An ancient environmental technology is making a comeback.
Five centuries ago, Spanish explorer Francisco de Orellana reported vast areas of indigenous settlement and cultivation along the Amazon River. Surprisingly, the incredibly rich and productive forests of this region were supported by poor soils. The ability of these soils to sustain such large populations was, until recently, a mystery.
The discovery of terra preta — a fertile black soil manufactured by these ancient civilizations — now paints a picture of how these peoples were able to sustain themselves. More importantly, the discovery teaches us much about how we can sustainably support ourselves on this increasingly crowded planet. Recent experiments with terra preta have produced large increases in crop yields. And the primary component of terra preta — the key to its fruitfulness — is biochar.
Biochar is the material remaining after biomass (in this case, plant material) is burned through a special process called pyrolysis. Pyrolysis differs from regular combustion, such as that of a campfire, in that it occurs in the presence of little to no oxygen. Without oxygen, the biomass does not fully burn to smoke and ash. Instead, much of the carbon remains as a black, lightweight substance, very similar to ordinary charcoal.
Proponents of biochar advocate its production and use for many reasons.
The first reason relates to the fertile terra preta soils found in the Amazon. Biochar can significantly increase soil quality. Using biochar helps soil retain nutrients, decreasing the need for fertilizers. It also helps some soils retain water, which decreases the need for irrigation. Through a one-time application, farmers around the world can potentially increase the productivity of their crops.
The second advantage of biochar is its ability to store carbon in the soil for long periods of time. Biochar proponents view this ability as a possible way to reduce atmospheric carbon dioxide levels that contribute to global climate change. Plants store atmospheric carbon dioxide as carbon, and when they die and decompose that carbon is released back to the atmosphere. If those plants are converted to biochar, however, most of their carbon can be sequestered in the soil indefinitely because biochar does not decompose. Thousands of years later, the terra preta soils in the Amazon are still high in carbon, according to recent research.
At the Bard Center for Environmental Policy, students spent several weeks this January studying the application of biochar in soils around the world. With the assistance of Dr. Hugh McLaughlin, a leader in the field, students built and used pyrolysis stoves to make biochar. They conducted small greenhouse experiments to observe the growth of wheat, radishes and mung beans in soils that included the biochar they’d produced.
The students also interviewed biochar entrepreneurs, including Jason Aramburu, CEO of Re:char, an organization testing the use of biochar in Kenya and working to encourage the creation and use of biochar by farmers in sustainable and productive ways. Re:char has developed a stove to produce biochar that is inexpensive and easily manufactured within the country.
With the world’s population growing and arable land shrinking, this ancient technology offers a promising, sustainable route toward food security and carbon sequestration.
Nick Martin and Justin Wexler are first-year master’s degree students at the Bard Center for Environmental Policy. Martin is in the climate science and policy program and Wexler is in the environmental policy program. They took a short-course elective on bochar in January, which examined the problem of scaling up environmental solutions by focusing on the use of biochar.