Composting economical, environmentally friendly option

STRATFORD, Wis. — Rising costs and regulations are decreasing the options farmers have for disposing of carcasses, an unfortunate inevitability on all livestock farms.

Heather Schlesser, a dairy agent with University of Wisconsin Extension, explained strategies and methods for one option — composting — Oct. 22 at the University of Wisconsin Marshfield Agricultural Research Station near Stratford.

“Mortalities happen,” Schlesser said. “It’s a part of life that animals die.”

Options for carcass disposal include rendering, burying, burning and composting.

Rendering services have become costlier and harder to find. Burying is allowed in Wisconsin but frowned upon, Schlesser said, because the carcass stagnates in anaerobic conditions, increasing the chance for groundwater contamination. Burning carcasses properly requires the expense of an incinerator to minimize air pollution.

With those limiting factors, composting mortalities is becoming an increasingly popular option on dairy farms.

Composting is an aerobic process requiring oxygen, a carbon source and a nitrogen source, which is the carcass, Schlesser said. Microbes work to break down the organic matter, leaving humus as the final product that can be put back on the land as a fertilizer.

Composting helps ensure farm biosecurity and is affordable.

“It’s low-cost because most farms have everything needed to compost,” Schlesser said. “Farms have the equipment to build and maintain the pile, and the carbon sources needed to create the pile. If it is done correctly, composting is low-odor and environmentally friendly, providing a rich amendment to incorporate into soil.”

One of the first considerations in composting is the location of the pile on the farm, Schlesser said, noting that farms operating as a Concentrated Animal Feeding Operation will have to file an application before composting.

“The state is most concerned that you pick the right spot to put your pile,” Schlesser said. “The main thing for any size farm is to avoid wet areas. Don’t put your compost pile in a wetland. First, we don’t want that much water because it will affect the process; but also we don’t want to put our dead animal where it’s going to seep into our water supply. You want to be at least three feet above the high water table. You also need to be at least 250 feet from surface water and property lines.”

Schlesser cautions to consider where private wells are located, both on your property and neighboring properties. Composting piles need to be located at least 1,000 feet from state highways, interstates, public parks or state natural areas and 1,200 feet from any public wells.

Piles can be built on concrete or gravel pads or on a grass pad that has been skimmed, Schlesser said.

“You have to provide for leachate collection and preventing stormwater runoff,” she said. “We’re providing for that by putting in our sawdust base to make sure our pile doesn’t leak. It’s important to ensure that you can access it in all weather, to add carcasses, to monitor and turn the piles, to add carbon sources. Maintain suitable access to your carbon sources, too, and consider other farm traffic.”

There are three ways to compost: static piles, trenches and improved trenches.

A static pile is one that will be undisturbed during the initial heating phase. Multiple static piles can be placed next to each other, creating a windrow effect.

“To build a static pile, you want to start with a base that is at least 24 inches deep, using a coarse material so it can breathe,” Schlesser said. “The oxygen is going to come in through this base to feed the bacteria that are in it. You’re going to place the animal on it, making sure it’s at least 18-24 inches from the edge of the pile. Then you’ll cover with at least another 24 inches of bioactive material.”

Certain areas do not allow static composting because of predator pressure, Schlesser said, making the best option in those areas an improved trench. To build an improved trench, a 24-inch-deep trench is dug at a width to accommodate the animal. A base of 24 inches of a carbon source is laid in the trench to help keep it aerobic, promoting the composting process. The animal is placed on the carbon source, then covered with another 24 inches of bioactive material, and finally covered with the soil that was removed from the trench.

The carbon source used as a base is an important consideration, Schlesser said. The carbon source is typically some type of bedding material, such as hay, corn stalks, shavings or wood chips and bark; that will allow adequate oxygen flow without being so porous that it allows seepage through.

“The optimal ratio for carbon to nitrogen is 25 to 1,” Schlesser said. “It’s kind of a forgiving process, as long as you have more carbon than nitrogen available. The main thing is to make sure your carbon source, especially the base layer, has enough absorption properties that when the animal starts to decompose and gets into the liquefying stage, we don’t end up with leachate or seepage from the pile.”

Schlesser noted that it is important to use some sort of tool to puncture the rumen of the animal before covering, to prevent the organ from exploding and opening the pile.

The moisture content of the compost pile plays an important role, Schlesser said.

“Our piles need to be wet, but not too wet,” she said. “We want the moisture range between 45% and 60%. If it’s too dry, we get poor bacterial growth. If it’s too wet, those bacteria suffocate. Both lead to poor decomposition. It should clump in your hand, but water should not run out of it.”

The compost pile needs to be regularly monitored as the decomposition process begins, Schlesser said. The pile’s temperature should be checked daily, using a 36-inch probe thermometer. The pile needs to actively heat to a range of 110 to 150 degrees, ideally reaching 130 degrees for at least three consecutive days to kill all pathogens. Between 7 and 10 weeks, the pile needs to be turned to add more oxygen to create a second heating cycle. Once the pile cools to ambient temperature, it is typically considered completed and ready to be used as fertilizer.

“Done correctly, composting is an easy process that can work on farms of any size,” Schlesser said. “It’s relatively low-cost and environmentally friendly and provides a good source of organic matter that can help reduce commercial fertilizer needs. It takes a little time, effort and diligence, but most find the pros outweigh the cons.”