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Serving: WI

A Dry Autumn Creates Challenges for Land Applied Manure

Weather creates hazards for manure spreading.

Appreciation is extended to Tony Smith, Resource Conservationist for the Manitowoc County Soil and Water Conservation Department, for the following article on manure management concerns during extremely dry field conditions, especially after corn silage harvest.

The repeat of extraordinarily dry weather in Manitowoc County following a wet early summer has again created hazardous conditions for spreading liquid manure.

September through November are generally times of low stream flow. Small water volumes tend to be warmer and hold less dissolved oxygen needed by fish and other aquatic organisms. As a result, very small discharges of pollution from field-applied manure to streams can result in killing fish. Rain showers during the fall can result in runoff, even from dry fields, especially after manure applications. All farm operators and manure applicators should be aware of the increased risk. Ample buffer zones and incorporation with tillage that thoroughly blends, mixes, or combines soil and manure will reduce risk of runoff.

Fields harvested for corn silage have been problem sources in the past. Corn silage harvest typically leaves fields relatively residue free, and compacted. Manure applications that are not incorporated are vulnerable to runoff, even on modest slopes. Both the Manitowoc County SWCD and UW-Extension recommend that farmers and custom manure haulers loosen the soil around the edge of fields where runoff may be a concern. The entire field does not need to be tilled---simply make a couple of passes near the edge of the field where runoff may occur if the manure is not tilled in immediately. Remember that due to prolonged dry conditions, some fields resemble concrete in their ability to absorb moisture. We need to make sure these fields do not pose a runoff threat. Prior planning is a must this year.

Fields with heavy soils that have tile drains are potential problems. Root channels, worm holes and cracking (macro pores) in heavy soils in Manitowoc County are known to quickly take manure water into tile drain lines and release the contaminated water to a stream or lake system. Highly liquid manure creates the highest risk.

Manitowoc County SWCD staff are finding numerous tile breaks that have occurred due to the very wet summer. Be sure to inspect all waterways and areas where concentrated flow of water has occurred. Repair all tile breaks before manure application.

To reduce the risk of manure water entering tile lines, the following recommendations have been developed by Michigan State University:

Actions to prevent a tile line discharge

  • Excessive application rates increase the chance of runoff and a tile line discharge. Calibrate manure spreaders and verify that the calibrated rate is the rate that is actually applied to the field. Based on observation and evaluation, determine the right application rate for your fields.
  • On some fields, the right rate may be considerably less than the allowable rate based on manure nutrient content.
  • Use soil and water conservation practices such as crop residue management, and grassed waterways that prevent local ponding and overland flow. Local ponding can funnel waste water into tile lines through macro pores and tile breaks.
  • Use surface tillage to disrupt the continuity of worm holes, macro pores and root channels and reduce the risk of manure reaching tile lines. Avoid deep injection of manure over drain tiles.
  • Do not apply manure to tile drained fields when the tiles are flowing.
  • Observe and monitor tile outlets. Keep a map of tile outlet locations so they can be found as needed.
  • Match the manure application rate with soil infiltration rates and water holding capacity.
  • Make more frequent, lower rate applications rather than a single heavy application.
  • Should a discharge occur, have a plan for dealing with manure that may reach tile lines, such as blocking outlets or blocking the flow once it reaches the ditch.
  • Surface applications with rapid incorporation may be the best choice on land with subsurface drainage. Conservation tillage before spreading will create a rough, permeable surface. Injection may actually increase problems by placing the manure closer to the tile lines.
  • Decrease the manure application rate, and avoid spreading in the rain or when rain is in the forecast. 14,000 gal/acre of liquid manure is equal to ½ inch of rain.

Even nearly flat fields may have some runoff during times of snow melt, spring rains, and fall rain. If manure is not injected or incorporated, observe a 300 foot setback from streams and ditches. Avoid spreading manure through areas where field runoff flows. Accurate record keeping of manure application is extremely important. Recording and saving your manure application information will help you manage and lower your crop input costs, while maintaining appropriate crop yields. Field-applied manure that flows into streams, lakes, or groundwater can cause serious health concerns, and can lead to fines for both the farm operator and the manure applicator. Think ahead - if it looks bad, don't do it.

Manitowoc County Prevention and Response Guides for Manure Spills and Runoff are available from the Manitowoc County UW Extension Office and Manitowoc County Soil and Water Conservation Department.

Manure hauling hazard maps are available from Manitowoc County SWCD, USDA NRCS, and most local agronomists.

In all cases, if a spill occurs, contact the Wisconsin DNR Spill Hotline at 1-800-943-0003 and the Manitowoc County SWCD staff at (920) 683-4183.

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