Biochar is defined simply as charcoal that is used for agricultural purposes. It it created using a pyrolysis process, heating biomass in a low oxygen environment. Once the pyrolysis reaction has begun, it is self-sustaining, requiring no outside energy input. Byproducts of the process include syngas (H2 + CO), minor quantities of methane (CH4), tars, organic acids - and excess heat.
Once it is produced, biochar is spread on agricultural fields and incorporated into the top layer of soil. Biochar has many agricultural benefits. It increases crop yields, sometimes substantially if the soil is in poor condition. It helps to prevent fertilizer runoff and leeching, allowing the use of less fertilizers and diminishing agricultural pollution to the surrounding environment. It retains some moisture, possibly helping plants through periods of drought more easily. Most importantly, it replenishes exhausted or marginal soils with organic carbon and fosters the growth of soil microbes essential for nutrient absorption.
Studies have indicated that the carbon in biochar remains stable for millenia, providing a simple, sustainable means to sequester historic carbon emissions that is technologically feasible in developed or developing countries alike. The syngas and excess heat can be used directly or employed to produce a variety of biofuels.
When biochar is created from biomass, approximately 50% of the carbon that the plants absorbed as CO2 from the atmosphere is "fixed" in the charcoal. As a material, the carbon in charcoal is largely inert, showing a relative lack of reactivity both chemically and biologically, and so it is strongly resistant to decomposition. Research scientists have found charcoal particles as old as 400 million years in sediment layers from wildfires that occurred when plant life first began on earth. (Sediment Records of Biomass Burning and Global Change, James Samuel Clark)
Of the many organic and inorganic substances that contain carbon atoms, only diamonds could potentially provide a more permanent carbon store than charcoal. Hence, biochar offers us a golden opportunity to remove excess CO2 from the atmosphere and sequester it in a virtually permanent and environmentally beneficial way.
Effect of Biochar on Soil Fertility
Below are a series of photos demonstrating the effect of biochar on soil fertility. They were taken during the International Biochar Initiative Conference held in Terrigal, Australia from April 29 to May 2, 2007.
The test plots shown in the photographs compare the following after 10 weeks:
1) Plain soil
2) Soil + NPK (Nitrogen, Phosphorous, and Potassium fertilizer)
3) Soil + Biochar
4) Soil + NPK + Biochar
Application rate of biochar on test plots 3 and 4 is 50 tons per hectare.
Similar effects are seen in a variety of soils and locations throughout the world.