By Kevin A. Janni and Larry D. Jacobson, Extension agricultural engineers
ST. PAUL, Minn. — Heavy rains can add water to manure storage. This reduces space for manure and freeboard and makes emptying pits more difficult.
Preventing manure overflow from an uncovered manure storage tank or earthen lined basin is critical. Wet soils can make emptying in ground manure pits risky.
Owners and managers of animal feeding operations should first check whether and how much rainwater and surface runoff entered the manure storage. This is important for all manure storages, even pits below barns. If there is a way for water to get in, it probably will.
It's important to remove some of the manure slurry if a manure storage is filled with rainwater or surface runoff. You could land-apply it to cropland at appropriate agronomic rates where there is little chance of contaminating surface or ground waters. Another option is to pump or move some of the manure slurry to a nearby storage to buy time for a longer term solution.
Because concrete pits are not designed to have large pressures from very wet soils pushing against empty pit walls, now is probably not a good time to completely empty a manure pit or lined earthen storage. Some manure in the pit helps counterbalance the pressure. Empty pits may also float like a boat in water-laden soil. If pits are full, remove some of the manure, but avoid emptying more than halfway if surrounding soil is wet.
Avoid driving near the empty pit walls so the tractor and tanker weight do not add to the wet soil forces pushing against the pit walls. Also, be sure to check around manure storage facilities for signs of erosion or settling.
All uncovered manure storages are designed to have some freeboard, which is space for rainwater and wind-induced waves. The freeboard also provides some extra storage space when there is a heavy rain events.
Heavy rain in some areas have used up the freeboard space. In these cases, remove some manure to allow for additional manure and to maintain the freeboard design.
Even if you did not have a lot of rainwater or surface runoff get into your manure storage, if some did, the normal storage period will be reduced. If you usually have a full year of manure storage, you might have a few weeks less this year. This could be important if all of your land application is done on cropland after fall harvest. Plan ahead if you lost some manure storage to rainwater and surface runoff.
Rain-diluted manure may have fewer nutrients depending on whether you agitate the pit before removing manure. Keep track of the nutrient loading for your nutrient management plan.
If you have a manure spill and live in Minnesota, be sure to report it immediately to the Minnesota Pollution Control Agency (MPCA) by calling the Minnesota duty officer at 800-422-0798. Follow your emergency response plan for manure spills. Additional online resources for dealing with manure spill emergency planning are available here.
Each operation is unique so owners are encouraged to check their manure storage facilities to see if the rain and runoff have caused a need for some manure management action.
Source: University of Minnesota