Researcher probes manure management
Research measures ammonia emissions of spraying, deep injection of manure
By CAROL RYAN DUMAS
KIMBERLY, Idaho -- Research shows injecting dairy manure 12 inches below the soil surface results in 67 percent less ammonia emissions than laying it on top of the soil or mixing it in a few inches below the surface.
The practice also reduces odor and better captures nitrogen for crop use, resulting in decreased need to purchase fertilizer.
"That (odor reduction) would make their neighbors a lot happier," said lead researcher April Leytem, soil scientist at USDA-ARS Northwest Irrigation and Soils Research Laboratory in Kimberly.
Also, because the manure is underground, there'd be no potential runoff issues, said ag engineer Dave Bjorneberg, the lab's research leader.
The research was aimed at the sludge left in dairy lagoons, which dairymen empty every two to three years.
"Control of ammonia emissions is important from an air-quality standpoint, and it conserves nitrogen for crop use," Leytem said.
The research, done in cooperation with four southern Idaho dairies, compared applying manure to cropland through surface broadcasting, using a rolling tine aerator to incorporate manure in the top few inches and injecting it 12 inches below the surface.
Researchers found there was virtually no difference in emissions when broadcasted or with shallow incorporation, but there were 67 percent less emissions with the subsurface injection.
The aeration method mixed the manure a little with the soil, but it was still on the surface, Leytem said.
"It has to be below the surface of the soil to reduce emissions," Bjorneberg said.
Injecting the manure produced about the same result as applying no manure, he added. A dairyman could get the same results, however, if he applied the manure and immediately tilled it in.
Ammonia emissions can form particulates in the air, which can harm humans, harm vegetation or pollute water, Leytem said.
"The ammonia is going someplace," Bjorneberg said. "You can control it here (in the soil) and use it; you're not putting it somewhere you can't control it."
Dave Roper, a Kimberly pork producer and past president of National Pork Producers Council, secured a $395,000 conservation innovation grant from Natural Resources and Conservation Service to fund the study.
EPA's intention to regulate air quality on livestock operations, a growing number of nuisance lawsuits by environmental activists and lack of scientific data fueled Roper's desire to study deep-soil injection as an effective option.
He also owns Magic Valley Products, a company that desludges lagoons, and was able to perform the field work for the study. He's been using injection for the past 15 to 20 years.
"But it was never compared to airway injection (incorporating manure in the top few inches); that's why we did the study," he said.
The study didn't address the economics of the different management practices. The cost to pump and inject the sludge is 1 cent to 1.5 cents a gallon, which one cooperating producer said was cheaper and quicker than conventional methods of hauling it to application sites, he said.
An unintended bonus of the research was that it showed injection captured 200 to 400 units of nitrogen, compared with not even 30 units in broadcast application. And 80 percent of the nitrogen from the manure was available to the crop in the first year, he added. That compares to about 33 percent when manure is applied on the surface.
"Farmers who have done this are sold on it," he said.
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