Could biochar be an answer to lower manure emissions and increase farm resiliency?

Heather Darby, professor and agronomy specialist with University of Vermont Extension, spoke about the topic at the recent North American Manure Expo at Patterson Farms Inc. in Springport, N.Y.

Considering the recent floods and tornadoes, “we’ve had some pretty extreme weather” in the region, Darby says. “We’re trying to help farmers build resiliency. With all these extremes, our farmers are focused on soil health.”

One method of improving soil health while reducing carbon dioxide and nitrous oxide emissions is applying biochar with manure. Darby and Carol Adair, professor and director of Aiken Forestry Sciences Laboratory at the University of Vermont Rubenstein School, and other staff conducted a corn silage experiment at Borderview Farm with eight different treatments.

Their first theory was that manure injection would increase nitrous oxide emissions vs. broadcasting manure. Their research showed that nitrous oxide does, in fact, increase with injection, and additional winter emissions can occur when the soil thaws.

With injection, “you put a lot in a small area,” Darby says. “Injection in narrow bands provides an ideal site for denitrification,” the process that converts nitrates to nitrogen gas and removes bioavailable nitrogen, returning it to the atmosphere.

“Injection has all these benefits,” Darby says. But the question is, “How can we reduce emissions?”

They looked at cover crops thinking that they could reduce nitrous oxide emissions by taking up excess nitrogen.

“Would it create more aeration and take up more nutrients? But contrary to our hypothesis, it increased N₂O emissions by an average of 50%. Plus, having no cover crop adds carbon to the soil,” Darby says.

“We tell farmers to cover crop, inject to improve resilience, but we’re emitting more gas,” she adds. “Without covers, yields are suppressed, especially in very difficult years.”

EMISSION REDUCER? Heather Darby, professor and agronomy specialist with University of Vermont Extension, spoke about biochar at the recent North American Manure Expo in Springport, N.Y. (Photo by Deborah Jeanne Sergeant)

Another experiment looked at biochar combined with manure and synthetic fertilizer to reduce nitrous oxide emissions. Biochar is a charcoal-like product made from biomass waste, such as wood or agricultural waste, paper mill waste, or other biological residues. According to Utah State University, it is made by heating biomass in a contained system. 

“There’s evidence it can suppress N₂O under the right conditions,” Darby says. “It’s not clearly understood how, but it acts as an ‘electron shuttle.’”

She adds that the experiments showed that biochar reduced nitrous oxide emissions by 50%, but only with manure additions. “But biochar increased emissions in manure-only plots,” she says. “We’re not sure why. There was no impact on yields, quality, mineral uptake or soil nutrients quality.”

At $1,500 to $1,800 per ton, using biochar may not be cost-effective for many farmers because it appears its only benefit is reducing emissions. Still, Darby says it is not clear if reducing the rate of application and, thus, the amount needed would provide the same emissions benefit. It’s also not evident how long the effects last, or if this approach will provide any benefits regarding carbon organic matter.

“We’re now evaluating if it will work again,” she says. “What are the long-term effects? There are a lot of questions to answer.”

Darby and her colleagues used biochar made from wood. The powdery material, she says, was easy to apply and she notes that some people mix it with the contents of their manure pit.

She encouraged farmers to explore the possibility of processing industrial wood ash to create biochar.

“There are opportunities to explore,” she says.

Sergeant writes from central New York.