October 27, 2016

Biochar: How Farm Waste Can Reduce the Impact of Climate Change


Climate change can have a severe impact on coffee farmers: lower yields, lesser quality, increased risk of pests and disease… It’s no surprise that some producers are switching to alternative crops like cacao.

But what if there were a way for farmers to manage the problems of climate change? What if they didn’t have to see a decrease in coffee quality or yield? And what if they could do this by reusing farm waste?

SEE ALSO: Coffee Farming: Will Shade Trees Reduce the Effects of Climate Change?


A Kon-Tiki kiln, complete with a thermometer, creates biochar. Credit: Benjamin Evar

A Force of Nature: Damage Caused by Climate Change

Over the past year, Latin American coffee farmers have come to know the force of climate change intimately. The weather phenomenon El Niño hit Colombia, Nicaragua, Honduras and several other countries especially hard between the spring of 2015 and the summer of 2016. Average temperatures were higher than normal, rainfall didn’t fit normal patterns, and higher than usual rates of droughts and fires were observed.

With the lower rainfall came a poor nutrient exchange with plants, and this meant increased susceptibility towards fungi and pests – especially coffee leaf rust or roya.

As a result, coffee cherry yield decreased and the quality suffered. And that had severe economic consequences for many farmers.

While the El Niño phenomenon only happens every so often, climate change means that higher temperatures and lower rainfall are likely to continue in years to come.

Biochar: A Soil Conditioner Made From Farm Waste

But one product can increase yields, store rainwater and help regulate soil temperatures, allow root systems better access to nutrients, and reduce nutrient run-off to water sources.

And even better, it can be produced locally on farms, or within cooperatives, using “waste” materials.

This product is biochar, a soil additive or conditioner. In layman’s terms, this means it’s something you can add to soil to see a positive impact on crop growth.

But What Is Biochar?

Biochar is the solid char that results from heating organic matter, such as wood or leaves, with nutrient mixes such as compost and fertilisers to above 400 degrees C with a low amount of oxygen – something called low-oxygen gasification.

If that sounded complex to you, don’t worry. The processes may be scientific, but it’s possible to do it all with just a kiln.

Dried wood

Dried wood is used as organic matter for biochar. Credit: Benjamin Evar

The Benefits of Biochar

Numerous research studies have been done on biochar. They’ve shown that, when added to compost and organic fertilisers such as cow urine, it increases yields significantly for a variety of crops. These include maize, pumpkin, rice, potatoes, beans and… coffee.  

What’s more, since biochar may help store rainwater in the soil during droughts, it helps to prevent soil temperatures from getting too hot.

How to Produce Biochar

Perhaps the best thing about biochar is that smallholders can produce it themselves. All they need is the kiln and, perhaps, an industrial thermometer.

Biomass will be converted to biochar at a rate of around 4:1. So how much biomass is needed? Well, research studies use varying amounts of biochar, ranging between a few hundred kilos and several tons per hectare. But if a farmer wants one ton, they should use approximately four tons of biomass.


Building a Kon-Tiki cone kiln. Credit: Benjamin Evar

Building or Buying the Kiln

The kiln can be constructed onsite, and farmers have multiple options available to them. The simplest – and completely free – approach is to create a conical hole in the ground and simply burn the biomass inside.

You then have models that require minimal equipment and can help control the burning. These include the Kon-Tiki cone kiln and various top-lit updraft (TLUD) models. Depending on where in the world a farm is located, these will cost between 50-500 USD and provide a more controlled setting.

An industrial thermometer is optional, but helpful for keeping the temperature between 400 and 700 degrees C. Burning biomass above or below this range produces inferior char.

Practical Advice for Using Biochar

Now that you have your biochar, it’s time to add it to the soil. When using it for planting new coffee fields, it would be good to also consider changing soils. This should be done both on the surface and in the planting holes to maximise root system contact.

As biochar is not directly a source of nutrients, it should always be mixed with one when amending soils – this could be compost, minerals, cow urine or a more complex mixture based on fermented native microorganisms.

Whichever mixture is used, those nutrients must also be added when first planting. This will make sure that they are adsorbed onto the surface of the char and so are available to the roots.

Biochar is not a miracle solution – but it is an effective and cheap management option when used alongside others. It can help ensure that, despite those warmer temperatures and lower amounts of rainfall, farmers’ yields and quality remain high. And that is vital.

Perfect Daily Grind

Want to read more articles like this? Sign up to our newsletter!