These above statements can all be true. Manure is a desirable plant fertilizer and has positive impacts on soil and soil health, but management decisions during land application influence the relative environmental benefit or risk resulting from manure. Timing, location, and amount of manure applied all must be carefully considered.
A nutrient management plan (NMP) is a document that spells out rate, timing, location, and other manure and fertilizer application factors. The two nutrients that are watched most closely, relative to water quality, are phosphorus and nitrogen.
An NMP for any farm generally follows the same outline. Regulated or permitted operations will have the most specific requirements. In some states, even small farms are required to develop NMPs. There is a great deal of technical assistance available for developing NMPs from extension, agencies, and private consultants. In some areas, cost-share assistance may be available. There are also many software tools available; one example is the Manure Management Planner Software. Since every state is different, it is recommended to look for state-specific resources and requirement before developing your NMP.
One of the first steps in developing an NMP is to estimate the amount of manure produced on a farm. Some other important pieces of information include: nutrient content as determined by a manure test (Related information: Sampling Manure) and the availability of nitrogen from that manure (consult your state extension service to obtain calculations on nitrogen availability appropriate for your area). Last, but not least, it is important to calibrate manure application equipment to ensure that you know how much manure was actually applied to each field.
Manure application should be set back from wells, streams, lakes, sinkholes, or other environmentally sensitive features. Most states have rules dictating exactly how farm this setback should be.
Tile-drained fields should also receive special consideration with regard to manure application. If manure is applied while soils are saturated or right before a rainfall event, the manure may preferentially flow through tile drainage to water bodies.
Manure application in spring, shortly before crops are planted, is generally recommended as it allows a short window where nutrients are prone to leaching or runoff. When manure is applied to fruit or vegetable crops, this recommendation may differ.
Manure application during crop growth will closely match nutrient needs, but can be destructive to the growing crop. One way to avoid crop damage is to apply liquid effluent through irrigation systems. (Also see Ohio research on top-dressing liquid swine manure to wheat and side-dressing on corn).
Applying manure in the fall, after the main crop is harvested, is a common practice and helps ensure manure storage structures are emptied before winter--reducing the chances of a overflow. Given the high price of fertilizer and the increased awareness of water quality, more farmers are following fall manure application with a cover crop.
Winter manure application is a controversial topic in many areas. Manure applied to snow-covered or frozen soils may be more likely to runoff under some conditions. Winter applications should only be made in order to prevent a manure storage overflow and should be done in low-risk areas with little slope or potential for runoff to water.
Whole Farm Nutrient Balance (WFNB) is a way to evaluate if the farm is currently accumulating more nutrients than are being exported from the farm. If this analysis is repeated from time to time, the trend can tell if a farm's efforts are working or not. This website includes a dairy example and a swine example of WFNB.
Related information: Snap-Shot Assessments of Nutrient Use on Dairy Farms
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Reviewers: Rick Koelsch, University of Nebraska, Doug Beegle, Pennsylvania State University, Ron Wiedreholdt, North Dakota State University.
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