Biochar Traps Water and Fixes Carbon in Soil, Helping the Climate. But It’s Expensive

As droughts become longer, the soil additive could save on irrigation water and, if mass produced, might compete with energy sources such as oil and gas.

A farm worker applies biochar in the field during a demonstration at a farm near Windhoek, capital of Namibia, on Oct. 8, 2020. Credit: Musa C Kaseke/Xinhua via Getty Images
A farm worker applies biochar in the field during a demonstration at a farm near Windhoek, capital of Namibia, on Oct. 8, 2020. Credit: Musa C Kaseke/Xinhua via Getty Images

Share this article

Biochar, a charcoal-like substance made from burning organic materials in a low or zero-oxygen environment, can improve the quality of soil and trap carbon dioxide in the earth for potentially hundreds, or even thousands, of years. 

But a recent study suggests that it may also have another benefit: it could reduce irrigation costs for farmers, thanks to its highly porous and water-absorbent properties.

The meta-analysis, published in GCB Bioenergy, found that mixing biochar with sandy-textured soils could increase the amount of water the soil stored, meaning farmers would need less water to irrigate their crops and could recycle water from rainfall and runoff, said Jennifer Kroeger, a fellow at the Science and Technology Policy Institute in Washington, D.C., who led the study. 


We deliver climate news to your inbox like nobody else. Every day or once a week, our original stories and digest of the web’s top headlines deliver the full story, for free.

Warming temperatures due to climate change are making droughts longer and more frequent, particularly in arid regions of the United States. Experts say that biochar may help alleviate the effects of climate change by saving on wasted water from irrigation, fixing carbon into the soil and—if produced at an industrial scale—potentially compete with polluting energy sources such as oil and gas. 

In a 2019  special report on climate change and land degradation, the United Nations Intergovernmental Panel on Climate Change said that biochar “can improve soil chemical, physical and biological attributes, enhancing productivity and resilience to climate change.”

Jeff Schahczenski, an agricultural and natural resource economist with the National Center for Appropriate Technology, a Montana-based nonprofit dedicated to sustainable energy and agriculture, said that using biochar was still expensive for farmers “because there hasn’t been economies of scale.” 

But he added that in locations like Montana, where raw materials to produce biochar could be sustainably sourced and where biochar could significantly improve the quality and water-retention properties of the soil, these benefits could make investment in this technology worthwhile. 

“It’s going to be locationally specific. It’s not something you can just throw across the entire United States and say, it’s going to be efficient and economic,” Schahczenski said.

Steve Charter, a rancher from Montana, said he uses biochar to improve the soil and grass quality of his land for cattle grazing. He adds biochar to a nutrient-rich worm manure mixture—also known as vermicast—which he spreads over his land. Doing so, he said, allows more rainfall to be absorbed, enriches the soil and allows the vermicast to cover a larger surface area.

For now, using biochar is relatively costly, he said, but he hopes the investment will pay off once the market grows and the benefits associated with biochar result in higher quality and more sustainable beef. 

“I think it could be developed where it would be cost effective. But right now, it’s kind of questionable,” Charter said.

The researchers who conducted the new study found that in regions like Florida, northern parts of Michigan and Nebraska, biochar could increase the amount of stored water by 72 to 74.5 percent, according to their highest estimates. 

The researchers’ model also estimated that biochar would be effective in regions of the United States like California and Arizona, that frequently face periods of severe drought.

“The water benefits are a really big deal, especially as we move into an earth system where we’re going to be seeing more rain and so potentially more flooding, simultaneously with more droughts,” said Caroline Masiello, professor of earth, environmental and planetary sciences at Rice University in Houston, the study’s senior author.

The research provides added incentive for farmers and agricultural stakeholders to use biochar, a technology that promises to play an important role in improving soil quality and reducing carbon emissions relating to land use, said David Laird, a retired professor of soil science at Iowa State University, who was not involved in the study. 

However, some experts question whether the findings will be enough to sway farmers to begin using biochar. Little is known about what crops, soils, irrigation and management systems would be most cost-effective, said Andrew Zimmerman, a professor of biogeochemistry at the University of Florida, who also did not participate in the study. 

Information about biochar is also not always readily available to farmers, making a transition away from more traditional agricultural practices unlikely, he added.

Improving Water Absorption in Soil

The new analysis looked at 16 peer-reviewed studies that investigated the effects on water storage capacity of mixing biochar with sandy soils, both in the laboratory and in real-world settings. The team considered how factors like biochar type, particle size and the proportions mixed with soil could affect its water holding capacity.  

Kroeger and the team found that biochar made from decomposed wood, straw, shells and non-traditional raw materials stored water less effectively than biochar made from grass. They also found that biochar with larger particle sizes trapped more water, compared with smaller particles. 

Biochar is filled with water-trapping pores that help it act like a sponge and that, when mixed into soil, rearrange how densely it is packed, creating additional spaces to store water, Kroeger said.

The research team also created a model estimating which regions of the United States would show the greatest percentage change in water holding capacity from using biochar. They found that areas with the sandiest soil textures—including the Northeast, West and Southeast—would reap the most benefits.

Rather than striving to account for all the water and biochar-associated costs in an economic model, the Rice University researchers created a mathematical formula that farmers could use to tailor the costs to their own practices. 

Some experts argue that the lack of a comprehensive economic analysis means it’s still unclear whether the water storing advantages of biochar translate into cost savings for farmers. “They could have taken a wide range of costs [associated with biochar], and then said, OK, in this place, you’re going to see economic benefit from it. And this place, you’re not,” says Zimmerman.

Doing so, however, would be enormously complex, said Laird, since costs ultimately depend on a wide array of factors, from biochar and soil type to irrigation and management systems employed.

It’s also hard to discern what regions should adopt biochar, said Zimmerman. In Florida, for instance, citrus and winter vegetables that rely on irrigation might benefit from the application of biochar, but the state is not water stressed. 

Things get even more tricky when trying to determine which specific crops would most benefit from biochar application. While some crops, like wheat and corn, respond well to biochar-mixed soils, others, like kiwi fruits and potatoes may actually see a decline in yields, Masiello said.

 “If you’re a farmer and you’re trying to make plans, you want to know: Is this right for my soil type? Is this right for my crop?” she said.

The team applied their economic model using data from a site at the University of Nebraska-Lincoln’s Agricultural Water Management Network. They calculated that biochar could lead to a 38 percent reduction in irrigation need, compared with soil without biochar added in. 

But some experts question the assumptions underpinning these calculations. The study presupposes a biochar application rate that is more than double what you would expect on an average U.S. farm, said Andrew McGuire, an irrigated cropping systems agronomist at Washington State University, who was not involved in the study. It also doesn’t account for this in the economic model, making it difficult for farmers to know what the true cost of using biochar may be, he added. 

Incentives For Farmers 

Without resolving some of these key questions it’s unlikely that farmers will feel motivated to adopt biochar to their agricultural practices anytime soon, said Laird.

For now, it is predominantly small-scale farmers willing to spend extra money to experiment on their crops that are driving the market for biochar, Zimmerman said. Compared to other products used to improve soil quality—such as fertilizers and commercial adsorbents—biochar prices are still running high across the United States, according to a 2019 study. A major reason for the high prices is that industrial-scale production of biochar is virtually non-existent, said Laird. 

Charter, the Montana rancher, said he is keenly aware that he is only one of few farmers in the United States adopting biochar in their farming practices. The reason, he said, comes down to just how novel this technique is to farmers across the nation.

“We’re a very small percentage of people thinking about this. More and more people are coming to these ideas, but it’s all very new,” he said.

Laird said approaches that put a price on carbon, rewarding farmers for using carbon-sequestering techniques such as biochar and providing disincentives for methods that pollute the climate, might be the way forward. Such strategies will make biochar more lucrative, and make biofuel—a byproduct of some forms of biochar production—more competitive with oil and gas. It might also help the industry switch away from using biomass to generate electricity to using it for producing biochar, he added. 

But, Laird said, until priorities change, and scientists find out more about biochar’s properties, the future of the technology remains uncertain.