Uta Krogmann, Ph.D., Extension Specialist in Solid Waste Management, Michael L. Westendorf, Ph.D., Extension Specialist in Animal Sciences, and Barbara F. Rogers, Environmental Scientist
Compost from horse farms can be used as a soil amendment providing organic matter and some nutrients. Composting manure on small horse farms can be part of an overall effort to better manage manure and reduce non-point sources of pollution (nitrogen, phosphorus, and pathogens) to drainage basins in New Jersey. Composting produces a stable, volume reduced, and storable product with greatly reduced pathogen levels while conserving some of the nutrients. The compost can be used on- or off-farm when and where the nutrients are needed.
On-farm composting is only a solution when done correctly. If you do not have time and interest to compost, then other methods of disposal might be a better solution.
This fact sheet provides Best Management Practices (BMPs) for composting horse manure on small horse farms in New Jersey. These practices include information about horse manure production and characteristics, preparation of the compost mix, the composting operation and siting, monitoring and testing of manure and compost, environmental issues, compost use, and costs. These practices can be part of the nutrient management plan which may be required for all horse farms in New Jersey in the future. This fact sheet is for a reader who is somewhat familiar with the basics of composting. Useful sources for the basics of on-farm composting are Rynk (1992) and Dougherty (1999).
What is Composting?
Composting is a managed biological process that converts organic material into fine particled humus. A series of microorganisms decompose or digest the organic material. Oxygen must be present and heat is generated as the organic material decomposes. In this case, the organic material is horse manure.
Horse Manure Production and Characteristics
Horse Manure Composition: Horse manure is mainly composed of feces and urine but is often mixed with bedding material and feed. The amount and characteristics of horse feces and urine vary with horse type (pony, mature horse, lactating horse, etc.), body weight, feed (composition, intake and digestibility), exercise levels, and waste collection practices. The quantity of bedding and feed mixed with the urine and feces will vary for pasture horses and stabled horses, with waste collection practices and bedding material choice (see also RCE fact sheet, FS537, Horse Manure Management: Bedding Use). Minimizing the amount of bedding used will reduce the amount of total waste for disposal. Therefore, farms need to find the balance point in bedding amounts ensuring the horses’ health and minimizing waste.
Horse Manure Production: Horse manure production is variable and depends on horse physiology, horse management, and manure collection practices. A 1000 pound (lb) horse produces 31 lb of feces and 2.4 gal. of urine, which adds up to 51 lb/day. The amount of feces and urine ranges between 42 and 68 lb/day for 900–1300 lb horses. In addition to feces and urine, about 8 lb–15 lb of spoiled bedding is disposed per day per animal. Based on the above listed ranges for feces and urine and spoiled bedding, one horse produces a total of 50–83 lb/day. This equals about 1.5–3 ft3/day per horse.
Due to this variability in horse manure production, it is best if you measure the production on your farm before you size your composting facility. One way is to determine the weekly production by collecting the manure for one week in a cone-shaped pile and measuring height and diameter of the cone (repeat three times and take the average of the 3 measurements).
Bacteria and Other Pathogens in Manure: Horse manure contains bacteria and other pathogens that can be harmful to horses as well as humans. Parasitic roundworms, such as strongyles, are potential health problems for horses that ingest them. Pathogens such as Escherichia coli, Listeria monocytogenes, Salmonella spp. and Clostridium tetanican be present in horse manure and are pathogenic to humans. Protozoan pathogens such as Giardia spp. andCryptosporidium spp. can be found in horse manure and are known to cause waterborne human disease. Careful composting will help to reduce these pathogens.
Selected Chemical and Physical Characteristics: The chemical and physical characteristics of the horse manure need to be known for successful composting. Table 1 provides a summary of ten manure analyses collected from four different horse farms in Monmouth County, New Jersey (see also additional data for comparison). The manure piles sampled in Monmouth Co. each had different percentages of feces, urine, bedding, and feed. The table shows that horse manure piles have a wide range of moisture levels (44.3–71.2%), carbon contents (18.7– 47.5%), and bulk densities (160 –990 lb./yd3) while the other parameters did not vary as much. However, as indicated by the additional data, other parameters might vary as well. In general, the addition of bedding tends to increase the carbon content and reduce the moisture, nutrient, and bulk density of manure. If straw is used as bedding, the manure is more easily composted than when wood shavings are used (see also RCE fact sheet, FS537, Horse Manure Management: Bedding Use).
In summary, the characteristics of horse manure are variable and, therefore, should be determined carefully. It is very important that representative samples are sent to a commercial laboratory if using the manure for composting or direct land application. Guidance about sampling and testing is provided below.
Compost Mix Preparation
The right compost mix is necessary to ensure proper composting and a good final product.
Moisture, Oxygen Availability, and Particle Size: Water is needed for the growth of the microbes, transport of nutrients, waste product removal, and mobility of the microbes. A low moisture content slows the composting process. A high moisture content reduces open pore space and limits aeration (oxygen), because there is competition between air and water in the pores (see Figure 1).
The optimum moisture content varies depending on the particle size of the feedstock and the composting technology. The moisture content in the compost pile should be adjusted to 55–65%. If the horse manure contains bedding material that effectively absorbs water (e.g., wood shavings), the optimum moisture content is at the upper end of the range. In this case, a moisture content up to 70% is acceptable. However, care needs to be taken if very fine bedding materials are used that do not have any structure and therefore a low porosity (e.g., sawdust). In this case, at high moisture content sufficient aeration might be hindered. Consider replacing the very fine bedding with bedding that has a higher porosity.
While feces and urine may be too wet, the moisture content of the horse manure including the bedding material can range between too low and optimum (see Table 1). Water addition is needed if the moisture content is too low. In a few rare cases, the moisture content might be too high. However, because the bedding material generally adsorbs water and organic material dries during the composting process, no additional dry material is needed to balance the moisture content.
Carbon/Nitrogen (C/N) Ratio: C/N ratios that are too high slow down the microbial degradation and too low C/N ratios result in the release of nitrogen as ammonia, which is a source of unpleasant odors. Optimum C/N ratios at the beginning of the composting process are between 20/1 and 30/1. However, the C/N ratio can depart from this range if the carbon is not accessible to the microbes. For example, for woody feedstocks (such as wood shavings and sawdust) where a portion of the carbon is not accessible to the microbes, C/N ratios of 35/1 to 40/1 are considered optimum. The C/N of manure alone (feces and urine) is too low (Table 2), which will result in the release of ammonia when composted. However, if the bedding is added, the C/N is usually at optimum or too high. If the C/N ratio is too high, wastes high in nitrogen such as dairy manure or grass clippings can be added. The addition of a nitrogen fertilizer also decreases the C/N. However, generally, this is not a recommendable practice since the goal is to reduce the overall nutrient load.
Additional information about how bulking materials (in this case the bedding) help to prepare the right composting mixture can be found at Cornell Waste Management Institute (2004a).
Composting Operation and Maintenance
There are various methods of composting horse manure ranging from pile or windrow to undercover or in-vessel facilities (Dougherty, 1999). However, on small horse farms the choices are more limited because the purchase of dedicated equipment like a windrow turner is not efficient or affordable. Pile and shed composting are options for small horse farms. We recommend shed composting because of easier handling of the horse manure, aesthetics, and there is less likelihood of nutrient run-off and leaching issues. In addition, shed composting allows for batches to be kept separate ensuring pathogen reduction in the batch. If the pile method is chosen for economic reasons, facility siting needs special attention.
Siting: Buffer zones for composting facilities from residences and water sources are generally recommended to reduce water pollution due to leachate and run-off and air pollution due to odors (Dougherty, 1999). Make sure that you are in compliance with local ordinances. In the case of the shed composters (see description below) leachate and run-off are not an issue because the compost is under the roof. However, if the manure is collected in an uncovered storage area, if the pile composting method is used (see description below) or if curing (see glossary) takes place outside the shed, the appropriate buffer zones from water sources are recommended. More information about reducing water pollution while storing manure can be found in Wheeler and Smith Zajaczkowski (2002) or NRCS (2004).
Regarding buffer zones from residences, general on-farm composting recommendations include distances of 50 feet from the property line and 150 feet from residences and businesses (Dougherty, 1999). Furthermore, the facility should not be located in a flood plain unless protected against the 100-year flood event (NRCS, 2004). The bottom elevation of the composting facility should be above the seasonal high water table or installed on a concrete slab. For more information see NRCS (2004).
It is also important that the area around the composting site allows access to the composting site all-year round and is well drained. Wet weather can cause soils to become muddy making it difficult to access and turn the piles. The use of asphalt or concrete around the composting site is preferred when cleanliness and aesthetics are important objectives. However, this option is more expensive and adds a permanent structure to the farm. Gravel beds are another option. However, our own experience showed that, when gravel is used, it is difficult to keep the site clean.
There needs to be a way to provide water to the site in case the compost is too dry and water needs to be added.
Pile Composting: The horse manure is piled in freestanding hay stack type piles. Waste is regularly added to the pile until it is 4’–6’ tall. The site should have room for 2–3 piles so that the first pile can mature while you are building your next piles. Regular mixing (also called turning, see shed composter for turning frequency) is recommended to ensure pathogen reduction and enhancement of the process. During inclement weather this might be difficult to accomplish, in severe winter months you may not want to turn piles because incorporating ice tends to shut piles down. Pile composting is a simple and inexpensive option, but careful consideration of siting to prevent leaching and run-off is required.
The pile can also take the form of a windrow if you have more manure. A windrow is 6’–10’ wide x 6’ tall x as long as you have space. To produce compost with a finer particle size more turning will be necessary. If a higher nutrient and organic matter content is desired and the farm has space and time, good stacking with a minimum of turning will make a good product. Again, careful consideration of siting to prevent leaching and run-off is required.
Shed Composter: A shed composter consists of several three-sided bins. (Figure 2). When designing the shed composter, make sure that the bucket of your front-end loader fits into the structure. The manure can be collected in one bin at a time or a storage area that already exists on the farm. When the manure pile in the bin reaches 5 feet high, the contents should be turned into the next bin and the first bin refilled. The pile height should not exceed 6 feet to ensure that the compost is aerated. Bins can be covered with a roof to reduce possible run-off. Because the bedding material is very absorbent, generally, no leachate is generated under the roof.
For turning, a front-end loader (skid loader with 1/3 yd3 bucket or tractor loader with 1 yd3 bucket) transfers the compost from one bin into another bin. The purpose of turning is to move the outer portions of the pile into the hotter inner portions of the pile for pathogen and weed seed reduction, to homogenize the pile, and to aerate the pile to some degree. Turning has only a partial effect on aeration because the oxygen is used quickly after turning and the oxygen content in the inner portions of the pile decreases within hours after turning. That is why both moisture and particle size are important. Generally, the requirement for the turning frequency to ensure pathogen reduction in windrows is 5 times in 15 days while keeping the temperatures above 131oF (USDA, 2002). Since it is not realistic for farmers on small farms to turn the piles 5 times during the first 15 days, weekly turning is suggested. This reduces pathogens in the compost, however, does not comply with the requirements for compost used in organic agriculture.
After 3–4 months, compost turning can be reduced to once per month. At that time, the compost from two bins can be combined in one bin to compensate for volume reduction, which results as the material decomposes through the compost process. If necessary, water can be added during turning to adjust the moisture content to 55–60%. Towards the end of the composting process, the moisture content does not need to be adjusted to 55–60% because a lower moisture content is preferable when the compost is stored, transported, or used. If the bins are full before 9 months, the compost should be moved outside the bins to a dry, well-drained area. It is preferred that the compost is moved outside the roofed area after 3–6 months at the earliest. Possibly if stored outside, the compost should be covered loosely with a tarp or fleece until it is used. There are certain fleeces available that prevent rain from entering the compost but allow gas and water vapor exchange. Additional on-farm composting information or information about troubleshooting can be found in Dougherty (1999).
The sizing of the shed composter depends on the amount of horse manure collected. The amount collected from one horse can vary considerably. Table 3 gives an example calculation of how much space is needed to compost the manure from one horse. Ranges are given. The lower numbers of the ranges are the calculated volumes and area requirements assuming a bulk density of 31.3 lb/ft3, a volume reduction of 50% during the first 3 months and a pile height of 4 feet. The upper numbers of the ranges include 50% additional space for varying manure production and possible expansion of the facility. In addition to the space for composting, space to access the composting area and to maneuver a front-end or skid loader is needed.
Fires: Spontaneous combustion in composting piles are rare, but they have happened. The general rule to avoid spontaneous combustion in composting piles is: “Small is beautiful and wetter is better” (Buggeln and Rynk, 2002).
Monitoring and Testing
The initial raw manure needs to be tested to determine the appropriate compost mixture, the composting process needs to be monitored to ensure it proceeds well, and the final compost should be tested to ensure its appropriate end use.
As a first step when considering composting horse manure, the initial raw material characteristics need to be determined. An initial laboratory test of key feedstock characteristics such as moisture, pH, and C/N ratio is suggested. Organic matter and nutrient content also could be useful.
While composting, temperature and moisture content in the compost should be monitored and recorded. Within a few weeks the horse manure is partially degraded and the squeeze moisture test can be used to determine the moisture content. If compost releases water when a compost sample is squeezed in your hand, it is too wet. Water needs to be added, if the compost breaks apart after squeezing a sample in your hand. Temperatures need to be recorded regularly. While daily measurements would be best, temperature should be measured at least weekly. A temperature probe (thermometer with a 3–5 foot stem) should be placed in the center of the pile at different locations. Backyard composting thermometers can be found through the internet. Alternatively, your local Extension office might be able to help to locate a temperature probe. If an oxygen meter is available, it is also useful to measure the oxygen level in the compost. Oxygen levels should be above 5–10%.
The final compost should be tested occasionally in a laboratory for moisture content, pH, conductivity, C/N, nutrients and maturity (e.g. respiration activity). There are additional laboratory analyses such pathogen levels or seed germination that might be useful, but costs might be prohibitive.
Representative sampling and the selection of a laboratory that is familiar with manures and composts is essential. CWMI (2004b) provides some guidance about sampling and testing.
If managed appropriately (sufficient aeration), odors released from composting horse manure on small farms are less of an issue. However, stronger odors are expected when the horse manure compost is turned. If wood shavings are used as bedding material, and if the composting is operated properly, after several turnings the compost releases an earthy smell during turning.
Bioaerosols (see glossary), primarily Aspergillus fumigatus are of potential concern to the health of operators of composting facilities and the neighboring communities. Typically, the general public is not affected, but immune compromised, asthmatic and allergic persons may be at risk (Millner et al., 1994). A final risk assessment has not yet been conducted. However, our measurements confirmed that Aspergillus fumigatus spores (indicator for bioaerosols) are predominantly released when the compost is turned. After turning, if the compost is at rest, the levels are quickly reduced to typical farm background levels. It is suggested that persons at risk avoid the compost area during turning. Be aware of wind speed and direction during turning, which is when most odors and other airborne materials would be released. Be considerate of neighbors and don’t turn when they are most likely to be outdoors. As with other dust generating operations on the farm, wearing a dust mask might be useful.
Appropriate management of pests such as flies and small rodents does not only apply to composting of manure but to manure management in general. More details can be found in Wheeler and Smith Zajaczkowski (2002).
The investment costs for shed composters may be as high as $5,000 per horse with half of the composting area under a roof. The investment costs for the pile composting would be considerably less.
Overview: If the farm has enough acreage requiring nutrients (about 1–2 acre/horse excluding wetland or erodible soil) the compost can be used on the farm. If not, the compost should be used off-farm.
Compost can be applied to soil as a soil conditioner, mulch, or a supplemental nutrient source for plants. The specific end use of horse manure compost depends on the quantity and form of nutrients present in the compost, which will vary depending on the initial horse manure characteristics, the composting operation, and the compost maturity. Compost maturity or stability (see glossary) is a measure of a compost’s readiness for use. Compost that is not matured or stabilized can harm plants and seedlings either by harmful break down products or by depletion of the soil of nitrogen (nitrogen immobilization) that is needed by the crops to grow.
Compost adds organic matter to the soil and can benefit soil structure, aeration, moisture retention, and permeability, but should be managed in a way to maximize plant utilization of nutrients and minimize runoff and leaching of nutrients. The major fertilizer nutrients of horse manure compost are nitrogen, phosphorus, and potassium. However, horse manure compost also contains the secondary nutrients magnesium, calcium, and sodium as well as micronutrients. The availability of these plant nutrients varies depending on the compost maturity, soil type, and timing of the application. When applied at the optimum time, horse manure compost can be a supplemental nutrient source for pastures, field crops, and horticultural crops. The horse manure compost should be included in a nutrient management plan since it does add nutrients and minerals to the soil. Also, depending on the amount of manure in the initial compost mixture, P levels in the soil (Mehlich-3 method) should be monitored and a P-Index determined for each field. Interpretation of the soil P level can be found in Heckman (1998).
The C/N ratio and organic matter content of the horse manure compost decreases with age (see Table 4). When the compost has a higher C/N ratio and organic matter content the compost should be used as a soil conditioner or mulch. When the less mature compost is incorporated in a field, sufficient time between application and planting should be provided to allow for stabilization.
Horse manure compost applications and use should be based on compost characteristics including compost maturity, soil test results, and crop needs. Different end uses require composts with different characteristics (for more information see CWMI (2004c and 2004d)). The Monitoring and Testing section above discusses how to determine the compost characteristics. Soil test results give an indication of the fertility status of the soil. For example, a soil test determines the P level of a pasture helping to determine if an additional P source such as compost should be applied. The crop needs determine how the needs of the crops can be matched with the nutrient levels of the compost.
The compost can be used as mulch or on pastures after 3 months. Take into account that the compost might still deplete the soil of nitrogen that is needed for crop growth. For other uses the compost needs to be composted 6 to 9 months. For composts whose source material was high in wood chips composting for more than 9 months might be necessary. Generally, turned compost takes 9–12 months to mature , stacked will take up to 2 years.
Timing of Application: Compost should be spread in the spring or a month before planting to ensure maximum nutrient availability to the plants. This supplies nutrients for the upcoming growing season and minimizes the amount of time for potential losses before crop uptake. An alternative is to spread manure in the early fall. Avoid applying manure in winter since nutrients from the manure are more likely to be lost in erosion and runoff.
Potential End Users: Neighbors, landscapers, conventional and organic farmers, gardeners and nurseries can be potential end users for horse manure compost. If the compost is not fully mature, be sure these users know how to properly use the compost and that it is not suitable for direct contact with garden or nursery plants. Compost may also be spread on the horse farm pastures if the compost process has been managed properly and the compost is included in the overall farm’s nutrient management plan. A properly managed compost process significantly reduces initial pathogen levels found in raw manure and decreases the likelihood of infection of horses grazing on pastures where horse manure compost has been applied. However, due to the small scale of the small horse farm composting operation and recontamination potential, pathogen reduction may not be as complete as in a large scale composting operation. Unless a laboratory test confirms pathogen levels in the compost are below detectable levels, avoid the use of compost from small horse farms on food crops, particularly crops that contact the compost or are eaten raw, and limit compost use to field crops. If the compost is used in organic agriculture, the once-per-week turning frequency is not sufficient.
Horse manure composting contributes to the reduction of non-point source pollution from horse manure and results in a useful soil conditioner. However, appropriate Best Management Practices need to be followed for proper composting and a good composting quality.
Additional information concerning horse manure management and other aspects of agricultural management practices of equine operations can be found in the RCE bulletin E296, Agricultural Management Practices for Commercial Equine Operations. Other relevant fact sheets include:
Please contact your local county Cooperative Extension office, the Rutgers Publication Distribution Office, or visit the RCE, Cook College Web site, http://njaes.rutgers.edu/extension/ to obtain more information.
During composting the maturity or stability of the compost increases over time. This means that the readily degradable substrate decomposes over time. The most odorous substrates decompose at the beginning of the composting process, and, generally, pathogens are reduced initially, when the temperatures are the highest.
Curing takes place at a later stage during composting. Pathogens are already reduced and the most odorous substrates are degraded. During curing the compost reheats less after mixing. The earlier started process of humus formation continues.
Compost bioaerosols are airborne particles, which may contain bacteria, fungi, and parts and products of organisms and feedstock materials.
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Auvermann, B.W., McDonald, L.A., Devin, R., and Sweeten, J.M. 1999. Composting Horse Manure, publication B-6084, Texas Agricultural Extension, College Station, USA.
Buggeln, R. and Rynk, R. 2002. Self-Heating in Yard Trimmings: Conditions Leading to Spontaneous Combustion. Compost Science & Utilization, 10(2), 162-183.
CWMI 2004a. Compost Quality Fact Sheet #5: Compost Bulking Materials. Cornell Waste Management Institute, Ithaca, NY. http://cwmi.css.cornell.edu/ compostfs5.pdf.
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Dougherty, M. (Ed.) 1999. Field Guide to On-Farm Composting. Publication NRAES-114, Natural Resource, Agriculture, and Engineering Service, Ithaca, NY.
Heckman, J.R. 1998. Soil Fertility Test Interpretation. Rutgers fact sheet, FS719, 1998.
James, R. 2003. Horse Owner’s Guide to Good Stewardship. Ohio State University Extension.www.cals.ncsu.edu/waste_mgt/smallfarms/ Horse%20Owners.pdf.
Millner, P.D., Olenchock, S.A., Epstein, E., Rylander, M.D., Haines, J., Walker, J., Ooi, B.L., Horne, E., and Maritato, M. 1994. Bioaerosols Associated With Composting Facilities. Compost Science & Utilization, 2(4), 6-57.
NRCS. 2004. Composting Facility. Conservation Practice Standard 317. U.S. Department of Agriculture, http:// efotg.nrcs.usda.gov/references/public/NJ/NJ317.pdf.
Rynk, R. (ed.) 1992. On-Farm Composting Handbook. Publication NRAES-54, Natural Resource, Agriculture, and Engineering Service, Ithaca, USA.
USDA. 2002. National Organic Program. 7 CFR 205, Washington, USA.
Wheeler, E., Koenig, B., Harmon, J., Murphy, P., and Freeman, D. 2005. Horse Facilities Handbook. Midwest Plan Service, Ames, Iowa.
Wheeler, E. and Smith Zajaczkoswki, J. 2002. Horse Facilities 3: Horse Stable Manure Management. Pennsylvania State University, http:// pubs.cas.psu.edu/freepubs/pdfs/ub035.pdf.
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