What is Biochar? Biochar is a type of charcoal made from plant materials such as hardwoods, grasses, and agricultural and forest residues that are decomposed at high temperatures, often during renewable energy production. During the process, the physical and chemical properties of the plant material change into a porous, stable, carbon-rich by-product known as biochar. Why use it? Biochar has been used in agriculture for many centuries. Adding biochar to soil has the potential of increasing soil carbon, soil nutrient content, increased water retention and water-soluble nutrients, and increased beneficial microbial life.