Composting Horse Manure for Environmental and Economic Benefits

Neely Heidorn  |  2/26/2012 7:59:37 AM

Checking the Temperature

Uses of a mixing wagon

Compost Bin

A typical horse weighing 1,000 pounds will produce approximately 50 pounds of manure and 10 pounds of urine per day. Horses that are housed in stalls may generate an additional 20 pounds of soiled bedding, depending on the type of bedding and the amount removed. Improper management of this waste has the potential to pollute Louisiana’s surface- and groundwater.

Composting is a great way to convert horse manure into a more desirable product. It is the acceleration of a natural biological process that converts organic matter into a stable humus-like material. Composting produces a material that can be used as a low-grade fertilizer, mulch for reducing weed infestation and soil amendment for retaining soil moisture. Land application of compost is also more environmentally friendly than stacking horse waste in low-lying areas and sinkholes or applying it directly to pastures. Besides volume reduction, as much as 50 percent composting kills unwanted microorganisms and weed seeds while creating a more stable nutrient source.

Important Issues

Monitoring the four factors listed below will ensure that the best product is obtained and will help the environment. The carbon to nitrogen (C:N) ratio of typical horse manure has a C:N ratio of approximately 10-18:1. However, commonly used bedding materials, such as straw and wood shavings, contain higher ratios. Approximately 80 percent of horse stalls are bedded with wood shavings, which may have C:N ratios of nearly 500:1. The blend of horse manure and bedding called muck will typically provide a C:N ratio of 50:1, which explains one reason why muck piles will not noticeably decompose over time.

Microorganisms need carbon (C) and nitrogen (N) to live, but they need these elements in the correct ratios. The ideal ratio is 30 parts carbon to 1 part nitrogen (30:1). Low C:N ratios (less than 20:1) provides more than enough energy for beneficial microorganisms to function. Therefore, compost piles with low C:N ratios will decompose somewhat slower and will properly lose N in the form of ammonia gas. Low C:N ratios can be a source of noticeable odor. Conversely, N is immobilized in compost piles with high C:N ratios (greater than 40:1), which also impedes the decomposition process.

Research has shown that raw horse muck applied to soils immobilizes the N in the soil creating forages low in N, which exhibit light green to yellow-green hues. The existing C:N ratio can be adjusted up by adding more C (straw, dried leaves, wood shavings, sawdust, dried grass, etc.) or down by adding N (green grass, ammonium nitrate, fecal material – manure without bedding material – etc).


Moisture allows compost to degrade properly by helping to mediate the temperature and provide a means of transportation for microorganisms. Ideally, the moisture content should be between 40 and 60 percent. Lower moisture contents allow the temperature to rise too high, which destroys beneficial bacteria and decreases decomposition rates. Moisture content above 60 percent reduces oxygen in the compost pile to make it anaerobic (without oxygen), which decreases decomposition rates and can cause offensive odors. (Although the sense of smell is subjective, an anaerobic smell can be described as a putrid odor similar to rotting garbage.)

Adjusting the moisture content is simple. If the moisture content is below 40 percent, add water. If the moisture content is above 60 percent, turn the pile every day to allow the compost to dry out. A quick method for determining the moisture content is to squeeze a sample of the waste in your hand. A pile is too wet if more than three drops can be removed and too dry if the palm of your hand is not wet.


Aerobic (with oxygen) decomposition is more efficient than anaerobic (without oxygen) decomposition. Aeration keeps the biological processes from becoming anaerobic and allows the compost to reach and maintain optimum temperatures. A common method of aeration is turning compost piles. Small, rotating drums can be used to store and turn the compost for small quantities. For larger quantities, windrows are formed and turned with a tractor and front end loader. The turning frequency depends upon the moisture content and temperature of the compost. Normally, the pile should be turned at least every seven days when the moisture content is between 40 and 55 percent. However, greater aeration (turning) in the initial stages of composting intensifies microorganism activity. The increased activity decreases the time and land area needed for composting.


Because the microorganisms produce heat, temperature is a good indication of the level of biological activity taking place. The ideal temperature range is 135 to 160 degrees F. Temperatures below this range require more composting time to kill pathogens and other unwanted pests, while temperatures above this range will kill beneficial bacteria needed for decomposition. It is best to maintain temperatures at approximately 150 degrees to kill the eggs of parasites, oocysts (dormant larvae in a capsule-like sac) and flies.

Temperature should remain constant until the compost reaches its final stage of curing. Compost is considered cured when, after turning and when optimum conditions are met, the core temperature does not rise more than 15 degrees above ambient temperature. A temperature drop prior to curing is a sign that microbial processes are being affected by a lack of moisture and/or oxygen. Thermometers with a 3-foot stem are recommended for easy monitoring of temperatures (Rynk et al. 1992). The temperature may be read directly off the dial. The easiest way to cool the pile is to lower the height; raising the height will allow heat to be retained. Another way to cool a pile down is to turn it more frequently.

Mixing and Handling the Ingredients

Beef and dairy manure, when available, are excellent sources of N for decomposing horse muck. Inorganic forms of N (34-0-0) can be added when N sources such as beef manure are not available. A simple way to lower the C:N ratio at the beginning of the mixing process is to add ammonium nitrate to the horse muck as the stall is being cleaned out. Research shows that only one-third pound (150g) of ammonium nitrate per horse per day must be added to reach proper conditions when wood shavings (not straw) are being used.

If proper moisture and air space requirements are met but the compost pile is not heating up, add 1/3 cup of a commercial nitrogen fertilizer. Mixing horse muck with other N sources to achieve the proper blend can be accomplished using a front-end loader, dump wagon or mixing wagon. Typical rules of thumb can be developed from practice. For example, a properly formulized compost windrow may require two front-end bucket loads of beef/dairy manure to three loads of horse muck Occasional turning of the pile is required to mix the windrow contents to allow the heat to destroy pathogens, cool the pile to prevent overheating and provide needed oxygen to beneficial microorganisms. Turning can be accomplished using a front-end loader; however, horse muck requires more mechanical aeration to break up the horse dung. Another method to accomplish turning is to use a mechanical turner.

Ways to Compost

Obviously, several factors remain the same regardless of the method used to compost. Some aspects of the pile, however, may vary depending on the volume of manure produced as well as the type of bedding material used. The factors that vary mainly deal with the dimensions rather than the content of the pile. Below are the suggested ways to compost manure in small and large volumes.

Bins and Vessels

Small farms (one to three horses) may need only small composting bins. The bins may be boxes, areas on the ground or cylindrical containers supported above the ground and rotated around an axis. While rotating bins look nicer and are easier to maintain, they have a higher initial cost and may not hold enough volume to generate sufficient temperatures to kill pathogens. In addition, rotating cylinders may not turn fast enough to adequately disintegrate horse dung. Therefore, rotating cylinders may not be the best choice. If bins are on the ground, they need sufficient drainage to keep the bottom of the pile from becoming too moist.


Larger farms (more than three horses) may need to use windrows for composting. The length of the windrows does not matter, but the height is crucial for proper composting. Short windrows will lose heat and moisture, decreasing rates of decomposition. Tall windrows will compress under their own weight, reducing pore space and hindering the aerobic process. Tall windrows also increase compost temperature by retaining more heat, which can kill needed bacteria.

Ideally, the windrow should be about 4-6 feet tall with a rounded top so rain will run off. Research has shown that properly managed windrows are able to destroy 99.9 percent of the harmful pathogens within four days of building and turning. The amount of time needed to properly decompose horse muck ranged from 12 to 18 weeks depending on the time of year and the moisture conditions. A covered composting structure has added benefits because, typically, the winter months slow down the decomposition process. Additional water can always be added to compost in a covered structure, but it is difficult to remove excess moisture from compost on an open lot when temperatures and precipitation events are working against you.

End Product

The final product should have a texture and color similar to peat moss or potting soil media. Stable compost can be applied to pastures and gardens and around trees and shrubs as a mulch or soil amendment. Stable compost will contain low concentrations of macro nutrients (N, P and K) with a ratio of approximately 2:1:2. However, if the compost material is not stable (continues to reheat when wet), it will require additional nitrogen. Studies have shown that the compost material will draw N from the soil after land applications have been made. Compost should be applied during the growing season. Excess compost may be stored, given away or sold.

Rate This Article:

Have a question or comment about the information on this page?

Innovate . Educate . Improve Lives

The LSU AgCenter and the LSU College of Agriculture