New research suggests silage has been overlooked as a substantial producer of nitrous oxide. A team at K-State figured out why – and a potential way to tackle the problem.
A common fermented feed for livestock churns out a potent greenhouse gas, but scientists in Kansas say they’ve figured out an affordable way to one day tackle the problem.
A team of scientists at Kansas State University has published the best estimate yet of how much nitrous oxide enters the atmosphere from silage, which they suggest could be the country’s third-largest farm source of the gas.
Now, they want to grab the attention of federal regulators and the agriculture industry to address the problem.
“So that we can do something to minimize it,” civil engineering associate professor Jeongdae Im said. “Luckily, we have a simple solution.”
The new research suggests silage may churn out 30 times as much nitrous oxide as does another common practice, burning corn stubble and other crop residue after harvest. But while the U.S. Environmental Protection Agency regularly factors field burning into its reports on emissions, the impact of silage gets overlooked, K-State scientists say.
The scientists’ proposed fix involves an inoculant. Treating 1 ton of silage with it would cost 4 cents, K-State researchers concluded. Im says $5 million could treat all the silage produced in the U.S. each year.
“It’s really, really exciting,” Im said. “We can reduce 2% of (the U.S.’) total nitrous oxide emissions.”
Im, who is also an environmental microbiologist, won one of the National Science Foundation’s most coveted awards to carry out this research.
The K-State team’s findings appear in last month’s issue of the National Academy of Sciences’ PNAS Nexus journal.
Trapping heat and depleting the ozone
The Intergovernmental Panel on Climate Change says the Earth’s atmosphere now contains 20% more nitrous oxide than before the Industrial Revolution.
Unlike the rise in carbon dioxide that primarily comes from fossil fuels, humans add nitrous oxide to the atmosphere mostly through agriculture.
Though this gas makes up a small slice of global greenhouse emissions, its potency worries scientists. Compared to carbon dioxide, nitrous oxide is about 265 times more effective at trapping heat over a 100-year period, a report from the EPA says. It also depletes the ozone layer that shields humans and other life on the Earth’s surface from harmful solar radiation.
Im and his colleagues carried out lab experiments with several kinds of silage as a first, crucial step to figuring out how much of the gas comes from that source.
Silage is chopped plant material — often corn, sorghum or alfalfa — that is fermented and stored in silos, bunkers and plastic-covered mounds across the country.
The team homed in on the bacteria in it that produce nitrous oxide and tested a variety of additives and inoculants to deal with them.
The bacteria produce nitrous oxide under stress, Im said, when they don’t have access to enough carbon compounds. So the team found a combination of ingredients that kills off most of the bacteria and then reduces this stress on the survivors. It gives the lingering microbes a boost of carbon compounds.
This two-pronged approach prevented 99% of the nitrous oxide emissions in the scientists’ silage experiments.
Verifying the safety of the treatment
Scientists and policymakers use formulas to tally up the estimated toll that different kinds of emissions take on society, such as by harming human health and property.
Those formulas suggest that the nitrous oxide wafting off of silage may cost society hundreds of millions of dollars annually in the U.S., Im said.
Several steps must happen, though, before it’s likely that a fix of the type proposed by K-State civil engineers and agronomists would potentially gain widespread traction.
Researchers will conduct larger-scale studies to verify their findings.
They’ll also further investigate to what extent chlorate, one of the ingredients in the treatment, remains in the silage after fermentation.
This will be vital to verifying the treatment’s safety.
“Anything toxic to microorganisms can be toxic for humans,” Im said. “So one of the things that we have to answer is the fate of this chlorate at the end of this silage process. And we are looking into it.”
But eventually, Im hopes carbon markets or other incentives could make treating silage to reduce emissions an attractive option for farmers.
