Heavy rains witnessed in many areas can add water to manure storage, reducing space for manure and freeboard and making it more difficult to empty manure pits.
Kevin A. Janni and Larry D. Jacobson, agricultural engineers with University of Minnesota Extension, offer suggestions to meet the manure storage challenges presented by heavy rain events.
Manure overflow prevention from an uncovered manure storage tank or earthen-lined basin is critical, and wet soils can make emptying in-ground manure pits risky.
Owners and managers of animal feeding operations need to first determine if rainwater or surface runoff did indeed enter the manure storage. After that determination is made, then it needs to be established just how much extra water did enter the 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.
If your manure storage is filled with rainwater or surface runoff, it’s important to remove some of the manure slurry. This can be land-applied to cropland at appropriate agronomic rates where there is little chance of contaminating surface or ground waters. Keep in mind that 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 the luxury of additional storage nearby, you can pump or move some of the manure slurry to this other 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 ‑ space for rainwater and wind-induced waves. The freeboard also provides some extra storage space when there is a heavy rain event.
Heavy rain in some areas has used up the freeboard space. In these cases, remove some manure to allow for additional manure and to maintain the freeboard design.
The normal storage period will be reduced if your manure storage facility did take in some extra rain water or runoff. 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 capacity to rainwater and surface runoff. Again, you’ll want to keep in mind that rain-diluted manure may have fewer nutrients, thus take that into consideration for your 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 by calling the Minnesota duty officer at 800-422-0798. Follow your emergency response plan for manure spills. Obviously, check with the pollution control agency in your respective state to follow manure spill protocol.
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.
Additional online resources for dealing with manure spill emergency planning are available online.