Any time plant nutrients, both commercial fertiliser and manure, are broadcast onto farm fields, lawns or recreational turf, there is a degree of inherent risk of a small percentage being captured in precipitation run-off and eventually ending up in a nearby ditch, stream or other surface water. It is the responsibility of home owners, turf grass managers and farmers to follow best management practices (BMPs) developed to limit run-off and keep plant nutrients out of surface water and in the root zone for crop uptake.

With frozen soil and the potential for snow build up followed by a spring thaw, winter spreading of manure, or any other crop amendment, carries with it a greater degree of risk and potential for run-off into surface waters. As a result of this increased risk with winter spreading, many within both agriculture and environmental groups have begun to question the practice. Others continue to research methods of reducing the risk associated with winter spreading and maintain that manure application option.

Listed below are some of the risk factors one should consider when selecting fields for winter manure application.

Residue cover: Residue cover has three main functions. First residue helps hold things in place, including soil particles and manure nutrients. Second, residue will slow run-off down reducing the amount of soil and manure the run-off picks up. Finally, residue will act as a filter by capturing manure and soil particles suspended in run-off before they reach surface water.

The Michigan Right to Farm Generally Accepted Agriculture Management Practices for Manure Management and Utilization (Manure GAAMPs) recommend conservation practices including vegetative buffers between surface waters and fields used for winter manure applications. It is preferable if the entire field has some type of residue cover, including undisturbed corn stalks, wheat stubble or established hay.

Field slope: Naturally slope increases manure application risk. The Manure GAAMPs state liquid manure should not be winter applied to fields with greater than three per cent slope and solid manure should not be winter spread on fields with greater than six per cent slope.

Manure should not be allowed to run-off on adjoining property owners. Avoid areas that slope towards and pond in neighboring fields no matter what the slope.

Setbacks: According to the GAAMPs manure should not be applied within 150 feet of any surface water unless incorporated within 48 hours of application, which is not practical on frozen, snow covered fields. Catch basins, grass waterways and any area water collects and flows toward surface water are also high risk areas. Maintain the 150-foot set-back from those areas as well. Preferably the set-back should be growing established vegetation or covered with undisturbed crop residue.

Weather forecast: Research has shown that nutrient loss increases if manure is winter applied five to seven days prior to a run-off event. Monitor weather forecasts and avoid manure applications if a warm up in temperature or rain is predicted for the immediate future. Nutrient losses are reduced by a larger window of time between the application of manure to snow covered, frozen fields and a snow melt, winter run-off event.

Timing of manure application: Apply manure early in the winter. Avoid spreading in late February or early March when there are greater odds of a large sudden snow-melt and/or rainfall event. Or, if manure must be spread throughout the winter, choose fields with a higher degree of risk early in the winter saving low risk fields for later in the winter and early spring.

Application rate: Follow the normal farm manure application rates based on the nutrients in the manure and the needs of the crop to be grown. Do not exceed the nitrogen needs of the crop to be grown.

Reducing the environmental risks associated with winter manure spreading requires planning. There are resources available to help livestock farmers evaluate, on a field by field basis, the risk of winter spreading.

The Michigan Right to Farm Manure GAAMPs referenced above outline specific practices for winter application of manure in Michigan.

The Manure Application Risk Index (MARI) ranks the environmental risk of winter manure applications to fields, rating each field from a “Very low” to “High” risk. According to the MARI guidelines, fields rated as “Very low” and “Low” have a reasonably good potential for winter spreading. The Michigan Department of Agriculture and Rural Development and the Michigan Department of Environmental Quality recognize MARI as the appropriate tool for determining a field’s suitability for winter manure application. In Michigan, county NRCS Conservation Technicians and Michigan Agriculture Environmental Assurance Programme technicians are available to assist farmers with the MARI tool.

The Livestock and Poultry Environmental Learning Center (LPE) is an online resource dedicated to helping livestock and poultry farmers identify and reduce environmental risk. One of LPE’s resources is a section dedicated to helping farmers identify and reduce the risks associated with winter manure application. This section on winter manure applications is available at bit.ly/winterspreading.

There are legitimate reasons for winter manure application. From delayed field work in the fall resulting in farmers needing to empty manure storages in the winter, to farms with bedded housing dependent on daily hauling, there will be times when manure must be applied in winter months. Livestock farmers need to recognise the associated environmental risks with winter spreading. Individually evaluating each field and utilising the practices listed above helps reduce those risks.

August 2014