Biochar Belongs in Soil

By Julie Major, PhD

Biochar is gaining more interest as a tool for improving soil fertility and sequestering carbon in soil.[1] “Environmental celebrities” such as James Lovelock [2], Tim Flannery [3] [4] and James Hansen [5] have spoken about the “promise of biochar”[6]. But soil scientists, who might find biochar to be pretty exciting stuff, are still poorly aware of it.

Biochar is charcoal made from biomass by “baking” it with low or no oxygen, with the specific intention of applying it to soil. Biomass used to make biochar should be sustainably obtained from crop residues, forestry, agricultural, municipal and even some industrial waste streams, including manures. Biochar can be obtained as a by-product of producing energy from such biomass sources, and several biochar systems are being designed at a variety of scales, for example, to provide heat for barns or greenhouses while producing biochar from locally available biomass.

Although it is not a fertilizer itself, applying biochar to soil has been shown to improve crop yields and soil fertility, mostly through increasing soil pH and thus nutrient availability. Biochar has also reduced nutrient leaching in poor tropical soils, most likely due to greater nutrient retention. Since biochar surfaces gradually become oxidized (and thus develop cation exchange capacity) after application to soil, beneficial effects on crop growth have been observed over several years after single applications. Perhaps the most striking example of the durability of biochar effects on soil fertility is the Terra preta soils of the Amazon, which were enriched with charcoal and nutrients and remain highly fertile hundreds to thousands of years after they were formed. Other potential, under-studied beneficial effects of biochar include the promotion of favorable microbial interactions and water retention in dry areas. Biochar has been shown to favor biological nitrogen fixation and root colonization by mycorrhizal fungi, but its effect on soil biota in general are not well known.

Interest in applying biochar to soil is also motivated by its potential environmental benefits. It is estimated that biochar will remain in soil for centuries to millennia. In contrast, the biomass it is made from mineralizes relatively rapidly. Reductions in soil emissions of nitrous oxide and methane have also been observed with biochar, adding to its potential for directly mitigating global warming. Carbonizing biomass to produce biochar releases excess energy which may be used in place of fossil fuels in some applications. This type of energy production system has the potential to be “carbon-negative,” as biochar sequesters carbon in soil for long periods while it increases plant productivity.

However, much of the work on biochar has been carried out in tropical soils which are very poor and acidic. There is a great need for biochar to be appropriately tested in temperate climates, and trials are now beginning across the US. One major obstacle at this time is the difficulty in obtaining biochar to work with, as providers are just starting to appear. However, the possibility of undertaking integrated projects for combined biochar production and use exists for a wide variety of scales and situations. There is also a great need for a testing and classification system for biochar, because biochar characteristics can vary tremendously depending on how it is made and what it is made from.

For answers to your biochar questions, you might start with the International Biochar Initiative, an NGO whose mission is to promote the development and exchange of knowledge on biochar technology and use in soil. The IBI promotes policy development in support of sustainable biochar production and utilization systems at the international, national, and sub-national levels. It provides extension services and is involved in organizing international conferences on biochar. The IBI’s website provides information on all aspects of biochar, and will soon offer a searchable member directory where you can find information on a variety of biochar testing projects. IBI is also helping to network a growing number of national and regional biochar initiatives. IBI hopes that networking and collaborative learning will help researchers, technologists and farmers to begin to realize the many potential benefits of biochar in soil.

Julie Major is the Extension Director for the International Biochar Initiative. She is the prime author for Biochar effects on nutrient leaching. In: Lehmann C and Josephs S (Eds). Biochar for Environmental Management: Science and Technology. The book can be purchased from Earthscan and through Amazon.com.

Julie can be contacted for further information at julie@biochar-international.org.