Correspondent
LOMIRA
Forecast warmer temperatures and rain has raised concerns over potential runoff from manure spread on fields. The University of Wisconsin Extension Discovery Farms program has issued information for farmers to consider during this high-risk period for manure runoff.
Studies from farms cooperating in the Discovery Farms program indicate that manure applied to snow covered and/or frozen soils during conditions of snowmelt or rain on frozen soils can contribute to the majority of the annual nutrient losses. The combination of warm air temperatures and increasingly stronger sunshine could lead to melting snow. Rainfall could contribute to additional snowmelt and increase the potential for surface runoff from farm fields.
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.
Discovery Farms has some suggestions for what farmers can do, as follows:
• During the period of active snowmelt 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 nutrient 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.
Fred Madison, a soil scientist with the Wisconsin Geological and Natural History Survey at the UW-Madison and co-director of Wisconsin Discovery Farms, talked about that topic and also provided information about how karst topography in some of Wisconsin’s biggest dairy counties in northeastern Wisconsin makes spring manure application even more risky. This karst area is riddled with sinkholes, fractured bedrock and uninhibited underground drainage.
He comments, “My work is with manure, but the karst report deals with all things that are put on the land.”
Karst features in Wisconsin follow a U-shaped pattern from Door County in the northeast, down along Lake Michigan, across southern Wisconsin and northward into the hilly country of southwestern Wisconsin. He explained how there can be rapid downward flow of surface water via vertical fracture networks in the uppermost carbonate bedrock. What can be problematic for producers farming karst topography in northeastern Wisconsin is the rapid lateral flow of groundwater along fractures.
While there is karst bedrock features in other portions of the state, what makes the northeast so vulnerable to groundwater contamination is the thin soil over the fractured rock. In the southwestern part of the state, for instance, the area isn’t glaciated. There is red dense clay over bedrock serving as an important barrier and good protection for the underlying water system.
Madison explains, “The cracks are everywhere. They are also under flat ground, where there is little surface runoff. Water goes down at a rate of about a foot a day and the water table comes up quickly.”
The Natural Resources Conservation Service soil surveys have accurately mapped depth to bedrock in karst areas. It is well-known how many feet of soil is over the top and the soil texture, both of which dictate the speed at which surface water will move into karst fractures and possibly groundwater.
Madison describes the piece of equipment the university uses to assist with site investigations.
He concludes the challenge is to determine where vulnerable materials are on the landscapes and what can be recommended for rates and timings of manure applications.
