Livestock farms under the NPDES permit system are required to have manure storage systems emptied down to the point of having 6 months of available storage sometime between the November 1 and December 31. This available volume also has to include freeboard and expected precipitation. The storage does not have to be empty, just emptied down enough to have the estimated 6 months of storage, which may mean being empty for some farms.
The concept is good advice for all livestock farms but calendar dates do not provide any promise the weather will cooperate. But the requirement does reduce the need to spread manure during the winter. In general, winter manure is surface applied and surface applications during the winter are vulnerable to random weather conditions; the worst being rain on frozen ground or snow melting so fast that runoff occurs before the ground can thaw and take in the moisture and manure. Winter applications not only have to be concerned with the weather and soil conditions the day of spreading and several days after, but also several months later when thaw occurs.
One way to reduce the risks of manure applications is to avoid winter application. And one way to achieve that is to have manure storage systems emptied down in the fall to the point of having the storage capacity to get through till spring without having to haul manure.
The rain and snow events that have already occurred this fall have made have made empting manure storages very challenging to say the least. Given the wet field conditions across the state there will not be many spreading days left until winter sets in. Those farms needing to haul additional manure before spring do have options.
It is still legal to winter spread manure in Michigan, as long as it does not reach waters of the state via runoff, rain or snowmelt any time after application. Permitted farms are required to utilize the manure application risk indicator (MARI) to determine which fields are acceptable for winter spreading and which ones to avoid. This spreadsheet can be helpful to any size farm and can be found at www.maeap.org and search for MARI. This spreadsheet helps you look at soil type, slope, rate of manure, distance to waters and other factors that are important in estimating and reducing the risk of manure running off in the winter.
Research at the University of Wisconsin has shown that fall applications, ahead of winter snow events, are generally safer for water quality than manure applied in the winter months, and especially manure applied onto snow covered fields. For a recorded webcast on their research, visit http://www.extension.org/pages/60034/spreading-manure-in-winter-what-are-the-risks.