Loading soil with biochar allows farmers to cut way back on irrigation. By Emma Bryce, for Anthropocene Magazine, October 23, 2020


Loading soil with biochar allows farmers to cut way back on irrigationAt high applications levels, researchers found that biochar can not only soak up a lot of carbon, but also reduce the need for irrigation by almost 40%.

Biochar – the charcoal product used to enrich agricultural soil and trap carbon—may have a hidden commercial benefit for farmers: it could lock moisture in the soil and save on gallons of costly irrigation. 

The coarse, black material, made by combusting wood, grass, and other organic materials under low-oxygen conditions, helps to sequester carbon in the soil. Biochar’s major benefit in this regard is that it doesn’t easily decompose, meaning it can become a reliable long-term carbon sink. Its application to farmland soils is recognized as one way to turn agriculture into a force for climate mitigation, helping it redress some of its immense emissions damage so far.

Biochar also reduces the need for fertilizer by enriching the soil, and gives soils the capacity to soak up excess water, which can cut the risk of runoff that strips vital topsoil off the land. 

But while experts have been aware of these environmental benefits for some time, the researchers on the new BCG Bioenergy study say that not as much attention has been devoted to how these advantages could translate to benefits for farmers – especially considering that they’re the ones who need to be motivated to spread biochar on their land. That’s where their research comes in.

They examined several studies which explored how biochar increases the water-holding capacity in the soil: that’s a measure of how sponge-like soil is—or in other words, how much water it preserves for plants to slurp up, later on. This meta-analysis revealed that adding biochar to sandy soils, in particular, has notable benefits. They also showed that larger particles of biochar, instead of a finely-crushed medium, made soil more absorbent, partly because it makes the ground more porous and available for storing water. 

When the researchers then followed up this analysis with a field trial on a small test plot of farmland, they were able to show that, at high applications in the soil, biochar can reduce the need for irrigation by a strikingly large amount: almost 40%. 

Based on this discovery, the researchers identified regions across the United States where sandy farm soils infused with this product would result in large water savings. These are spread mainly across the north, north east, south east, and western parts of the United States—places where, in many cases, there’s a heightened threat of droughtDiscover more:  How climate change could shorten pregnancies

The researchers conclude that investing soil with biochar would enable farmers to cut back on irrigation that could save them huge amounts of money. “There’s a lot of biochar research that focuses mostly on its carbon benefits, but there’s fairly little on how it could help stakeholders on a more commercial level,” they say.

To remedy that, they also used their findings to develop a formula that farmers can use to calculate the precise water-saving potential of adding biochar to their land.

One caveat to the study is that farmers would need to apply biochar at much higher rates than is currently typical, to achieve similar savings. Though even at lower quantities on sandy soils, it would bring water-saving benefits. The researchers also note that despite the focus on sandy soils in their study, biochar could bring substantial benefits in other types of farmland too: most of the studies they examined just happened to focus on sandy soils. 

Biochar may also have other, subtler benefits for farmers. Consistently dry soils can cause stress in plants that compromises their resilience to disease, and their productivity as well. So shoring up water reserves in the soil through biochar may be good for farmers’ bottom lines in other ways: it could help to create the conditions for healthier crops that require fewer costly pesticides, and which produce higher yields and generate more profit.

In any case, agriculture now accounts for 80% of the United States’ water consumption—a massive amount that will need remedying, under the threat of climate change and increasing drought. Farmers are going to need to use whatever sustainable resources they can to bring that consumption down. Biochar—which already brings many other environmental co-benefits—is at least one viable candidate to add to that toolbox.

Source: Kroeger et. al. “Water Cost Savings from Soil Biochar Amendment: A Spatial Analysis”. GCB Bioenergy. 2020

How biochar helps improve your soil’s ecosystem

The Role of Biochar in the Soil:

The role of biochar in the soil is electron transfer and adhering to a coating of materials that help it capture and exchange nutrients. See this article explaining what co-composting does to biochar. Nearly all of the benefits of biochar in the soil come from the coating of decomposition products that adheres to its surface:


Carbon coating gives biochar its garden-greening power



Organic coating on biochar explains its nutrient retention and stimulation of soil fertility



In order to achieve this coating in the least time and with the greatest effect, mix biochar with compostable materials at a rate of about 10% by bulk volume. (It is very forgiving; anywhere from 10-50% yields beneficial results, but 10-15% seems to make the biochar go the furthest.) Then, let them go through the composting process together.


We do not recommend directly adding biochar to soil. Charcoal that has gone through high temperature processes tend to be aggressive adsorptive media, comparable to a charcoal filter. If you mix this with soil by itself, it will adsorb and cling onto nutrients and the substances that plants need, and the plants will not be able to get these substances off. When this happens, it can take up to two years for the soil to recover from the stunted growth and nutrient depletion. This is not a trivial effect, and many of the early papers that reported negative effects from the use of biochar were due to attempts at directly adding it to the soil.


However, when you mix biochar with compostable materials and let them decompose together, many benefits are obtained. Firstly, the odour is dramatically reduced. Ammonia odours (and therefore, ammonia emissions, which are harmful), in particular, are significantly reduced when biochar is mixed together with compostables. Secondly, the compost tends to compost quite hot when conductive (high temperature processed) biochar is part of the mix. At Gill Tract Farm, our main composting partner, they observed that adding biochar to the compost caused it to compost at nearly 68-70˚C for most of a month, whereas prior to the addition of biochar, the compost would rarely get hotter than 54˚C. The resulting compost was much more thoroughly decomposed, and seemed to retain far more fertilizer value. We now know why: co-composted biochar retains a tremendous amount of nitrates which are normally lost as leachate or as harmful emissions:


Plant growth improvement mediated by nitrate capture in co-composted biochar



I’d like to share a couple of galleries of growing comparisons and growth results that our composting partners have observed with the use of biochar: 


LCN Biochar paired results



Biochar Effects


Biochar not only is fantastic for soil fertility, but it also has two major climate benefits:

  1. the charcoal itself does not revert to CO2 without combustion. The gradual accumulation of biochar in soil amounts to reverse coal mining— the production of solid black carbon whose carbon was drawn from the air, and the interment of this carbon in the ground.
  2. When co-composted biochar is added to the soil, it triggers many additional effects which continue to draw down additional carbon in the form of increased soil biology. This effect is quite significant; there can be a 5-10x multiplication of the amount of carbon added to the soil over the subsequent decade due to biological carbon storage effects, especially increased soil fungi.


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