NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

October 22, 1998

Animal Waste: An Emerging Water Quality Issue

Unless you live directly downwind from a feedlot, environmental impacts from animal waste are generally not an important consideration for most people in this region. That may be changing, says a North Dakota State University water quality expert.

An increase in concentrated livestock operations, added government regulation of livestock operations and research showing that animal waste can be a significant contributor to surface and groundwater contamination—all are likely to keep animal waste management in the news for some time to come, according to Bruce Seelig, water quality programs coordinator with the NDSU Extension Service.

"It is clear that animal feeding operations generate large amounts of waste, generally in a very small area, and if this waste is not properly managed or used it may contribute to water quality problems," Seelig says. "What is not so clear is the most effective management technique to be used in each situation."

Studies show that the connection between water quality and animal waste is quite variable and some water contaminants respond to management while others do not. For instance in a watershed project in Vermont, the application of animal waste best management practices (BMP) reduced the levels of fecal and streptococcus bacteria in local streams, but had no effect on nutrient concentrations. These types of results should not be used as an excuse for inaction or improper management, Seelig says, but they should be used to point out the need to understand the connection between management and water quality at a site-specific level.

Seelig says most investigators agree that animal waste can be managed to protect water quality; however, doing so requires knowledge of how a combination of practices affects each contaminant. These practices need to be tailored to each situation.

Is manure really a serious environmental threat? Absolutely says Seelig. He cites the massive worldwide release of ammonia to the atmosphere as manure decays as an example. Research estimates that waste from domestic animals releases approximately 20 to 35 million tons of ammonia per year compared to 6 to 18 million tons per year released in combination from wild animal waste and the combustion of fossil fuels.

And animal waste can threaten water resources. Seelig notes that manure provides energy for the growth and proliferation of aquatic microbes, which reduce oxygen concentrations in streams and lakes. Manure contributes phosphorus and nitrogen to surface water, which may lead to excessive growth of aquatic plants. Animal waste also contains microorganisms such as bacteria, which may cause human diseases such as the 400,000 cases of gastroenteritis due to Cryptosporidium in Milwaukee's water supply in 1993.

Some studies have shown a correlation between nitrate concentrations in groundwater and distance to feedlots. Other studies have found increased levels of microorganisms and nitrates in groundwater beneath fields fertilized with animal waste.

"But," Seelig points out, "the threats can be managed and animal waste can be a resource."

There are opportunities to utilize the nutrients contained in animal waste for crop production in North Dakota, where crops use more total nutrients than are produced by the state's animal feeding operations, according Seelig. Unfortunately, studies show that the nutrient value of manure is often not credited properly and over-application of nutrients is the result. That increases potential for contamination of both groundwater and surface water resources.

Another factor to be considered is that the nutrient value of animal waste is substantially less than that available from a commercial fertilizer. When animal waste is applied to meet crop needs, it is applied in amounts equivalent to tons per acre as compared to commercial fertilizer applications of pounds per acre. This means that the labor and time expended to haul and apply manure can become a significant deterrent to its use as a source for crop nutrients. Distance hauled is another critical factor that must be considered in any animal waste application management plan.

"Practices that reduce the potential for land-applied animal waste to contaminate water resources need to be tied to knowledge of the exact nutrient content of the material and nutrient requirements of the crop grown," Seelig says. "Manure and soil testing are essential information for proper management." Manure application equipment must be calibrated so producers know how much of each nutrient is applied.

Scott Birchall, livestock waste management specialist at NDSU's Carrington Research and Extension Center, agrees and is encouraging producers to develop manure-application plans. Birchall says manure application plans need to take into account the following:

• Existing soil fertility levels via a soil test and a history of past manure applications.
• A manure test not more than one month before application.
• Calculation of the crop's nutrient requirement at the target yield.
• Calculation of the required application rate so that no nutrient is supplied in excess of requirements.
• Calibration of the spreader.
• Crediting the nutrients in the manure and reducing the application of inorganic fertilizer.

Manure applications have often been based only on nitrogen content. Research suggests this approach has resulted in the accumulation of excessive amounts of phosphorus in the topsoil in many areas.

"That's is not a critical fertility problem but is an environmental problem because of the increased availability of phosphorus to runoff and surface water resources. All nutrients must be properly accounted for in nutrient management plan," Seelig says.

Recent long-term studies in Saskatchewan indicate that the natural process of organic material decay also must be accounted for in nutrient management plans. Seelig notes that the decay process releases nutrients throughout several years. As a result, annual applications of manure at the same rate will eventually cause over-fertilization. The decay rate is different for different types of manure and must be determined to ensure the proper amount of manure is applied each year. The Saskatchewan research indicated that failing to account for the manure-decay rate significantly increased the potential for nitrate contamination of groundwater in irrigated and dryland fields.

Seelig says there are some general guidelines for handling manure that will reduce the potential for surface and groundwater contamination:

• Under similar application conditions dry manure poses less of a threat to water resources than liquid waste.
• Avoid applications during wet periods or on frozen ground before spring run-off.
• Don't apply manure any closer than 25 to 30 feet to water resources when soils are thawed or any closer than 200 feet when soils are frozen.
• Incorporate manure to reduce the potential of surface-water contamination, but be aware that injected liquid waste has greater potential to cause groundwater contamination.
• Apply manure to the surface of reduced tillage fields to avoid disturbing soil residue. In this situation, less runoff from reduced tillage should serve to counterbalance the negative effects from exposed manure on water resources.

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Source: Bruce Seelig (701) 231-8690 and Scott Birchall (701) 652-2951

Editor: Tom Jirik (701) 231-9629