A soil amendment created from organic waste materials such as dead trees and manure could help some farmers increase their crop yields — and fight climate change at the same time. Called biochar, the charcoal-like substance has been shown to help with water and nutrient retention in agricultural soils, and to improve biological activity. It’s also seen as a promising method of trapping carbon, storing it in the soils where it won’t be released into the atmosphere for potentially thousands of years.
While biochar’s roots can be traced back millennia to its use among Indigenous cultures in the Amazon basin, interest in biochar has spiked in recent years in the face of climate change, spurring collaborations between scientists and farmers to better understand its benefits. It’s even starting to get attention in the Hudson Valley.
In June, farmers Ben and Lindsey Shute of Hearty Roots Farm in Germantown hosted a field day to kick off a five-year biochar study they’re conducting in partnership with Cornell Cooperative Extension. The event was organized by CCE’s Ag Climate Resiliency Program, Cornell Soil Health, Scenic Hudson, and the Glynwood Center for Regional Food and Farming. On top of an education session from experts in soil health, the field day featured a hands-on demonstration of how biochar is applied to the soil.
“As climate change advances, we’re going to need to try new things, and do new things,” says Annie Christian, Land Project Manager/Agricultural Specialist for Scenic Hudson. “Biochar is one of those practices that we’re trying to help advance” in situations where it would be appropriate, she says.
Biochar can be made from many different organic materials, including agricultural waste products such as rice hulls and corn stover (a corn field’s leftover stalks, leaves, and cobs). But the most common material for it in the Hudson Valley is woody waste, according to Debbie Aller, senior extension associate for the Cornell-led New York Soil Health Initiative.
That doesn’t mean cutting down trees, but instead making use of things that are already entering the waste stream. This could include wood chips made from dead and dying trees that were removed during powerline maintenance or downed in storms, or even waste from annual prunings on orchards and vineyards. Biochar made from dairy manure is also being tested in New York.
To create biochar, these waste materials are heated in a low-oxygen environment — a process called pyrolysis. The resulting product is carbon-rich and highly porous. This makes it a good option for degraded and sandy soils that are low in organic matter and thus may not retain water and nutrients well. Biochar contains pores of various sizes and shapes, which work together to help the soil use water and nutrients more efficiently, Aller says.
“Soils that have both small pores, like nano- and micropores, and large pores like macropores — these are the best when it comes to water retention and plant available water within the soil,” Aller says, “because we have pore spaces that allow for drainage of water but pores that also allow for that retention of water.” In that way, it works a lot like a sponge, and can help to reduce irrigation frequency and provide a buffer during dry spells.
Biochar on its own doesn’t typically add nutrients — though it’s been suggested that manure-derived biochar may do so — but it helps the soil hold onto nutrients and release them to the crops over time. “It tends to act a bit like a slow release fertilizer,” Aller says. “And biochar can help facilitate greater microbial activity.”
The process of making biochar also locks carbon from the organic waste materials into a stable form, meaning it won’t break down anytime soon and release carbon dioxide into the atmosphere. Aller says this longevity, or its “ability to resist degradation in the soil environment,” is what really sets biochar apart from other organic soil amendments like compost and manure. “We’re able to capture that carbon and put it back in our soils, which has a tremendous benefit from an agricultural standpoint.”
Biochar can work hand-in-hand with these other amendments, and is often mixed with compost. In small-scale operations, it can be created on site in kilns or stoves, in many cases using organic waste farms are already producing. “There’s a lot of potential circularity,” Aller says.
In larger integrated bioenergy facilities producing biochar, “the heat that’s generated within the pyrolysis process can keep the machine running, and you can have a continuous production system,” Aller says. When that biochar — with the carbon it’s trapped — is put into the soil, you’ve got a carbon net-negative process on the whole.
Biochar isn’t a silver bullet for land productivity and climate woes, though, and there’s still much to be learned about its effectiveness long term and on large scales. It’s not a “one size fits all” kind of solution, either — it won’t work for every type of soil, and it’s crucial to know when, where, and how much to apply. And the cost can be high.
There have also been concerns around plans for the development of industrial biochar facilities that aim to use unconventional materials, like human waste. One such effort in Saratoga County has been met with pushback from locals, who are trying to block a USDA grant of over $20 million for a plant that would create biochar from woody waste and biosolids, or “sewage sludge” created during the wastewater treatment process.
For the most part, experiments with biochar in the U.S. have been carried out on a small scale. The American Farmland Trust is currently trying to nudge things forward, and is helping to sponsor biochar trials in eight states that seek to assess its impacts on working farms under different regional environmental conditions, and the agricultural impacts of different types of biochar.
If there’s one thing both Aller and Christian emphasize, it’s that anyone interested in trying out biochar for themselves should reach out to experts before taking the plunge. It’s important to know if the soil fits the bill to avoid any adverse effects to nutrient availability, and there are safety precautions that should be taken during its application. There may also be grants that can help farmers get financial assistance, from the USDA or on the state level. Scenic Hudson can help farmers leverage these resources. “We’re really supportive of helping farmers to think through ways to try new things in a way that doesn’t create more risk for them,” Christian says.
