The manure management progress is documented in a series of three studies conducted in 1998, 2004 and 2009 — a period of rapid change in the U.S. pork industry.

In its 34-page report, USDA researchers note that pork producers are more likely to have a nutrient management plan, which also reinforces the trend to larger, more specialized hog operations and reflects producers’ responses to nutrient application constraints and environmental policies. In addition, changes in the Clean Water Act, state regulations and local conflicts over air quality were cited as key drivers affecting manure management decisions.

The three surveys also document the shift to fewer, larger hog operations that are specialized in a single phase of production and a trend toward more production contracts. Fewer, larger operations often mean more manure is produced on a site with fewer nearby crop acres to utilize manure nutrients. The higher manure-to-cropland ratio also magnifies the risk that manure nutrients — nitrogen, phosphorus and potassium — and pathogens could affect ground and surface water if excess manure is applied or a manure storage facility leaks. And, the USDA report notes, the higher concentration of hogs per site has created odor and air-quality conflicts with nearby residents and communities.

Study Details

Survey data was gathered and analyzed as part of the USDA’s annual Agriculture Resource Management Survey (ARMS), designed to cover a cross-section of U.S. hog operations. Information was collected on production costs, business arrangements, production facilities and practices, farm operator and financial characteristics. More specifically, the surveys documented manure storage, application methods and rates; fertilizer use; the use of a comprehensive nutrient management plan (CNMP); and payments received under the Environmental Quality Incentives Program (EQIP).

Sample farms were chosen from a list maintained by the USDA’s National Agricultural Statistics Service. Hog operations in 22 states were surveyed in 1998; in 2004 and 2009, operations in 19 states were surveyed. Survey samples represented more than 90% of the hog and pig inventory on U.S. farms. Data is separated by farm size using the number of animal units produced (one animal unit = 1,000 lb. of live animal weight).

“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,” the report explains. “The number of animal units on each farm is the steady-state live-weight of sows, piglets and other hogs, which is computed using the average hog inventories and weights from the ARMS. The environmental implications of hog production depend on the manure management decisions of operations with at least 50 animal units. These operations accounted for 97% of the hog sales in the sample frame in 1998, and 99% in both 2004 and 2009.”

Industry Structural Changes

Changes in the scale, organization, location and methods of production are reflective of changes seen in manure management practices. The surveys separated production into four phases — breeding/gestation, farrowing, nursery (~30-80 lb.), and finishing (nursery to slaughter weights of 225-300 lb.). Further, production was classified as farrow-to-finish, farrow-to-wean, farrow-to-feeder pig, wean-to-feeder pig, wean-to-finish or feeder pig-to-finish.

In the study, farrow-to-finish operations declined from 49% in 1998 to 31% in 2004, and to 23% in 2009 (Table 1). The number of hog operations fell by about 60% over the 11-year period, and the average per-head sales rose from 2,589 to 7,930 head.

The popularity of contract production more than tripled during the survey period, which also allowed producers to specialize in a phase of production while increasing the scale of their operations. Currently, almost half of all hog farms use contracts. When ranked by share of output, contract production has grown even more. The 48% of farms using production contracts accounted for 71% of hog production in 2009.

The responsibility of managing the hog manure under contract production agreements generally falls to the contract grower. Failure to comply with local, state and federal regulations can result in contract termination, providing the motivation to do it right.

The contribution of hogs to a farm’s total production increased from 56% to 70%, with all of the change occurring between 1998 and 2004. This trend spurred more specialization in manure management, the report notes.

Feed processing became more specialized as well. In 1998, 50% of hog feed was processed on the farm where it was fed; by 2004, that figure had fallen to below 20%, indicating more feed was processed off-site.

As expected, greater specialization meant the cropland/animal unit of hog farms fell — declining from 2.14 acres/animal unit (AU) in 1998 to 1.41 acres/AU in 2004. By 2009, the ratio had fallen to just 0.86 acres/AU. Hog operations with no cropland grew from 8% to 19% during the 11-year period.

Where hogs were raised shifted too. Historically, hogs were raised in the Corn Belt, where feed costs were relatively low and there was ample acreage to apply manure. The dramatic growth of the hog industry in the Southeast during the ’80s and ’90s — particularly in North Carolina — was fueled by the popularity of contract arrangements. However, the growth presented a huge challenge of managing the growing volume of hog manure, where the cropland/animal unit ratio fell to just ¼ acre/AU. Consequently, most hog producers in the Southeast stored manure in earthen lagoons and applied manure via irrigation systems.

In 1997, a moratorium on the building of new or expanded hog operations was enacted in North Carolina, which shifted hog production growth between 1998 and 2009 back to the Midwest and southwestern states, including Colorado and Utah, where human populations were less dense.

The trend to more specialized, large-scale hog production systems was more efficient, producing more pork on less feed, which translated into less manure per unit of gain.

Manure Storage, Handling

Swine manure is generally stored in lagoons, pits or above-ground storage tanks. Lagoons are earthen containment structures that hold manure and wastewater, most common in southeastern states and associated with larger hog operations. Pits are typically concrete storage structures under slotted floors. Manure and urine passes through the slots and is held as slurry until it is removed and land applied. Above-ground storage tanks generally receive manure slurry periodically, where it is held for application later.

Lagoon liquids are often applied through irrigation systems. Land application includes slurry spreaders/tanks, where manure may be incorporated directly into the soil or top-applied and incorporated with tillage equipment soon after. The method of application can have important implications for air quality, affecting release of ammonia and hydrogen sulfide, as well as particulate matter and greenhouse gases such as methane and hydrous oxide.

Handling and storage options have very different impacts on the nutrient content of the manure, particularly nitrogen, which naturally affects the land base needed for application.

The USDA trends study reported 41% of operations with 1,000 head or more used a lagoon. “Despite the trend toward larger operations, there was a shift toward the use of pit/tank systems between 1998 and 2009,” the report notes. “By 2009, 62% of hogs were raised on farms using pits or tanks, up from 37% in 1998, while 37% of hogs were raised on farms using a lagoon system, down from 55% in 1998.”

The move to more pits/tanks reflects the regional shifts in hog production — more recent growth in the Midwest and stagnant production in the Southeast, restricted by the moratorium in North Carolina. “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 cropland,” the report states.

Manure Application Trends

Solid and liquid manure can be incorporated into the soil, retaining more nutrients for plants, reducing odor and nutrient volatilization, and reducing risk of nutrient runoff. Irrigation/sprinkler systems increase volatilization, which reduces the nitrogen available to plants.

In general, larger hog operations applied more manure to a higher percentage of cropland (Table 2). From 1998 to 2009, the average amount of cropland on a hog farm increased from 448 to 578 acres, and the number and percentage of acres receiving manure applications grew from 85 (19.1%) to 136 (23.5%), on average. The trend was driven by large operations injecting more hog manure on more acres.

“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,” report authors observed. Therefore, the potential exists to spread manure over more on-farm crop acreage, although the distance between hog facilities and cropland can add considerably to manure transport and application costs, they concede.

Larger hog operations tend to apply larger amounts of manure for two reasons — they simply generate more manure and they have proportionately less cropland available. “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% increase in the 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%,” they note.

It is important to qualify manure application intensity because different storage and handling methods impact the quantity of nutrients applied. “Application intensity does not measure actual nutrient application rates,” the authors state.

Improved feed conversion in modern hogs has likely reduced nutrients excreted. Some of the nitrogen and phosphorus in hog feed is retained by the animals as meat, but most of the nutrients are excreted in urine and manure.

Feed efficiency was positively correlated with scale of production, with larger operations generally using less feed per hog produced. “Hence, the nutrient application intensity (e.g. nitrogen application/acre) is generally lower on large farms than the estimated manure application intensity (animals/acre) would imply,” they note.

In 2009, 76% of hog operations applied some manure on their farms, slipping from 82% in 2004 (Table 3). Some of the decline may reflect the shift to larger operations, which are less likely to apply manure on their farms. Between 1998 and 2004, the share of farms removing manure from the operation’s site grew 50%, but between 2004 and 2009, that percentage held steady.

Interestingly, much of the manure removed from the farm was given away, although there is a growing trend toward selling manure. In 2009, 9% of large farms sold manure, compared to just 1% in 1998. “The increasing manure sales could be partly explained by the dramatic rise in chemical fertilizer prices, which increased 174% between 1998 and 2009,” the report notes.

Nutrient Management

Manure nutrient testing, required in many state-mandated manure management plans, was positively associated with larger hog operations (Table 4). In 1998, just 18% of farms tested for nitrogen. By 2004, 29% tested for nitrogen. By 2009, the percentage rose to 49%. From an animal units perspective, farms testing for nitrogen grew from 51% to 73% to 86%, respectively, during the three survey sample years. Testing for phosphorus reflected similar trends.

When land base is limited, some producers have opted to apply manure to crops with a high rate of nutrient uptake, such as Bermuda grass.

The use of microbial phytase as an additive to finishing diets to improve organic phosphorus absorption has lessened the need for supplementation of the mineral, thus reducing feed costs. In turn, phytase reduces the amount of phosphorus excreted in manure — a key consideration when application rates are limited by phosphorus vs. nitrogen.

Farms with at least 300 animal units were more likely to use phytase in swine diets, although the overall share of farms utilizing phytase grew from just 4% to 23% during the survey period and the percentage of hogs receiving phytase grew from 12% to 39%.

Environmental Policies

Greater concentrations of hogs influenced environmental policy decisions, which in turn influenced manure management decisions. However, pork producers soon found that environmental quality and better manure management practices go hand-in-hand.

Nonetheless, in 2003, the U.S. Environmental Protection Agency (EPA) revised the Clean Water Act regulations to control runoff of manure nutrients from the largest animal feeding operations (AFOs). Finalized in 2008, the Clean Water Act regulations now require concentrated animal feeding operations (CAFOs) — designated as “discharging or proposing to discharge manure effluent” — to obtain National Pollution Discharge Elimination System (NPDES) permit coverage. CAFOs with permits must have a comprehensive nutrient management plan (CNMP) that outlines site-specific practices to ensure agronomic use of the nutrients.

The survey showed that in 2004, 30% of farms followed a CNMP. By 2009, 55% of farms had such a plan, and they represented 82% of the hogs raised.

Much of the enforcement responsibility for the updated CAFO rules has been transferred to state authorities at various rates of adoption.

Managing for Air Quality

Atmospheric emissions of pollutants, regulated by the Clean Air Act, requires state, local and tribal governments to identify areas that do not meet national air quality standards for fine particles (less than 2.5 microns) — one of six criteria pollutants regulated under the act. “This regulation could affect animal operations because ammonia emitted from barns and manure storage facilities is a major precursor of fine particles,” the USDA report states.

In 2006, in an effort to develop air quality protocols, an EPA consent agreement encouraged livestock producers to volunteer for emissions monitoring in exchange for clemency for past air pollution violations. The National Air Emissions Monitoring Study (NAEMS) ended in 2010. Analysis of the data is pending with release anticipated in early 2012.

Odors associated with livestock operations remain controversial and contentious. Some states have adopted policies containing objective odor standards or require management initiatives, such as separation distances, explicit odor plans or good neighbor practices. “To the extent that odor is correlated with levels of certain air emissions (particularly hydrogen sulfide and ammonia), state policies to limit such emissions may also help control odors,” the USDA report continues.

“The type of manure storage facility affects the level of ammonia and other odorous gases. Lagoons can 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,” the report concludes.

Survey Summary

The structural changes apparent in the U.S. hog industry, higher fertilizer prices, more regulations with stricter enforcement, and the availability of federal cost-share programs help explain the evolution of hog manure management practices, 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 reduction in solid and liquid spreading without incorporating manure;
  • A larger share of hog farms removing manure for application elsewhere;
  • An increase in manure nutrient testing; and
  • Increased use of microbial phytase in hog feed.

“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,” wrote the survey’s authors. “The findings (of the survey) show that there is still significant room for reducing the impact of manure disposal practices. The research suggests that in addition to the influence 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,” they conclude.

The authors of “Trends and Devel­opments in Hog Manure Manage­­ment: 1998 to 2009 Economic Infor­mation Bulletin No. 81 (EIB-81)” are Nigel Key, William D. McBride, Marc Ribaudo and Stacy Sneering. A complete copy of the survey results is available at