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Making Terra Pretta at Grow Heathrow

Posted: December 19th, 2013 | Author: | Filed under: Cool Projects | Tags: , | 1 Comment »

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Recently some Grow Heathrow residents paid a visit to a small scale farmer in South Wales to see what he’s been doing in the way of reversing the cycle of releasing carbon into the atmosphere by actually locking into the ground.

The first thing you see when you get there is his teeming one acre no dig annual vegetable plot. He combines alleys of perennials, including trees, with annual crops grown on 100metre long raised beds. The tree roots go deep into the soil, retrieving otherwise ‘lost’ nutrients. They also encourage symbiotic fungae which remain present when the annuals have been harvested. The trees will provide food crops and fuel for his biochar producing stove systems.

Just beyond the no dig agro-forestry garden is another field, currently grazed by horses with a small orchard forest garden and two poly-tunnels at the southern side. He plans to plant this field as a larger forest garden with willow and hazel coppice and other food and fuel tree crops which will also increase carbon draw down. These trees will be planted on the berm (the downhill side) of swales (water retaining landscapes) and it is hoped that, through creating these wetlands, some of the carbon drawn down by the trees will be stabilised in the soil.

In his home and in various guest and worker accommodation buildings and caravans, the heating and cooking is done using indoor wood burning stove systems which use pyrolisis rather than combustion to burn the volatile component of wood, leaving the biochar unburnt. This has the effect of stabilising much of the carbon in the wood, preventing it from readily decomposing when it is added to soil.  The biochar is used on the stable floors, the chicken coop floor or added to composting organic matter in order to nutritionally activate the biochar before it is added to the soil.

Ed Revill is working towards closing the loop of his food and fuel crop cycle. More than closing the loop, he does the reverse of food and energy systems which release carbon dioxide into the sky. This he does in two ways; firstly by optimising carbon draw down through optimising plant surface areas and growth rates and secondly by stabilising some of the carbon which the plants have drawn down, making it resistant to bacterial and other decomposition and holding it in the soil. this in turn builds soil and improves soil structure.

He has been using conventional organic farming methods since 1997, using horses to ridge up the soil and hoe the weeds, but now he has turned to preserving the soil structure through using no dig raised beds which have biochar incorporated into the mulch material. The biochar helps to stabilise much of the organic matter used as the mulch through which crops are grow, saving work, conserving precious resources (the organic matter) and reducing run off and atmospheric pollution.

By adding the biochar to the mulch, the soil builds up because the biochar (which is around 95% carbon) will not readily decompose. It has a massive surface area and strong adsorptive properties which enable it to hold nutrients and encourage micro organisms such as arbuscular mycorrhizal fungae (AMF) which have a symbiotic relationship with crops and which help to build soil aggregates. Biochar has been found to dramatically increase the CEC (cation exchange capacity) of soil. This enables the electrical bonding of soil components (adsorption) which further builds soil aggregates.

Tilling or disturbing the soil can disturb the symbiotic fungal networks and destroy the aggregate properties of the soil. The symbiotic fungae (AMF) also produce a form of stabilised carbon called glomalin. This carbon is given to the fungae by plants and in return the fungae bring nutrients to the plant roots. Glomalin acts to bind particles in the soil to create soil structure with strong aggregate properties, soil which retains water, nutrients and fertility and which is resistant to erosion and decomposition.

The inspiration for using biochar to build soil whilst reversing the causes of climate change came from studies of Terra Preta, (Portugese for ‘black earth’), a man made soil found in much of the Amazon basin. This soil supported a large, settled civilisation. This is an important discovery because this civilisation grew as a result of the practice of building soil through stabilising carbon in soil. This is the reverse of our ‘civilisations’ practice of burning fossil fuels and degrading soil, releasing carbon dioxide into the sky, in order to produce food and energy.

Our agro industrial system is failing. It relies on burning fossil fuels, it degrades soil, releasing soil carbon which contributes to climate change which in turn further degrades soil. It relies on land grabs, deforestation and transgenic technologies. If we continue to discourage small scale, soil building, climate change reversing systems of food and energy production through the massive tax payer subsidies to the fossil fuel and agro industrial corporations and through buying food and energy from corporations which destroy soil, burn oil and pollute the Earth then we will inevitably continue to destroy the biosphere.

Inspired by this form of agriculture, some residents at Grow Heathrow have added these tools to it’s array of features, and is producing biochar using a gassifying wood burner and adding it to the mulch. We also have a new willow coppice for the production of fuel to be used in it, as well as drawing carbon out of the atmosphere. Come visit to see how the system works.

To find out more and to see plans for making biochar producing stoves please visit www.soil-carbon-regeneration.co.uk


One Comment on “Making Terra Pretta at Grow Heathrow”

  1. 1 Paul V. Cassidy said at 8:35 pm on July 29th, 2014:

    Excellent stuff. I’ve been at something similiar myself using willow verge, reedbed filtration, mulching trenches, composting, meadow and weed lawns. I love the connection with pyrolisis and biochar. I suspect the ash left from pellet burners is essentially biochar too and that many pellet stoves more or less involve gassification. So it is possible to burn an industrially produced waste byproduct and avoid burning timber though the amount of ash produced is minimal. Still it all gets added into the compost heap where it belongs. I’ll surely visit if I’m ever over. The real thing is to get the airport to sponsor the farm – and others like it – based on a carbon sequestration/stabilisation contract. This is the critical missing link, in my view.


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