By Robert Meinen
Manure storages that capture runoff from barn roofs or other impervious surfaces are likely to fill up sooner than expected due to the extreme rainfall this summer.
With the extreme rainfall over the last month, some farms may need to start emptying manure storages sooner than normal. Here are some points to consider when doing so.
Much of Pennsylvania has seen about 6 months worth of normal rainfall levels accumulate within the last month. Many farms have manure storage structures designed for only a 6 month holding capacity. For storages that receive rainwater, especially those collecting runoff from barn roofs or exercise lots, manure storage capacities may fill up sooner than normal due to all the rain. Farmers should be aware of the need to maintain freeboard, the vertical height between the manure level and the top edge of the storage structure that is reserved for holding manure and rainfall during emergency situations to prevent an overflow. Farms that have exceeded or are approaching the freeboard level should make plans to spread some amount of manure to bring the storages down to safe levels.
During this time of year, options for where to spread manure are more limited than typical fall and spring spreading periods. Potential options include fields where small grains were recently harvested, hay fields, and pastures. Some farms may soon have fields available after short season corn silage varieties are harvested. When spreading manure in this situation, there are several important management considerations to make, including determining the manure nutrient analysis, determining a spreading rate, preventing nitrogen losses after spreading, and avoiding soil compaction.
One of the challenges with spreading manure in this situation is that the nutrient analysis of the manure may not match historical values from the structure or typical book values. Two factors that will affect the nutrient composition are the extent to which the manure is more diluted with rainfall than normal, and whether or not the structure is agitated as normal prior to spreading. Extra rainwater diluted in the manure will tend to reduce the nutrient content while unagitated structures will have stratified nutrient levels as solids and associated organic nitrogen and phosphorus accumulate at the bottom of the structure. To verify the nutrient content of the manure that is spread, have a manure sample analyzed at a lab. Based on the lab analysis, the nutrient availability from the manure that is actually spread can be used to make adjustments to additional N, P, and K fertilizer requirements of the following crops.
Because the manure nutrient analysis may be atypical, farms wishing to make the most efficient use of nutrients may want to spread with a conservative rate. This would help to prevent over application of nutrients should the manure nutrient content be greater than typical, which might occur if manure is drawn out from the bottom of an unagitated structure. Of course, conservative spreading rates require more acreage to spread a given volume, and not all farms may have the luxury of extra acreage to spread on at this time of year. Nonetheless, spreading rates should not exceed those typically allowed by a nutrient management plan or manure management plan for a given scenario.
When spreading in late-summer, there is increased potential for nitrogen losses depending on manure management and the timing of the next crop. In warm weather, ammonia volatilization tends to be greater. Also, if the next crop is not to be planted until the following year, then there is a potential for wintertime leaching losses. Applying manure to a field with existing vegetative cover, such as after a cutting of hay, or to a fallow field that will be planted to a crop later this fall, such as a cover crop or a new hay seeding, will help scavenge nitrogen against wintertime losses.
Finally, avoiding soil compaction during manure spreading is worth considering. Soil moisture levels are currently at their most conducive for creating compaction, and compaction can have negative effects on crop productivity that last years into the future. Utilize fields that have well drained soils first. Fields with living plant cover, such as hay fields, may also dry down faster due to plant transpiration.
While having to unload a manure storage structure earlier than anticipated is never an ideal situation, keeping these considerations in mind will help you manage your particular situation as best as possible.