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The Manure Problem

Manure is generally considered to be the total urine and feces excreted from animals, and in some operations includes plant-based bedding material.[1]

Definitions of manure types can vary and “lack universal consensus.”[2]

 

  1. Pagliari, P., et al., (2019) Animal Manure Production and Utilization: Impact of Modern Concentrated Animal Feeding Operations, Animal Manure: Production, Characteristics, Environmental Concerns and Management, Waldrip, H.M. et al. (eds.) American Society of Agronomy, Special Publication 67, Madison, WI, p. 1.
  2. Kleinman, P. J. A., et al., (2022). Envisioning the manureshed: Toward comprehensive integration of modern crop and animal production. Journal of Environmental Quality, 51(4), 481, p. 482. [“Even definitions of animal manure types can be difficult to pin down, as exemplified by the terms “dry,” “liquid,” “slurry,” “solid,” and “semi-solid” that may be defined consistently within certain contexts but lack universal consensus.”]

Twenty years ago, the EPA explained, “Because large numbers of animals are confined in relatively small areas at CAFOs, a very large volume of manure is produced and must be kept in a correspondingly small area until disposed of. The age old practice of land application is used, but the volumes of manure that must be disposed in this way frequently exceed the assimilative capacity of land within economic transport distances. This may result in the release of excess manure to watershed environments during the catastrophic breach of holding facilities or more commonly, during the intermittent runoff of excess manure applied to already saturated land.”[1]

In fact, the nutrient losses into air and water are so pervasive in the factory farming system, that only ~10% of the nitrogen in factory farm manure – the key nutrient – is applied to crops. Most of the nitrogen is lost to the environment.[2]

Wendell Berry famously explained, “Once plants and animals were raised together on the same farm which therefore neither produced unmanageable surpluses of manure, to be wasted and to pollute the water supply, nor depended on such quantities of commercial fertilizer. The genius of America farm experts is very well demonstrated here: they can take a solution and divide it neatly into two problems.”[3] 

 

  1. U.S. EPA (2004) Risk Assessment Evaluation for Concentrated Animal Feeding Operations. EPA/600/R-04/042, p. 1.
  2. See, Total Nutrient Volume in Manure
  3. Berry, W. (2004). The Unsettling of America: Culture & Agriculture. Counterpoint, Berkeley, ISBN 978-0871568779.

Manure contains two key nutrients that support plant growth – nitrogen and phosphorus. Though the impacts vary, applying manure generally improves the chemical, physical, and biological health of the soil.[1,2]

Before the advent of chemical fertilizers and factory farming, the use of manure was the primary method to fertilize crops. Farms with both animals and crops were the norm, and mixing manure with soils or having grazing animals deposit manure on croplands was the traditional approach.

 

  1. Rayne, N. & Aula, L. (2020). Livestock Manure and the Impacts on Soil Health: A Review. Soil Systems, 4(4), 64.
  2. Lim, T., et al., (2023) Increasing the Value of Animal Manure for Farmers, UDA Economic Research Service, AP-109, pp. 1-2.

There are many reasons farmers prefer chemical fertilizers over manure. Most factory farm operations see manure as a liability – a waste product that is rarely used as fertilizer and is mostly dispersed into the environment with calamitous impacts for air and water quality and biodiversity.[1-6]

 Chemical fertilizer is more economical for crop producers, better matches the nutrient requirements of the crops, is easier to apply, and leads to larger and more predictable yields.
 The huge amounts of manure produced in a single location do not match up to the nutrient requirements of nearby croplands. 
 The de-coupling of livestock and crop production often make inter-farm transactions necessary.
The supply of manure can be unpredictable compared to purchasing chemical fertilizers; nutrient application must occur during a small timeframe.
Because the nitrogen in manure quickly volatizes, it is often phosphorus-heavy and nitrogen-light.
The nutrient content of manure varies and must be tested off-site for effective application.
Manure is heavy and transport costs are high, severely limiting the potential radius of use.
Manure often has high levels of contaminants, including antibiotics, hormones, heavy metals, and pathogens, along with weed seeds.
Users have concerns about regulations or reactions from homeowners. 
 Chemical fertilizers are heavily promoted; manure has no corporate sponsors.

Dairy and pig manure generally has the least value, and poultry manure the most because it is usually dry, more concentrated, and therefore more economical to transport.[7]

 

  1. Kleinman, P. J. A., et al., (2022). Envisioning the manureshed: Toward comprehensive integration of modern crop and animal production. Journal of Environmental Quality, 51(4), 481, p. 483. [“Further, variability in manure quality between and within livestock operations challenges manure’s predictability as a fertilizer. So too does inconsistency in testing procedures… Manure nutrient ratios often do not match those required by crops… Manure can serve as a vector for pathogens (plant and animal) as well as for weeds… measures generally come at costs not associated with commercial fertilizers.”]  
  2. Lim, T., et al., (2023) Increasing the Value of Animal Manure for Farmers, UDA Economic Research Service, AP-109, pp. 2-12. [“The low quantity of nutrients per ton, relative to commercial fertilizers, results in time-intensive and costly transportation. Depending on the weather, in any year, farmers may have a few days with suitable conditions that allow them to prepare fields, spread fertilizer, and plant. Crop planting takes priority, so to save time, farmers may choose commercial fertilizers rather than manure. Second, manure as excreted and after storage has a nitrogen-to-phosphorus ratio that does not align with most crops’ nutrients requirements… Manure nutrient levels vary within and across farms, so manure must be tested to be used efficiently. Manure tests measure the nitrogen and phosphorus in manure samples and have typically required sending samples to a laboratory.”]
  3. Waller, D. M., et al., (2021). Shifts in precipitation and agricultural intensity increase phosphorus concentrations and loads in an agricultural watershed. Journal of Environmental Management, 284, 112019, p. 2. [“Because manure spreading typically occurs within an economic hauling radius (<3–10 miles under most Wisconsin permits), CAFOs have an incentive to overapply manure to save on transport and distribution costs….Large manure lagoons must be emptied or managed regularly, creating incentives to spread manure at times and at levels that may not be optimal for crop production…”]
  4. Ribaudo, M., et al., (2003) Manure Management for Water Quality: Costs to Animal Feeding Operations of Applying Manure Nutrients to Land. USDA ERS, Rpt. No. 824, p. 21. [“There are several potential drawbacks to land application of manure that could discourage greater use on cropland. These factors include uncertainty associated with the nutrient content and availability, high transportation and handling costs relative to commercial fertilizer, soil compaction from spreading equipment, dispersion of weed seeds, concerns about added regulatory oversight, and public perception regarding odor and pathogen issues.”]
  5. U.S. EPA (2013) Literature Review of Contaminants in Livestock and Poultry Manure and Implications for Water Quality, EPA 820-R-13-002, p. 1. [“Manure often contains pathogens (many of which can be infectious to humans), heavy metals, antimicrobials, and hormones that can enter surface water and ground water through runoff and infiltration potentially impacting aquatic life, recreational waters, and drinking water systems.”]
  6. Keplinger, K. O. & Hauck, L. M. (2006). The economics of manure utilization: model and application. Journal of Agricultural and Resource Economics, 414-440, p.415. [“When supplies of manure become large, its value falls and an incentive is created to apply manure at rates exceeding crop requirements or to otherwise dispose as inexpensively as possible, despite negative externalities. Consistent with externality theory, degradation of public resources (air and water) has occurred in regions of the country with high concentrations of livestock.”]
  7. Keplinger, K. O. & Hauck, L. M. (2006), Figure 2, p. 427.

A typical pig farm with 30,000 pigs generates more than 900 tons (1.8 million pounds) of manure per week.[1] This is about equal to the weekly human waste from a small city of 80,000 people.

This immense volume of a low to negative-value product incurs infrastructure and storage costs, is a potential air and water pollutant, can be dangerous to animal and human health due to pathogens, is costly and cumbersome to transport, difficult to apply to crops, contains contaminants and generates gases and odors, and is subject to local and/or federal regulations along with potential pushback from local communities.[2-4]

 

  1. Kellogg, R. L., et al., (2014). Estimates of recoverable and non-recoverable manure nutrients based on the census of agriculture. USDA Natural Resources Conservation Service. https://www.nrcs.usda.gov/sites/default/files/2022-10/ManRpt_KelMofGol_2007_final.pdf  [Calculation: A typical pig farm holds about 30,000 pigs, which is about 3,300 “animal units” generating about 14.7 tons of manure per year for each AU. 3,300 * 14.7 / 52 = 933 tons of manure per week. For animal units, see Table 1, p. 4. (using 9.1 for “Hogs for Slaughter.”) For manure generated per AU, see Table 5, p. 33. Human waste = 80,000 x 3.33 lbs. x 7 = 932 tons]
  2. U.S. EPA (2013) Literature Review of Contaminants in Livestock and Poultry Manure and Implications for Water Quality, EPA 820-R-13-002.
  3. Varma, V. S., et al., (2021). Dairy and swine manure management–Challenges and perspectives for sustainable treatment technology. Science of The Total Environment, 778, 146319.
  4. U.S. EPA (2004) Risk Assessment Evaluation for Concentrated Animal Feeding Operations. EPA/600/R-04/042.

Through volatilization, discharges from storage facilities, transport, and over-application, the key nutrients in manure – nitrogen and phosphorus – are dispersed into the nation’s air and water.

Immediate Dispersal – Portions of the nitrogen in manure are dispersed into the air and soil as soon as it is excreted and continue to be lost during every stage of “manure management” regardless of management systems.[1]

Nutrient Loss from Storage Sites – Manure can leach or overflow from storage piles, enclosed manure pits, and open manure lagoons and ponds. This can be due to regular expected occurrences (like leaching), intentional releases, structural failures, or severe weather events.[2] Large amounts of nitrogen are lost throughout the storage process.[3] For example, dairy flush barns and uncovered hog lagoons lose ~80% of total excreted nitrogen prior to field application; poultry and feed cattle operations lose about 30 to 40% of manure N.[4] Phosphorus tends to sink to the bottom of storage systems where it can remain for years, eventually reaching soil or water.[5]

Manure Land-Applications – When manure is over-applied on surrounding farmland, the plants and soil cannot absorb the excess nutrients which are then carried into surface waterbodies. Manure is regularly over-applied, presumably as a method for dispersing a waste product.[6,7]

Atmospheric Deposition from Manure – Ammonia escaped into the atmosphere (NH3) comes primarily from manure on factory farms (both livestock and poultry) and is eventually deposited back in the soil or in waterways.[8,9]

 

  1. Rotz, C. A. (2004). Management to reduce nitrogen losses in animal production. Journal of animal science, 82 (suppl_13), E119-E137, Table 2. [“Volatile loss begins soon after excretion, and it continues through all manure handling processes until the manure nutrients are incorporated into soil.” “The primary pathways of N loss are volatile emissions into the atmosphere and leaching and runoff losses to
    ground and surface waters.” pp. E-119 and 120]
  2. Burkholder, J., et al., (2007) Impacts of Waste from Concentrated Animal Feeding Operations on Water Quality. Environmental Health Perspectives, 115(2), 308–312, p. 308 [“Contaminants from animal wastes can enter the environment through pathways such as through leakage from poorly constructed manure lagoons, or during major precipitation events resulting in either overflow of lagoons and runoff from recent applications of waste to farm fields, or atmospheric deposition followed by dry or wet fallout.”]
  3. U.S. EPA (2002) Non-Water Quality Impact Estimates for Animal Feeding Operations, pp. 1-2. [“Nitrogen losses from animal manure as ammonia can easily exceed 50 percent.”]
  4. Aillery, M. P., et al., (2005). Managing manure to improve air and water quality. USDA ERS Rpt 9, Table 2-1, p. 12.
  5. Lim, T., et al., (2023) Increasing the Value of Animal Manure for Farmers, USDA Economic Research Service, AP-109, p. 13. [“Nitrogen can volatilize before being land-applied, and phosphorus can settle to the bottom of lagoons where it may remain for years.”]
  6. Lim, T., et al., (2023), Table 2, Figure 4. [The great majority of manure was applied to corn crops; more than half of corn producers that land-applied manure did not reduce their normal usage of chemical fertilizer.]
  7. Ribaudo, M., et al., (2017). The potential role for a nitrogen compliance policy in mitigating Gulf hypoxia. Applied Economic Perspectives and Policy, 39(3), 458-478, p. 12. [USDA scientists acknowledge that, “Farms with confined animals generally have inadequate cropland to assimilate nutrients produced, and are characterized by excess nutrient applications on cropland they control.”]
  8. U.S. EPA (2024) 2020 NEI Supporting Data and Summaries – Data Queries for Sector Summaries.
    [Query: National/Ammonia NH3/Livestock Waste (49.2%), fertilizer application (33.5%), agricultural field burning (2.7%)]
  9. Robertson, D. M. & Saad, D. A. (2021). Nitrogen and phosphorus sources and delivery from the Mississippi/Atchafalaya River basin: An update using 2012 SPARROW models. JAWRA, 57(3), 406-429, Figure 5, p. 18. [Atmospheric manure nutrients are the source of ~13% of nitrogen in waterways.]

Because of weak regulations and the continuing consolidation of farmed animals onto larger factory farms, economic incentives encourage dispersal into the commons through a wide variety of routes.[1,2]

The USDA and the EPA have made some efforts over the years to limit manure dispersal and its accompanying nutrient pollution.[3-5] But so far, their research reports, incentives, and court-constrained regulations have had insufficient impact. Moreover, the EPA fully concedes that “little data is available demonstrating the impacts of CAFOs specifically on ‘waters of the United States.’” In 2023, responding to non-profit petitions and lawsuits, the agency suggested that it will likely take several years before deciding whether it is even feasible to revise CAFO regulations due to the agency’s limited resources and higher environmental priorities.[6] 

The poor conditions of the nation’s waterways, especially the high levels of nutrient pollution, are a concrete reflection of the ongoing failure to address the problem. The air-quality impacts of ammonia emissions from factory farm manure are highly damaging and weakly regulated. These failures must be added to the expense sheet of factory farming.[7]

 

  1. Rosov, K., et al., (2020). Waste nutrients from U.S. animal feeding operations: Regulations are inconsistent across states and inadequately assess nutrient export risk. Journal of Environmental Management, 269, 110738. https://doi.org/10.1016/j.jenvman.2020.110738
  2. Spiegal, S., et al., (2020). Manuresheds: Advancing nutrient recycling in US agriculture. Agricultural  Systems, 182, 102813, p. 2. https://doi.org/10.1016/j.agsy.2020.102813  [“Nutrient recycling is fundamental to sustainable agricultural systems, but few mechanisms exist to ensure that surplus manure nutrients from animal feeding operations are transported for use on nutrient-deficient croplands.”]
  3. Dell, C. J., et al., (2022). Challenges and opportunities for manureshed management across US dairy systems: Case studies from four regions. Journal of Environmental Quality, 51(4), 521-539.
  4. Lim, T., et al., (2023) Increasing the Value of Animal Manure for Farmers, UDA Economic Research Service, AP-109.
  5. U.S. EPA (2022) EPA Legal Tools to Advance Environmental Justice, Pub. No. 360R22001, p. 75. [“Many CAFOs are not regulated and continue to discharge without NPDES permits because successive court decisions have severely limited EPA’s ability to require CAFOs to obtain an NPDES permit.”]
  6. U.S. EPA (2023) Effluent Guidelines Program Plan 15, EPA-821-R-22-004, pp. A-2, A-3.
  7. For more information on conditions of the nation’s waterways, see, Pollution of Lakes River & Streams; on ammonia emissions from factory farm manure, see, Animal Ag Ammonia & PM2.5

Manure & Other Outputs