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Biochar for Environmental Management

Book Review by Ed Sears

edited by Johannes Lehmann and Stephen Joseph

(2009), Earthscan Books.

Biochar is an idea that has recently gained prominence as it holds out the possibility of tackling soil improvement, energy production, mitigation of climate change, and disposal of organic waste.  Biochar is organic material which has been heated (to between 350 and 700 degrees C) in the absence or restricted supply of oxygen.  It is therefore similar to charcoal, although intended specifically for application to farmland for environmental improvement.

Biochar for Environmental Management, edited by Johannes Lehmann and Stephen Joseph, two biochar researchers from Cornell University in the USA and the University of New South Wales, Australia, is a summary of the current state of scientific knowledge on this technology.  There has been localised interest in charred woody material or plant waste for some time, but it was the growing awareness triggered by the discovery of pockets of dark, carbon-rich, fertile soils known as Terra Pretta de Indio in the Amazon and the realization that these soils were the result of human activity hundreds or thousands of years ago, that has led to increased interest in its properties and potential.

 

This book covers the background to biochar (1 chapter), production systems both ancient and modern (3 chapters), and some of the economic and climate change implications (6 chapters), but concentrates on properties of biochar in itself and when added to soils (12 chapters).

When organic material is heated in the absence of oxygen, it breaks down into solid, liquid and gas components.  Charcoal production tends to be inefficient and polluting, and only makes use of the solid component, but modern methods such as pyrolysis and gasification harness the liquid and gas fractions for energy production and can accommodate a wider variety of inputs such as crop wastes.  Case studies are presented for domestic to industrial-scale production and subsistence-farming to high-tech processes, although experience is limited in the UK, so this book is not really a practical how-to guide for producing biochar for domestic horticulture.

The interesting feature of biochar is that it can persist in soils for hundreds of years, and produces a fertilisation effect without breaking down itself.  Its characteristics can be categorized as physical, biological and chemical, and like compost it varies enormously in composition depending on the feedstock and production method.  I recently reviewed the latest UK biochar research to compare results in this country to the experience in the book, mostly derived from experiments in the USA, Australia, Japan and developing countries in Africa and Latin America.  With UK soils, the most obvious effects are an increase in soil pH (a similar effect to liming on acid soils) and improving drainage by increasing it in clay soils and reducing it in free-draining sandy soils.  There are a host of other impacts that are more or less certain to occur, such as creating micro-sites for mineral retention and improving root formation.

Apart from benefits to agriculture, biochar is a carbon-negative technology if produced from waste material or sustainable cropping, as carbon drawn from the atmosphere by photosynthesis to fuel plant growth is then stored in the soil for thousands of years.  Biochar use, if scaled up, could then provide a proportion of the emissions reductions needed to mitigate climate change, while also addressing the need for increased sustainable food production.

For further information, try the International Biochar Initiative (http://www.biochar-international.org/), the UK Biochar Research Centre (http://www.biochar.org.uk/) or the Biochar website (http://www.biochar.org/joomla/).  The large-scale use of biomass for any purpose is a contentious issue as demand outweighs supply, so you can find criticisms of the push for biochar from Biofuelwatch and George Monbiot, among others, although as yet it is nowhere near being adopted on a wide enough scale to have a global impact.  Any experiments you try at home will definitely be adding to the sum of knowledge on the subject, so you could consider participating in biochar trials lead by Oxford Biochar (http://oxfordbiochar.com/) and Earthwatch.

In summary, this book provides a detailed technical resource, loads of references, and an outline of the applications and implications of biochar, both locally and for the global climate.

Ed Sears

Ed Sears is Energy Consultant at T4 Sustainability, Honorary Research Assistant at the University of Exeter, and Trustee at the Permaculture Association and Plants For A Future.

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