Chapter 8
Agricultural and Environmental Issues in the Management of Swine Waste
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Robert L. Mikkelsen Department of Soil Science, North Carolina State University, 3205 Williams Hall, Raleigh, NC 27695-7619
The concentrated and regionalized nature of the U . S . swine industry results in large quantities of animal waste being produced in a relatively small area. Although animal wastes can be used for a variety of purposes (e.g. animal feed, biogas generation, and composting) their primary use has been as a source of plant nutrients for crop production. Since the concentration of essential plant nutrients is generally low in manures compared with inorganic fertilizers, there is often little incentive to recover the full agricultural value from these materials. Waste is commonly stored in pits or in lagoons prior to application, depending on the type of production system. Manure management practices may have significant impacts on surface water, groundwater, and atmospheric emissions. When swine manure is applied to crop land for extended periods of time, an accumulation of nutrients can occur in excess of the plants nutritional requirement.
Swine production is an important agricultural enterprise throughout the United States. During 1995, over 60 million swine were produced, with the majority of the production occurring in the Midwestern U.S. (Table 1). Traditionally, swine production was characterized by relatively small numbers of animals located on farms in proximity to corn production, a primary feed source. However modern swine production has become more intensive and centralized, typically characterized by large farms that are dependent on purchases of animal feed from off of the farm. Increasing numbers of animals are raised in specialized housing facilities that allow more control over the production environment. Additionally, integration of the swine industry has become common, where the supply of feed and the sale of the animals is handled by a contractor. However, swine production remains a major agricultural activity world-wide (Table 2) which is difficult to generalize due to the extreme diversity in production and management practices. This discussion will focus primarily on swine-production issues in the United States. 110
© 1997 American Chemical Society
In Agricultural Uses of By-Products and Wastes; Rechcigl, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
8. MIKKELSEN
Management Issues of Swine Waste
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Table 1. Inventory of hogs produced in the top ten swine-producing states in the U.S during 1996 (7) State
Millions of hogs
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Iowa North Carolina Illinois Minnesota Indiana
13.0 9.3 4.7 4.9 4.0
Million? Qf hogs Nebraska Missouri Ohio South Dakota Kansas
3.7 3.6 1.9 1.5 1.3
As swine production continues to become geographically concentrated and the number of animals on an individual farm increases, problems associated with both air and water quality can become a serious challenge. Odor control has become a major concern on large swine production facilities in relation to nearby neighbors. Ammonia loss from animal waste has been a major environmental issue in Northern Europe during the past decade and will likely be the future subject of regulation in nutrient-sensitive areas. The production of other gases associated with animal production (such as methane) also remain important environmental concerns.
Table 2. Inventory of hogs produced in the top ten swine-producing countries in 1995 (2) Country
Millions of hogs
P.R. China United States of America Brazil Russian Federation Germany
415 60 32 25 25
Country
Millions of hQg$
Poland Spain France Ukraine Netherlands
19 18 15 14 14
Modern nutrition of swine generally consists of concentrated, high-energy grain-based feeds with only a small proportion of roughage. Proper nutrition is particularly essential for swine because they grow much faster in proportion to their body weight than larger farm animals and also produce young at an earlier age (5). However in comparison with other commonly raised animals, swine excrete larger amounts of manure that must be dealt with (Table 3). The majority of the nutrients initially present in the feed pass through the swine digestive system and are ultimately excreted in the manure and urine (more than 80% of the ingested N and P, and more than 90% of the K is typically excreted). This relatively inefficient nutrient recovery by swine results in large amounts of manure-derived nutrients that are available as a valuable resource i f managed properly. Nutrients arrive on the farm as feed and
In Agricultural Uses of By-Products and Wastes; Rechcigl, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
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AGRICULTURAL USES OF BY-PRODUCTS AND WASTES
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mineral additives, then subsequently converted into swine body mass and waste. The nutrients that are not removed when the animal is sold will remain on the farm and must be incorporated into a nutrient management plan. Unless these wastes are properly managed, the nutrients may accumulate to concentrations harmful to growing crops and become detrimental to surface and ground water. The most common method of managing the nutrients is to apply the wastes to cropland and attempt to remove the nutrients in the harvested portion of the plant for sale off of the farm. This practice ideally allows the redistribution of nutrients back over a large area when the crops are sold and dispersed.
Table 3. Annual manure production by various animals (equalized on 1000 pounds of animal mass) Animal Species Broiler Sheep Horse Beef Dairy Swine
Annual Production (Tons manure/year) 4.5 6 8 8.5 12 16
Manure management practices vary tremendously depending on the objectives of the swine producer (Figure 1). For example, the primary objective in manure management on a specific farm may be to optimize nutrient recovery and utilization, to minimize land or labor inputs, to control odor, or perhaps some combination of these objectives. By combining the management objectives with factors such as the amount of available land, labor, climate, management skills, and local regulations, an appropriate waste utilization plan can be developed. A successful waste management plan will include consideration of the form and source of nutrients, the amount of nutrient that must be managed, the appropriate placement of the nutrients, and the timing of nutrient applications. Swine manure is most commonly handled as either a slurry (4 to 15% solids) or a liquid (
