Charles Linderman, P. E., Livestock Waste Management Specialist

North Dakota State University Extension Service

Carrington Research/Extension Center

Livestock manure is a resource that can supply valuable nutrients for crop production while improving soil physical condition as well. Livestock manure out of place may pollute the environment. Decomposing manure organic matter can enhance soil physical condition, but can reduce oxygen levels in water, resulting in fish kills. Manure contains nitrogen (N) and phosphorus (P), valuable nutrients for crop production, but which can cause eutrophication of surface water when they reach sufficient concentrations. Most livestock producers are aware of regulations requiring containment of manure and manure-contaminated runoff. However, once contained, manure and manure nutrients must be utilized in a way that does not have negative impacts on water quality.

Land application as fertilizer and soil amendment is usually the most cost effective way to manage livestock waste. To reduce cost and time, most manure is land applied close to the animal feeding operation where it was produced. Often, N and P from successive manure applications exceed the use by crops. It is well known that N is easily water soluble and transported in runoff and leachate. P is known to be only moderately soluble and adsorbs to soil particles, and is therefore less likely to move in runoff and leachate. However erosion can transport soil-adsorbed P to surface water. In great enough concentrations, P may exceed the retention capacity of the soil. In that case, P also may move in runoff and leachate. Organic P from manure may be more mobile than fertilizer P.

The ratio of P to N in most manures is greater than the ratio of P to N use by most crops. As a result, when enough manure is land applied to satisfy the N requirements of a crop, the supply of P exceeds the crop use. One solution is to limit manure application to the P requirements of the crop and supply the N deficit with purchased N fertilizer. A more economical alternative, if the soil is not already overloaded with P, is to apply enough manure to supply the crop N requirement, but rotate annual applications to different fields so that the P application matches crop use over the rotation period. A useful strategy is to plant crops and plan rotations that use the most P.

When planning organic fertilizer applications to a crop rotation, consider that not all the nutrients will be available to the crop the year of application. Some will be available for plant uptake in the second and third years as the organic matter mineralizes.

Increasingly, regulatory agencies are emphasizing nutrient management as part of environmental compliance for animal feeding operations (AFOs). Records will be required of manure production and application. It will be necessary to test and keep records of manure and soil nutrients and to calibrate application equipment.

Ideally, applied manure should be incorporated into the soil. Manure with 10 percent or less solids can be pumped as a liquid and machinery exists to inject it into the soil in zero till situations. Runoff from outdoor AFOs can be easily applied to zero till fields with irrigation sprinklers. Solid manure can also be successfully applied in zero till, but obviously cannot be incorporated without tillage. A consideration with zero tillage is that much nitrogen from surface exposed manure will volatilize back into the atmosphere so that the P build up problem may be more critical.

In North Dakota, the ND Department of Health (NDDoH) is the agency in charge of environmental regulation of AFOs. Certain AFOs, because of size or location, require approval to operate. Some of the requirements for approval are having a nutrient management plan and following land application guidelines.

Manure must be applied at least 100 feet from streams or lakes if soil incorporated and 200 feet away if not immediately incorporated. Surface application must not be made to grass waterways or drainage ways. If application to frozen ground cannot be avoided, manure should be applied to fields with less than 6 percent slope, with stubble or plant cover, and less than 8 inches of snow cover.

NDDoH guidelines call for soil tests of manure application areas at least every other year. The sum of soil N, fertilizer N, available manure N, and N carry-over from previous manure applications must not exceed recommended crop needs. If soil P tests exceed 16 ppm (Olsen test), or if manure is applied in two consecutive years, manure application should not exceed P needs of the crop.

Research indicates that manure application on zero till will increase soluble P concentration in runoff compared to tilled systems. However, the volume of runoff will be less with zero till, so the total P loss to surface water may be less.

Land application of manure in zero till fields presents some unique challenges, but with planning, can be successful.