Delayed Harvest Impacting Fall Manure Application

The challenging weather conditions of the past summer have led to slower crop development, sluggish harvest, and delayed manure application this fall. Approximately 90 percent of soybean and 60 percent of corn have been harvested with higher percentages still standing in some localized regions of Iowa. With freezing temperatures occurring, it is essential to consider the impact weather has on manure management on the farm.

“Given our current harvest levels and expected weather conditions, it’s important for farmers to review their manure application process,” says Dan Andersen, Iowa State University Extension and Outreach ag engineer and assistant professor in Agricultural & Biosystems Engineering. “It will be especially important for farmers to ensure that adequate storage is available for continued use during the winter months.”

He noted that it is crucial for farmers to get their storages pumped down so that they have adequate capacity to make it through critical storage periods, such as winter. “Confinement feeding operations must retain all manures produced by the farm during periods between land applications,” Andersen said.

According to state law, all manure must be applied in a manner that does not cause surface or groundwater pollution. No matter the time of year, manure application requires adhering to setback distances as a means to minimize environmental impacts. Manure that is not injected or incorporated into the soil on the date of application must be applied at least 200 feet from a creek, well or other water body. High quality waters, listed on the Iowa Department of Natural Resource’s website at, require an 800-foot setback. If a National Pollution Discharge Elimination System permit is in place, additional requirements may also apply.

If the operation is required to follow Iowa DNR’s Master Matrix, farmers should ensure compliance with the land application requirements previously selected. State law requires manure applicators in Iowa be certified. Personal application of manure, even a couple of loads, needs proper certification.

Wet soils absorb manure and water at a slower rate because of their capacity to hold liquids is already utilized and they are prone to compaction and surface runoff. While there are options to reduce the risk of environmental impacts, there are no guarantees of complete prevention. When applying manure using tankers, the risk of environmental impacts is reduced when the tankers are not filled to full capacity, which reduces the weight limit and reduces compaction. Applying manure to the driest fields or driest portions of the fields first and then adjusting the application rate ensures that the soil is capable of holding the manure and its nutrients in the soil profile.

“Looking ahead, Iowa’s restrictions on manure application to frozen or snow covered ground will be in full effect this winter,” said Andersen. “The law applies to all confinement animal facilities with liquid manure that have more than 500 animal units.”

This amounts to about 1,250 finishing pigs, 5,000 nursery pigs, 500 steers, immature dairy cows, or other cattle, and 357 manure dairy cows.

“We want to remind farmers that the law prohibits manure application from these operations between Dec. 21 and April 1 if the ground is snow-covered, unless the manure can be properly injected or incorporated,” says Andersen. He noted that starting Feb. 1, manure application from these operations is also prohibited on frozen ground.

Source: Iowa State University 

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