Biochar - The Underdog in the Fight to Save Our Soil

KF - Writer

Soil health is the frequently mentioned but never fully explained fourth horseman of the Anthropocene. This period when humans are the overriding force of change over the planet is fuelled by 4 umbrella issues: overexploitation, overpopulation, pollution and soil degradation. Now, the first 3 are widely spoken about: exploiting animals to extinction for food or for sport, plastic in the ocean, urban encroachment, climate change. These issues are all covered by the first 3 headings and so receive far more of the limelight than any others. However, soil degradation often gets cast to the bottom of the pile for the simple reason which is that: too few people understand how vital soil is to everything we do.

It’s true. Soil might not be the sexiest subject on a Saturday night but like the kid in the movie who was bullied by the lead in the first act, mistreated soil will later return as the villain to take its revenge. So how do we avoid this tired movie cliché and stop soil from turning against us?

Well, we have to treat our soil with the respect it deserves. Soil is a major part of every nutrient cycling system in one way or another, allowing dead organic matter to be broken down and the nutrients taken back up by the plants that we eat. Soil naturally filters our water; it provides habitats for soil organisms and a base for every ecosystem in the world. The presence of soil reduces the impact of flooding as it absorbs water downward rather than allowing fast overland flow which can devastate crops and homes. Most importantly, soil helps to regulate the climate by holding both water and CO2. When soil is overgrazed, aggressively ploughed and not allowed to rest between crops, it becomes nutrient deficient and sandy. This sandy soil is more easily eroded by the wind and can be flushed down into rivers, overloading them with sediment.

With an ever-growing population and an unparalleled demand for food, how can we meet the demands of the population without completely destroying the soils we depend on? One method is adapting the way that we farm: rotating crops to allow fields to remain empty, or planting crops with plants such as legumes which will fix nitrogen back into the soil. Using less aggressive ploughing techniques and never using heavy machinery when the soil is wet (which can lead to extreme soil compaction) can help improve soil health.

However, a more imaginative method is the use of terra preta, otherwise known as biochar. This biochar is most similar to charcoal and can be formed by burning organic matter (like dead plants or sewage sludge) in a low oxygen environment. Under these conditions up to 50% of the source carbon is sequestered or ‘locked’ into the biochar and not released to the atmosphere as CO2 as it would be through normal burning. This biochar can then be laid down in to the soil and therefore prevents the CO2 from being released into the atmosphere. If carried out on a global scale, Wolf et al. (2010) calculate that this sequestration could equate to a 12% reduction in anthropogenic CO2 release.

When looked at purely as a method of reducing human emissions, it could be argued that biochar is yet another excuse for humans to continue ‘business as usual’ and only reduce the harm they’re causing by 12%. However, biochar has something special over other CO2 reduction methods: all the other cool stuff it does. 

That’s right, this is no one trick pony. Biochar is very carbon dense, meaning a lot of carbon can be stored over a small area. It is also microporous which means it soaks in water like a little black sponge and holds onto it, this not only reduces the water needed to irrigate crops but also means that nutrients dissolved in water and kept in the soil longer. This allows plants to take up more nutrients through the roots as they are not washed out of the soil like they would be in a degraded soil.

Not only does biochar benefit the health of the soil, but also of the ecosystem. As it holds onto water, keeping it in the soil it also absorbs fertilisers and pesticides being washed through the soil by rain. By keeping these locked into the soil, they can do their jobs better and increase the productivity of poor-quality soils while additionally avoiding being washed into rivers where they can cause serious damage to the ecosystem. By lining agricultural fields with buffer rows of biochar, chemical runoff can be restricted. However, the negative side of this sequestration is that herbicides can be locked into the soil, preventing them from entering the plant system and killing the weeds they’re designed to kill.

Similarly, biochar has been studied to keep harmful elements locked into the soil. One 2014 study by Khan et al. found that some populations in rural China experienced cancer rates far higher than normal. As an area with very high rice consumption, potentially toxic and carcinogenic elements such as arsenic and cadmium are abundant in the soil due to mining and these can be absorbed into the rice crop. When eaten, the toxic elements are transferred into unknowing villagers and therefore contribute to increased cancer rates. By growing the rice crop in a soil with biochar sewage sludge added, Khan et al. (2014) found that the cancer risk was reduced by 59.8-66.3% compared to the control crop.

With this information to hand it is impossible to overlook how badass soil can be, just how much it does for every organism on the planet and most importantly, how essential it is to look after it. How many other things out there can boast the same long list of contributions that soil makes to our world? Soil is the water filtering, greenhouse gas trapping, temperature regulating, chemical prison that we all rely on for every part of our lives. It’s clear to see that we need to stop bullying our soil and treat it like the superhero it really is, and biochar just might be the Robin to our soil’s Batman.


Agrafioti, E., Bouras, G., Kalderis, D. and Diamadopoulos, E. (2013). Biochar production by sewage sludge pyrolysis. Journal of Analytical and Applied Pyrolysis, 101, pp.72-78.

Chan, K., Van Zwieten, L., Meszaros, I., Downie, A. and Joseph, S. (2007). Agronomic values of greenwaste biochar as a soil amendment. Soil Research, 45(8), p.629.

DeLuca, T., Gundale, M., MacKenzie, M. and Jones, D. (2015). Biochar for environmental management. Routledge.

Khan, S., Reid, B., Li, G. and Zhu, Y. (2014). Application of biochar to soil reduces cancer risk via rice consumption: A case study in Miaoqian village, Longyan, China. Environment International, 68, pp.154-161.

Lehmann, J., Rillig, M., Thies, J., Masiello, C., Hockaday, W. and Crowley, D. (2011). Biochar effects on soil biota – A review. Soil Biology and Biochemistry, 43(9), pp.1812-1836.

Sohi, S. (2012). Carbon Storage with Benefits. Science, 338(6110), pp.1034-1035.

Woolf, D., Amonette, J., Street-Perrott, F., Lehmann, J. and Joseph, S. (2010). Sustainable biochar to mitigate global climate change. Nature Communications, 1(1).

Photo by Dylan de Jonge on Unsplash

Photo by Patrick Hendry on Unsplash


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