It may not work for every operation, particularly those with a lot of hogs, but composting is an interesting manure management option.
The process can help you stabilize manure before you haul and spread it. It produces a less objectionable material to spread near neighbors who might be prone to complain about odor.
But composting manure takes some effort. Outdoor temperatures and moisture levels can affect how well the process works. So can the carbon source you use.
University of Missouri researchers John Hoehne and Charles Fulhage mixed solids separated from hog manure with some low-value carbon sources. They looked at using old fescue hay and sawdust as carbon sources. Sawdust worked much better than fescue, even when the hay was chopped.
Hoehne and Fulhage found winter temperatures can get low enough to stop the chemical process that renders the manure less offensive. They began by using 32-gallon plastic garbage cans. The surface of the cans got cold enough to drop the compost’s internal temperature as low as 81° F.
A good compost must reach 120° F to kill pathogens and up to 150° F to create a positive reaction in the manure. The researchers switched to bins 4 foot by 4 foot by 3 foot and got a better response. “Working with a small mass of compost was presenting problems,” Hoehne reports.
They aimed for a carbon:nitrogen ratio between 25:1 and 35:1. Moisture levels were between 55 percent and 65 percent. With fescue that meant adding water to the compost. They also found mixing the fescue was difficult.
The process eventually produced a material with a stable odor that was musty but not offensive, Hoehne reports. Weight of the material decreased about 35 percent over the 36 to 44 days the project ran.
“You lose mass,” Hoehne reports. That means less manure to haul and apply to fields.
In Missouri, composting is legal for dead animal disposal. It’s also allowed for manure, but check with your state regulators. You may need a permit, especially if you use a carbon source other than sawdust.
While the technique may work best on smaller operations, a large-scale production unit may be able to afford a mechanical solids separator that would help produce a better compost. Separators can cost up to $25,000, Hoehne points out.
For more information on manure composting, contact Hoehne or Fulhage. You can reach both at the University of Missouri at (573) 882-2731.