Composting Horse Manure

Courtesy of extension

Composting horse manure is relatively simple but does involve more than simply piling the water. While many farms stockpile their manure, few truly compost. Composting is essentially managed decomposition. Managing the process can virtually eliminate odor, flies, weed seeds and internal parasites found in horse manure and create a valuable soil amendment for resale or for pasture application. To manage a compost pile, the following factors must be taken into consideration: carbon to nitrogen ratio, oxygen, moisture and temperature.

The microorganisms found in compost are most active when their diet contains about 30 times more carbon than nitrogen, or a C:N ratio of 30:10. Horse manure’s C:N ratio is typically 40:1 due to the large amounts of bedding mixed with it but generally doesn’t require additional nitrogen provided it has enough moisture and oxygen.

Composting is an aerobic process, that is, it requires oxygen. If a compost pile doesn’t get enough oxygen, these anaerobic conditions can result in unpleasant odors, such as those normally associated with stockpiling manure, and slowed decomposition. There are several ways to provide oxygen to a compost pile. The most common way is to turn the pile. For large piles or windrows, turning is generally done using the bucket of a tractor or front-end loader. For smaller piles, a pitchfork will certainly get the job done; but for these operations, you may want to consider using an aerated, static-pile design, which doesn’t require turning.

Typical horse-stall waste tends to be dry and will need added moisture to create the ideal conditions for compost microbes. The moisture content should be about 50 percent, or roughly the consistency of a wrung-out sponge. If rainfall does not provide enough additional moisture, the pile may need to be watered periodically. On the other hand, too much water can also be detrimental, displacing oxygen inside the pile and causing anaerobic conditions. If environmental conditions such as rain or snow are providing too much water, the pile may need to be covered. Some compost-storage designs call for permanent roofs, but properly anchored plastic tarps can be just as effective.

Compost Trouble Shooting
Problem Possible Cause Remedy
Fresh manure, but pile won’t heat up. The pile is: 1) too dry,
2) too wet; and/or
3) Outside temp is too cold.
1) Add water evenly to pile.
2) Aerate and cover.
3) Wait for warmer temps and turn as needed.
Pile was hot, but now temps are falling. 1) Pile is settling.
2) Moisture is less than 50 percent.
1) Turn pile; and/or
2) Add water evenly to pile.
Pile is more than 160-degrees F and has gray ash-like mold. Pile is too dry. Add water evenly to pile.
Pile has gone through two or more heat cycles but still has some material that has not decomposed. Wood shavings decompose slowly. Ensure pile has proper moisture content, add water if needed.
Pile emits bad odor. Pile is too wet and has become anaerobic inside. Turn to aerate and increase water evaporation, apply cover to limit additional rainwater.

* Table does not include all scenarios

One of the best ways to monitor your compost pile is by using a thermometer. Compost thermometers should have a probe at least 36 inches long and are available through many garden supply stores. The goal is to have sustained temperatures of 130- to 150-degrees F in the pile interior. This will optimize decomposition and also kill pathogens and weeds.

Compost-pile design and storage facilities will depend on the size of the operation and the equipment available. For a farm with two to six horses, small static piles, which use perforated PVC pipes to draw in air and don’t require turning, may be ideal. While not necessary, the use of multiple bins can allow separation of distinct batches. In this situation, horse manure should be piled approximately 5 to 8 feet high with a base that is two times the width and length of the height. For example, a 10-foot by 10-foot bin could accommodate a pile that is 5 feet high. PVC pipes should be placed after the pile is about 1 foot high so that the ends remain visible as more manure is added.

For larger farms with access to bucket loaders, manure spreaders and/or specialized composting equipment, larger piles or windrows may be the most efficient design options. These piles may be slightly larger in height and width and considerably longer but will require periodic tuning.

Compost will decompose more efficiently if the mix is uniform. Starting with a uniform mix is even more important in the case of static piles, since they will not be turned during the decomposition process. Some farms utilize a temporary storage and mixing area to aid in this process.

Benefits of Composting

  • Creates valuable soil amendment
  • Stabilizes nitrogen into a slow release form
  • Avoids the problem of nitrogen immobilization
  • Reduces manure volume by 50 percent
  • Destroys weed seeds, fly larvae and internal parasites
  • Eliminates or reduces the cost of off-site disposal