Reducing ammonia loss in manure

MARSHFIELD, Wis. — Ammonia is a major component of dairy manure susceptible to being lost to the atmosphere during spreading. Injecting manure in the soil versus applying it on top of the soil is proven effective for retaining ammonia and preventing its escape into the environment.

Using low disturbance injection to reduce ammonia losses in dairy manure has been a focus of research for the U.S. Department of Agriculture’s U.S. Dairy Forage Research Center. A key area of scientists’ work at the University of Wisconsin’s Marshfield Agricultural Research Station was to examine low disturbance manure application, especially in hay fields, versus the traditional approach of broadcasting manure on the surface without incorporating it into the soil.

Eric Young is a research soil scientist in the Environmentally Integrated Dairy Management Manure Management unit with the U.S. Dairy Forage Research Center. Before he came on board in 2018, his predecessors looked at shallow disc injection and using an aerator to poke holes in the soil with the idea of increasing infiltration of the manure.

“This gives liquid manure a place to go and get under the surface,” Young said. “It showed quite a bit of promise, particularly shallow disc injection where a large disc creates a crease or slot in the soil where manure is placed and then covered back up. There are a whole bunch of companies that make these products now.”

Young said using low disturbance injection to reduce ammonia losses from liquid dairy manure reduces and minimizes tillage where possible, so the soil will not be disrupted or erosion increased.

“The ultimate in low disturbance is no till – using coulters or discs to open and close the soil,” Young said. “Low disturbance manure injection gets manure under the surface of the soil, which reduces that ammonia loss. Ammonia is very volatile. We’re really limited in terms of trying to capture that ammonia unless we do some kind of physical disturbance to the soil.”

Approximately half of the total nitrogen found in liquid dairy manure is in the ammonia end form, Young said.

Research at the Marshfield farm showed immediate incorporation of manure into the soil can create a reduction in ammonia losses of around 90-95% compared to broadcasting manure on the surface.

“This level would be achieved with plow tilling,” Young said. “For example, a farm could apply liquid manure in the spring when ready to plant corn and come back through with a disc or chisel plow to incorporate manure into the soil. You see a little less reduction in ammonia loss when using no-tillage tools.”

Young said a shallow disc produces decent results above 90% reduction in ammonia loss, whereas an aerator-band system would be less effective, reducing ammonia loss by two-thirds to three-quarters. Both units can be used in hay fields or corn fields.

“A shallow disk injection unit more effectively reduces ammonia and other soluble nutrient losses in runoff than an aerator-band unit,” Young said. “The aerator doesn’t quite get it in the soil as effectively.”

In addition to ammonia capture, Young said another benefit of these systems pertains to water quality and runoff.

“By mixing that manure into the soil, it’s less vulnerable to runoff during rain events and snowmelt losses,” he said. “If manure is broadcast on a corn field or hay field versus being incorporated into the soil, it sits on the surface and is much more vulnerable to being lost in surface runoff.”

At the Midwest Manure Summit Feb. 26 in Green Bay, Dr. Horacio Aguirre-Villegas, a scientist at the University of Wisconsin-Madison, shared results from a study on ammonia emissions from conventional, organic and grazing dairy farms. During his presentation, Aguirre-Villegas highlighted how the farms’ unique management practices impacted how much ammonia was emitted.

Thirteen dairy farms were modeled: five conventional, five organic and three grazing. Farms ranged in size from 50-1,000 lactating cows and maintenance animals. Aguirre-Villegas said diet composition determines the nutrients in excreted manure.

“Organic and grazing dairies feed more pasture and forages which have more crude protein and nitrogen in the diet,” he said. “Higher crude protein results in higher nitrogen excretion that has a potential to be emitted as ammonia throughout manure storage and land application. During the grazing season, manure is excreted on the pasture in small pockets, creating high concentrations of nitrogen, which might not all be utilized by growing pastures as opposed to a controlled application of manure on growing crops when manure is stored and land applied.”

The study revealed farm size does not significantly affect results when expressed per excreted manure. Despite a reduced surface area exposed to wind because it is stacked, solid manure has higher ammonia levels than other forms of manure due to its higher pH, which is one of the main drivers of ammonia emissions, Aguirre-Villegas said. When looking at storage, the average pH was 7.4 for liquid manure, 7.8 for slurry, and 8.5 for solid manure.

Liquid manure or slurry, which has less total solids, has higher infiltration rates into the soil, and therefore reduced ammonia emissions from land application. Barns have the lowest ammonia emissions when compared to stoarge and land application, except for two organic farms with bedded packs, as those create ideal conditions for ammonia to be emitted. 

“Higher temperatures create more opportunity for ammonia to be lost,” Aguirre-Villegas said.

The study revealed that the top practices for reducing ammonia emissions were solid liquid separation and injection, which reduced ammonia loss by about 40%. Injection alone lowered ammonia loss by 30%. Reducing crude protein in the diet reduced ammonia loss by more than 20% as did a combination of anaerobic digestion, solid liquid separation and injection. However, anaerobic digestion and solid liquid separation without injection could increase ammonia emissions Aguirre-Villegas found if proper management is not applied. Furthermore, he found compost increases ammonia emissions by 25% from high temperatures and aeration caused by turning the compost.

Research conducted at the UW-Marshfield Agricultural Research Station is aligned with the Ruminant Farm Systems model for testing and validating best practices, such as manure incorporation and crop rotation on nutrient losses. This whole-farm simulation model is designed to simulate all major nutrient flows on a dairy farm, including manure generation and nutrients in manure, as well as milk production. Young’s role in its development includes soil and water module aspects.

“We’re honing in on crop production, fertilizer, manure, runoff and nutrient cycling in the field,” he said. “A lot of our work up at the station is designed to help test that model by applying different types and rates of manure. The model will take this into account and provide recommendations.”

For example, if a farm has 100 acres and applied X amount of manure to a field that has been in corn for three years in well-drained soil with a certain pH, the RuFaS model will calculate nitrogen recommendations based on those inputs.

“You can look at these cascading levels across the whole farm and change different variables and test different scenarios,” Young said.

The RuFaS model is still in development and will be free for all to access once available.