Figure 1. The Mean Value of Ammonia in Aging Horse Manure Expressed in Parts Per Million
March 5, 2001
DRAFT Horse Manure Aging and Ammonia Content
By Robert E Griswold
Background
The presence of ammonia in water bodies, even in very small amounts, has been shown to be harmful to some aquatic life. Ammonia is never ambient in aquatic environments.1 As a consequence, livestock manure is coming under increasing scrutiny as a potential non-point source of ammonia pollution.
Nitrogen is needed to produce ammonia. In horses, nitrogen comes from the protein fraction of the horse's feed. Horses absorb protein in the form of amino acids directly into their small intestines. In the large intestine, some protein is readily converted into ammonia that is absorbed by the intestinal wall.2 The remaining ammonia that gets incorporated into manure comes from protein that is in the process of being converted to ammonia but has not yet been absorbed by the intestine.
An experiment was performed to determine the volatilization potential for horse manure left exposed to the environment on the surface of the ground.
Method
Manure was collected from three horses. The horses used in this study were members of the Morgan breed. They were similar to one another in size and use. Their weight was 430 kg +/- 10 kg. Their estimated3 protein requirement was 564 grams per day. The estimated amount of protein fed per day was 617 grams total, with 495 grams (est4) from hay and 122 grams from concentrates (label declaration). The feed had a slight excess of protein (53 grams) in the daily ration. The impact of this excess on the nitrogen content of the manure was estimated to be approximately 0.016%
Daytime temperatures averaged 70 degrees F and nighttime temperatures averaged 50 degrees F. The days were mostly overcast with some sun. Sampling took place from June 5 to June 24, 1998. The samples were placed in polyethylene containers and frozen at 0 degrees F until transferred for analysis to the Dana Analytical Laboratory at The University of California, Davis. Samples were collected at the following intervals 1). immediately after evacuation, 2). 12 hours later, 3). 24 hours later, 4). 1 week later, and 5). 19 days later.
After initial collection the manure piles were held on a polyethylene sheet and exposed to outdoor ambient conditions. This was done in order to approximate the conditions found by small manure piles on the trail or in a pasture. The polyethylene sheet was used to prevent the effects of ground moisture or other variables from influencing the experimental design.
Results
The ammonia content decreased rapidly in 24 hours.
Figure 1. The Mean Value of Ammonia in Aging Horse Manure Expressed in Parts Per Million
As the manure aged, this variability decreased markedly. See Fig 2.
Figure 2. Actual value of all samples taken, expressed as parts per million of ammonia
Conclusion
Among the many variables that will affect ammonia concentration in manure are diet, exercise, how the manure is handled once deposited, and the conditions in the environment where aging takes place.
Aged horse manure left exposed on the ground for seven days does not contain sufficient nitrogen to be considered as a fertilizer, although it is considered a superior soil amendment.
This study observed that the ammonia content in horse manure volatilizes rapidly.
1. In seven days or less, the total ammonia had diminished to 14 ppm, a number that translates to one half an ounce of ammonia per ton of manure.
2. The total Nitrogen content of all samples averaged 0.96% .
3. The 1% residual nitrogen in the manure is consistent with the amount of nitrogen found in the fibrous residues of grasses on uncultivated ground5
While this study sample is small, it confirms observations reported for years by those who are familiar with horse keeping.
References Cited
1. Dr. Michael Rugg, Toxicologist, Calif. Dept. Fish and Game
2. Nutrient Requirements of Horses, 5th Ed. P8.
3. Ibid. p.43
4. Ibid. pp. 50-66
5. Rodale, J. I. Encyclopedia of Organic Gardening. 1975. p. 746
Other References
1. Dr. Ishwar Murarka is a nationally known Certified Professional Soil Scientist who holds a PhD in Soil Science from the University of Oregon. Dr. Murarka has 25 years of research with several prestigious national & private research institutions, over 100 publications, and has served on the USEPA Science Advisory Board for over 12 years. ishinc@ix.netcom.com (personal interview February 25, 2001)
In the opinion of Dr. Murarka, inorganic fertilizers of ammonium nitrogen are considerably different than the organic forms of ammonium nitrogen found in horse manure. Horse manure requires treatment by composting or incorporation into soil to a depth of 9 inches to become inorganic and be bioavailable to plants. Without incorporation of manure into the soil subsurface where microbes could actively convert it to a bioavailable form, the chances that an occasional pile of horse manure on a trail could provide much nutrient enrichment to plants of any kind is very low. The organic and ammonium nitrogen from horse manure deposited on trails rapidly volatilizes when contact occurs with air, sun, rain, etc. In general, such small quantities of horse manure that may be occasionally deposited on trails would be insignificant compared to the demand of plants, which must have the N converted by soil microbes into forms that can be up-taken at the root level.
2. Winston Way "The Perishability and Profitability of Manure" www.eap.mcgill.ca/
Unless manure is appropriately stored, it will lose its liquid content and nutrients rapidly. Never leave manure on the ground exposed to sun and wind if you are interested in nutrient preservation. Manure must be either appropriately stored or incorporated into the soil as quickly as possible after deposition (within 1 hour) in order to preserve nutrients.
3. Manure Management in Small Farm Livestock Operations EM8649 May 1997, Godwin and Moore, Oregon State University. The nitrogen in fresh manure is in the form of ammonia and organic nitrogen. The organic nitrogen is in particles such as hay and grain (organic matter). In the soil, microorganisms convert the ammonia and organic nitrogen to nitrate (NO3) that is readily available to plants.
4. http://pasture.ecn.purdue.edu/ Dec 1992 Alan Sutton and Brad Joern
Growing plants can take up both nitrate and ammonium (NH4+) nitrogen from the soil, but manure contains mostly organic and ammonium nitrogen. These forms of nitrogen do not move through soils. However, some soil microorganisms convert these compounds to nitrate, the mobile form of nitrogen in soils.
5. http://hubcap.clemson.edu April 1996 Land Application of Animal Manure. The speed and extent of degradation are dependent on the type of manure, soil type, soil moisture and temperature and how well the manure is mixed with soil. Considerable quantities of ammonia/ammonium N occur in most manure. Most crops will uptake NH4+ as well as any other form of N but do not accumulate NH3 to any extent. Ammonia is readily lost to the atmosphere. As much as 15% of NH3 from surface applied manure can be lost each day …"
6. http://agri.gov.ns.ca/rs/greenplan/waste The Development of Weather-based Manure Spreading Index by Gordon, et al, Dec 1996. Approximately 50% of the N in manure is found in the liquid portion. Although soluble and therefore readily available for crop use, it is quite susceptible to loss through volatilization as NH3, particularly during the first few days after field application. Although estimates of NH3 emissions are still very uncertain, many studies have concluded that a great percentage of the N lost from manure occurs through volatilization of NH3 (Adriano et al, 1974; Lauer et al 1976, Hoff et al 1981, Beauchamp et al 1982 etc)
7. http://www.mda.state.mi.us/right2farm/manapp.htm The availability of N in manure for plant uptake will not be the same as highly soluble, fertilizer N. Therefore, total manure N cannot be substituted for that in fertilizers on a pound-for-pound basis, because a portion of the N is present in manure organic matter which must be decomposed, before mineral (inorganic) forms of N are available for plant uptake. (Assuming incorporation into the soil) the rate of decomposition (or mineralization) of manure organic matter will be less than 100% during the first year, and will vary depending on the type of manure and method of manure handlings and can take 2-4 years to become available for plants.
8. www.montana.edu Minimize Your Gamble When Applying Urea by Jim Bauder MSU Extension: It really cannot be over-emphasized that incorporating urea into soil will minimize loss. Do not allow manure to remain on the soil surface. Pennsylvania State University sources say that within a day of application, 66% of urea-nitrogen becomes ammonia-nitrogen. If not incorporated into the soil, significant nitrogen loss can occur…" DB Fowler Univ Of Saskatchewan emphasizes, "Once urea is well incorporated into soil, volatilization losses normally are minimal."
9. http://ceinfo.unh.edu/bmpnutr.htm plow down or disc manure within 2 days to avoid heavy losses of ammonia nitrogen
10. http://ohioline.ag.ohio-state.edu Ohio Livestock Manure and Wastewater Management guide Bulletin 604 "Manure should be incorporated into the soil as soon as possible after application"
11. H. A. Ajwa and Tabatabai, M. A. "Decomposition of different organic materials in soils". Biol. Fertil. Soils. 1994. Vol. 18. Pp. 175-182. In composted scenarios, total mineralization of horse manure (breakdown into CO2 and H2O) occurs within 21 days with more than 50% of the total CO2 produced during the first 6 days.
12. Horses spend most of their time in pastures or paddocks where the majority of their excrement is deposited, collected and managed. Horse manure is about 70-80% liquid and 20-30% solids. Personal communication with Dr. Deanne Meyer, UCDavis Manure Management Specialist, February 1997.