Angela George: Monitoring manure pits to tackle greenhouse gas emissions

PRO-DAIRY
Animal Science
Climate Change

Understanding how much methane comes from farm manure pits will help farmers make informed decisions as they seek to reduce methane emissions.

Angela George is a dairy environmental specialist with the Dairy Environmental Systems group of PRO-DAIRY. She focuses on researching greenhouse gas and methane emissions, utilizing renewable energy from dairy waste and assisting farmers with manure management.

We spoke with Angela about her latest research project focused on baselining greenhouse gas (GHG) emissions from dairy manure storages.

Why should we be concerned about GHG emissions from dairy manure storages?

Dairy manure primarily emits methane gas, but it can also emit varying levels of carbon dioxide, nitrous oxide and other gases depending on manure treatments and handling. Methane receives the most attention because it traps heat in the atmosphere 28 times more effectively than carbon dioxide. At the same time, it only survives in the atmosphere for 12 years. By reducing methane emissions now, we can expect to see positive climate changes relatively soon.

How is dairy manure currently stored?

Dairy manure storage varies depending on the size of the farm and the region in which the farm is located. Here in the northeastern United States, liquid dairy manure is commonly stored in an engineered earthen pit designed to hold it for months at a time.

In the past, storages were typically lined with a layer of clay to keep the manure from seeping into the ground. More recently, any newly built storages are required to have a high-density polyethylene liner to keep the manure contained.

Farmers will generally store manure during the winter, land apply the manure on their fields as fertilizer in the spring before they plant crops, allow the storage to refill during the summer, and then empty the storage again for fall application after the crops have been harvested. Smaller farms, usually 100 cows or less, that may not have the space or need for a storage pit may land apply the manure on the field daily as it accumulates.

a man stands in front of a manure pit on a farm — Jason Oliver, senior extension associate & dairy environmental systems engineer with PRO-DAIRY, carries the GHG analyzer in a backpack as he monitors manure pit emissions. The analyzer samples the air every second. Photo by Allison Usavage.

Your project looks at 12 different farms that use varying types of manure treatments. Can you tell us a bit about the differences between them?

Manure treatments vary quite a bit. Some farms scrape the manure straight from the barn to the manure storage pit. Others use solid-liquid separation, where the solid portion is reused as bedding for the cows and the liquid portion is stored in the storage pit.

We also have some farms that utilize an anaerobic digester where microorganisms consume the solid particles in the manure. This is followed by solid-liquid separation. Lastly, some farms co-digest food waste and manure in an anaerobic digester and also utilize a solid-liquid separator.

So even though the farms may treat the manure differently, they each have a manure storage pit that is producing some amount of methane?

Yes, that’s right. Once a month, we analyze the GHG emanating from each farm’s manure storage pit and pair that data with Global Positioning System data and wind data, among other things, to estimate how much methane the storage is emitting at that time.

In addition to monitoring the methane concentrations around the storage, we also take samples of the manure before it enters the manure storage and after it is drawn out to be applied to the field. We analyze each of these samples in a lab to see what kind of changes happened to the manure while it was being stored, such as changes in nutrient content, pH and solids content.

three people stand looking at a manure pit while a drone flies overhead — George and her colleagues use a drone-mounted gas analyzer to collect air samples from varying heights for a more comprehensive idea of the methane plume from a storage pit. Photo provided.

Once you know how much methane each manure pit produces, then what?

By working with these farms that have different types of manure treatment, we hope to be able to determine how effective treatments such as solid-liquid separators or anaerobic digesters are at reducing methane. We also want to discover if the models used for methane, from both untreated and treated manure, are accurate.

In the end, this information will be useful to farmers looking for ways to reduce on-farm methane emissions. Policymakers and state officials developing future climate policy and programs to regulate emissions from dairy farms should also find our research helpful.

When will we learn more about your research into baselining GHG emissions from dairy manure storages?

We just completed our first year of data collection and have another year remaining. Once we’re done, we will analyze the two years of data together and publish a full research paper. We also intend to produce extension materials and host educational sessions for farmers and other interested parties.

Jackie Swift is the communications specialist for the Cornell CALS Department of Animal Science.