Animal manure can be a viable source of crop nutrients such as nitrogen (N), phosphorus (P), and potassium (K). In the short term, it can supply nutrients for the growing crop and in the long term, help rebuild soil nutrient levels. However, the characteristics of manure make it difficult to manage in comparison to standard fertilizer. Manure can contain organic and inorganic material, be variable in nutrient concentrations from different animal sources and from sample-to-sample, be in liquid or dry forms, and because of low nutrient concentrations require large application volumes.1 Nutrients within manure can be tied up until microorganisms are able to free it from fibrous components from feed or bedding. The amount of available N and P is highly dependent on the amount of fibrous material; however, since K exists within manure in the ionic form (K+), it is available for crop uptake immediately.
Written Manure Management Plans (MMP) are an important component for livestock farmers or those who apply manure to their fields. The plans can be written by the farmer or a certified nutrient management specialist, but must be kept on the farmstead and available upon request. Livestock operations that are defined as Concentrated Animal Feeding Operations (CAFOs) or Concentrated Animal Operations (CAOs) must also have Nutrient Management Plans prepared by Certified Nutrient Management Specialists that are submitted to local county conservation districts for review and approval. The components of an MMP include:
Nutrient variability within manure can vary greatly because of animal species, diet, genetics and performance, bedding used, storage, handling, lagoon agitation, and other management factors.1 Because of the variability, manure samples should be sent to qualified laboratories for the determination of dry matter and total N, P2O5, and K2O concentrations.1 Manure application rates are easier to calculate if the analysis is provided on an as-received or wet-basis in lb/ton or lb/1000 gal units.1 Conversion factors must be used if the analysis is not in these units. Prior to receiving the laboratory analysis, standard estimations for the manure source can be used (Table 1).4 The variation in nutrient concentrations should be noted between and within animal species.
Knowing the analysis is also important for environmental reasons. Applying too much of a nutrient that has the ability to change and/or move by denitrification, volatilization, leaching, or erosion and cannot be used immediately by a crop can result in ground and surface water contamination. When manure is not incorporated, N can be lost through volatilization and if applied in the fall, the opportunity for leaching increases. Phosphorus can be lost when flooding carries the manure off of the target field and into creeks and other waterways.
Practicing good soil fertility stewardship is the premise of the 4Rs of nutrient management--applying the right fertilizer source at the right rate at the right time and in the right place.5 The first step is knowing the current fertility level of a manure targeted field. A comprehensive and representative soil sample can provide current fertility details. Based on projected potential crop yield, nutrient removal for a specific crop, and the current fertility, the right rate of manure based on its analysis can be applied to the field to help maintain the desired balance. In many situations, additional fertilizer may have to be added to the field to compensate for nutrients that are lacking in the manure. In addition, accounting must be made for any potential nutrient loss when manure is applied to the soil surface. The timing of manure application, usually spring or fall, and its placement can impact the rate. Fall and surface applied manure applications have greater opportunities for loss. Spring applications could be hindered by wet weather or result in lost N if volatilization occurs before incorporation.
The rate of manure applied is generally based on the plant-available N content of the manure and the recommended N rate needed for the crop to be grown. The available-N content is calculated as 60% of the organic-N and 80% of the NH4 + for the first year after manure application if the manure is incorporated immediately. The NH4 + component should be reduced 15% per day for each day the manure is unincorporated.6
Though still used, the traditional broadcast manure spreader has given way to other forms of application. Injection and irrigation of liquid manure forms are used to help control application variability, provide a better means of matching application to the crop's time of nutrient need, and help answer some environmental issues. Without incorporation, broadcast manure can result in complaints by neighbors from odor, be subject to the loss of P through surface runoff, and N volatilization. Injection allows for application to growing crops such as alfalfa, grass, cover crops, and can be potentially used as a sidedress in corn. Injection systems are also compatible with notill management. However, labor and equipment cost for injectable systems can be costly; therefore, several factors should be considered before investing in injection equipment: 1) the amount of manure produced by an operation, 2) the number of hours the equipment will be used, and 3) the need for nurse trucks, draglines, and other associated equipment.7 Liquid and when possible, solid manure should be placed 3 to 6 inches below the soil surface.9
The five primary application tools for injection that disturb soil the least are disk injection, chisel injection, high-pressure injection, aeration, and surface banding which may use a shoe device in standing forages.8 Aeration systems create holes in the soil that allow surface applied manure to seep into the soil. The Agricultural Research Service used a device referred to as the Subsurfer to place dry chicken litter into the soil.9
Regardless of the potential benefits of injection systems, many still prefer broadcasting manure because of the speed of application. Broadcasting may reach widths of 50 feet while injection systems are much narrower and would require more time to apply.8
Identified benefits of using center pivots (Figure 1) to distribute liquid manure include the ability to apply during the growing season when the crop is in most need of nutrients, potential for less risk of surface runoff, potential for less nutrient leaching because plants can start accessing the nutrients soon after application, lower distribution costs for producers and reduced risk of spills compared to manure haulers/tankers, reduced traffic and potential damage to roadways, and reduced soil compaction.10 However, issues have been expressed regarding odor spikes, risk of influencing air quality with particulates, surface and groundwater effects, and reduction of aquifers.10 Therefore, these issues should be evaluated for the local area before irrigation equipment is purchased for the sole benefit of manure distribution.
1Sawyer, J.E. and Mallarino, A.P. 2016. Using manure nutrients for cop production. PMR 1003. Iowa State University.
2Foulk, D. 2013. Have a horse in your backyard? You need a manure management plan. Penn State University. www.http://extension.psu.edu/animals/equine/news/2013/have-a-horse-inyour- backyard-you-need-a-manure-management-plan.
3The basics of manure management requirements. Penn State University.
4Nutrient & manure management tables. 2012. University of Minnesota. https://www.mda.state.mn.us/chemicals/fertilizers/~/media/Files/chemicals/fertilizers/nutmantables.pdf
54R nutrient management. American Society of Agronomy.
6Land application of animal manure. 1996. Clemson University. https://www.clemson.edu/public/regulatory/ag_svc_lab/animal_waste/manure.pdf
7Atiyeh, D., Ketterings, Q., Czymmek, K., Godwin, G., Potter, S., Bossard, S., Maquire, R. (Virginia Tech), and Kleinman, P. (USDA-ARS). 2015. Liquid manure injection. Fact Sheet 87. Cornell University.
8Fisher, M. 2011. Manure incorporation in no-till systems. Crops & Soils magazine. American Society of Agronomy.
9Leytem, A., Kleinmann, P., Dell, C., and Pote, D. Subsurface injection of manure to reduce ammonia losses and odor. Livestock GRACEnet. www.ars.usda.gov/livestockGRACEnet.
10Understanding manure irrigation. Benefits and Concerns. University of Wisconsin. 2016. Web sources verified 7/15/16 160405112620