Using Biochar (charcoal / agrichar / terra preta) to improve soil and sequester carbon





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Published on Jul 22, 2009

How to make biochar and use it to improve soil fertility and sequester carbon dioxide. A look at the implications for climate change, food production and carbon trading. Video by the Centre for Alternative Technology, Machynlleth, Wales
BIOCHAR (from wikipedia): Biochar is charcoal created by pyrolysis of biomass. The resulting charcoal-like material is a form of carbon capture and storage. Charcoal is a stable solid and rich in carbon content, and thus, can be used to lock carbon in the soil. Biochar is of increasing interest because of concerns about climate change caused by emissions of carbon dioxide (CO2) and other greenhouse gases (GHG).

Biochar is a way for carbon to be drawn from the atmosphere and is a solution to reducing the global impact of farming (and in reducing the impact from all agricultural waste). Since biochar can sequester carbon in the soil for hundreds to thousands of years, it has received considerable interest as a potential tool to slow global warming. The burning and natural decomposition of trees and agricultural matter contributes a large amount of CO2 released to the atmosphere. Biochar can store this carbon in the ground, potentially making a significant reduction in atmospheric GHG levels; at the same time its presence in the earth can improve water quality, increase soil fertility, raise agricultural productivity and reduce pressure on old growth forests.

About the video:
Biochar is made using a process called pyrolysis, during which organic matter is heated to temperatures below 700 C in the absence of oxygen. This leaves a compound consisting mostly of carbon, which we would call charcoal. The inert character of this carbon means that it is not prone to decomposition unlike most organic matter which eventually rots down and releases its carbon into the atmosphere. By charring plant waste material in this way, carbon is transferred from the relatively fast carbon cycle into carbon storage where it is able to remain for thousands of years in the soils of terrestrial ecosystems. Scientists say that only a small percentage of atmospheric carbon dioxide needs to be captured and stored in order to mitigate our emissions.

Biochar has also been seen, albeit mostly in the tropics, to have a positive effect on crop yields when applied to some soils. This is because it acts essentially as a nutrient sponge, holding on to minerals in the soil for plants to access, and preventing them from being washed out. Research in this area is not conclusive and much more work is needed to ascertain the true potential for Biochar to improve soil quality in other regions. At CAT we are running our own trials to address the use of Biochar as a soil conditioner with urine as a fertiliser. Indeed, it does seem that charcoal has a role to play in future environmental management, although the magnitude that it could be applied is unknown.

On paper it looks good land can be converted to biomass production, feeding the energy industry which profits from electricity production and again from the sale and distribution of Biochar as an industrial waste product. It is also expected that under the clean development mechanism (or whatever replaces it at Copenhagen later this year) Biochar will eventually benefit form tradable carbon credits as a way of buying and selling emissions rights globally. So whats the catch? Amongst the enthusiasts you will find those who urge caution to our optimism. In order to achieve such magnitude of sequestration, vast areas of land would be required- far outstripping the demand of bio fuels and threatening food security globally. We risk displacing current land use practices and people for energy crops and plantations.

We must check our enthusiasm and be sure not to fall for the magic bullet scenario which so many reports claim for Biochar. Most importantly, we cannot hope to have a stable global climate while emissions from the burning of fossil fuels remain so great. Initiatives such as bio-char hold some promise in terms of reducing the worst of climate change, and certainly in providing higher food yields and better soil quality, but only if we recognise this will have to come as part of a range of approaches, including a large scale reduction in direct emissions.



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