Biochar: a Slow-Burn Success

Biochar could help you get more from your plants and save the planet at the same time. What's the secret?


By Lia Leendertz
Telegraph

Growth area: Daylesford Organic gardener Jez Taylor extols the virtues of biochar, which has improved his germination rates his germination rates  Photo: Christopher Jones

Farmers in Belize are excited about it, as are carbon capture scientists, the United Nations Development Programme (UNDP), and multinationals such as Kraft and Nestlé. It may provide a carbon sink, it may save degraded soils, it may alleviate rural poverty.

"It" is biochar. For Jez Taylor, the head gardener at Daylesford Organic, the attraction is more simple: "The environmental benefits and its ability to capture carbon are delightful, of course. But I just get fantastic propagation results when I'm using it. That's what I'm interested in."

Biochar is "the oldest new thing you've never heard of", to quote a phrase coined by Wae Nelson, a US biochar expert, and its applications are wide ranging. It is essentially charcoal, but burnt at a lower temperature and with a more restricted flow of oxygen. Its proponents believe it was the force behind ancient cities in the depths of the Amazon, where poor, acidic, tropical soils would not otherwise have been able to sustain large populations. In such sites up to 2m (6ft 6in) of terra preta (Portuguese for "black earth") can be found: rich, dark and fertile pockets that occur naturally among the yellow surrounding earth.

Jez Taylor is one of a number of head gardeners who are pioneering the use of biochar in Britain. He manages 20 acres and six polytunnels of crops that supply Daylesford's own upmarket farm shops in the Cotswolds and London, and his main interest is in propagating the many plants that will fill those fields. Each starts off in a tiny plug of compost, desperately vulnerable to drying out.

"I don't claim to be an expert propagator, and often we have apprentices watering who may be even less expert," he explains. "The compost needs to be bombproof or young plants will be lost, particularly those in tiny modules, such as spring onions."


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Jez tried a mix of coir and biochar and found that the water-holding action of the biochar improved his results dramatically. "I now know I can water on a Friday and come back in on Monday to find that everything is OK. I can be certain that seeds are still moist at the crucial moment when the root emerges from the seed, and last year this improved germination rates from around 80 per cent to closer to 95 or 100 per cent."

Jez also uses a biochar-based compost for larger vegetables that go into the shops for sale as plants.

"It is great in the potting mix and I'm convinced it gives it more guts. Plants seem to be supported for longer and there is less yellowing of leaves. When we feed, the feed isn't given in one go but locked away by the biochar and released slowly to the plant, and it really shows."

Dr Saran Sohi, of the UK Biochar Research Centre, started his career researching soils and soil additives. He says the effect biochar has on soil is different from that of any other additive.

"Biochar brings a physical and permanent change to the soil. Every other additive decomposes but biochar remains, and its effects increase over time."

Biochar works in several ways. Though it is not filled with nutrients itself, it is able to attract and hold on to nutrients, so preventing them from leaching away, and holding them just where plants can reach them. Its porous nature provides refuges for mycorrhizal fungi, which in effect enlarge the plant's root system while also increasing its resistance to diseases. It makes soil far more attractive and stable for beneficial microbial activity. Essentially it does everything organic matter does to the soil, but better, and permanently.

All this goes some way to explaining the impressive results seen in Belize. Craig Sams, founder of Green & Black's chocolate, has a strong interest in biochar, having founded a company, Carbon Gold, that sells biochar mixes and kilns.

"I've been in organic food most of my life, so I've seen the difference that good soil management can make," he says.

He wanted to bring the two parts of his work together and see what impact biochar could have on cacao growers' crops. Two Belize farmers were taken to Cornell University and "pumped on biochar", as Sams puts it. On their return they were given kilns and asked to put what they had learnt into practice. The results surprised everyone. Cacao plants planted into soil rich in biochar started producing fruits when about three-and-a-half years old; they usually take seven years to reach this maturity.

This caught the eye of the UNDP, which has now provided $50,000 (£32,900) for more kilns, and there are several non government organisations working to create biochar gardens throughout Africa and the Third World. Large food companies have also started getting in on the act: a sure sign that the enthusiasts are onto something. Unlike charcoal – which is made from hardwood at high temperatures – biochar is made at low temperatures and from any waste, including animal dung, twiggy waste, softwoods and rice husks, making it a realistic proposition for farmers in developing countries.

"When diseases hit plants grown in biochar-rich soils they have to fight their way through a shield of beneficial fungi and bacteria, and we think this is why the Belize plants produced so much earlier than usual. They could grow unhindered," says Sams. In Britain he is working with Bartlett Tree Experts on a trial with ash trees infected with ash dieback, to see if biochar might give them a similar increase in armoury.

Elsewhere, Ed Ikin at National Trust property Nymans is the first head gardener to install a biochar kiln to deal with his garden's waste and improve its soils, and Great Dixter head gardener Fergus Garrett uses biochar in his compost mixes.

"It's an excellent peat substitute," says Garrett. "Better than green waste. I would use it as part of a John Innes mix."

While biochar's effect on soils and plants is exciting, there are also great environmental benefits to its manufacture and use, and these stem from its capacity to lock up carbon. Soil is naturally a carbon sink – it locks away carbon and prevents it from entering the atmosphere – but a chunk of our troublesome greenhouse gases arises from ploughing soil and releasing this carbon. Although normal composting and mulching takes carbon in the form of organic matter and puts it into the soil, this quickly breaks down as matter rots, and the carbon is released again. Every time we dig or disturb the soil we speed up this process. Peat mining is an extreme example of this: when we disturb peat bogs we release carbon that was locked away thousands of years ago. But at least 50 per cent of the carbon in any piece of waste turned into biochar becomes permanently stable.

Gardeners digging biochar into their soils are taking a small step in undoing the environmental damage caused by peat users.

While Dr Saran is particularly enthused about the use of biochar in tropical climates, he thinks it could have applications in British gardens.

"In the average back garden you can make a big impact," he says. "A little can have a big effect on the soil. The way biochar interacts with water, nutrients, microbes and fungi will improve growing conditions and make soils more stable and fertile."

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