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Biochar, bringing soil to life


Biochar has been the subject of numerous trials over recent years and Craig Sams discusses how biochar can help farmers and growers

ORGANIC FARMING Magazine, Winter 2015 Issue 117

Lady Eve Balfour wrote in The Living Soil in 1943: ‘The health of soil, plant, animal and man is one and indivisible.’   She assessed by observation what was going on with healthy soil. There is now greater and more detailed scientific understanding about microbial life in the soil and how it contributes to soil structure, humus building, plant nutrition and protection against disease. Lady Eve’s observations are vindicated, yet farming continues to ignore the implications.  An estimated 10 million hectares of land annually becomes too degraded to farm economically.  This is as big a threat to humanity as global warming.  Indeed, restoring our soils is a major tool in reversing global warming.

The sands, silts and clays that form the basis of soil are inert minerals – what makes them into living soil is the mass of microorganisms that bind together those different sized particles.  Mycorrhizae and their associated organisms supply nutrients, waters and plant defence chemicals to the plant in exchange for sugar that the plant has created in its leaves by photosynthesis.   They also protect the plant from incursions by opportunistic pathogenic fungi, bacteria and nematodes.  The microbial world is co-dependent with the plant – together they can both thrive.

Mycorrhizae also produce glomalin, the sticky material that aggregates soil particles, giving the soil structure.  The tentacle-like hyphae of mycorrhizae and actinomycetes bacteria create tiny porous passages through the soil to facilitate the passage of air and water.  Organic farmers manage this symbiotic relationship between plants and microbes by maximising the population of the fungi and bacteria that optimise plant health and productivity. Composting and humus-building activity enable a higher microbial population. The higher the microbial population, the greater the benefits to plant growth and health.

Historically the civilisations of the Amazon, the ‘cities of Gold’ or ‘Eldorado’ of early Spanish explorers, were based on maintaining a high level of microbial life in soils that are notoriously poor.  This was done by regularly incorporating ‘Terra Preta’ – charred plant material, or ‘biochar’ into their soils.  Biochar is almost pure carbon, the black material that gives humus its dark colour.  The effect of biochar in the soil is similar to that of humus.  Biochar stimulates the expansion of the soil microbial population. It can double it in humus-rich organic soil and increase it by up to 100 times in degraded soils.  Its porous structure provides ‘refugia’ that protect mycorrhizae and bacteria from predatory small animals in the soil – ‘grazers’ such as mites, springtails and protozoa.

Scanning electron microscope image of biochar - copyright Pete Brownsort UK Biochar Research Centre, University of Edinburgh


Biochar has a large surface area – one gram has the surface area of two tennis courts – so it reduces leaching of nutrients into the subsoil.  Biochar’s porosity means that in dry conditions it retains moisture long after the surrounding soil has dried out, enabling microbial life to survive periods of drought.   Like humates, biochar has a buffering effect that moderates extremes of acidity or alkalinity. Biochar, like humus, can chelate heavy metals, preventing their uptake.  These properties reduce the need for irrigation, allow better use of fertility inputs and support healthier plants.

Scanning electron microscope image of biochar ©Pete Brownsort UK Biochar Research Centre, University of Edinburgh

Fungal diseases fare less well in biochar-enriched soils. Pathogenic fungi attack weak plants through the air and the soil. If a plant has an ‘immune system’ of supportive fungi and bacteria, they provide the protective barrier against disease-causing organisms, manufacturing substances like jasmonic acid, ethylene and salicylic acid to help the plant resist infection.


Since 2008, this protection has enabled organic cacao farmers in Belize to overcome capacity shortfalls and fungal disease. Mayan growers are now establishing new nurseries to propagate 45,000 new cacao trees – each and everyone will be raised in and planted out in biochar-enriched soil.

Biochar supports robust grass and turf growth: Forest Green Rovers, Dale Vince’s (Ecotricity) football club in Stroud trialled a small patch of biochar in the 2013 season and got good results.  In June 2014 they covered the entire pitch in finely milled biochar in time for the 2014/2015 season and are impressed with their improved soil biology, evidenced by their regular soil analyses and visibly healthier turf.

Bartlett Tree Research Laboratory transplanted beech hedging, a species notorious for its failure to establish – the hedging planted in biochar-enriched soil had a 100% success rate compared to 60% losses in untreated soil.  Bartlett’s ash dieback trials in an infected Woodland Trust forest in Essex have shown no signs of infection after 2 years.  1 in 4 of the untreated trees has already contracted the disease.

The Whitmuir Biochar Project at Whitmuir Organic Farm, in conjunction with the Royal Caledonian Horticultural Society, both makes and trials biochar. They have achieved more than 100% yield increases in cabbages, onions and turnips.  That project is supported by the Scottish Government’s Climate Challenge Fund.  Every tonne of biochar placed into the soil represents nearly 3 tonnes of CO2 permanently removed from the atmosphere.  When carbon pricing becomes a reality, using biochar in organic systems will make organic production cost-competitive with fossil fuel-emitting, soil-degrading industrial systems.

The complexity of life in the soil will challenge researchers for many years to come.  Biochar’s benefits vary depending on soil type, crop type and climate.  But the overwhelming evidence is that this carbon-rich material leverages the benefits of organic farming and horticulture by maximising the life embodied in the soil.


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