United States 

Department of 

Agriculture

Economic

Research

Service

Nigel Key, William D. McBride, Marc Ribaudo, and Stacy Sneeringer

Trends and Developments in 

Hog Manure Management: 

1998-2009

Economic

Information 

Bulletin

Number 81

September 2011
www.ers.usda.gov

For additional information on the hog industry, see: 

www.ers.usda.gov/Briefing/Hogs

Recommended citation format for this publication:

Key, Nigel, William D. McBride, Marc Ribaudo, and Stacy Sneeringer. Trends 

and Developments in Hog Manure Management: 1998-2009. EIB-81. U.S. 

Dept. of Agriculture, Econ. Res. Serv. September 2011.

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A Report from the Economic Research Service

Abstract

In the past decade, hog production has increasingly become consolidated, with larger 

operations producing a greater volume of hog manure on smaller areas. With less cropland for spreading the manure, hog farmers may be compensating through more effective 

manure management. The authors use data from 1998 to 2009 collected in three national 

surveys of hog farmers. Over this period, structural changes in the hog sector altered how 

manure is stored and handled. Changes to the Clean Water Act, State regulations, and 

local confl icts over air quality also affected manure management decisions. The fi ndings 

further suggest that environmental policy has infl uenced conservation-compatible manure 

management practices. The authors examine how the use of nutrient management plans 

and of practices such as controlled manure application rates vary with scale of production 

and how these practices changed over the study period. This report is an update of an 

earlier report, Changes in Manure Management in the Hog Sector: 1998-2004. 

Keywords: hog production, manure management, structural change, environmental 

regulation

Acknowledgments: 

The authors would like to thank James MacDonald and Michael Livingston, USDA/

Economic Research Service; James Kliebenstein, Iowa State University; Mark Peters, 

USDA/Natural Resources Conservation Service; Kelly Zering, North Carolina State 

University, and an anonymous reviewer for their helpful reviews and comments. We 

would also like to thank our editor, Courtney Knauth, and our designer, Curtia Taylor.

Nigel Key, nkey@ers.usda.gov

William D. McBride, wmcbride@ers.usda.gov

Marc Ribaudo, mribaudo@ers.usda.gov

Stacy Sneeringer, ssneeringer@ers.usda.gov

Trends and Developments in 

Hog Manure Management: 

1998-2009

Economic

Information

Bulletin

Number 81

September 2011
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Contents

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Structural Change and Manure Management . . . . . . . . . . . . . . . . . . . . . . . . 3

Environmental Policy Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Manure Management on U.S. Hog Farms . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Manure Storage and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Manure Application and Disposal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

 Manure Nutrient Management Practices. . . . . . . . . . . . . . . . . . . . . . . . . 18

 Manure Management for Air Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

 Environmental Policy Effects on Manure Management . . . . . . . . . . . . . 23

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
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Summary

What Is the Issue?

Over the last decade, U.S. hog industry production has shifted to fewer and 

larger operations that specialize in a single phase of hog production and the 

use of production contracts. Consolidation of operations has meant that an 

increasing volume of manure is often produced on farms with less cropland 

per animal for spreading the manure. A higher manure-to-cropland ratio has 

magnifi ed the risk that manure nutrients (nitrogen, phosphorous, and potassium) and pathogens might fl ow into ground and surface water due to overapplication of manure on crops or leakage from manure storage facilities. These 

runoff contaminants can harm aquatic life and livestock and affect human 

drinking water. In addition, increased concentration of hogs per farm has led 

to confl icts with nearby residents or communities over odor and air quality. 

Legislative initiatives, such as the Clean Water Act and various State regulations, have implemented environmental policies to mitigate the risk of water 

pollution and reduce confl icts. Despite the pronounced shifts in hog industry 

structure and regulation, little information exists for assessing how these 

changes have affected manure management practices and environmental 

quality. Using data from three surveys of hog farmers, the authors shed light 

on these issues by examining how hog manure management practices vary 

with the scale of production and how practices have changed since 1998.

What Are the Major Findings?

• Hog farm operators altered their practices between 1998 and 2009 in 

ways that suggest intent to manage manure in a more environmentally 

sound manner. In 2009, operators were more likely to have comprehensive nutrient management plans and, accordingly, to have increased 

their efforts to apply manure at rates not exceeding the nutrient needs 

of the crop. They were more likely to have applied manure over a larger 

share of their cropland and to have increased their use of feed additives 

that reduce phosphorus in hog manure, increased the nutrient testing of 

manure, and removed excess manure from their premises. They were less 

likely to have added commercial fertilizer to crops receiving manure.

• Changes in manure management practices and outcomes from 1998 to 

2009 are related to structural changes in hog production, particularly 

the increase in farm size and regional shifts of production. The changes 

include more use of pit/tanks and less of lagoons for manure storage; a 

decline in spreading solid manure, as well as in spreading liquid manure 

without incorporating it into the soil; and less intensive manure application by the largest farms.

• Environmental policies are likely behind some of the observed patterns 

of change in hog manure management between 1998 and 2009. For 

example, the relatively slow growth in production in the Southeast 

compared with the Heartland may be partly attributable to State regulations in North Carolina designed to reduce risks associated with manure 

lagoons. Nationally, greater use of comprehensive nutrient management plans, as well as a decline in intensity of manure applications by 
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the largest operations, may be in response to Federal and State policies 

designed to reduce overapplication of manure nutrients. These changes 

suggest that larger hog operations are altering their manure management 

decisions in response to legal nutrient application constraints and that 

environmental policy is contributing to the adoption of conservationcompatible manure management practices.

How Was the Study Conducted?

This study uses information from surveys of U.S. hog producers conducted 

in 1998, 2004, and 2009 as part of USDA’s annual Agricultural Resource 

Management Survey (ARMS). The detailed surveys cover a cross-section 

of U.S. hog operations and collect information on production costs, business arrangements, production facilities and practices, and farm operator 

and fi nancial characteristics. The surveys also provide information about 

manure storage and handling, fertilizer use, manure application techniques, 

Environmental Quality Incentives Program (EQIP) payments, the use of 

comprehensive nutrient management plans, and manure application rates. The 

data allow the authors to document the current state of manure management 

and track producers’ manure management practices during a period of rapid 

change in the hog industry. Data from the surveys are disaggregated by farm 

size according to the number of animal units produced (by 1,000 pounds of 

live animal weight). Because larger hogs produce more manure, animal units 

provide a consistent measure for comparing manure handling trends among 

farms with different levels of manure output. 
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Introduction

Over the past several decades, economic competition has driven substantial 

changes in the hog industry; production has shifted regionally and to larger 

operations that increasingly specialize in a single phase of hog production 

and use production contracts. In turn, the changing farm structure is altering 

manure practices as larger operations seek to manage nutrients on a smaller 

cropland base. At the same time, chemical fertilizer prices have increased 

markedly, providing an incentive for producers to adopt methods that 

conserve and better utilize manure nutrients. 

Changes to the Clean Water Act, State regulations, and confl icts with nearby 

residents over odor and air quality are also infl uencing manure management 

decisions. Changes in the regulatory climate have been driven by increased 

environmental risk to air and water associated with larger livestock operations. Nutrients (nitrogen, phosphorous, potassium), ammonia, hydrogen 

sulfi de, methane, pathogens, and odor can originate at production houses 

where animals are kept, at manure storage structures such as tanks and 

lagoons, or on land where manure is applied. The concentration of animals 

and manure into smaller areas increases the risk of environmental contamination, the nuisance potential of farms, and the overall challenge of managing 

manure. 

We use data from recent surveys of hog farmers to examine how hog manure 

management practices vary with the scale of production and how practices 

changed between 1998 and 2009 (see box, “Data”). The fi ndings provide 

information about the potential effects of recent policies and structural 

changes on manure management technologies and practices, the use of 

nutrient management plans, and manure application rates.
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Data 

We analyzed information from surveys of U.S. hog producers conducted in 1998, 

2004, and 2009 as part of USDA’s annual Agricultural Resource Management 

Survey (ARMS). The detailed surveys cover a cross-section of U.S. hog 

operations each year and collect information on production costs, business 

arrangements, production facilities and practices, and farm operator and fi nancial 

characteristics. The surveys also provide information about manure storage and 

handling, fertilizer use, manure application techniques, payments received under 

the Environmental Quality Incentives Program, the use of comprehensive nutrient 

management plans, and manure application rates. 

The sample of hog farms was chosen from a list of operations maintained by 

USDA’s National Agricultural Statistics Service. The target population of each 

survey was farms having 25 or more hogs at any time during the year. Farms 

with fewer than 25 hogs were screened out to exclude operations that raise hogs 

primarily for on-farm consumption and other noncommercial activities, such as 

youth projects. Each surveyed operation represents a number of similar farms 

in the population as indicated by the observation’s expansion factor, or survey 

weight. The ARMS hog survey sampled operations in 22 States in 1998, 19 States 

in 2004, and 19 States in 2009. When the samples in each survey are expanded by 

their population weights, they represent more than 90 percent of the hog and pig 

inventory on U.S. farms in each survey year. 

Estimates from the three surveys are comparable because of the consistent way in 

which the surveys were conducted and processed. Each survey had broad national 

coverage, represented the same target population, was conducted the same way 

(hand-enumerated) by the same organization, and collected much the same 

information in a similar format. More information about the ARMS and the hog 

surveys, including copies of the questionnaires, can be found at:www.ers.usda.

gov/Briefi ng/ARMS/.

Data from the surveys are disaggregated by farm size according to the number 

of animal units (1,000 pounds of live animal weight) produced. Because 

larger hogs produce more manure, animal units provide a consistent measure 

for comparing farms that produce hogs at different stages of the production 

cycle. For example, farrow-to-fi nish and hog fi nishing operations produce much 

larger hogs, and thus more manure per animal, than do farrow-to-feeder pig and 

specialized nursery operations. The number of animal units on each farm is 

the steady-state live weight of sows, piglets, and other hogs, which is computed 

using average hog inventories and weights from the ARMS.

The environmental implications of hog production depend primarily on the 

manure management decisions of operations having at least 50 animal units. 

These operations accounted for 97 percent of hog sales in the sample frame in 

1998 and 99 percent in both 2004 and 2009. For this reason, and to simplify the 

tabular presentations, statistics for operations with fewer than 50 animal units are 

not reported in most tables and fi gures.
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Structural Change and Manure Management

Changes in manure management practices refl ect changes in the scale, organization, geography, and methods of hog production. The production of hogs 

to be slaughtered for pork involves four phases: (1) breeding and gestation 

(breeding females and their maintenance during gestation); (2) farrowing 

(birth of pigs and care until weaning); (3) nursery (care immediately after 

weaning until about 30-80 pounds); and (4) fi nishing (feeding hogs from 30 

to 80 pounds to a slaughter weight of 225-300 pounds). Hog producers are 

commonly classifi ed according to the number of production phases conducted 

on the operation: (1) farrow-to-fi nish (all four phases); (2) farrow-to-feeder 

pig (phases 1, 2, and 3); (3) feeder pig-to-fi nish (phase 4); (4) wean-to-feeder 

pig (phase 3); (5) farrow-to-wean (phases 1 and 2); or (6) wean-to-fi nish 

(phases 3 and 4).

Historically, most U.S. hog production has occurred on farrow-to-fi nish operations located in areas with an abundant supply of corn. Hog farmers typically used corn produced on the farm as an inexpensive source of feed and 

applied hog manure as fertilizer on farm fi elds. Advancements in breeding 

and genetics, swine housing, nutrition, feeding, and farm management since 

the 1970s have allowed producers to become increasingly specialized in only 

one or two of the production phases. During the period of this analysis, hog 

farms using the farrow-to-fi nish approach declined from 49 percent in 1998 

to 31 percent in 2004 and 23 percent by 2009 (table 1). 

Increases in the scale of production have accompanied changes in organization. Between 1998 and 2009, the number of hog operations fell by about 60 

percent, and the average inventory grew from 2,589 to 7,930 head (table 1). 

Table 1

Hog operation characteristics, 1998, 2004, and 2009

Characteristics for all farms 1998 2004 2009

All farms:

 Number of hog operations 61,971 40,940 24,394

 Hog sales and contract removals (head per farm) 2,589 4,646 7,930

 Hog inventory (animal units per farm) 194 294 546

 Producer type: Farrow-to-fi nish (% of farms) 49 31 23

 Producer type: Feeder pig-to-fi nish (% of farms) 31 40 46

 Used a production contract (% of farms) 15 28 48

 Value of production from hog enterprise (% total) 56 71 70

 Acres of cropland per animal unit 2.14 1.41 0.86

 Farms with no cropland (%) 8 19 19

 Observations in sample 1,633 1,198 1,290

Note: A farm is defi ned as an operation having 25 or more hogs at any time during the year and includes independent hog producers and 

growers who produce hogs under contract. The sample covered operations in 22 States in 1998 and 19 States in 2004 and 2009. Animal 

units are defi ned as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the average number of 

hogs and pigs on the operation in each year. Farrow-to-fi nish operations are those on which pigs are farrowed and then fi nished to a slaughter weight of 225-300 pounds. Feeder pig-to-fi nish operations are those on which feeder pigs are obtained from outside the operation, either 

purchased or placed under contract, and then fi nished to a slaughter weight of 225-300 pounds. Crop acres include land used for hay production, but exclude land used for pasture only.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.
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Over this period, the number of hog operations producing fewer than 300 

animal units declined rapidly, resulting in a shift in production to larger operations (fi gs. 1 and 2). 

Figure 1

Small hog operations declined in number and large operations grew between 1998 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

1998 2004 2009

Farm size (AU)

Number of farms

0

5,000

10,000

15,000

20,000

25,000

30,000

< 50 50-299 300-999 > 1000

Figure 2

Large operations produced an increasing share of output between 1998 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

1998 2004 2009

Farm size (AU)

Percent of production

< 50 50-299 300-999 > 1000

0

10

20

30

40

50

60
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The introduction of contract production arrangements has also played a 

signifi cant role in the evolution of U.S. hog production. In contract production, a pig owner (the contractor) engages a producer (the grower) to take 

custody of the pigs and care for them in the producer’s facilities in exchange 

for a predetermined formula for compensation. Contractors typically furnish 

inputs to growers, provide technical assistance, and collect the livestock to 

pass on for fi nal processing or marketing. Packers or processors obtain hogs 

through marketing arrangements with the contractors (integrators) or directly 

from growers. Contract arrangements allow individual producers to specialize 

in one phase of production and increase their scale of operations.

Over the 11 years analyzed, the share of farms using a production contract 

more than tripled, and now almost half of all hog farms use contracts. An 

even larger share of output is now produced under contract, as the 48 percent 

of farms using production contracts in 2009 accounted for 71 percent of hog 

production. One issue with production contract arrangements is liability for 

managing the hog manure. Most contracts require growers to comply with 

all State, Federal, and local regulations in operating their facilities, and 

failure to comply can result in contract termination (Ogishi et al., 2003). 

Since contract growers are heavily invested in facilities, they are highly 

motivated to avoid liability.

Another structural change with implications for manure management is 

the increasing specialization by operators in the hog enterprise. Among 

hog farms, the contribution of hogs to the farm’s total value of production 

increased from 56 to 70 percent over the study period, with all of the change 

occurring between 1998 and 2004 (table 1). Sources of hog feed also indicate 

increasing specialization in hog production – the share of feed consumed 

by hogs and produced on the same farm fell from about 50 percent in 1992 

to below 20 percent by 2004 (Key and McBride, 2007). The increasingly 

specialized operations, with greater shares of production value from hogs 

and more hog feed from off-farm sources, often produce hogs under contract. 

In a contract arrangement, contractors deliver feed from off-farm sources to 

their growers. This allows individual growers to use their time and fi nancial 

resources to increase the scale of their hog enterprise rather than to cultivate 

crop acreage for feed production. As a result, cropland per animal unit on hog 

operations has steadily declined from 2.14 acres in 1998 to 1.41 acres in 2004, 

and to 0.86 acres in 2009 (table 1). The share of operations with no cropland 

increased from 8 to 19 percent over this period.1 This increase has created 

concerns about how to manage the large quantities of manure generated on 

hog operations with less available cropland per animal unit.2

Geographical shifts in hog production have accompanied structural and organizational changes in the industry. Historically, hog production was concentrated in the Heartland, particularly in Iowa and Illinois, where an abundant 

corn supply provided a cheap source of hog feed and suffi cient acreage on 

which to spread hog manure. During the 1980s and 1990s, hog production 

grew dramatically in the Southeast, especially in North Carolina, driven 

mainly by the growth of large contract operations. Growth in the Southeast 

has posed the challenge of managing an increasing volume of hog manure in 

areas with a denser population and much less crop acreage for manure application than in the Heartland. In 2009, hog operations had about a quarter-acre 

of cropland per animal unit in the Southern regions compared with about 

1Cropland includes land used for hay 

production, but excludes land used for 

pasture only.

2As farms have grown in size, some 

have divided into multiple operations, 

each specializing in hog or crop production. These hog operations selected in 

the ARMS would have reported little 

if any crop acreage because the crop 

acreage was part of the other operation. 

Partnerships between family members 

may organize farms by specializing 

operations in this manner. This arrangement lowers the estimated crop acreage 

per farm and increases the percent 

of hog operations with no crops. The 

extent of this infl uence is unknown, 

but it should not affect the interyear 

comparison of hog farms. 
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1 acre per animal unit in other regions (fi g. 3). Most hog producers in the 

Southeast treat and store manure in lagoon systems and apply manure to farm 

acreage with an irrigation system. In 2009, 90 percent of hogs produced in 

the South were on operations with a lagoon system compared with only 20 

to 30 percent of hogs in other regions (fi g. 3). The lagoon-sprinkler manure 

system increases nitrogen volatilization and allows producers to apply hog 

manure on less acreage than other manure management systems. 

Between 1998 and 2009, the regional distribution shifted again: hog production increased in the Heartland and declined slightly in the South (fi g. 4). 

Production increased in Western States like Colorado and Utah, where 

low population density provides fl exibility in managing animal manure. 

Production in the Heartland region now accounts for about two-thirds of U.S. 

hog output. Lack of growth in the South could be attributed partly to a 1997 

moratorium on the construction of new and expanded hog operations in North 

Carolina (North Carolina General Assembly, 1997). The moratorium was 

enacted in response to environmental concerns about managing hog manure 

from increasingly larger operations.

Structural changes have coincided with substantial effi ciency gains for hog 

farms, particularly on specialized hog-fi nishing operations. Most of these 

productivity gains were attributable to increases in the scale of production 

and technological innovation (Key, McBride, and Mosheim, 2008). Effi ciency 

gains included higher feed productivity (output per unit of feed), which 

can reduce the amount of manure produced by hog operations and thus the 

amount of manure nutrients that must be disposed of. 

Figure 3

Lagoon use high and cropland availability low in Southern Regions, 2009

Note: Regions are ERS designations. Southern Regions include Southern Seaboard and Mississippi Portal; Heartland includes Heartland; 

Western Regions include Northern Great Plains and Prairie Gateway; Other Regions include Northern Crescent, Eastern Uplands, Fruitful Rim, 

and Basin and Range.

Map of regions can be found at: http://www.ers.usda.gov/Data/FarmandRelatedEmployment/DataFiles.htm.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Percent of hogs on operations with lagoon Acres of cropland per animal unit

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

10

20

30

40

50

60

70

80

90

100

Southern Regions Heartland Western Regions Other Regions

Percentage of hogs with lagoon

Cropland acres per animal unit
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Figure 4

Hog production has increased in Heartland region

Note: Regions are ERS designations. Southern Regions include Southern Seaboard and Mississippi Portal; Heartland includes Heartland; 

Western Regions include Northern Great Plains and Prairie Gateway; Other Regions include Northern Crescent, Eastern Uplands, Fruitful Rim, 

and Basin and Range.

Map of regions can be found at: http://www.ers.usda.gov/Data/FarmandRelatedEmployment/DataFiles.htm/.

Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the average 

number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Number of animal units

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

Southern Regions Heartland Western Regions Other Regions

1998 2004 2009
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Environmental Policy Background

Changes in environmental policies have also infl uenced manure management decisions. Many hog producers value the preservation of environmental 

quality and have found that profi table business practices are consistent 

with improved manure management practices. Nonetheless, concerns about 

water quality and air quality (primarily odor) have spurred local, State, and 

Federal action to mitigate environmental impacts of animal manure. The U.S. 

Environmental Protection Agency (U.S. EPA) revised Clean Water Act regulations in 2003 for controlling runoff of manure nutrients from the largest 

animal feeding operations (AFOs). These regulations were fi nalized in 2008. 

Clean Water Act regulations now require animal feeding operations designated as Concentrated Animal Feeding Operations (CAFOs) and discharging 

or proposing to discharge manure effl uent to seek National Pollutant 

Discharge Elimination System (NPDES) permit coverage. Discharge from 

the production area and any land application areas under the control of the 

CAFO are included in the permit. CAFOs with permits must have a nutrient 

management plan that identifi es site-specifi c practices to ensure agronomic 

use of nutrients. 

Under the new regulations, CAFOs that are not required to have an NPDES 

permit, but that wish to claim the agricultural stormwater exemption for 

runoff from fi elds receiving manure, must implement a nutrient management plan to minimize polluted runoff. If a waterway becomes polluted 

with animal waste from fi eld runoff and a CAFO does not follow a nutrient 

management plan, the CAFO will be violating the Clean Water Act. 

Enforcement of these updated Federal CAFO rules is largely devolved to 

individual States, which have adopted the new rules at various rates. In April 

2010, the EPA reported that most States are expected to complete revisions to 

comply with the updated Federal rules by the end of 2010.

Atmospheric emissions of pollutants are regulated by the Clean Air Act 

(CAA). The CAA authorizes regulatory programs primarily for protecting 

human health. EPA recently initiated development of regulations for reducing 

fi ne particulates in the atmosphere (referred to as PM2.5, for particles less 

than 2.5 microns in size). The Clean Air Act requires State, local, and tribal 

governments to identify areas not meeting national air quality standards for 

fi ne particles (one of the six criteria pollutants regulated under the act) (U.S. 

EPA, 2004). States with designated nonattainment areas were required to 

submit plans outlining how they would meet the standards by 2010. This 

regulation could affect animal operations because ammonia emitted from 

barns and manure storage facilities is a major precursor of fi ne particulates. 

Controlling ammonia from animal operations would be a likely priority in 

nonattainment areas with high concentrations of animals (U.S. EPA, 2000a). 

To gather data and develop generalized protocols, a 2006 EPA consent agreement encouraged livestock producers to volunteer for emissions monitoring in 

exchange for clemency for past air pollution violations (U.S. EPA, 2006). The 

National Air Emissions Monitoring Study (NAEMS) was concluded in 2010, 

and in early 2011 the EPA stated that the data were available for release (U.S. 

EPA, 2011). 
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Since 2010, a new Greenhouse Gas Reporting Rule has required owners and 

operators of facilities that contain manure management systems emitting at 

least 25,000 metric tons of greenhouse gases per year (expressed as carbon 

dioxide equivalents) to report emissions from all sources at the facility for 

which emission calculation methods are defi ned. EPA estimates that this rule 

will cover from about 85 to 95 of the Nation’s largest livestock facilities (U.S. 

EPA, 2009b).3

Other legislation covering air pollution includes the Comprehensive 

Environmental Response Compensation and Liability Act (CERCLA) and 

the Emergency Planning and Community Right-to-Know Act (EPCRA). 

Both laws use information disclosure to increase the information available 

to governments and citizens about the sources and magnitude of chemical 

releases to the environment. CERCLA requires that facilities report to EPA 

when releasing more than a “reportable quantity” (e.g., 100 pounds in a 

24-hour period) of a hazardous substance. EPCRA requires that a facility 

report to State and local authorities any releases reported under CERCLA. 

EPA is authorized to require long-term remedial action that signifi cantly 

reduces threats to public health. Though CERCLA was originally focused on 

hazardous wastes from industrial plants, the increased size and consolidation 

of animal feeding operations may make their ammonia and hydrogen sulfi de 

emissions subject to the notifi cation provisions of the act. EPA has enforced 

the CERCLA and EPCRA reporting requirements of animal feeding operation releases of hazardous pollutants in two cases (Copeland, 2008). 

However, due to controversy over the use of these laws for agricultural emissions (Copeland, 2008), the EPA issued a reporting exemption for air releases 

of hazardous substances from animal waste at farms in 2009 (U.S. EPA, 

2009a). The rule exempts all farms that release hazardous substances from 

animal waste to the air from reporting under CERCLA. Farms that do not 

meet the size defi nition of a CAFO (as defi ned by the Clean Water Act) are 

also exempt from reporting under EPCRA. However, farms that do meet the 

size defi nition of a CAFO are still required to submit the appropriate reports 

to State and local offi cials under EPCRA if they release hazardous substances 

to the air that meet or exceed their Reporting Quantity.

Odor arising from livestock operations has become a source of controversy 

in many agricultural communities, prompting numerous States to adopt 

some form of odor regulation (Redwine and Lacey, 2000; Sneeringer, 

2010). These State policies may contain objective odor standards or require 

management methods such as separation distances, explicit odor plans, or 

“good neighbor practices.” Several States include odor stipulations in their 

general permits for livestock operations (U.S. EPA, 2002b). To the extent 

that odor is correlated with levels of certain air emissions (particularly 

hydrogen sulfi de and ammonia), State policies to limit such emissions may 

also help to control odor.

Most States have implemented regulations for controlling at least some of 

the environmental impacts of AFOs, including permits, licenses, and zoning 

requirements. To prevent large amounts of waste from being carried into 

coastal estuaries during major rain events such as hurricanes, North Carolina 

entered into a legal agreement with the State’s largest swine producers 

to develop innovative waste management strategies that would replace 

3The EPA report does not specify 

which types of livestock facilities will 

be covered. 
10

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uncovered lagoon and sprayfi eld systems for storing and treating waste from 

large hog operations (Williams, 2004; Bales et al, 2000). In 1997, the State 

issued a moratorium on the construction of new or expanded facilities in 

order to study and put in place a regulatory system to ensure that waste structures were sound, that waste application methods were adequate, and that 

viable waste utilization plans were in place. Iowa, Pennsylvania, Arkansas, 

and Kentucky are among States that have introduced rules for curbing water 

pollution, ammonia, and odor from AFOs (Patton and Seidl, 1999; U.S. EPA, 

2002a,b).

Agricultural-residential confl icts at the rural-urban interface seem to 

be increasing as residential development expands further out into rural 

areas, while market conditions push farmers to intensify their production 

(Bergstrom and Centner, 1989; Centner, 2002; Duke and Malcolm, 2003; 

Jacobson et al., 2006). Confl icts that arise over environmental concerns are 

most prevalent for animal operations (Duke and Malcolm, 2003; Centner, 

2002). Agricultural-residential proximity can result in citizen complaints to 

local authorities and actual and threatened lawsuits over perceived threats to 

health and environmental quality, even when no laws have been broken. Such 

actions may force farmers to modify their production practices. Adoption of 

“acceptable” nutrient management plans and practices is a way that farmers 

can demonstrate due care and possibly protect themselves from confl ict over 

environmental quality (Centner, 2002).

To help defray the costs of meeting the regulations, producers can apply 

for fi nancial assistance from the USDA’s Environmental Quality Incentives 

Program (EQIP).4 A farmer or entity may receive up to $300,000 for all 

EQIP contracts entered during a 6-year period to help develop and implement a nutrient management plan, construct appropriate animal and manure 

handling and storage facilities, or transfer and apply manure to land in an 

approved manner (Ribaudo, Cattaneo, and Agapoff, 2004).

Some major hog producers, such as Smithfi eld Foods, are taking the necessary steps for meeting voluntary environmental performance standards established by the International Organization for Standardization. ISO 14001 is 

the Environmental Management System (EMS) standard that measures how 

well companies manage those parts of their operation that affect the environment (Wall et al., 2001). The EMS includes such elements of hog production 

as sanitation, waste treatment systems, and nutrient management. The EMS is 

certifi ed by a qualifi ed third party.

4For more information about EQIP 

see the USDA Natural Resource 

Conservation Service website: http://

www.nrcs.usda.gov/programs/eqip/. 
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Manure Management on U.S. Hog Farms

One consequence of structural change in U.S. hog production has been 

the manure management challenge posed by concentrating more animals 

on a limited land base. Hog manure is primarily handled in two types of 

storage structures, lagoons and pits or tanks (see box, “Manure Storage and 

Handling Strategies”). Lagoons are large earthen containment structures 

into which manure and wastewater are fl ushed and maintained in liquid form 

until removed. Manure pits are often located under hog production facilities 

where, in the typical system, manure drops into pits through slatted fl oors 

and is stored in a slurry form until removed. These storage structures hold 

the manure until it can be land-applied on the same farm or nearby farms to 

meet crop nutrient needs. Technologies for land application include liquid/

slurry manure spreaders that may or may not incorporate manure into the soil 

at application and irrigation systems that spread the liquid lagoon solution on 

nearby fi elds.

The different systems for manure management have very different impacts 

on the nutrient content of the manure, primarily nitrogen, and thus on the 

amount of land needed to spread manure (McBride and Key, 2003). For 

example, handling manure in pit or tank storage and using slurry spreaders to 

inject the manure into the soil manages the manure for its potential fertilizer 

value. This system is designed to retain manure nitrogen for crop use, and 

thus it requires more land on which to apply the manure if the operation is 

following a nitrogen-based nutrient management plan. In contrast, handling 

manure from lagoon storage and distributing it with irrigation increases 

the release of nitrogen into the atmosphere, reducing the manure’s nutrient 

content and requiring less land for application. 

Manure Storage and Handling

Lagoon use has a strong positive association with the scale of production 

(fi g. 5). For example, in 2009, 41 percent of operations with at least 1,000 

head used a lagoon, compared with only 22 percent of small-scale operations 

and 27 percent of medium-scale operations. Despite the trend toward larger 

operations, there was a shift between 1998 and 2009 toward the use of pit/

tank systems. By 2009, 62 percent of hogs were raised on farms using pit/

tanks (up from 37 percent in 1998); in 2009, 34 percent were raised on farms 

using a lagoon system (down from 55 percent in 1998).5 This shift can be 

partly attributed to regional shifts in hog production. In the Southern region, 

more hogs are produced on operations that use lagoon systems, while in other 

regions more hogs are produced on operations using pit/tanks (fi g. 3). Hence, 

the largely stagnant hog production in the South, combined with an increase 

of production in the Heartland between 1998 and 2009 (fi g. 4), partly 

explains the increasing national use of pit/tanks. The shift to pit systems may 

also have been encouraged by rising prices of chemical fertilizers, which 

increased incentives for new hog facilities to adopt designs that conserve 

manure nutrients for use on nearby crop or hay land.

The manure storage facility generally determines how manure effl uent is 

transported and applied to crops. Pit/tank systems commonly use a slurry or 

liquid spreader, while irrigation technology (solid-set sprinklers, traveling 

5In tables 2–7, “all farms, weighted 

by animal units” gives the mean values 

computed using a weight defi ned as the 

sample weight times the animal units 

on the operation. This weighted mean 

describes the manure system used on 

the average animal unit rather than the 

average farm.
12

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Manure Storage and Handling Strategies

Comprehensive nutrient management plan (CNMP) - Following 

a comprehensive nutrient management plan for applying manure and 

commercial fertilizer to land can reduce losses of nutrients to water 

resources through runoff or leaching (USDA, NRCS, 2005). Nutrient 

management matches applications to crop needs so that as few nutrients 

as possible are lost to the environment. A CNMP is a group of conservation practices and management activities that ensure that both production and natural resource protection goals are achieved. Specifi c elements 

of a CNMP include background and site information; plans for manure 

and wastewater handling and storage, farm safety and security, land treatment practice, and prevention of soil erosion; nitrogen and phosphorus 

risk assessment; plans for nutrient management in accord with criteria in 

the Nutrient Management Conservation Practice (code 590); and recordkeeping. Important objectives in comprehensive nutrient management 

planning include soil and manure testing for nutrient content, balancing 

farm-available nutrient resources with farm crop needs, and monitoring 

the operation’s total nutrient balance to account for nutrients generated, 

fi eld-applied, removed in products, or transferred offsite. Plans can also 

account for atmospheric losses of nitrogen, as well as for atmospheric 

deposition of nitrogen on cropland. 

Manure incorporation and injection - Rapidly incorporating manure 

into the soil, either by plowing or disking solids after spreading or injecting 

liquids and slurries directly into the soil, reduces odor and gaseous emissions (Abt, 2000; Arogo et al., 2002). It also reduces the risk of nutrients 

being transferred to adjacent water bodies.

Slurry pits - Slurry systems store undiluted, untreated manure in watertight tanks or pits until it can be land-applied. Storage can be either under 

the house or outdoors. The stored slurry is surface-applied to fi elds by 

sprayer trucks or wagons, incorporated into the soil with chisel plows 

behind nurse tanks, or directly injected into the soil with drag hoses (U.S. 

EPA, 2004a).

Lagoons - Lagoon systems use holding ponds to treat diluted manure for 

an extended period of time. Lagoons stabilize organic matter, reduce the 

nutrient mass that must be land-applied, and vent a large quantity of the 

manure nitrogen as ammonia. Some of the diluted lagoon liquid is used 

to fl ush the production houses. The “digested” lagoon liquid is eventually sprayed on cropland. Lagoons are used primarily in warmer climates 

where the anaerobic processes can take place year-round (U.S. EPA, 

2004a). 
13

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guns, and linear or circular traveling booms) is used to move and apply 

lagoon liquid. The method of applying manure can have important implications for air quality, affecting the level of odorous gases (ammonia and 

hydrogen sulfi de), particulate matter (including byproducts of ammonia), and 

greenhouse gases (methane and nitrous oxide) (Aillery et al., 2005). 

Both solid and liquid manure can be incorporated into the soil, which reduces 

odor and nutrient volatilization (escape into the atmosphere) relative to 

spreading, keeping more nutrients available for plant uptake. Incorporation 

also reduces the risk of nutrient runoff. Sprinkler application increases 

nitrogen volatilization, which reduces the nitrogen available for plant use. 

Lagoon/sprinkler systems allow producers to dispose of manure from a given 

operation on fewer acres when a nitrogen criterion is used to determine application levels.

The type of manure-spreading technologies used is often related to the scale 

of production. Among large farms that applied manure to crops, irrigation 

was the most common form of manure application, followed by injection of 

liquid manure (table 2). In contrast, smaller operations were more likely to 

spread solid manure, or to spread liquid manure without injection. Between 

1998 and 2009, the share of appliers who spread solid manure declined 

overall, from 64 percent of operations in 1998 to only 34 percent in 2009. 

Most of this change occurred because (1) the number of small farms, which 

are more likely to handle solid manure, declined and (2) small and medium 

farms handled manure in solid form less often. 

Growers altered their spreading technologies between 1998 and 2009 toward 

methods that produce less odor, nutrient volatilization, and runoff. The share 

Figure 5

Changes in the share of operations having lagoon and pit manure systems, 1998 to 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Percent

50-299 300-999 > 1000

0

10

20

30

40

50

60

70

80

90 Lagoon 1998 Lagoon 2004 Lagoon 2009

Pit 1998 Pit 2004 Pit 2009
14

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of animal units on operations where liquid manure was applied without 

soil injection declined from 25 to 12 percent. The share of large operations 

applying liquid manure with injection technologies increased 10 percentage 

points and the share of large operations applying manure with irrigation 

declined 15 percentage points (although neither of these are statistically 

signifi cant).

Manure Application and Disposal

On average, larger hog operations harvested more cropland, applied manure 

to more acres on-farm, and applied manure to a larger share of their cropland (table 3). These relationships are refl ected in the aggregate statistics, as 

the average farm size increased between 1998 and 2009. Over this period, 

the average amount of cropland on a hog farm increased from 448 to 578 

Table 2

Hog manure application technologies used on farms applying manure

Application technology 1998 2004 2009

All farms that apply manure:

 Solid spreader 64 45** 34**

 Liquid spreader (no injection) 27 18** 19**

 Liquid spreader (injection) 20 21 25

 Irrigation 12 13 19*

All farms that apply manure, weighted by animal units:

 Solid spreader 36 19** 14**

 Liquid spreader (no injection) 25 17* 12**

 Liquid spreader (injection) 30 34 34

 Irrigation 34 36 35

Farm size category (farms that apply manure):

 Small (50 – 299 animal units)

 Solid spreader 66 40** 38**

 Liquid spreader (no injection) 40 28** 38

 Liquid spreader (injection) 28 31 23

 Irrigation 9 10 16**

 Medium (300 – 999 animal units):

 Solid spreader 32 23 15**

 Liquid spreader (no injection) 28 19 14*

 iquid spreader (injection) 42 37 42

 Irrigation 32 28 21

 Large (> 1,000 animal units):

 Solid spreader 10 10 10

 Liquid spreader (no injection) 7 12 8

 Liquid spreader (injection) 20 30 30

 Irrigation 58 57 43

Note: Asterisks indicate level of signifi cance for the test of the null hypothesis that mean equals 

1998 mean: ** =5%, * = 10%. Some operations may have used more than one technology or 

none of the technologies. Therefore, the columns may add up to more than or less than 100 

percent. 

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.
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acres, and the number of manure-applied acres increased from 85 to 136. As 

a result, the share of cropland on hog farms on which manure was applied 

increased from 19.1 to 23.5 percent. This trend was mainly driven by the 

largest operations, where the share of cropland with manure application 

increased from 25 percent in 1998 to 30.9 percent in 2009.

Even though the share of on-farm cropland with manure application increased 

between 1998 and 2009, the average hog operation applied manure to less 

than a quarter of its cropland in 2009. This indicates that the potential exists 

to spread manure over more on-farm crop acreage. However, farmland is 

often separated by considerable distances from hog facilities, implying that 

operators could face substantially higher manure transportation and application costs if they were to apply manure on more acreage. 

Figure 6 illustrates the strong positive association between scale of production and manure application intensity (animal units per manure-applied acre, 

Table 3

Hog manure application technologies used on farms applying manure

1998 2004 2009

All farms that apply manure:

 Acres with manure application 85 86 136**

 Acres of cropland 448 483 578**

 Percent of cropland with manure application 19.1 17.8 23.5*

 Application intensity (AU/acre applied) 2.1 3.0** 3.7**

All farms that apply manure, weighted by animal units:

 Acres with manure application 147 218** 278**

 Acres of cropland 596 855** 919**

 Percent of cropland with manure application 24.7 25.5 30.2

 Application intensity (AU/acre applied) 7.2 7.4 6.4

Farm size category (farms that apply manure)

 Small (50 – 299 animal units):

 Acres with manure application 95 85 101

 Acres of cropland 517 599 592

 Percent of cropland with manure application 18.4 14.2* 17.1

 Application intensity (AU/acre applied) 1.3 1.6 1.5

 Medium (300 – 999 animal units):

 Acres with manure application 156 169 178

 Acres of cropland 565 652 661

 Percent of cropland with manure application 27.6 26.0 27.0

 Application intensity (AU/acre applied) 2.9 3.0 3.2

 Large (> 1,000 animal units):

 Acres with manure application 159 224 281**

 Acres of cropland 643 1016* 909

 Percent of cropland with manure application 25.0 22.0 30.9

 Application intensity (AU/acre applied) 9.4 8.0 6.2**

Note: Asterisks indicate level of signifi cance for the test of the null hypothesis that mean equals 

1998 mean: ** =5%, * = 10%.

Source: USDA, ERS, 1998, 2004 and 2009 Agricultural Resource Management Surveys.
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adjusted for the share of manure removed from the operations).6 The higher 

application rates for larger operations refl ect the large amount of manure 

generated by larger hog operations compared with the cropland on these 

operations available for manure application. Between 1998 and 2009, the 

increase in total animal units produced outpaced the increase in crop acreage 

on which manure was applied, resulting in a 74-percent increase in average 

manure application intensity. However, this increase was driven mainly by 

operations with fewer than 1,000 animal units. For operations with more than 

1,000 animal units—which are more likely to be subject to nutrient management restrictions—the application intensity actually declined by 34 percent 

(fi g. 6). Because large farms are responsible for a large share of hog output, 

the application intensity for the average unit of production (rather than the 

average farm) fell by 11 percent between 1998 and 2009.

Qualifying the measure of manure application intensity is important. 

Different storage and handling techniques help determine the quantity of 

nutrients in applied manure, so application intensity does not measure actual 

nutrient application rates. In addition, increases in feed effi ciency have likely 

reduced the quantity of nutrients excreted by hogs. Nitrogen and phosphorus 

enter the production system in animal feed. Some of the nutrients are retained 

in the animal product (meat), but most are excreted in urine and manure 

(Follett and Hatfi eld, 2001; ASAE, 2005). In addition, feed effi ciency is 

positively correlated with the scale of production – larger operations generally use less feed per hog produced. Hence, the nutrient application intensity 

6For the intensity ratio, the denominator is the acres of land on the hog 

operation on which manure was 

applied. The numerator is the farm 

inventory (AU), adjusted for the 

removal of manure off the farm. For 

farms that moved manure off the operation, the number of AU was reduced 

by the equivalent amount of manure 

removed. For example, if 50 percent of 

the manure was moved off a 1,000-AU 

operation, only 500 AU was used to 

compute the ratio. 

Figure 6

Manure application intensity increased with scale of production, but large-scale operations reduced 

intensity between 1998 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year. The manure application intensity is the hog inventory (AU) adjusted for the 

removal of manure off the farm divided by the acres of land on the hog operation on which manure was applied. For farms that moved manure 

off the operation, the number of AU was reduced by the equivalent amount of manure removed. For example, if 50 percent of the manure was 

moved off a 1,000-AU operation, only 500 AU was used to compute the ratio.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Application intensity

1998 2004 2009

50-299 300-999 > 1000

0

1

2

3

4

5

6

7

8

9

10
17

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(e.g., nitrogen per acre) is generally lower on larger farms than the estimated 

manure application intensity (animals per acre) would imply.

Among all hog operations, 76 percent applied some manure on their farms 

in 2009, a decrease from 82 percent in 2004 (table 4). The share of farms 

applying manure declined over this period for all size categories, particularly the medium- and large-size groups. Part of the overall decline can be 

explained by the shift to larger operations, which were less likely to apply 

Table 4

Manure application and removal

Percent

1998 2004 2009

All farms:

 Applied manure on farm 83 82 76*

 Removed manure from operation 14 21** 21**

 Sold manure 0 2* 5**

 Paid for manure removal 2 2 2

 Manure given away free 12 18* 16*

All farms, weighted by animal units:

 Applied manure on farm 85 76 74*

 Removed manure from operation 23 31 34**

 Sold manure 1 5 9**

 Paid for manure removal 4 4 5

 Manure given away free 19 23 24

Farm size category

 Small (50 – 299 animal units):

 Applied manure on farm 89 89 83

 Removed manure from operation 16 14 17

 Sold manure 0 2 2**

 Paid for manure removal 2 2 3

 Manure given away free 14 11 13

 Medium (300 – 999 animal units):

 Applied manure on farm 90 83 79**

 Removed manure from operation 31 27 29

 Sold manure 2 5 9

 Paid for manure removal 8 5 3

 Manure given away free 23 18 22

 Large (> 1,000 animal units):

 Applied manure on farm 85 69 75

 Removed manure from operation 26 38 37

 Sold manure 1 3 9**

 Paid for manure removal 1 3 1

 Manure given away free 24 31 26

Note: Asterisks indicate level of signifi cance for the test of the null hypothesis that mean 

equals 1998 mean: ** =5%, * = 10%.

Source: USDA, ERS, 1998, 2004 and 2009 Agricultural Resource Management Surveys.
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manure on-farm than smaller operations in each of the three surveys. In 2009, 

75 percent of large farms applied manure on-farm compared with 79 percent 

of medium-size farms and 83 percent of small farms. 

Manure that is not applied on-farm is usually hauled off-farm for application to cropland on neighboring farms. Because large hog operations have 

relatively less cropland available on-farm, the relationship between the 

scale of production and the quantity of manure removed is positive (table 

4). The overall share of farms removing manure grew 50 percent between 

1998 and 2004, and this increase was attributable mainly to large operations. Between 2004 and 2009, the share of farms removing manure did 

not increase markedly. Most of the manure removed from farms was given 

away to nearby farms. However, there appears to be a growing trend toward 

selling manure—the share of farms selling manure increased in all farm size 

categories between 1998 and 2009, albeit from a very low beginning level. 

Larger operations were more likely to sell manure. In 2009, 9 percent of the 

largest operations sold manure, compared with only 1 percent in 1998. The 

increasing manure sales could be partly explained by the dramatic rise in 

chemical fertilizer prices, which increased 174 percent between 1998 and 

2009.7

Manure Nutrient Management Practices

Table 5 describes the evolution of manure management practices between 

1998 and 2009. Manure nutrient testing, a practice required as part of many 

State-mandated manure management plans, was positively associated with 

7From “Fertilizer Use and Price 

Tables: Fertilizer Price Indexes,” USDA 

Economic Research Service. Accessed 

November 2010 at: www.ers.usda.gov/

Data/FertilizerUse/Tables/Table8.xls.

Table 5

Nutrient management practices

Percent

Management practices 1998 2004 2009

All farms:

 Tested manure for N content 18 29** 49**

 Tested manure for P content 17 28** 48**

 Applied commercial fertilizer and manure 61 58 50**

 Applied manure to Bermuda grass (appliers only) n.a. 11 7

 Followed CNMP1 n.a. 30 55

 Added microbial phytase to feed 4 13** 23**

All farms, weighted by animal units:

 Tested manure for N content 51 73** 86**

 Tested manure for P content 50 72** 84**

 Apply commercial fertilizer and manure 48 39* 44

 Applied manure to Bermuda grass (appliers only)

 Followed CNMP1 n.a. 62 82

 Added microbial phytase to feed 12 30** 39**

N=Nitrogen; P=Phosphorous. Asterisks indicate level of signifi cance for the test of the null 

hypothesis that mean equals 1998 mean: ** =5%, * = 10%. n.a. indicates data not available. 1CNMP is a comprehensive nutrient management plan (see box, “Manure Storage and 

Handling Strategies,” page 12).

Source: USDA, ERS, 1998, 2004 and 2009 Agricultural Resource Management Surveys.
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scale of production (fi g. 7). Larger operations are more likely to face State 

regulations that require nutrient management plans. The share of farms 

testing for nitrogen (N) increased from 18 to 29 percent between 1998 and 

2004 and to 49 percent in 2009. The share of animal units on farms that 

tested manure for N increased from 51 percent to 73 percent to 86 percent 

over the three surveys. Nitrogen testing rates increased for all farm size 

categories, especially medium-scale operations (fi g. 7). Large operations did 

not have as much scope to increase their testing rate because 81 percent of 

these farms tested in 1998 (fi g. 7). The patterns for phosphorus (P) testing are 

similar to those displayed for N testing. 

Commercial fertilizer is applied to crops in addition to manure if the manure 

nutrients do not meet the nutritional needs of the crops. Testing the nutrient 

content of manure thus saves costs by avoiding the overapplication of supplemental commercial fertilizer. Larger operations are more likely to have a 

surplus of nutrients provided by the manure produced on their operations and 

are therefore less likely to require supplemental commercial fertilizer. The 

association between the scale of production and the application of commercial fertilizer on acreage where manure was applied is negative (fi g. 8). 

One strategy for increasing manure disposal on a limited land base is to 

plant crops that have a high rate of nutrient uptake. Bermuda grass, which is 

grown primarily in the South and Southeast, is especially appealing to hog 

producers because it consumes large amounts of nitrogen per acre. The scale 

of production and the application of manure to Bermuda grass had a strong 

positive association in 2004 and 2009 (fi g. 9). Between 2004 and 2009 (the 

only years for which the data are available), the share of operations applying 

manure to Bermuda grass dropped. This drop may be explained by the 

Figure 7

Operations increased rate of manure nitrogen (N) testing between 1998 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Percent of operations

1998 2004 2009

50-299 300-999 > 1000

0

10

20

30

40

50

60

70

80

90

100
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Figure 8

Application of commercial fertilizer with manure declines with size

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Percent of operations

1998 2004 2009

50-299 300-999 > 1000

0

10

20

30

40

50

60

70

80

Figure 9

Larger operations are more likely to apply manure to Bermuda grass 

2004 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory 

of animal units is based on an estimate of the average number of hogs and pigs on the 

operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Operation size (AU)

Percent of appliers

2004 2009

50-299 300-999 > 1000

0

5

10

15

20

25

30

35
21

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increasing use of manure as a substitute for commercial fertilizer—which 

increased in price by 106 percent in nominal terms over this period—and by 

the shift in the share of total production from the South and Southeast to the 

Heartland.

Microbial phytase is used as an additive in fi nishing hog diets to increase the 

absorption of organic phosphorus, meaning that supplemental inorganic or 

mineral phosphorus may not be needed and feed costs are reduced. Increases 

in the price of phosphorus over the study period boosted incentives to add 

phytase to feed to reduce phosphorus supplements. In addition, phytase use 

reduces phosphorus excretion in manure. When application rates are limited 

by phosphorus as opposed to nitrogen, lower manure phosphorus content can 

lead to increased spreading options by reducing the acres required to safely 

absorb manure nutrients. Farms with at least 300 animal units were much 

more likely to use microbial phytase than were smaller scale operations (fi g. 

10). The share of farms using phytase grew in all size categories between 

1998 and 2009, with the overall share of farms using phytase increasing from 

4 to 23 percent. The share of hogs raised on farms using phytase increased 

from 12 to 39 percent. Concern about manure phosphorus levels is also 

evident from the increase in the share of farms testing manure for phosphorus 

content between 1998 and 2009 (table 5).

In 2004, about 30 percent of all farms followed a CNMP that required 

growers to apply manure nitrogen at or below the agronomic rate (see box, 

“Manure Storage and Handling Strategies”).8 By 2009, the share of farms 

following a CNMP had increased to 55 percent. The share of animal units 

raised on farms using a CNMP increased between 2004 and 2009 from 62 

to 82 percent. The association between the scale of production and the use 

8The goal of manure application is 

to apply manure at rates that meet crop 

needs while avoiding overapplication 

that could impair water quality. Rates 

that meet this goal are often called 

agronomic rates.

Figure 10

Use of microbial phytase in feed increased between 1998 and 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Percent of operations

1998 2004 2009

50-299 300-999 > 1000

0

5

10

15

20

25

30

35

40

45
22

Trends and Developments in Hog Manure Management: 1998-2009 / EIB-81

Economic Research Service/USDA

of a CNMP is positive (fi g. 11). About 46 percent of operations with 50-299 

animal units followed a CNMP in 2009, compared with more than 80 percent 

of those with at least 300 animal units. 

Manure Management for Air Quality

Air quality concerns related to manure include odorous gases (including 

ammonia and hydrogen sulfi de), particulate material (byproducts of 

ammonia), and greenhouse gases (methane and nitrous oxide). Air pollutants 

are emitted from livestock buildings and manure management and treatment facilities, and from the land application of manure (National Research 

Council, 2003). Hydrogen sulfi de and ammonia have been implicated in 

human and swine health problems (Carson, Osweiler, and Thorne, 2002; 

Donham, 2002). Modeled predictions suggest that the livestock sector is the 

source of a signifi cant share of total U.S. ammonia emissions (EPA, 2000b). 

Individual health incidents involving livestock operation employees and 

public health fi ndings pertaining to residents in the vicinity of livestock facilities provide indications of hog production’s role in air pollution (Sneeringer, 

2009; Cole, Todd, and Wing, 2000). 

One of the challenges in addressing the environmental problems associated with livestock waste is the tradeoff between air and water pollution. 

Regulations designed to improve water quality may encourage manure 

management practices that result in greater air emissions, or vice versa 

(Aillery et al., 2005). For example, in order to reduce manure’s nutrient 

content and meet regulatory nutrient application limits on cropland, operators 

may allow manure to decompose in uncovered lagoons rather than enclosed 

pits, which may result in more air pollution. 

Figure 11

More operations followed a CNMP and received EQIP payments in 2009

Note: Animal units (AU) are defined as 1,000 pounds of live animal weight, and the inventory of animal units is based on an estimate of the 

average number of hogs and pigs on the operation in each year.

Source: USDA, ERS, 1998, 2004, and 2009 Agricultural Resource Management Surveys.

Farm size (AU)

Percent of operations

50-299 300-999 > 1000

0

10

20

30

40

50

60

70

80

90

CNMP 2004 CNMP 2009

EQIP 2004 EQUIP 2009
23

Trends and Developments in Hog Manure Management: 1998-2009 / EIB-81

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The type of manure storage facility used affects the level of ammonia and 

other odorous gases. Lagoons reduce manure’s nitrogen content through 

anaerobic digestion and ammonia volatilization. This allows farmers to apply 

more manure on less land without exceeding crop nutrient requirements, 

thereby lowering manure transportation costs by eliminating the need to 

transport manure to more distant cropland. In contrast, pit manure facilities, 

which conserve manure nutrients for use on cropland, emit less ammonia. It 

has been estimated that operations using lagoons emit almost twice as much 

ammonia per animal as operations using pit systems (Key and Kaplan, 2007).

Lagoon covers – plastic covers that fl oat on the lagoon surface or that are 

tented over lagoons – can greatly decrease gaseous emissions, including 

ammonia (Jacobson et. al., 1999; Arogo et al., 2002). In 2009, 5 percent of 

the hog farms in the survey that had a lagoon used a cover to control odor 

and air emissions. Among hogs produced on operations with lagoons, only 

4 percent were produced on operations with lagoon covers, suggesting that 

operations with covers are somewhat smaller than average. Covering manure 

storage tanks can also greatly reduce the discharge of ammonia to the atmosphere. Storage tanks can be covered with a roof, concrete lid, or fl exible 

plastic cover. The surface of the stored waste can also be covered with straw 

or other materials (polystyrene foam, air-fi lled clay balls) that act as biofi lters. 

While reducing ammonia emissions from the storage facility, lagoon and pit 

covers increase the nitrogen content of effl uent that is eventually spread on 

fi elds. This raises the potential for both ammonia emissions and nitrate pollution of water resources from the manure applied to fi elds. 

Some covered systems (anaerobic digesters) also capture methane and burn 

it as a biofuel to generate electricity. Methane is produced when livestock 

manure decomposes anaerobically (without oxygen). Lagoon and pit manure 

handling systems that are common on dairy and hog operations emit large 

amounts of methane. Methane is a potent greenhouse gas that has about 25 

times the global warming potential of carbon dioxide. Burning the methane 

captured from an anaerobic digester greatly reduces the gas’s global warming 

potential. (See box, “Anaerobic Digesters and Greenhouse Gas Emissions.)

Manure can be managed in a variety of ways to control odor. Chemicals can 

be added to manure during its collection in order to bind odorous compounds 

and reduce ammonia emissions. Trapping air vented from production houses 

and treating it before discharge to the atmosphere can also reduce odorous 

compounds. Table 6 displays the percentage of farms in 2004 and 2009 that 

used additives or fi lters to control odor. Between 2004 and 2009, the share 

of farms that added chemicals to manure rose from 13 to 17 percent, while 

the share of animals on operations that added chemicals fell slightly, from 31 

to 29 percent. About 5 percent of operations used fi lters to ventilate barns to 

control odor in both years, although the share of livestock produced by these 

operations decreased slightly, from 10 to 8 percent.

Environmental Policy Effects on Manure Management

Recent policy initiatives may explain some of the changes in manure management practices. Federal and State policies implemented in recent years have 

set limits on the amount of nutrients that can be applied per acre of land. 

Restricting application rates may help explain increases in the crop acreage 
24

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receiving animal manure and the amount of manure moved off the farm, as 

well as the widespread adoption of nutrient management plans observed in 

the ARMS. 

States have adopted the updated 2008 Federal NPDES rules regarding 

CAFOs at different paces, creating variation in regulation status. 

Consequently, examining how manure management practices vary 

according to a State’s degree of regulation adoption is possible. States are 

placed in one of three categories according to EPA’s summary of the status 

of CAFO rule adoption (EPA, 2010b). The fi rst category includes States 

Anaerobic Digesters and Greenhouse Gas Emissions

Anaerobic digesters, also known as “methane digesters,” “biodigesters,” 

or “biogas recovery systems,” can be used with lagoon or pit-type manure 

storage facilities to collect manure, optimize it for the production of 

methane by adjusting temperature and water content, capture the biogas, 

and burn it for heat or electricity generation. Methane digesters can provide 

numerous benefi ts to livestock producers and the environment. Digesters 

can supply a renewable source of electricity to power farm equipment or be 

sold to the electricity distribution grid. Digesters can reduce greenhouse 

gas emissions, odors from manure, and the potential for surface water 

contamination. They can also be used to recycle manure solids for animal 

bedding material. Currently, 157 methane digesters operate in the United 

States, of which 126 are on dairy operations and 24 are on hog operations 

(U.S. EPA, 2010a). 

Digesters have received attention lately because of their ability to reduce 

greenhouse gas (GHG) emissions from livestock manure. Burning 1 ton 

of methane is equivalent to eliminating about 24 tons of carbon dioxide. 

If the emissions reductions from methane digesters meet certain criteria, 

farmers may be able to sell these GHG reductions, or “carbon offsets,” to 

other GHG emitters who face emissions caps or who voluntarily wish to 

offset their own emissions. Currently, only a few U.S. livestock operators 

sell offsets in regional or voluntary carbon offset markets, partly because 

the price of carbon offsets in these markets has been low. However, future 

efforts to reduce greenhouse gas emissions could result in substantially 

higher carbon prices, which could provide a new source of income for 

farmers who adopt methane digesters. A recent ERS study found that with 

a moderate carbon price, revenues from the sale of carbon offsets could 

have a large effect on the number of hog operations that would adopt a 

methane digester. (See Key and Sneeringer, Climate Change Policy and 

the Adoption of Methane Digesters on Livestock Operations, Economic 

Research Report No. 111, http://www.ers.usda.gov/Publications/ERR111/

ERR111.pdf for more information.)
25

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Table 6

Practices used to control odor, 2004 and 2009

Percent

Management practices 2004 2009

All farms:

 Manure additives 13 17

 Filters for barn ventilation 5 5

All farms, weighted by animal units:

 Manure additives 31 29

 Filters for barn ventilation 10 8

Note: Asterisks indicate level of signifi cance for the test of the null hypothesis that mean 

equals 2004 mean: ** =5%, * = 10%.

Source: USDA, ERS, 2004 and 2009 Agricultural Resource Management Surveys.

that needed no further updates as of 2009 (this includes States that have not 

received NPDES program authorization from the EPA, meaning that the 

Federal regulations apply). Of the 19 States included in the ARMS survey, 

3 fall in this category (Michigan, Minnesota, and Oklahoma). The majority 

of States in ARMS fall in the second category, which includes those 

completing their regulation updates in 2010. The third category consists of 

States that the EPA has listed with a regulatory update completion date “to 

be determined.”

Table 7 shows the percentage of farms following certain nutrient management practices by regulation adoption status. Farms in States with fully 

updated regulations appear to be the most active in pursuing nutrient 

management practices, followed by States with planned completion in 2010. 

For example, 62 percent of operations in States with fully updated regulations follow a CNMP, compared with 55 percent in States that planned 

to complete updating in 2010 and only 38 percent in States that had not 

updated by 2010. 

Financial assistance from USDA’s Environmental Quality Incentives 

Program (EQIP) can help defray the costs of meeting environmental regulations by funding planning, installation, maintenance, and technical support 

for protective conservation practices. Between 2004 and 2009, the share 

of farms in each size category receiving some EQIP payments related 

to hog production increased (fi g. 11). The overall average share of farms 

receiving EQIP payments increased from 1.5 to 4.4 percent between 2004 

and 2009, and the share of animal units raised on farms receiving EQIP 

payments increased from 3.2 to 7.1 percent (table 8). EQIP payments were 

used primarily for installing manure handling and storage facilities and for 

developing and maintaining a nutrient management plan. While the number 

of operations that received payments was relatively small, these payments 

may have facilitated some of the changes observed in the study, such as 

the increased use of liquid spreading with injection, growth in the amount 

of cropland on which manure is applied, greater use of manure nutrient 

testing, greater use of microbial phytase in feed, and more widespread use 

of CNMPs. 
26

Trends and Developments in Hog Manure Management: 1998-2009 / EIB-81

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Policy initiatives may partially explain the increased use of such practices 

as manure injection and development of a nutrient management plan, but 

agricultural-residential confl icts at the rural-urban fringe may also play a 

role (Ribaudo and Johansson, 2007). Manure injection reduces odors from 

land application, and developing a nutrient management plan demonstrates 

due care on the part of livestock producers in avoiding harm to the nearby 

community. 

Table 7

Manure management methods by EPA State regulatory status, 2009

(a) (b) (c)

All States with 

data in ARMS

Fully updated 

regulations

Planned 

completion 

of update in 

2010

Completion 

of update of 

regulations to be 

determined

Number of States 19 3 11 5

Number of farms 24,421 3,998 18,003 2,419

Number of animal units (1,000) 13,313 2,425 10,318 571

Percent

All farms: 

 Followed CNMP1 55 62c 55c 38ab

 Test manure for N content 37 43 38 24

 Test manure for P content 37 43 37 24

 Adjust manure application according to N content 29 34 28 25

 Adjust manure application according to P content 26 30 26 24

Percent

All farms, weighted by animal units: 

 Follow CNMP 82 88 80 78

 Test for N content 64 69 62 69

 Test for P content 63 69 61 69

 Adjust manure application according to N content 31 46b 28a 24

 Adjust manure application according to P content 28 41 25 24

1CNMP = Comprehensive Nutrient Management Plan (see box, “Manure Storage and Handling Strategies”).

aDenotes statistically different at the 5% level from column (a).

bDenotes statistically different at the 5% level from column (b).

cDenotes statistically different at the 5% level from column (c).

Note: States with “fully updated regulations” include MI, MN, and OK (OK does not have NPDES program authorization and thus is directly regulated by the Environmental Protection Agency; it is therefore assumed to be up to date with EPA regulations); States with “planned completion 

of update in 2010” include PA, GA, KY, NC, IL, IN, OH, IA, MO, NE, and CO; States with “completion of update of regulations to be determined” 

include VA, WI, AR, KS, SD. 

Source: USDA, ERS 2009 Agricultural Resource Management Survey.
27

Trends and Developments in Hog Manure Management: 1998-2009 / EIB-81

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Table 8

Environmental Quality Incentives Program (EQIP) payments related to 

hog production, 2004

Percent

2004 2009

All farms:

 Any hog-related EQIP payments 1.5 4.4**

 Manure handling and storage facilities 0.6 1.9*

 Nutrient management plan 0.8 2.1*

 Manure application 0.2 1.3**

 Other1 0.4 2.0**

All farms, weighted by animal units:

 Any hog-related EQIP payments 3.2 7.1**

 Manure handling and storage facilities 1.5 2.8

 Nutrient management plan 2.2 4.0

 Manure application 0.6 1.8

 Other1 1.1 3.3*

1Includes animal facilities, manure hauling, and unspecifi ed. 

Note: Asterisks indicate level of signifi cance for the test of the null hypothesis that mean 

equals 2004 mean: ** =5%, * = 10%.

Source: USDA, ERS, 2004 and 2009 Agricultural Resource Management Surveys.
28

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Conclusions

Manure management practices and outcomes have changed signifi cantly over 

the past decade. Many of these trends can be attributed to the pronounced 

structural changes and regional shifts in hog production that occurred 

between 1998 and 2009. In particular, the relatively strong production growth 

in the Heartland compared with that of the South likely explains much of the 

shift from lagoons to pit/tank systems, despite lagoons being more prevalent among larger operations. Another important structural change has been 

growth in farm size, which has contributed to the decline in the use of solid 

manure spreading. 

The shift to larger operations has meant that an increasing share of 

production falls under the purview of regulations governing the application 

of manure nutrients to cropland. Larger farms with less cropland available 

per head for spreading manure are more likely to remove manure from the 

operation; are less likely to apply both commercial fertilizer and manure to 

crops and more likely to apply manure to crops with a high rate of nutrient 

uptake (e.g., Bermuda grass); and more likely to add microbial phytase 

to feed, to test soil for nutrients, and to follow a comprehensive nutrient 

management plan. 

While the manure-nutrient application intensity generally increases with farm 

size, the decline in application intensity on the largest operations between 

1998 and 2009 suggests that environmental policy is contributing to the adoption of conservation-compatible manure management practices. The number 

of Federal and State policies designed to reduce overapplication of manure 

nutrients grew between 1998 and 2009, and the number of States implementing and enforcing Federal policies increased. In 2009, 55 percent of 

farms, representing 82 percent of animal units, followed a nutrient management plan – a substantial increase from 2004, when only 30 percent of farms 

followed a CNMP. The share of farms receiving EQIP payments related to 

manure handling, storage, and application also increased substantially over 

this period. 

Structural changes in hog production, combined with increasing fertilizer 

prices, an increase in regulations, stricter enforcement of regulations, and 

more generous cost-share programs, jointly explain many of the changes in 

hog manure management between 1998 and 2009, including: 

• An increase in the share of hog operation cropland receiving manure;

• An increase in total cropland receiving manure per animal unit on hog 

operations;

• A decline in spreading solid manure and in spreading liquid manure 

without injection, among hog farms applying manure;

• An increase in the share of farms removing manure from their 

operations;

• An increase in manure nutrient testing rates; and

• Increased use of microbial phytase in feed. 
29

Trends and Developments in Hog Manure Management: 1998-2009 / EIB-81

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Since 2004, higher chemical fertilizer prices have raised the value of manure 

as a source of crop nutrients. In response, producers applied more manure to 

crops on-farm and applied less to Bermuda grass. In addition, a greater share 

of producers sold manure.

The increasing concentration of hog production on large operations is 

expected to continue, meaning that manure management will remain an 

important issue for the hog industry and others concerned with its environmental impacts. The fi ndings show that there is still signifi cant room for 

reducing the impact of manure disposal practices; for example, hog operations, on average, apply manure to only about 30 percent of their available 

crop acreage. The research suggests that in addition to the infl uence of market 

and structural forces, hog producers have responded to policy incentives that 

address environmental side effects of manure management. Policy incentives, 

along with technological innovations, are likely to play an important role in 

the future of hog manure management and its environmental impacts.
30

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