustainable landscape. It’s almost like transporting a parcel of terra preta right out of Brazil for the benefit of your clients’ trees and shrubs.
The author is an arboricultural researcher at Bartlett Tree Experts.