Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: June 10, 2009
Publication Date: June 6, 2011
Citation: Laird, D.A., Novak, J.M. 2011. Biochar and soil quality. In Encyclopedia of Soil Science, Second Edition. Taylor and Francis: New York. p. 1-4. Interpretive Summary: When biomass, such as crop residue and wood wastes, are heated in the absence of oxygen in a process known as pyrolysis, the biomass is transformed into a liquid known as bio-oil and a solid known as biochar. Bio-oil is a greenhouse gas neutral renewable energy product that has the potential to replace some petroleum products. Biochar is a type of charcoal. Biochar can be burned as a substitute for coal, but using biochar as a soil amendment may have many benefits for the environment. One of those potential environmental benefits is an improvement in soil quality. In this article we report that application of biochar to soils reduces the density of soils and this makes the soils a better medium for plant growth. We also report that biochar amendments add plant nutrients to soils and increase the capacity of soils to retain both plant nutrients and water. These improvements in soil quality can increase crop yields. However, we also report that the quality of the biochar is very important. While some types of biochar increase crop yields, other types of biochar can reduce crop yields. This encyclopedia article will be used by scientists, students, and the general public who are interested in learning more about the impact of biochar on soil quality. The article will help farmers and land managers who are considering applying biochar to their fields avoid problems associated with putting the wrong type of biochar on their fields.
Technical Abstract: Biochar is a form of char that is used for environmental applications, principally as a soil amendment or for water treatment. Biochar is produced by the incomplete combustion of biomass and is primarily a mixture of single and condensed ring aromatic carbon with lesser amounts of aliphatic carbon, hydrogen, oxygen, nitrogen, and other elements. Addition of biochar to soils returns most of the nutrients that are removed from the soil when biomass is harvested. Biochar has the capacity to retain bioavailable water and is a very strong adsorbent of plant nutrients and dissolved organic compounds. Biochar is an effective soil conditioner that reduces soil bulk density and increases the capacity of soils to retain and supply nutrients and water to growing plants. Because of these positive effects on soil quality, most studies have reported enhanced plant growth for soils amended with biochar, however, caution is urged as biochar quality is critical. Some biochars have the capacity to tie up nutrients whether by immobilization, nutrient adsorption or by raising the soil pH to the point that the nutrients are no longer bioavailable.