Now is the High Risk Period for Manure Runoff

February 8, 2011

Livestock producers who apply manure to agricultural fields need to be aware that spreading manure from now until the ground thaws have an extremely high risk of runoff.   Studies from farms cooperating in the Discovery Farm Program indicate that manure applied to snow covered and/or frozen soils during conditions of snow melt or rain on frozen soils can contribute the majority of the annual nutrient losses.    

Forecasted air temperatures are predicted to become milder starting the week of February 13 throughout much of Wisconsin, with daytime highs expected to occasionally climb into the 40’s. Daily high temperatures are predicted to be above freezing for at least a week in southern Wisconsin. This relatively prolonged period of warmth is expected to be accompanied with chances for rain. The combination of warm air temperatures and increasingly stronger sunshine could lead to snow ripening and starting to melt next week. Rainfall additions could contribute to additional snowmelt and increase the potential for surface runoff from farm fields.

Snowmelt runoff has the potential to be big this year. Snow depths are generally 1-2 feet throughout much of Wisconsin, which is much higher than normal, especially in Southern Wisconsin. In Madison, for example, there is typically about 5 inches of snow on the ground in early February. As of February 3, there was nearly 20 inches. If all of this snow were melted, the liquid equivalent would be approximately 2-4 inches, with as much as 6 inches or more in some areas of the state.

Frost depths are generally ranging from 8 inches to over 2 feet. Although the snow is deep – which tends to insulate soil and limit frost depth – the brief warm up near the end of December reduced the snow pack and allowed the cold air to penetrate deeper into the soil. The brief warm-up also consolidated some of the heavy December snows, and in many places there are icy layers within the snowpack and on top of the soils. In addition to frozen soils, these ice layers may further reduce infiltration and increase the potential for surface runoff.

As the temperatures moderate producers need to listen to the weather forecast.  Avoid spreading manure when there is a high probability of rain on frozen soils.  What can producers do to reduce the risk of manure run off?

  • During the period of active snow melt or when rain is predicted on frozen soils, producers who must haul manure from their barns should stack it in an area where the potential for runoff or groundwater infiltration is low,
  • Farmers who daily haul manure should work with their local conservation departments to identify safe stacking sites that have minimal potential to runoff into either surface or groundwater,
  • Producers who have lots or facilities with bedded pack systems need to be cautious about spreading this manure during this high risk period.  Cleaning lots and getting the manure on the fields before the frost goes out can greatly increase the potential for nutrients losses,
  • Producers who must haul manure during this high risk period should identify fields that are away from streams or lakes and have minimal risk of manure running to surface or groundwater.

We are saying that there is a high potential for manure runoff this year based on the current field conditions and typical weather patterns.  This doesn’t mean it will happen!  If temperatures rise slowly, cloudy days or the lack of rain can greatly reduce the chance of runoff.  Producers need to listen to the weather forecast and make good management decisions.  Good decisions can reduce the risk of runoff events and continue to protect our farms and our water.

Written by drframe@wisc.edu.

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