For some, manure is a waste or a nuisance, something to be disposed of rather than utilized. It is true that mismanagement can cause problems with water quality, but when managed properly, manure can be a valuable resource. The primary use for this resource is as a plant fertilizer in crop fields. When land applied from the right source, at the right time and rate, using the right methods and in the right place, manure can provide agronomic benefits while minimizing risks to water resources.
Figure 1. Manure nutrients move and cycle around the farm system. All elements of this cycle might not occur on the same farm as many import feed from other farms or commercial sources and export manure to other farms.
As Figure 1 (above) shows, manure is an integral part of the nutrient cycle that occurs on farms. Manure contains many nutrients including all three of the major (macro) nutrients needed by crops: nitrogen (N), phosphorus (P), and potassium (K). Manure also contains organic matter, an important part of soil health. Soil health encompasses biological, physical, and chemical properties. Soil water holding capacity, nutrient cycling, and microbiological activity all can be improved by manure land application.
Photo 1. (Above) On-farm research plots showing differences in fertilizer application. The middle rows show how much crops can be affected if there is a deficiency in nutrients. Photo courtesy of Glen Arnold, The Ohio State University.
The interaction of manure with soil is important to nutrient management. Manure contains organic N and ammonia N. Organic N is not immediately available to crops; it must be transformed through microbial activity into plant-available forms. This process is part of the nitrogen cycle. The mineralization of organic N into plant-available nitrate or ammonium occurs over time, and most states have Extension publications available to estimate the amount of nitrogen that will be available to plants each year following manure application.
Even the time of year that manure is applied has an impact on nutrient availability. Two examples of research in this area include:
Solid manure spreaders can be hitched to a tractor or mounted on a truck. They are engineered to discharge manure from the back or side of the spreader. Most of the photos and video on this page show large equipment, but specialized equipment is available for small farms to handle their manure. The video clip to the right shows a solid manure spreader applying beef feedlot manure at a rate of 10 tons per acre.
Solid manure is spread on the surface of the soil. Sometimes it is incorporated (using a disc or other tillage equipment) into the soil to reduce odors or as part of normal field operations.
The following photo slide show depicts examples of solid manure spreaders and related solid manure handling equipment. It also shows a field after manure has been spread on it.
The video below, produced by the University of Wisconsin, describes the equipment used to transport and apply liquid or slurry manure to fields. It shows examples where manure is surface-applied as well as injected below the surface. The final section describes ways to achieve consistent application rates and shows drag line systems.
Liquid and slurry manure require different application equipment than solid manure. Most liquid and slurry manure can be applied with the same equipment with one exception. Only liquid manure (very low solids) can be pumped through typical irrigation systems. Slurry or liquid manure is pumped into a tanker that is either truck mounted or hitched to a tractor. There are a variety of attachments (toolbars) that connect to the rear of the tanker. The choice of toolbar depends on several factors, but usually comes down to how much, or rather how little, the farmer wants to disturb the residue on the surface of the soil.
There are also slurry or liquid manure application systems that connect a very long hose (up to 2 miles long) to the toolbar, omitting the tanker. The tractor drags the hose as it crosses the field and manure is continuously pumped to the applicator. Usually it is pumped directly from the manure storage structure.
Slurry or liquid manure can be applied on the soil surface or injected into the soil. Injection is preferred whenever possible because it reduces odors and conserves some of the nitrogen that would otherwise be lost to the air as ammonia. Injection also reduces the risk of manure-contaminated runoff during precipitation.
The following slide show includes pictures of equipment used to apply liquid and slurry manure and a field immediately after manure was injected below the soil surface.
Photo 2. (Above) A new liquid or slurry manure tanker next to an antique solid manure spreader.
Modern farms use an incredible amount of science and technology every day. Animal diets are computer formulated and phased to match the animal's needs at different stages of growth. The use of global positioning systems (GPS) is commonplace on farms as is the use of high-tech ventilation, cooling, and heating systems for animal housing. Manure management also incorporates technology to improve accuracy and placement of manure nutrients. Below are some examples of recent innovations in manure application and nutrient management.
Global Positioning System monitoring of manure application
Some manure applicators are beginning to use a high-tech approach to calibration. Manure spreaders or tankers are equipped with load cells, flow meters (liquid or slurry), and GPS. As manure is applied, the weight or volume of the manure as well as the area spread is recorded. Related: Why and how to do traditional manure spreader calibration.
The video below, produced by the University of Wisconsin, explains GPS and manure application.
Subsurface Injection of Solid Manure
Photo 3. (Above) A prototype solid manure injector or "subsurfer".
Researchers with the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) have created a prototype manure injector for solid manure. This machine is not yet commercially available (as of late 2016). On commercial farms, incorporating solid manure currently involves two field operations.The first is application and second is incorporation with tillage. Solid manure Injection or incorporation is often of interest because, as with liquid manure, injection reduces odors, reduces the risk of runoff from fields, and conserves nutrients in the form of ammonia that would otherwise be volatilized to the air. Related: Researchers in Canada have also developed a prototype solid manure injection system.
Before liquid or slurry manure can be land applied, it must be mixed thoroughly. This is accomplished by agitating (mixing) it. There are many different types of agitators, including a new type known as floating agitation units or "manure boats".
Agitation boats are coming into use for their ability to move around the storage structure and resuspend solids throughout the entire manure storage. Related: Watch a short video of several boats being demonstrated at the North American Manure Expo.
Photo 4. (Above) Several manure agitation boats being demonstrated during the North American Manure Expo. The manure storage structure shown was being prepared for pumping and decommissioning as the farm had replaced it with a new concrete manure storage structure.
Smartphone apps are increasingly being used for manure management and record keeping. Several of these were discussed on the archived webinar "Mobile Manure Apps".
These apps provide functionality for calibration, record keeping, calculating manure nutrient application, and estimating the economic value of manure.
Over-applying manure nutrients wastes this valuable resource and can lead to water quality problems. Under-applying manure nutrients leads to crops that do not reach projected yields which results in reduced profits for the farm.
How do farms balance between applying "too much" and "not enough"?
As discussed above, manure and fertilizer nutrients need to be balanced as closely as possible to match crop yield goals. To figure out how many manure nutrients will be or were applied to a field, a farmer needs two pieces of information.
Nutrient Content. This value should come from a manure test, with samples sent to a lab for analysis. The report returned from the lab will list the N, P, and K content of the manure in lbs/ton (solid manure), lbs/1000 gallons (slurry or liquid), or lbs/acre-inches (liquid manure intended for irrigation). "Book value" or published estimates based on large numbers of manure samples can be used if manure tests are not available. Numbers from properly sampled and tested manure are always preferable to book values.
Farms that have several years of manure test data can use the average of past tests with the caveat that the values being averaged are consistent relative to time of year, animal feeding program, manure handling system, and manure storage structure.
Amount Applied. This refers to the number of tons or gallons of manure that was (or will be) applied to the field and the number of acres that received the manure. Most measurements of manure application rate rely on a process known as calibration. Recommended resources for calibration are linked below.
Combining the application rate (tons per acre or gallons per acre of manure applied) with the nutrient content (lbs N or P per ton or per 1000 gallons of manure) allows a farmer to calculate the total N or P applied per acre.
Manure is mostly used as a crop fertilizer but there are a lot of other creative ways to use this resource.
Renewable energy is a "hot topic" and manure is suitable for many technologies that generate energy. Most of these technologies are currently expensive and may not be feasible for most farms. Progress is being made in that area and technologies for generating renewable energy from manure are expected to become more accessible to more farms.
Thermal technology includes processes like gasification, pyrolysis, and combustion (Photo 5, below). While similar, they use differing amounts of heat and oxygen to convert manure into heat, combustible gases, oil, and more. Thermal technologies also produce materials like ash and biochar that can be applied to fields as a fertilizer or soil amendment. After undergoing thermal transformation, manure nutrients are much more concentrated and easier to transport. Interest is especially high in areas with high concentrations of livestock and poultry farms. Thermal technologies are best suited for dry, solid manure. Recommended Resource: Case studies of thermal technologies on broiler farms in the Chesapeake Bay region.
Photo 5. (Above) Looking into a boiler that uses broiler litter as a fuel source. Photo courtesy of the Farm Manure-to-Energy Initiative.
Photo 6. (Above) An anaerobic digester in use on a northeastern U.S. dairy farm.
Anaerobic digestion completely encloses manure to exclude oxygen and provides some heat (Photo 6). These conditions are just right for methane-producing bacteria to thrive. Methane from decomposing manure is a greenhouse gas. When the methane is captured in a digester, it can be used to generate heat and electricity. The EPA AgSTAR program maintains a database on anaerobic digestion projects on farms and offers many more resources. Related: Take a virtual tour of a digester in the northeastern U.S.
Anaerobic digestion by itself does not address concerns about nutrient concentration in areas with many livestock and poultry farms. Almost all of the manure nutrients are conserved through the digestion process and are present in the effluent that leaves the digester. Digestion is well-suited to include add-on technologies that can remove nutrients from the manure and concentrate them in a form feasible for transport. One example is described in the video below. The system described creates struvite, a phosphorus-containing compound, from digested animal manure.
Algae biomass systems use diluted wastewater from a liquid manure storage to produce algae (Photo 8, below). The algae feed on the nutrients in the wastewater and use sunlight to produce biomass. The algae biomass can be processed into bio-oil or the biomass can be utilized in technologies like the thermal systems and anaerobic digesters mentioned above. Research is ongoing into these systems including an Arkansas project growing algae with swine manure as a potential greenhouse gas mitigation technology.
Photo 8. (Above) Algae growing in diluted liquid pig manure. Photo courtesy of Rick Fields and Tom Costello, University of Arkansas.
Manure can be separated into two components, one being mostly solid and the other being mostly liquid. Solid-liquid separation is a key step in many alternative technologies for manure management. The liquid stream is usually applied to crop fields as a fertilizer.
The solid stream can be applied to fields but has a variety of other uses as well. The solids are usually composted and then they can be recycled on the farm for cow bedding. They can also be used to create value-added products like paper or biodegradable horticulture containers (Photo 9, below).
Photo 9. (Above) Horticultural containers made from recycled dairy manure fibers. Photo courtesy of Leslie Johnson, University of Nebraska.
EPA has also partnered with pork and dairy producers, USDA, and environmental and scientific experts to host the Nutrient Recycling Challenge - a competition to develop affordable technologies that recover nutrients from livestock manure and create value-added products.
The video below, produced by the U.S. Poultry and Egg Association, describes nutrient management planning and implementation.
These materials were developed by the Livestock and Poultry Environmental Learning Center (LPELC) with funding from the U.S. Environmental Protection Agency and with input from the Natural Resources Conservation Service, National Cattlemen's Beef Association, National Milk Producers Federation, National Pork Board, United Egg Producers, and U.S. Poultry and Egg Association.
For questions on these materials, contact Jill Heemstra, firstname.lastname@example.org. All images in this module, unless indicated otherwise, were provided by Jill.
Reviewers: Tetra Tech, Inc.; Joe Harrison, Washington State University; Rick Koelsch, University of Nebraska; Mary Berg, North Dakota State University; Mario de Haro Marti, University of Idaho; Leslie Johnson, University of Nebraska; and Tom Hebert, Bayard Ridge Group