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Windrow Composting

Article-Windrow Composting

Iowa State University researchers find windrow composting to be a workable emergency cattle disposal method

If a disease outbreak akin to Great Britain's 2001 foot-and-mouth disease crisis were to hit the U.S., it would require the emergency disposal of millions of animals. Imagine the environmental and logistical implications on cattle-rich states in the High Plains.

Iowa State University (ISU) may have part of the answer if such a luckless reality came to pass. New research shows emergency composting could be part of the disposal solution.

“We've learned we can break some of the rules and composting will still work,” says Tom Glanville, ISU associate professor of agricultural and biosystems engineering. “The emergency composting process may be a little slower, but it gets the job done.”

Emergency composting may be one of the only viable solutions should a disaster occur, he says. Many states have limited or no rendering capabilities, and a plant's capacity could be exceeded in the event of large-scale death loss.

“You don't want to transport infected carcasses to a remote location in any event,” says Don Reynolds, associate dean of ISU's College of Veterinary Medicine. “Emergency composting can be done on the premises.”

On-farm burial could lead to water pollution. In every 1,000 lbs. of carcass, for example, are 22 lbs. of nitrogen and 8 lbs. of phosphorus, notes Glanville, who worked closely with Iowa's Department of Natural Resources on emergency composting. Burial could pose problems in states such as Iowa, where nearly 40% of the land has shallow bedrock or a shallow water table, he points out.

Incineration is another alternative, but it requires high-temperature, high-capacity equipment to avoid serious air pollution.

“This can be expensive, and incineration didn't go over well in Britain,” Glanville adds.

Composting protects biosecurity

After composting more than 54 tons of 1,000-lb. cattle in the past three years, ISU researchers found on-farm emergency composting offers affordable, immediate carcass containment that reduces air pollution and disease transmission potential. In addition:

  • Composting can be achieved by using typical farm equipment and common agricultural products such as corn stalks, silage and straw.

  • Composting works when the ground is frozen.

  • Composting keeps potential water pollution away from groundwater.

“Emergency composting, done properly, minimizes risks and increases biosecurity,” Reynolds says. “We feel very secure in this because we introduced viruses into the compost piles to see if strains could escape. We stationed sentinel animals (pathogen-free chickens) in cages located 10 ft. from all sides of the composting test units and had no problems.”

The scientists found windrow composting systems made with ground straw, ground cornstalks, wood chips or corn silage to be well suited for emergency livestock disposal.

“These can be easily sized to fit varying quantities and sizes of carcasses,” Glanville notes.

Windrow composting

Building a windrow involves laying down an absorptive base layer, positioning a single layer of beef carcasses on the base and covering the carcasses with more coarse-textured material. Plan on using 12 cu. yds. of cover and base material per 1,000 lbs. of carcasses. This is equivalent to 3.2 tons of corn silage, 1.4 tons of ground cornstalks or 1 ton of ground hay or straw.

Narrow-row widths improve the oxygen concentration at the center of the pile. ISU recommends a maximum base width of 16-18 ft./1,000 lbs. of cattle. Carcass-loading rates shouldn't exceed 1 ton for every eight ft. of row length. Here's what else ISU researchers have learned about successful emergency composting:

  • Oxygen

    While turning the pile to maintain a desirable oxygen concentration is typical in routine composting, it requires time and mechanized equipment, and could pose a biosecurity hazard in emergency composting.

  • “We've never turned one of our compost windrows, which breaks one of the rules of traditional composting,” Glanville says. “We just put the cows in there and leave them until they're done. It works, and it improves biosecurity.”

  • Moisture content

    One of the most important factors of successful composting, Glanville says the windrow will be too dry below 40% moisture but too wet above 65%.

    “You don't need to run lab tests to identify appropriate moisture levels,” he adds. “Use the squeeze test. Materials with 40-65% moisture should feel moist, but you shouldn't be able to squeeze water out of them.”

  • Carbon:nitrogen (C:N) ratio

    While the ideal C:N ratio for composting ranges from 20:1 to 30:1, bacteria will still break down organic material, though more slowly, at C:N ratios as low as 10:1 and as high as 50:1.

    “A lot of literature on composting stresses the perfect C:N ratio, but forget it,” Glanville says.

  • Temperature

    ISU researchers found compost windrows that were started in warm weather break down 1,000-lb. beef carcasses in 6-7 months; windrows started in cold weather will break down carcasses in 10-12 months. Large bones that aren't broken down can be crushed with a hammer-mill spreader.

“We thought the compost would create good fertilizer, but it didn't,” Glanville notes. “It's not nearly as good as nutrients from routine composting. The system does offer a good solution, however, for disposing of large carcasses on an emergency basis.”

For more information on emergency livestock composting, visit

Darcy Maulsby is an agriculture writer based in Granger, IA.