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Chapter 16 Waste and nutrient management.


In years past, pig waste was typically disposed of by spreading it on the land. In modern times, producers generally recognize that waste is actually valuable nutrients needed for crop production and other purposes. Utilization of manure nutrients is an integral part of a sustainable pork operation. To be sustainable, the manure nutrients must be utilized in a manner that recycles or captures the nutrients. While some manure management programs can reduce the nutrient load by various fermentation or aerosolization processes, in the scheme of the world's shortage of plant nutrients and energy, a more sustainable option is to utilize these manure nutrients for some productive purpose.

Waste and manure management is all about options and choices (Melvin et al., 1979). Producers have many methods at their disposal to accomplish manure management and utilization. This chapter discusses some of the options and choices.


There is great public concern about potential environmental pollution resulting from run-off of animal manure from feedlots and fields on which it is spread for soil fertilization. This concern has led to federal regulations to control discharges of pollutants from concentrated animal feeding operations (CAFOs) to water supplies. The United States Environmental Protection Agency (EPA) is responsible for monitoring and enforcing the regulation as part of the Clean Water Act of the U.S. Congress. The acronym "CAFO" applies to animal feeding operations that confine or house livestock or poultry prior to the animal being marketed or slaughtered. In the case of swine, any production unit with more than 1,000 animal units (defined as 2,500 or more swine weighing 55 lb (25 kg) or more) is classified as CAFO if the following criteria are present (Concentrated Animal Feeding Operations, 2001):

1. Animals are maintained in confinement for 45 d or more in a 12-mo period.

2. Crops, post-harvest residues, or vegetation forage growth are not sustained in the area of confinement in the normal growing season. This criterion distinguishes confined feedlots from pasture settings.

3. The facility meets a threshold of 2,500 or more swine weighing 55 lb or more. For dual discharges that pass through the area of confinement or indirect discharge via a man-made conveyance, the threshold is 300 animal units (750 or more swine weighing 55 lb or more).

Each producer should consult agricultural engineers and local regulators before deciding on a manure management system. In addition to cost and ease of management, producers should consider the impact of design features on neighbors and the environment. Each farm should have a manure management plan that defines design features of the production system. The manure management plan should also attempt to minimize the risk of environmental pollution.

Manure is the combined feces, urine, and added products such as water, wasted feed, hair, and bedding (if used). Manure can be handled as a liquid slurry, a semi-solid, or a dry form. Manure has characteristics of a liquid when it has 15% solids or less. When manure has over 20% solids, it may have the characteristics of a solid.

The volume of manure produced by pigs of various stages is given in Table 16-1. Among growing pigs, finishing pigs produce the greatest volume of manure compared with other stages of production--clearly, larger pigs produce a greater volume of manure. Among the breeding herd, lactating sows and their piglets produce far more manure than do pregnant sows primarily because the lactating sows are fed ad libitum and may consume up to 9 kg/d (20 lb/d) compared with the pregnant sows who are fed ~2 kg (4 to 5 lb/d). Limit-fed animals produce less manure than do full-fed animals.

Producers can calculate the amount of land required for a pig production unit to fully utilize the nutrients it produces. The exact amount of land required depends, in large part, on the crop to be grown and its nutrient needs as well as what the pigs are fed and the amount of manure produced. Thus, a sustainable pig farm will require about 1 acre/sow for a farrow-to-finish unit. If the farm contains only pregnant sows, lactating sows, nursing piglets, and nursery pigs, the farm will require about 2.7 acres/sow. Finishing pigs require, on average, a land area of 10.4 pigs/acre (see Table 16-2).

Less land is needed if certain technologies are used to reduce the manure mass. For example, if a methane digester is used to turn manure nutrients into gas and if the gas is utilized for heat production, less land is needed. If a series of anaerobic and aerobic digestion is used, the land requirement for disposal of nutrients is less.

The largest bulk of material in manure falls into a discrete number of categories. Each nutrient must be either released into the air or recycled, often through crops. Categories of manure nutrients are:

* Water ([H.sub.2]O)--Hydrogen and oxygen

* Carbon--Primarily in the form of partially digested plant materials. Carbon is often overlooked as a manure nutrient. Carbon is utilized by direct spreading of solids or semi-solids or released into the air in various forms such as carbon dioxide (C[O.sub.2]) or methane (C[H.sub.4]).

* Nitrogen--The nitrogen content of pig manure varies, but is about 0.5 mg/kg (10 lb/ton) of manure. Nitrogen is found in the forms of elemental nitrogen, ammonia (N[H.sub.3]), ammonium (N[H.sub.4]), and urea (CO[(N[H.sub.2).sub.2]) as well as various metabolites of urea. Urea is a product of the breakdown of protein. Overfeeding protein will increase the nitrogen content of the manure. In liquid pits, nitrogen is found at 36 lb/1,000 gal (16 kg/3,785 l) but the concentration is only 4 lb/1,000 gal (1.8 kg/3,785 l) in lagoons. Figure 16-1 shows how nitrogen flows through the environment.

* Phosphorus--Phosphorus is found as a part of partially digested plant material in the form of phytate and in the plant-available form of [P.sub.2][O.sub.5]. Phosphorus (as [P.sub.2][O.sub.5]) is found in manure at about 0.4 mg/kg (9 lb/ton) of manure. In liquid pits, phosphorus (as [P.sub.2][O.sub.5]) is found at about 27 lb/1,000 gal (12.2 kg/ 3,785 l), but in lagoons its concentration is only about 2 lb/1,000 gal (1.1 kg/ 3,785 l).

* Potassium--Potassium is found in partially digested plant materials and in the available form of [K.sub.2]O. In liquid pits, potassium in the form of [K.sub.2]O is 22 lb/1,000 gal while it is only 4 lb/1,000 gal (1.8 kg/3,785 l) in a lagoon.

* Sulfur--Sulfur compounds are found in proteins of plant, animal, and bacterial matter. As a part of proteins, sulfurs do not have much of an odor. However, in the form of hydrogen sulfide ([H.sub.2]S[O.sub.4]), manure has the odor of rotten eggs.

* Other--Many other manure chemicals are produced. Some are harmless and some have a strong odor. A detailed list of components of manure, including the less-concentrated but more volatile (and thus more odorous) compounds, are given by Mackie et al., 1998.

The N:P:K ratio in manure is about 10:9:8, while a plant such as corn needs 10:4:10. As an example, 180 bu/acre corn requires 240 lb/acre N, 100 lb/acre [P.sub.2][O.sub.5], and 240 lb/acre [K.sub.2]O. Thus, because plants pick up and incorporate nitrogen and potassium at higher levels than they do phosphorus, it is the phosphorus that accumulates on cropland. If a producer applied enough manure nutrients to meet only the phosphorus needs of the crop, then either supplemental nitrogen and potassium would have to be added, or the crop yield would be reduced.

Pork producers should be careful when they consider which crops to use to utilize manure nutrients. Conventional wisdom is that legumes, which fix nitrogen from the air, require less nitrogen than do nonlegume crops. However, legumes will absorb and utilize nitrogen at a higher rate than will corn or other grains when nitrogen is applied. Table 16-3 lists some values of crop utilization of the three primary nutrients (nitrogen, phosphorus, and potassium).

If the objective is for the selected crop to pick up the most nitrogen, alfalfa is a good choice as a crop. However, if the objective is to recycle the greatest amount of phosphorus, corn is the best choice among the crops listed in Table 16-3. Plant utilization of manure nutrients is an important research topic worldwide. The search for plants that utilize manure nutrients efficiently in a manner that can be utilized by other animals, particularly ruminants, is very important for worldwide development of sustainable pork production systems.



The potential for pig manure-related pollution can fall under one of two categories: water or air pollution. Every U.S. pig production unit should strive to minimize the risk of environmental pollution.

Water pollution can kill fish and other wildlife and it can pollute drinking water to the point at which it is not safe for drinking and other uses. Because water is necessary for life and because the federal government claims ownership of the waters of the United States (the same for other countries), water pollution is of concern to national governments and citizens.

Fresh manure does not have much of an odor. However, with just a few minutes of bacterial fermentation, the manure takes on an offensive odor. The key is to contain the odor by a physical barrier, to spread it over a large area in a short period of time, or to allow the animals to spread the manure themselves. Odor pollution is of greatest concern to people who live or work near the source of the odors. Offensive odors have been studied in many industries, including pig farms. People who live near pig farms that have what they report as offensive odors, report symptoms of physical and psychological illness that they associate with the pig farm (Schiffman, 1998).

Pig production units in the United States are nonpoint sources of pollution, by regulation. Pig farms are not allowed, except by an act of God, to discharge into U.S. waterways (streams, lakes, or underground aquifers). Some states have extensive regulations regarding liquid manure handling, but minimal regulations about handling of dry manure. Dry manure poses a lower risk of environmental pollution than liquid manure handling systems. Dry manure is less likely to flow toward a waterway than is liquid manure. Secondly, dry manure, if it is truly dry, has less of an odor than liquid manure.

Extensive safeguards can be put in place to minimize the risk of environmental pollution with liquid manure systems, usually by adding more expensive liquid manure handling systems.


The first choice in manure nutrient collection is to determine if manure is handled in a dry or liquid form (semi-solid is included in the liquid category here). If the manure is handled in dry form, there are two options (with sub-choices): (1) Allow the pigs to self-distribute the manure nutrients or (2) collect and mix the manure with a bedding source (see Chapter 13).

When manure is handled in a dry form mixed with bedding, the largest challenge is to get the manure-bedding mixture out of the building or lot. This is accomplished either by hand or with the use of machines. The dry manure-bedding mix can either be applied directly to croplands or composted.

Some degree of separation is needed when manure is handled in a liquid form. Two methods are common: use of a settling basin or use of a liquid-solid separator. If the liquid-solid separator is used, the solids must be either composted or spread directly on the fields. If a settling pond is used (see Figure 16-2), the settling basin must be emptied at some time.

Liquid manure systems can be anaerobic or aerobic. When a manure pond is deeper than 2 ft (0.6 m), and especially when it is deeper than 4 ft (1.22 m), the lower portion of the pond will be anaerobic. Anaerobic and aerobic ponds have a different odor. An aerobic pond has a more constant odor year-round and has a less-intense odor. Anaerobic ponds may have little odor at some times, but at other times a very strong odor. Deep, anaerobic ponds will "turn over" when the seasons change from warm to cool or cool to warm. This temperature inversion causes the smelly bottom materials to move up toward the surface.


Manure handled in a dry form

Manure is handled in a dry form in different ways for outdoor and indoor production systems.

* Outdoor

** With a vegetative ground cover and posture rotation (recommended)

** Without a vegetative ground cover (not recommended unless there is a vegetative or other boundary)

** On solid concrete or hard ground with slotted floors

* Indoor with bedding

** Manure handled by hand or machine

** Manure removal automated

Manure handled in liquid or semi-solid form (indoors with slotted floors)

Manure under slotted floors is best handled in a liquid or semi-solid state. Being liquid facilitates movement of the material out of the facility.

* Under-floor storage; pit pumped out as needed

* Under-floor flush

** One or more flushes/d

** Pull-plug system (plug pulled and building flushed as needed)

* Under-floor scraper

** Scraped each day

** Scraped as needed

* Other

Liquid manure storage and handling options

After the manure leaves the building, it is stored for short or long durations (hours through years). Storage containers can be equipment on site or can be built into the ground.

* Multi-stage lagoon (anaerobic or aerobic)

* Slurry-storage tank (anaerobic or aerobic)

* Covered lagoon or tank for fermentation and possible methane production and capture

* Under-floor pit

* Other


Pigs generate manure which in the past was considered a waste product. Today, manure is recognized as a valuable nutrient that can be recycled through one of several means including on crops or generation of an alternative fuel such as methane. Manure nutrients should be balanced with the crop or other system that will use these nutrients. Manure storage and handling facilities should be properly designed to accommodate the numbers and types of pigs on the farm.


1. Define and discuss the terms manure, waste, lagoon, and nutrients.

2. Why might odors from hog farms cause problems with people? Is human perception important in understanding hog odor issues?

3. When you search the Web, do you find more sites for or against or neutral toward potential pollution problems associated with pig production units?

4. Describe a well-designed waste management system using a dry manurehandling system.

5. Describe a well-designed waste management system using a liquid manure-handling system.


Concentrated Animal Feeding Operations. 2001. Available at: Accessed May 22, 2001.

Mackie, R. I., P. G. Stroot, and V. H. Varel. 1998. Biochemical identification and biological origin of key odor components in livestock waste. J. Anim. Sci. 76:1331-1342.

Midwest Plan Service. 1987. Structures and environment handbook. MWPS-1. Ames, IA.

Melvin, S. W., F. J. Humenik, and R. K. White. 1979. Swine waste management alternatives. Pork Industry Handbook. Purdue University, West Lafayette, IN.

Schiffman, S. S. 1998. Livestock odors: implications for human health and well-being. J. Anim. Sci. 76:1343-1355.


A group of environmental activists who focus on the NC hog industry has a Web page at:

North Carolina State University provides research and education information about pig housing and waste management as well as other topics at: and

The University of Georgia provides a site that focuses on animal waste management at:
TABLE 16-1
Manure Production by Pigs of Various Stages. Manure Is Assumed to
Be about 91% Water. Consult the Midwest Plan Service for More
Complete Data (MWPS-1).

                            PIG WEIGHT        MANURE PRODUCTION


Nursery pig                  35    16      2.3      .038        .27
Finishing pig               150    68      9.8      .16        1.13
Pregnant sow and boar (a)   275   125      8.9      .15        1.1
Sow and litter of 8 pigs    375   170     33        .54        4.0

(a) Assumes sows and boars are the same weight and are
limit-fed and eating less than 50% of ad libitum intake.

Source: Adapted from Midwest Plan Service (MWPS-1) (1987).

TABLE 16-2
Whole Farm Design Values for Total Manure Production/Animal
Unit. See Pork Industry Handbook (PIH-67) for More Details.

                                PIG WEIGHT


Farrow-to-finish        Sow     1,417   644
Farrow-to-feeder pig    Sow       522   237
Finishing only          Pig       135    61

                                     ANNUAL N     LAND NEEDED
                         MANURE,     PRODUCED,   PER ANIMAL (b)

Farrow-to-finish          14.2         248         1 acre/sow
Farrow-to-feeder pig       5.2          91       2.7 sows/acre
Finishing only             1.4          24       10.4 pigs/acre

(a) Multiply by 1.52 to get tons/year. N content is 11.4 lb/ton on

(b) Land needs is a generalization based on a crop that requires
250 lb/acre of N for optimum yield. Specific crops may need more
or less N/acre. Other nutrients, particularly P and K, must be
considered as well as metals that may accumulate.

Source: Adapted from Melvin et al. (1979), Pork Industry Handbook

TABLE 16-3
Nutrient Utilization by Selected Crops.

Crop           Yield            N      [P.sub.2]     [K.sub.2]O

Com            180 bu/ac       240        100           240
Sorghum        4 tons/ac       250         90           200
Soybeans       60 bu/ac        336         65           145
Alfalfa        8 tons/ac       450         80           480
Tall Fescue    3.5 tons/ac     135         65           185

Source: Adapted from Midwest Plan Service MWPS-1 (1987).
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Title Annotation:Section IV Housing, Environment, and Nutrient Management
Publication:Pig Production, Biological Principles and Applications
Geographic Code:1USA
Date:Jan 1, 2003
Previous Article:Chapter 15 Production systems for growing pigs.
Next Article:Chapter 17 Management of the breeding herd.

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