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bioweb.sungrant.org » Technical » Biomass Resources » Agricultural Resources » Animal Manure » Swine
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Animals generate a significant amount of wastes (urine, feces, etc.) and the management and disposal of these wastes can be problematic. Currently, most livestock waste is applied to fields as fertilizer. However, animal wastes can potentially be used for bioenergy through the capture of biogas (from anaerobic digestion), syngas (from gasification), or bio-oils (from pyrolysis). Components of manure may also be recovered for use in producing bioproducts.
The swine industry in the U.S. has undergone substantial structural change over the past 20 years. During the 1970s and 1980s, production typically occurred in mostly small, farrow-to-finish (birth to market) operations. Today, hog production is specialized, occurring at three different locations. Breeding, gestation, and care until old enough for weaning (farrowing) occurs at one site. After weaning, piglets are moved to a nursery facility where they are fed special diets. Once they reach 40-60 pounds in weight (about 8-10 weeks of age), they are transported to a finishing facility, where they are fed until they reach market weight (200 to 250 lbs). Independent producers represent a diminishing portion of total production. Most production today is under contract, where large hog producers (called integrators or contractors) contract with smaller growers to feed the hogs until market weight (the finishing stage of production). The integrator provides management services, feeder pigs, medicine, and other inputs while the grower provides the labor, land, and facilities. In return, the grower receives a fixed payment, adjusted for production efficiency (Martinez, 1999).
Since 1990, pork production in the U.S. has increased by an annual average of 1.8% per year. U.S. exports of pork have increased more than five-fold and the U.S. is now a net exporter of pork (Martinez, 1999). Production has expanded from traditional areas in the Midwest (mostly Iowa, Illinois, Indiana, and Minnesota where corn is an abundant feed) to other parts of the country, predominantly the Southeast (especially North Carolina) and into the Southwest and the West (Martinez, 1999) (figure 1).
The average size of hog operations has increased substantially. In 1987, operations with inventories of greater than 1,000 hogs represented 37% of the total swine population, increasing to 71% of the total population in 1997. In the two largest hog producing states of Iowa and North Carolina, 63 and 98% of the pigs, respectively, were produced in operations of greater than 1,000 hogs. Nationally, operations with more than 2,000 hogs also increased significantly - from 28.8% in 1992 to 55% in 1997 and to more than 80% by 2006. Operations of more than 10,000 head account for more than half of the total pork production (Martinez, 1999; USDA-NASS, 2007). The total number of operations producing swine is decreasing as herd size increases. In 2006, the total number of swine operations was 65,540 which is a 3% decline from 2005 and a 6% decline from 2004 (USDA-NASS, 2007). Table 1 shows the breakdown of swine operations by number of hogs in inventory (herd size) for 2005 and 2006. In 2006, the total number of market and breeder hogs on inventory was 61.69 million, 65% of which were produced in five states: Iowa (16.6 million), North Carolina (9.6 million), Minnesota (6.8 million), Illinois (4.2 million), and Indiana (3.2 million) (table 2).
The amount and characteristics of wastes produced per animal depends on a number of factors including age, size, type of feed, and whether or not the animal is pregnant (gestating) or nursing (lactating). Feed rations are particularly important. Corn is widely fed to swine and is 90% digestible. Substitution of corn with other grains increases the total solid content of the manure. Physical properties of waste that are of interest include weight, volume, total solids and moisture content, as these properties describe the amount and consistency of the material that must be dealt with by equipment and in treatment and storage facilities. Chemical constituents (nitrogen [N], phosphorus [P], and potassium [K]) are important in use of livestock wastes as fertilizers, as well as for environmental considerations (USDA-NRCS, 1999).
Estimates of the average manure produced per animal and the composition of the manure can be found in a number of sources such as the National Resource, Agriculture and Engineering Service (NRAES), the American Society of Agricultural and Biological Engineers (ASABE), North Carolina State University, and USDA National Resource Conservation Service (NRCS), among others. Both estimated average quantities of manure produced per unit and manure characteristics differ due to different assumptions regarding feed ration composition, the use of feed additives such as phytases (used to reduce phosphate), and the efficiency of conversion of feed to meat, among other factors. Table 3 provides swine manure characteristics by animal type, as estimated by USDA-NRCS (1999). Waste characteristics are expressed as pounds per day per 1,000 pounds of livestock live weight (lb/d/1000#) for weight, total solidsa, N, P, and K; as cubic feet per day per 1,000 pounds of livestock live weight (ft3/d/1000#) for volume; and percent (wet basis) for moisture and total solidsb. Wastes characteristics are based on average amounts as excreted from the animal (i.e., wastes don’t contain bedding or other materials).
The USDA estimates that in 1997, 9.3 million tons (dry matter) of manure were generated by swine operations, of which 8.6 million tons were on operations where the hogs were confined (USDA-ERS, 2001). The manure that is collected from such operations is mostly disposed of via field application as a fertilizer. Sometimes field application is in excess of the nutrient assimilation capacity of the soil, leading to problems associated with nitrogen and phosphorus runoff (Ribaudo, 2003).
Concentrated animal feeding operations (CAFO, which for swine production means 2,500 hogs or more - based on the average annual number of hogs in inventory or sold) must be permitted under the National Pollutant Discharge Elimination System (NPDES) and must have a nutrient management plan for wastes applied to the field as fertilizer. A nutrient management plan is voluntary for non-CAFO operations.
Swine manure is generally collected and stored as a slurry in pits, or as a liquid in lagoons (EPA, 2001). Swine production often involves housing swine in facilities with slotted floors where the waste drops through the slots directly into storage tanks (pits) or falls into a gutter and is flushed into a storage tank. This form of storage generally provides from 3-12 months of storage and is periodically pumped out or drained. Lagoon storage is a liquid form of storage and is often used when treatment of the manure is desired in order to facilitate handling or reduce odor. Lagoons are designed to encourage anaerobic digestion of the organic material in the manure. Lagoons are generally larger than pits, and provide for storage of larger quantities of manure for longer periods of time (Harrison, 2004; EPA, 2006). Pit storage is more common in the Heartland, particularly on smaller operations, while lagoon storage is more common in the Southern Seaboard (table 4) (McBride, 2003).
The problem of excessive application of manure for fertilizer is
particularly important for large swine operations due to the large volumes of manure produced, the nature of the manure (mostly liquid), and the frequency of manure collection. The USDA identified 68 counties where manure nitrogen levels exceed the soil nutrient assimilative capacity of all the county’s crop and pasture land (primarily in North Carolina, northern Georgia, Alabama, central Mississippi, western Arkansas, and California) and 152 counties (concentrated in eastern North Carolina, northern Georgia, northern Alabama, western Arkansas, central California, and western Washington) where the manure phosphorus levels exceed the county assimilative capacity. Additionally, 155 and 337 counties were identified where manure nitrogen and phosphorus levels, respectively, exceed half of the county soil nutrient assimilative capacity (Gollehon, 2001; Ribaudo, 2003; Ribaudo, 2006). These counties are most in need of alternative waste management methods.
The EPA estimates that as of 2005, approximately 4,281 swine farms were good candidates for biogas collection and bioenergy production. Nearly 51% of these farms were located in North Carolina and Iowa; about 85% of the candidate farms were located in the top 10 swine production states (EPA, AgStar, 2006). |
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| References |
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American Society of Agricultural and Biological Engineers, Manure production and characteristics, Standard ASAE D384.2, March 2005, www.asabe.org
Gollehon, Noel, Margriet Caswell, Marc Ribaudo, Robert Kellogg, Charles Lander, and David Letson, Confined animal production and manure nutrients, U.S. Department of Agriculture, Economic Research Service, Agricultural Information Bulletin No. 771, June 2001.
Harrison, John D. and Dallen R. Smith, Types of manure storage, Utah State University, Agriculture Environment Management Systems, AG/AWM-01-2, April 2004.
Martinez, Steve W., Vertical Coordination in the Pork and Broiler Industries: Implications for Pork and Chicken Products, U.S. Department of Agriculture, Economic Research Service, Agricultural Economics Report No. 777, April 1999.
McBride, William D. and Nigel Key, Economic and structural relationships in U.S. Hog Production, U.S. Department of Agriculture, Economic Research Service, Agricultural Economic Report No. 818, February, 2003.
Natural Resource, Agriculture, and Engineering Service (NRAES), Manure Characteristics, MWPS-18, S1, April 2004.
North Carolina State University, 2007 North Carolina Agricultural Chemicals Manual, Livestock manure production rates and nutrient content, (K.A. Shaffer and B. Cleveland, chapter authors).
Ribaudo, Marc, Managing Manure: New Clean Water Act Regulations Create Imperative for Livestock Producers, USDA Economic Research Service, Amber Waves, February 2003.
Ribaudo, Marc, Noel Gollehon, Marcel Aillery, Johnathan Kaplan, Robert Johansson, Jean Agapoff, Lee Christensen, Vince Breneman, and Mark Peters, Manure management for water quality: costs to animal feeding operations of applying manure nutrients to land, U.S. Department of Agriculture, Economic Research Service, Agricultural Economic Report 824, June 2003.
Ribaudo, Marc and Noel Gollehon, Animal agriculture and the environment, U.S. Department of Agriculture, Economic Research Service, Agricultural Resources and Environmental Indicators, 2006 Edition/EIB-16.
U.S. Department of Agriculture, Economic Research Service, Confined animal and manure nutrient data system, August, 2001, www.ers.usda.gov/Data/manure
U.S. Department of Agriculture, National Agricultural Statistics Service, Farms, Land in Farms, and Livestock Operations 2006 Summary, February 2007.
U.S. Department of Agriculture, National Agricultural Statistics Service (NASS). (2007). www.nass.usda.gov
U.S. Department of Agriculture, Natural Resource Conservation Service, National Engineering Handbook Part 651, Agricultural Waste Management Field Handbook, Chapter 4: Agricultural Waste Characteristics, June 1999.
U.S. Environmental Protection Agency, Ag 101—Pork Production Manure Handling Systems, March 7, 2006, www.epa.gov.
U.S. Environmental Protection Agency, (2006). Market opportunities for biogas recovery systems: A guide to identifying candidates for on-farm and centralized systems, EPA-430-8-06-004, www.epa.gov/agstar
U.S. Environmental Protection Agency, Emissions from animal feeding operations, Draft, August 15, 2001
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