By: Gerald May and Shelby Bollwhan, Michigan State University Extension
Any time commercial fertilizer or manure is broadcast onto farm fields, lawns or recreational turf, there is a small percentage of risk that the nutrients could be captured in precipitation runoff and eventually end 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 runoff and keep plant nutrients out of surface water and in the rootzone for crop uptake.
With last fall’s late harvest combined with the early onset of cold winter weather, many livestock producers are faced with the need to haul manure this winter. 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 runoff 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 and management practices Michigan State University Extension recommends considering 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 down runoff reducing the soil particles and manure the runoff picks up. Finally, residue will act as a filter by capturing manure and soil suspended in runoff before they reach surface water. The Michigan Right to Farm Generally Accepted Agriculture Management Practices for Manure Management and Utilization 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: Sloping fields increase manure application risk, the greater the slope the higher the risk. According to the Manure GAAMPs, liquid manure should not be winter applied on fields with greater than 3 percent slope and solid manure should not be winter spread on fields with more than 6 percent slope. Manure should not be allowed to runoff on to the adjoining owner’s property. Avoid areas that slope toward 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 setback from those areas as well. Preferably the setback 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 5 to 7 days prior to a runoff 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 runoff event.
Timing of manure application: Apply manure early in the winter. Avoid spreading in late February early March when there are greater odds of a large sudden snowmelt 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 (N) needs of the intended crop.
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 and depending on daily hauling, there will be times when manure must be applied in winter months. Livestock farmers should recognize the associated environmental risks with winter spreading. Individually evaluating each field and utilizing the practices listed above helps reduce those risks.