Wet Weather and Issues for Manure Storage Structures and Open Feedlots
By Jeff Lorimor, Department of Agricultural and Biosystems Engineering


Iowa has been experiencing significant wet weather during this spring of 2004. Large amounts of precipitation can be a challenge to livestock producers, especially if they have containment basins to catch open feedlot runoff. Here are some ideas to consider for managing feedlot runoff and manure storage structures to protect nearby water resources.

The most important thing you can do is to prevent overtopping of any manure or runoff containment structure. If you have a confinement system such as a swine building or other roofed facility these heavy rains shouldn’t affect you very much. Your manure storage pit should not receive any extra precipitation if it’s under roof, or it should only receive the rainfall that falls directly on it if it’s an outside pit. Six inches of precipitation should increase the depth by 6 inches. The extra water in an outside pit will dilute the nutrients, so taking a manure test before land application will be more important this year than normal. Keep an eye on the level of outside pits to maintain freeboard requirements and develop a contingency plan to apply manure this summer on hay, oat or pasture areas if additional precipitation events occur and your outside manure pit capacity won’t last until normal fall land application. Remember to make appropriate changes to your manure management plan.

Keep your outside lots clean by scraping frequently. Rather than allowing precipitation to wash the lot off and carry manure to the stream, scrape it ahead of the rains to minimize the runoff strength. This is a good management technique for those with basins, and even more important for lot operators without containment basins since the runoff can reach nearby waterways.

Keep settling basins drained and cleaned. Porous outlets tend to plug; clean them frequently so your basin drains down and dries out as soon as possible. If possible remove solids from the basin with your tractor or scraper (if you don’t have a concrete bottom you may not be able to).

If you have an outside feedlot with a runoff containment basin below it, the containment may be filling up. Containment basins below feedlots receive not only the precipitation that falls directly on them, but also runoff from the feedlot above. Six inches of precipitation may add several feet of liquid to your containment.

Keep a close eye on the liquid level in your containment basin. If you have land that you can pump to, you may need to do so as soon as the soil dries enough. Your basin should always have capacity to contain the 25-year, 24-hour storm (about 5.2 inches in Iowa). In addition you need capacity to hold any additional precipitation and runoff between now and your scheduled pumping time. Since the crops are still small you may still be able to pump now without damaging the crops, whereas that will be impossible once the crops get larger. If you’ll be making hay soon, that hay ground may provide you a place to pump to. Open feedlot runoff typically will not damage forages, especially if applied immediately after harvesting.

Do not let your containment overtop. If we continue to get persistent rainfall, and the soil does not dry enough to pump out, contact DNR (assuming your structure is permitted) and request permission to pump onto saturated soils. This happened to several producers in 1993 and DNR allowed pumping. DNR understands that overtopping endangers the structural integrity of earthen containment basins, and that pumping onto saturated soil is a better alternative than allowing a basin to overtop and potentially fail.

If you must pump onto wet soils:

  • Pick the safest location possible.
  • Stay as far as possible away from waterways, streams, and lakes.
  • Pump onto shallow slopes.
  • Move the irrigation gun often to avoid applying large amounts to one spot.

By using good management you may be able to prevent manure from reaching our water resources. For more information contact your ISU Extension Area Ag Engineer by calling your local county Extension office.

Copyright © 1997-2004, Iowa State University. All rights reserved.

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