Welcome to what I hope will be a regular and interesting blog with cutting edge news from the environmental world of science and opinion. Expect the full range from solid and worthy, through depressing science, to outright optimism.

Optimism seemed a good place to start a new column, and so to “Biochar”. After “bail-out”, “biochar” could be the most important new word you will hear this year.

 

The story of biochar begins several thousand years ago in the Amazon basin where communities of people lived by ‘slash and burn’ agriculture. These communities lived at relatively high population densities in spite of the generally low fertility of Amazon soils. Around five hundred years ago Portuguese explorers started to venture into the Amazon basin, where they found these communities living on pockets of exceptionally fertile soils. What distinguished these soils wasn’t their geology but their blackness, so they were named the ‘Terras Pretas’ or ‘Black Earths’. For the next five hundred years they remained a garden centre curiosity – you could buy a bag of ‘Terra Preta’, put it in your flower pots, and get wonderful geraniums.

 

Then in the 1980s a Dutch professor of soil science, Wim Sombroek, decided to look more closely. What he found was intriguing. The soils were black because of carbon, clearly the agriculture was more ‘slash and char’ than ‘slash and burn’, and the carbon was hundreds or thousands of years old. What was really perplexing was how this carbon increased soil fertility. After all, after a thousand years of Amazonian rainfall any nutrients in the char or ash would have been long gone and carbon itself has no nutrient value.

 

So, what has this to do with global warming? Well, one man’s perplexing question has suddenly exploded into a small but rapidly growing scientific quest to get to the bottom of the ‘Terra Preta’ story – and where we have got to looks exceptionally exciting!

It seems that charcoal has a really complex structure that does two things that plants need. Firstly, it traps plant nutrients that are flowing naturally through the soil – preventing them being washed away by rain. Secondly, small pores in the charcoal act as secure, water filled refuges for the bacteria and fungi that move nutrients from soil to plant. Every charcoal particle becomes a nutrient rich fertiliser factory. This means that plants with the right dose of the right type of charcoal in the soil grow faster than plants in untreated soil, even with much less fertiliser.

 

Fertiliser manufacture, of course, is one of the world’s large sources of greenhouse gas emissions. Nitrous oxide is 230 times as powerful a greenhouse gas as CO2, and by reducing the amount of fertiliser we also reduce the amount of soil nitrous oxide emissions. Better still, making the charcoal produces energy rich gases which can be trapped and used to generate electricity – so avoiding the use of fossil fuels.

 

Best of all though, by taking plant waste (straws, husks, and so on), making charcoal and burying it in a stable form, CO2 is being removed from the atmosphere for a very long time. If we put 3% charcoal in the top 30 cms of the arable soils of the earth we would remove around 100ppm of CO2, equivalent to the total amount of human emissions over all time. If we can do this whilst also improving soil condition, increasing food production, and reducing fossil fuel use we shall have discovered something rather important.

 

The science is well demonstrated, but far from complete – we are trying to compress fifty years of research into five. To find out more look at the work being done by the team at Cornell University, have a look at this article by Johannes Lehman or visit the International Biochar Initiative website.

 

Mike Mason

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