Soil organic matter has a fundamental importance for soil fertility. Increased mineralization due to global warming and increased harvesting of crop residues such as straw for energy recovery will reduce soil organic matter. Thereby future harvests may decrease. Biochar may mitigate this and has in tropical soils demonstrated increased soil fertility lasting for thousands of years in the form of Terra Preta, which was produced by Indians in the Amazon before contacts with the Western culture. The Western scientific community was until recently not aware about biochar, although practitioners sporadically employed it as a soil conditiner in historic times.
Biochar is a charcoal-like material produced by heating organinc matgerials to several hundred degrees at limited oxygene supply, so called pyrolysis. It has a large specific surface, ranging from a few to several hundred square meters per gram char, depending of raw material, temperature, time and water content. Its large porosity makes it capable of holding large volumes of plant available water, nutrients and soil microbes. Mixed into soil, biochar is persistent to further degradation with a half life typically around 5000 years.
The potential of adding biochar to soil is threefold: I.) it mitigates high air CO2 levels by being a reliable carbon sink; II.) it improves soil fertility by increasing plant available water, nutrients, and soil microbes as well as improving soil structure; III.) it reduces nutrient leakage and losses to ground and surface waters. In addition, production of biochar delivers energy at the processing unit and other raw materials possible to use in the synthetic industry. Burning bioenergy for heating purposes can maintain the present CO2 level, but it cannot reduce air CO2 levels, as biochar production can. It should be observed that biochar, once spread into soil, cannot be recovered and its content of CO2 cannot intentionally be released as is the case if logging forests, initially intended to be a carbon sink. Similarly, Carbon dioxide Cap and Storage (CCS), presently being developed at certain fossil fuel fired power and heat generation plants, cannot reduce the actual CO2 content in the atmosphere. In addition, these techniques are costly and demands tchnically advanced units at large scale.
To sum up, biochar production and application to agricultural soils may create a triple wins scenario, where farmers get higher yields and compensation for environmental services; the society gets reduced eutrofication and less negative environmental impacts from intense farming practices; and humanity gets sustainable food production at the same time as climate change effects and the connected risk of reaching climate tipping points are reduced. Biochar contributes to a sustainable society in its true meaning for future generations by closing the cycles between arable land and human habitations. The technique is democratic, since it can be applied anywhere around the globe where plants are growing and it is not dependent of economic, technical or infrastructural development. It is independent of scale, too, so also home gardeners may transform garden waste into a soil improver to use in their own garden.
NJF seminar 430, Climate Change and Agricultural Production in the Baltic Sea Region, 4-6 May 2010 Sweden