Protecting our water quality with livestock waste management

Vincent J. McFadden, Extension Soil and Water Engineering Specialist; Stewart Melvin, Extension Agricultural Engineer; Iowa State University

The key to whether animal wastes help or hinder a livestock operation lies in proper management of manure. Livestock manure can be a valuable resource by providing necessary nutrients for crops and improving a soil’s physical properties. However, manure can become an environmental problem when it pollutes ground and surface water as a result of improper handling and storage. Manure also can create conflict between producers and neighbors due to runoff or odor problems. Proper management can help producers use manure as a valuable resource and not become an irritating or harmful pollutant.

Streams and other bodies of water have the natural ability to self-purify, but they may become polluted if manure runoff enters them. The main pollution problems with manure in surface water are associated with the organic matter, nitrogen and phosphorus in the manure. When runoff from animal operations enters a stream, the dissolved oxygen level may drop below the critical level in the water.

Oxygen reduction occurs because bacteria in water use oxygen as they decompose the organic matter in the manure. If too much oxygen is used for decomposition, the dissolved oxygen level can drop below acceptable levels for fish and other organisms in the stream. The dissolved oxygen level is raised naturally by various physical methods and by photosynthesis. Aeration occurs as water flows over falls or rapids, by absorption, by wind action and by dilution from other water sources.

Another surface water quality problem is the high ammonia level in feedlot runoff, resulting in reduced growth and gill damage to fish. The ammonia also forms nitrites and nitrates as it is oxidized bacterially. Both forms of nitrogen pose problems in surface water. Nitrites can harm fish, and excessive concentrations of nitrate may cause blue baby syndrome, or methemoglobinemia.

High phosphorus levels in manure also can cause water quality problems. Plants, especially algae, are encouraged by too much phosphorus which leads to eutrophication of surface water. Decaying algae will deplete the water’s dissolved oxygen level and lead to acute fish kills. Eutrophication affects ponds and lakes more than streams and rivers.

It is essential to prevent feedlot runoff from entering streams and other surface water and to properly manage manure until this resource can be used as part of an effective crop fertility program. This [article] addresses ways to handle problems in runoff, storage and application of livestock manure. Whether the livestock operation is small or large, all three areas must be considered for effective, responsible management of livestock wastes.

Feedlot runoff control

Begin a good manure management program at the source of the wastes, the feedlot. One of the most important ways to prevent manure runoff is to divert clean water away from the feedlot. This reduces the amount of water contaminated by manure that needs to be handled.

Water has the ability to lift and carry manure into drainage ditches, streams and ponds. The use of berms or terraces can divert clean roof and surface water around the feedlot. Eave troughs, gutters or mono-sloped sheds do an excellent job of keeping roof water off the feedlot. In cases where clean water runoff cannot be diverted, a sump system with an underground tile outlet can be used above the feedlot.

All solids in feedlot runoff must be removed. A common method is a settling basin. The basin usually is designed to handle runoff from a 10-year, one-hour storm – that is, a short, high-intensity rainstorm expected to occur once every 10 years. A properly designed settling basin will collect all feedlot runoff and slow the velocity of the runoff so larger solids can settle to the bottom of the basin. Some feedlots require only concrete or wood curbs around the lot to handle such a storm.

The settling basin should have a porous dam or perforated pipe that allows the liquids to flow out as the solids settle. Dams can be made of lumber with gaps between the boards, concrete with holes in it or expanded metal screen. Manure tends to plug openings over time, so the dam must be constructed so it can be cleaned occasionally. The basin should have a spillway so water will not back up into feeders or buildings in case the porous dam cannot handle the flow. In many areas, the bottom of the basin should be lined with concrete rather than soil. This allows the solids on the bottom to be scraped up and hauled away more frequently than is possible in soil-lined basins.

Liquids that drain out of the basin can be either infiltrated or stored to keep them away from surface water. Never discharge effluent from settling basins directly into a tile line, stream or sinkhole because of possible pollution to a nearby stream or water supply.

For most small lots (those that don’t require runoff impoundment), effluent from a settling basin can be discharged into a vegetative infiltration area, usually a long, grassy and gently sloping channel. This allows the liquid to soak slowly into the soil. The only water in this channel should be lot runoff that has gone through the settling basin and direct precipitation. Do not use waterways that drain other surface water from a surrounding watershed. The volume of water is too great to allow enough time for the water to soak into the ground, and pollution in a nearby stream is possible.

If feedlot size or site conditions are such that an infiltration area cannot be used, liquids may be collected in a temporary holding pond. The contents are usually removed soon after a rainstorm to prevent overflow. Irrigation equipment is often used to clean out holding ponds because of the large volume of liquid handled and the low concentration of nutrients.

Storage systems

Many livestock farmers select manure storage facilities that eliminate the need for daily hauling and allow timely application to row crops. Properly designed systems also help reduce environmental problems associated with feedlot runoff. Storage pits built under livestock buildings are often used in confinement operations. However, some producers prefer outside storage facilities because they can usually store more manure and improve air quality inside the building. Adequate storage facilities allow producers to frequently scrape wastes off the lot so runoff losses are kept to a minimum, too.

Select a good location for storage facilities to reduce water quality and odor problems. Odors are strongest when the facility is emptied. Locate new livestock production sites and manure storage facilities as far away from neighboring residences as possible, and consider the direction of prevailing winds with respect to public use areas and residences.

Contact the nearest field office of the Department of Natural Resources for permit requirements for manure storage facilities. There are minimum separation distance requirements for earthen manure storage facilities. Dairy farmers should check with their milk inspector to determine other specific requirements. Generally, all manure storage facilities should be located at least 100 feet away from a well. Earthen storage basins and lagoons should be located as far as possible from a well.

When the site is chosen, evaluate soil conditions to help prevent groundwater contamination. Soil conditions below the storage area and depth to bedrock will help determine whether the facility should be an earthen basin, a lined earthen basin or a concrete or steel structure. Use your county soil survey or check with your Soil Conservation Service office to get information on the suitability of your soil for construction.

Locate manure storage facilities for convenient filling and emptying. The storage facility should be adjacent to the feedlot if manure is to be scraped into it. The facility can be located some distance from livestock if manure will be pumped or gravity-fed into storage. Easy, all-weather access is essential as is plenty of room for operation of large unloading equipment.

For liquid storage, the facility must have space around the perimeter for use of agitation equipment. Decay of manure produces a deadly gas, hydrogen sulfide. Use extreme caution during agitation to prevent being overcome by this gas. Never enter a manure pit until agitation is complete and the pit has been ventilated. Always wear self-contained breathing tanks and an attached safety line. At least two people must be outside to pull you out if you have trouble.

For safety, fence the entire storage facility from livestock and people. Keep the site neat to help reduce complaints from neighbors. Carefully consider your economic situation, availability of appropriate land, labor for spreading and future expansion plans when you size your storage facility. A one-year storage capacity provides more opportunities for timely field applications than smaller capacities. It also allows for possible expansion of livestock numbers without building additional storage if a more frequent emptying schedule is used after expansion.

The minimum storage provided for earthen storage should be six months, and recommended minimum storage for other systems is four months. Size the storage to include all manure produced, bedding and any water that may enter the storage from runoff, snow-melt, milking center waste, waterer spillage and water used for washing crates or equipment.

An important part of manure management is proper application to row crops. To achieve the greatest benefit, producers must know how much manure to apply, when and where to apply it and the best method to apply it without causing environmental problems. Poor application methods can result in the contamination of ground and surface water and inefficient use of nutrients.

Surface runoff problems are reduced if the manure is incorporated during or shortly after application. Avoid surface application on frozen or snow covered ground, near a stream or sinkhole or on steep slopes. Manure should be spread to maximize the benefits from its nitrogen, phosphorus, potassium and organic matter. Test the soil to determine the amount of phosphorus and potassium required to reach a realistic yield goal. Apply enough manure to satisfy any of the three major nutrient requirements, and supplement the other two with commercial fertilizers if needed.

Animal manure varies by animal, its age and diet. Test several representative manure samples to determine nutrient content. Too much manure can result in nitrates leaching into groundwater. Therefore, it is important to credit the nitrogen in the manure to avoid overapplication.

The amount of nitrogen available from manure can vary greatly depending on how the manure is stored and spread. Approximately half of the nitrogen in liquid manure is in the ammonia form, which is subject to volatilization and can be lost to the atmosphere. Volatilization can be reduced by injecting manure or incorporating it with tillage equipment immediately following application. Incorporation of manure also helps reduce odors.

It is often difficult to apply manure uniformly at an appropriate rate. Some producers want to save time when hauling manure, so they use it in fields close to farm buildings and spread it at high rates. However, this often results in overapplication, environmental damage and is an inefficient use of the valuable nutrients in the manure.

Summary

Use and management of livestock wastes create challenges for livestock producers. However, knowledge, proper procedures and facilities will help make livestock waste a manageable resource that can benefit livestock producers. Whether it’s a help or hindrance, a problem or opportunity, it is up to you. ANM

—From Iowa State University Extension website