Mindful manure application
Reducing the risks associated with winter manure application
Any time commercial fertilizer or manure is broadcast onto farm fields, lawns or recreational turf, there is a risk that the nutrients could be lost in runoff and end up in a nearby ditch, stream or other surface water. It is the responsibility of homeowners, 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.
Wet conditions in late summer and fall can limit the ability of farmers to apply manure in ideal conditions resulting in a need to apply during the winter. 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.
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 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 (GAAMPs) for Manure Management and Utilization recommends conservation practices including vegetative buffers between surface waters and fields used for winter manure applications. It is preferred that if the entire field has some type of residue cover, including undisturbed corn stalks, wheat stubble or established hay.
Cover crops and vegetative buffer strips can help hold nutrients in the field where applied. Adoption of a cover crop management scheme allows for a responsive cover in the event of sudden thaws that characterize winter in Michigan. Cover crops proved to be effective in reducing nitrate nitrogen loading through tile-drainage across the spectrum of common nitrogen fertilizer management systems. You can learn more about cover crops from the MSU Extension Soil Health and Cover Crops experts.
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. A field-specific assessment, such as the Manure Application Risk Index v 4.0 (MARI) and the Michigan P Assessment Tool v 2.0 can help evaluate the risk for runoff losses.
According to the GAAMPs, manure should not be applied within 150 feet of any surface water unless incorporated immediately which is not practical on frozen, snow-covered fields. Preferably the setback should be growing established vegetation or covered with undisturbed crop residue. Catch basins, grass waterways and any area that collects water and flows toward surface water are also high-risk areas; manure should not be applied to these areas
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 warmup 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.
The MI EnviroImpact tool is a free decision support tool for short-term nutrient application planning that shows daily runoff risk across Michigan, including winter months. The tool’s runoff risk forecast comes from real-time precipitation and temperature forecasts, which are combined with snow melt, soil moisture, and landscape characteristics to forecast runoff events. With the tool, farmers can better determine when to apply fertilizers during times of lower runoff risk.
Timing of manure application
If manure cannot be applied in late summer and fall, 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.
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 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. Farmers should recognize the associated environmental risks with winter spreading. Individually evaluating each field and utilizing the practices listed above helps reduce those risks.