Biochar has been used by humans for thousands of years as a soil amendment. Long forgotten by much of modern civilization, it is recently becoming talked about more as both a soil amendment as well as a carbon sequestering tool.
What is biochar? Biochar is the material that is left over after burning biomass, such as wood straw and other plant materials in the absence of oxygen. This material is mostly carbon, in the form of what is commonly known as charcoal.
Biochar has been used as a soil amendment for thousands of years. One of the most well known examples is the terra-preta in the Amazon. These are areas that have deep carbon rich fertile soils. The carbon in these soils are remains of large amounts of biochar that were added to previously infertile the soils by humans over 2000 years ago. To this day these soils are extremely fertile from the biochar that was added over 2000 years ago. Studying the success of this example is a big part of what has created a recent interest in the benefits of biochar.
Biochar works by its ability to absorb water and nutrients. It holds them in place, instead of them leaching away and eventually becoming runoff. This moisture and nutrients are held in the root zone where the biochar is so they can be available to plants and other soil organisms.
Turning biomass into biochar is called carbonization of biomass, which is done through a process called pyrolysis. Pyrolysis is simply done by heating biomass to temperatures high enough to support combustion in an environment without oxygen. Without oxygen, the material cannot combust, instead it breaks down and gives off gasses until all that is left is the biochar.