Early European exploration into the Amazonian jungle produced few signals of any large inhabitations by indigenous people. However, more recent research in the Amazon Basin has indicated a complex agricultural network capable of sustaining significant populations. One of the strongest indicators has been the discovery of Terra Preta, or Dark Earths, which were the result of the systematic management of Amazonian soils using biochar.
Biochar is the solid material obtained from the carbonization of biomass, or simply, charcoal produced by the burning of wood and plant matter at low oxygen levels. Research being performed by Cornell University, the University of Oxford, and others has helped to bring further understanding of biochar and its use in the Amazon. By incorporating biochar in conjunction with nutrient additions, the early indigenous peoples of the Amazon converted extremely poor soils into highly fertile and productive land. The practice has been dated back to the pre-Columbian Indians from 500 to 2500 B.C. in the Brazilian Amazon. Today, it is seen as an important tool for increased food security and even to combat climate change.
How biochar can help soil
Contrary to popular belief, the soils of the Amazon jungle are very poor at supporting agriculture due to their high acidic nature and low nutrient content. The humid, tropical climate has led to highly weathered soils and loss of nutrients by leaching. But the addition of biochar into these soils has been shown to increase crop yields several times. Biochar is able to buffer the acidic soils, making it a desirable alternative to conventional liming applications, which can be very expensive. Biochar also improves the efficiency of fertilizers added to the soil because it increases retention and reduces leaching. Highly stable, biochar can persist in the soil for hundreds of years.
The mechanisms that give biochar such highly prized characteristics are largely due to its high cation exchange capacity (CEC). CEC is a measure of the number of positively-charged particles that a soil can hold. Important nutrients such as calcium, magnesium, potassium, and ammonium have a positive charge. Biochar consists of very small particles with an extremely high surface area. This gives biochar the ability to retain nutrients. The biochar itself is high in potassium, phosphorus, and various micronutrients necessary for plant growth.
Biochar as an Alternative to Slash-and-Burn
Slash-and-burn was thought to be the main system of agricultural land-use in the Amazon Forest. However, pre-Columbian Indians did not have steel tools, so the practice of felling trees would have been a very arduous task. Research into the history of Terra Preta has led scientists to believe that the early inhabitants of the Amazon practiced the intentional management of soil through the addition of charcoal. The difference is in how the biomass is burned. In slash-and-burn techniques, fallow fields or forest biomass is cut and burned to allow for the planting of crops. Burning the biomass leaves only 3% of the carbon from the organic material in the soil. By charring the biomass (burning it in low-oxygen level conditions), up to 50% of the carbon remains in the soil in a highly stable form.
A recent article from Science magazine has revealed the global effect of current slash-and-burn practices on black carbon leaching in the Amazon. The article highlights a study of black carbon export from the Amazon into nearby surface waters. The researchers estimate that the region sends between 50,000 to 70,000 tons of dissolved black carbon to the marine environment. Once there, the impact on the marine waters is largely unknown. The carbon mineralizes in water, which would cause pH to increase. Large amounts of black carbon are also emitted into the atmosphere through the burning of fossil fuels, which eventually are deposited over the grounds and oceans around the world.
Potential role of biochar in restoration
The deforestation and burning of rainforest biomass in the tropics is clearly not a small scale process, and very well could be effecting global climate change. So how does biochar play a role? The research being performed by Cornell and Oxford is helping to improve our understanding of how biochar can be used to improve soil fertility, reduce agricultural waste, produce energy, and even mitigate the effects of human-derived greenhouse gases on climate change. Not only does soil amended with biochar increase plant production and species richness in studies; it has been observed to be much more persistent in soil than any other form of organic matter commonly used in agriculture. This stability in the soil makes biochar a useful tool for long-term carbon sequestration. The production of biochar can also be used to produce energy, whether through hydrogen, biofuels, or electricity. And as part of a sustainable waste stream from farms, byproducts of agriculture such as peanut shells, rice husks, or sugarcane bagasse can be the principal ingredient for making a useful soil additive in biochar.
The role of biochar in the restoration of native ecosystems is an important study for the future. We need to consider when to use biochar in restoration projects because native vegetation thrives on “lean” or low nutrient soil. We don’t want to create a nutrient-rich soil that could potentially enable invasives to out-compete native species. Finding a local source of biochar can also be difficult and costly. We recently used charcoal as an additive in the floating wetlands project.
So, the indigenous people of the Brazilian Amazon have left us what may turn out to be an important tool for the future of restoration, conservation, and regenerative design. By incorporating biochar into our work, we may be able to promote the sustainable management of soils, improve the success of our projects, and perhaps even make a difference in the climate.