Biochar is a solid material obtained from the pyrolisys thermal conversion of biomass in an oxygen-limited environments. In more technical terms, biochar is produced by thermal decomposition of organic biomass under limited supply of oxygen, and at relatively low temperatures. This process mirrors the production of charcoal, which is perhaps the most ancient industrial technology developed by humankind. Biochar can be distinguished from charcoal—used mainly as a fuel—in that a primary application is use as a soil amendment with the intention to improve soil functions and to reduce emissions from biomass that would otherwise naturally degrade to greenhouse gases.
There is a large body of peer-reviewed literature quantifying and describing the crop yield benefits of biochar by amending soil. Field trials using biochar have been conducted by numerous universities over the past several years. Most show positive results on yields when biochar was applied to field soils and nutrients were managed appropriately. There is also evidence from thousands of years of traditional use of charcoal in soils. The most well-known example is the fertile Terra Petra soils in Brazil, but Japan also has a long tradition of using charcoal in soil, a tradition that is being revived and has been exported over the past 20 years to countries such as CostaRica. The Brazilian and Japanese traditions together provide long-term evidence of positive biochar impact on soils. Work is ongoing to develop ideal proprietary blends to specific soils and crops.
Biochar provides a unique opportunity to improve soil fertility for the long term. Used alone or as specialty blends in order to realize benefits and application rates can be reduced. Biochar remains in soil and single applications can provide benefits over many years. In both industrialized and developing countries, soil loss and degradation is occurring at unprecedented rates with profound consequences for soil ecosystem properties. In many regions loss in soil productivity occurs despite intensive use of agrochemicals, concurrent with adverse environmental impacts on soil and water resources. Biochar can play a major role in expanding options for sustainable soil management by improving upon existing best management practices, not only to improve soil productivity but also to decrease nutrient loss through leaching by percolating water.
Decades of research in Japan and recent studies in the U.S. have shown that biochar stimulates the activity of a variety of agriculturally important soil microorganisms, and can greatly affect the microbiological properties of soils. The pores in biochar provide a suitable habitat for many microorganisms by protecting them from predation and drying while providing many of their diverse carbon (C), energy and mineral nutrient needs. With the interest in using biochar for promoting soil fertility, many scientific studies are being conducted to better understand how this affects the physical and chemical properties of soil and its suitability as a microbial habitat. Since soil organisms provide a myriad of ecosystem services, understanding how adding biochar to soil may affect soil ecology is critical for assuring that soil quality and the integrity of the soil subsystem are maintained.
Biochar reduces soil acidity which decreases liming needs, but in most cases does not actually add nutrients in any appreciable amount. Because biochar attracts and holds soil nutrients, it potentially reduces fertilizer requirements. As a result, fertilization costs are minimized and fertilizer (organic or chemical) is retained in the soil for longer. In most agricultural situations worldwide, soil pH is low and needs to be increased. Biochar retains nutrients in soil directly through the negative charge that develops on its surfaces, and this negative charge can buffer acidity in the soil, as does organic matter in general. CEC stands for Cation Exchange Capacity, and is one of many factors involved in soil fertility. “Cations” are positively charged ions, in this case we refer specifically to plant nutrients such as calcium (Ca2+), potassium (K+), magnesium (Mg2+) and others. These simple forms are those in which plants take the nutrients up through their roots. Organic matter and some clay in soil hold on to these positively charged nutrients because they have negatively charged sites on their surfaces, and opposite charges attract. The soil can then “exchange” these nutrients with plant roots. If a soil has a low cation exchange capacity, it is not able to retain such nutrients well and the nutrients are often washed out with water.
Its characteristics vary depending upon what it is made from and how it is made. One unifying characteristic of biochar is that it mineralizes in soils much more slowly than its noncharred precursor material. Scientists have shown that the estimated amount of time that biochar carbon will persist in soils ranges from decades to millennia.