Agriculture is responsible for more than 10% of U.S. greenhouse gas emissions, according to the Department of Agriculture, and some in the industry are looking for ways to reduce their carbon footprint.
One of those efforts is replacing the kind of crushed rock farmers use to neutralize their soil’s acidity, from limestone to basalt.
Scientists are running tests in fields around the world to see if the swap will work to keep the soil healthy, increase yield and reduce agriculture’s contribution to greenhouse gas emissions.
Limestone, which farmers use now, sequesters some carbon, but basalt does it better.
“It turns out, because of the chemistry of the rock, carbon levels are higher for crushed basalt than it is for limestone,” said Chris Reinhard, a professor at Georgia Institute of Technology and one of the researchers working on the project.
One of the test plots is at Zumwalt Acres, a farm on the Illinois-Indiana border run by twin sisters Gavi and Remi Welbel. While they focus on small-scale regenerative farming, the Welbels are part of the effort to gather information on how successful replacing crushed limestone with crushed basalt can be on big fields.
“In our 12-acre hay field of alfalfa, oats and timothy grass, we saw consistently increasing yield in the higher basalt plots this year, so that was very exciting,” Gavi Welbel said. “But we’ll see, as years go on, if that is replicable.”
Farmers typically apply about 2 tons of limestone per acre to fields, but the experiment has plots ranging from a half-ton to 24 tons of basalt per acre. The more basalt used, the more carbon is sequestered in the ground.
“We’re looking at basically where we can get maximum carbon capture, and also what does it look like at an application rate that would be more comfortable for farmers and might be more economically feasible,” Welbel said.
The testing at Zumwalt Acres and other research plots is rigorous, with weekly soil samples and biweekly water samples. The data is then sent to Yale University for analysis.
The Welbel family is also testing limestone versus different amounts of basalt on corn and soybean fields. They will have more data this fall, but using the eye test, the corn and beans with basalt are looking as good or better than the ones using limestone, Gavi Welbel said.
While the initial data is encouraging, cost is still a significant issue. Basalt is not as prevalent throughout the Midwest as limestone, and mining and shipping could negate any benefit.
Even paying a higher price, farmers using basalt could profit by selling credits on the carbon exchange.
“This is enough of a carbon-negative process that you could think of this as another supplementary source of income for farmers. And that could be especially critical where farmers are going to get hit by more and more lousy years by climate extremes,” said Noah Planavsky, a Yale professor and one of the researchers tracking the experiments at Zumwalt Acres and other test plots.
Cost will also be a deciding factor for how willing farmers would be to trade out their limestone for basalt.
Matt Lambert, a corn and soybean farmer near Brookfield in northern Missouri, said he likes the idea and would pursue it — if it penciled out.
“I’d definitely consider it. My main concern with that would be the cost efficiency of that. Lime is pretty readily available in our location. It’s a cheap application. But if we could see additional benefit to it, yes, definitely,” Lambert said.
The pilot programs to test basalt rock will go for at least two more years, gathering data to test the environmental benefit and financial feasibility of making this change.
By Jonathan Ahl