Iowa State University
Ag & Biosystems Engineering
Iowa, U.S.A.
Introduction
Egg producers should have two overriding manure management objectives. First, they should manage their manure to provide a good environment within the layer house for the birds and workers, and second, they should manage their manure to protect soil, air, and water resources. There are a number of management techniques they can use to accomplish these objectives. As environmental consciousness increases, manure will have to be managed more carefully.
Collecting manure
Manure must be removed from the bird cages rapidly. Current caged systems provide that ability. Both liquid and solid systems result in rapid (essentially immediate) separation of the birds from their feces as the manure drops through the cages upon excretion. The question is...once it's separated from the bird, what then?
Indoor Stockpiles
Today's systems utilize solid stockpiles, rather than liquid holding ponds, to store manure until it can be land applied. In high-rise houses the stockpiles reside directly below the birds in the production houses, protected from precipitation (Figure 1). While water pollution risk is eliminated during in-house storage, stored manure can create significant air quality issues within the house if not managed properly. Ammonia is emitted from the stockpiles creating a potential air quality problem if ventilation is not adequate, or the ventilation system is not properly designed.
Research shows a close relationship between ammonia production and manure moisture content. Drier manure volatilizes less ammonia; so one way to minimize ammonia emissions within the house is to dry the manure as quickly as possible. Scraper systems, with manure boards, are beneficial to speeding up the drying process since manure lays in a thin layer on the boards with airflow across it until the scraper runs. Many producers have installed recirculation fans in the pits to enhance drying. It's extremely important to maintain adequate airflow through the house (particularly in the winter) to avoid high relative humidity, and to remove ammonia. Leakey waterers can cause wet spots in the manure. Monitor waterers closely to correct any leakage problems quickly.
Outdoor stockpiles
Outdoor stockpiles should be managed to minimize runoff and groundwater contamination potential. Iowa State University research comparing runoff from a stockpile with runoff from a cropped check plot shows that runoff is reduced slightly (4%) by the manure's ability to "soak up" liquid before runoff occurs. It also showed a large reduction in tileflow volume (78%) from beneath a stockpile as compared to the check plot, figure 2. The best way to minimize potential water quality risks from stockpiles is to minimize the time stockpiles are exposed to the weather. Don't clean out houses until the crop land is ready to receive the manure. Haul stockpiles out as soon as possible, or maintain them under some type of cover. Some producers do not stockpile manure outdoors anymore; they haul directly from the production house to the crop fields. If someone must build stockpiles, till the stockpile area to destroy macropores (worm holes and root channels) then recompact the area prior to building the pile. Stockpiles in crop fields should be constructed well away from ditches and tile intakes to minimize risk of runoff.
Minimizing air emissions
Keeping manure as dry as possible is recommended to minimize ammonia emissions. EPA has air emission standards that could impact poultry growers. They consider anyone emitting more than 100 tons/year of particulate matter (PM10 and PM2.5) or nitrogen oxides a "major source". EPA has been clamping down on western cattle feedlot's dust emissions. Ammonia is considered to be a PM2.5 constituent, so the regulatory emphasis could potentially impact the poultry industry. ISU and other universities are doing intensive research now to quantify, and help producers minimize, poultry emissions. It's important to minimize ammonia emissions from production facilities.
Besides drying, there are two methods of ammonia emission reduction being investigated (and used) today - alum use and belt systems. Alum has been widely adopted by the broiler industry. It was shown to be very effective at reducing ammonia emissions from broiler houses by Moore, et al. (1995). He showed up to 99% reduction in ammonia volatilization with alum treated litter versus untreated controls. Systems to spray alum onto dry stockpiles beneath layers have been researched and developed.
Belt manure removal systems are currently gaining recognition as a method to reduce emissions within production houses. The concept is simple...remove the manure quickly and often to minimize emissions within the house. Store the manure away from the birds. Researchers have reported emissions from belt houses are only approximately 25% of houses where manure was stored below the birds. Ammonia levels within belt houses are dramatically lower then "pit" houses. When manure from a belt system was composted, the belt-compost system retained approximately twice as much nitrogen within the manure than the stockpile system (Keener et al., 2001). Emission factors depend on ventilation rates as well as ammonia concentrations. They are currently being investigated and "fine tuned" by ongoing research.
Land application
Finally, manure must be properly land applied. Whether it's stockpiled under the birds or away from them, composted or not, liquid or dry, it must ultimately be spread on the land. Applying manure at appropriate agronomic rates is the most important management step producers can take to minimize environmental effects, especially water quality effects. Producers should use a good manure management plan that allows utilization of the nutrients for crop production without over applying them. The best way to protect water quality is to not over apply nutrients. Whether using your own plan, a state-mandated nutrient management procedure, or a federally mandated "comprehensive nutrient management plan" (CNMP), the plan should account for N, P, and K, and should consider, soils, potential losses, crop needs, and nutrient availability. Incorporating manure immediately after spreading minimizes air emissions, retains nutrients for crop use, and reduces water quality risks. Whole farm nutrient planning is a concept that can be utilized to do manure planning. It is simply a way to account for all nutrients coming onto the farm, the nutrients that stay on the farm, and the nutrients that are exported from the farm. Nutrients are imported onto layer facilities primarily as feed, and are exported primarily as eggs and/or manure. The imports and exports should balance. If they don't, losses are occurring somewhere, typically as ammonia volatilization losses to the air or increasing phosphorus levels in the soil. A whole farm nutrient plan can help producers see where improvements can be made, and what effect they will have on the overall balance. For instance, phytase can be added to the diet to allow feeding less dical, thus importing less phosphorus. Typically phosphorus in the manure can be reduced up to 30% resulting in 30% less acreage needed for the manure. Manure nitrogen can often be reduced by closely controlling protein levels. Whole farm nutrient plans allow you to look at your system as a whole, rather than in pieces.
Summary
Manure management for egg producers includes handling the manure to optimize the indoor environment for the birds and people working there. Keeping stockpiles under roof, or at least away from water resources is important, and stockpiles should be removed as soon after construction as possible. Several new techniques will help, such as the use of alum, and belt systems. Finally, manure should be land applied carefully using a good manure nutrient plan.
References
Moore, Jr., P.A., T.C. Daniel, D.R. Edwards, and D.M.Miller. 1995. Effect of chemical amendments on ammonia volatilization from poultry litter. JEQ 24:293-300.
Keener, H.M., D.L. Elwell, D. Grande. 2001. Atmospheric NH3 concentrations and N balances for 1.6 million caged layer facility- manure belt/composting vs. deep pit. ASAE paper 014094. St. Joseph, MI.
From Proceedings of the "Midwest Poultry Federation Convention", St. Paul, Minnesota, U.S.A.
