Manure tank

A nitrification inhibitor injection tank mounted on a manure applicator. (Image credit: Melissa Wilson, University of Minnesota Extension, Minnesota Crop News)

Replenishing the soil is one of the main focuses for farmers after harvest season, and those spreading manure were able to get a jump on the process in 2020.

Nearly 30% of crop acres in Iowa see manure applied, according to Daniel Andersen, an associate professor of agricultural and biosystems engineering at Iowa State University. The lack of issues during harvest this season has helped producers get out in the field quicker to spread any manure they need, with some even starting in early October.

With the early start, looking for the right conditions is extremely important, Andersen said.

“It’s better when it starts to cool down,” Andersen said. “We are always looking for the soil to get to 50 degrees and cooling for the high ammonium fertilizers. It helps it hold in the soil a little bit longer. We are always worried about fall rain and making sure we get it done before the soil freezes.”

A slight warmup in fall temperatures won’t typically cause an issue with soil temperature. Decisions should be made on the longer-term trends, Andersen said, noting that the beginning of November often brings ideal conditions for application.

Ted Funk, an agricultural engineer who consults with the Illinois Pork Producers Association, said taking advantage of this big fall window has been good for many Illinois producers. He said if it was easier to haul manure fertilizer, there likely wouldn’t be enough to go around in his state.

“It’s a great fertilizer and been used for a long time,” Funk said. “We are getting better at it all the time with rates, timing and equipment. If the weather holds out, you can get it done and you don’t have to do it in the spring when you are trying to get ready to plant.”

As for application rates, Andersen said using beef cattle manure may mean supplementing a field with anhydrous to get proper nitrogen rates. But over-applying beef manure could add too much phosphorous to the ground. Andersen said swine manure could go either way.

“I only want to put the amount of phosphorous that I need for this year and maybe next year,” he said. “Oftentimes swine manure can be your only source of fertility. It can supply the nitrogen your crop needs and the phosphorous you need for the next few years. Manure is a complete fertilizer but not a balanced one.”

Funk encourages every producer using or providing manure to get it tested for nutrients. That information will be key for deciding appropriate rates depending on what the livestock producer is feeding.

“These days, with changes in diets, pork manure is probably going to be a little better balanced as far as nitrogen versus phosphorous, looking at a corn crop,” Funk said. “The ratio is almost perfect nowadays for swine liquid manure.”

In an effort to stack benefits, Andersen said he is hearing more people ask questions about injecting manure into an existing cover crop operation.

“That’s great to see,” he said. “It’s good to see people stacking those water quality practices out there and doing something else to help hold nitrogen in the field.”

For those applying, Funk noted safety is paramount for both producers and the environment.

He encouraged farmers to keep an eye out for any field issues when applying manure, looking for waterways or terraces in need of repair to solve possible runoff concerns.

Funk said runoff from too much manure application or rains can directly impact waterways. He reminds people to keep buffers around sensitive areas such as streams and sinkholes and be prepared to clean up any spills that might occur during an emergency.

Hydrogen sulfide, a toxic gas, can be released when working with liquid manure. Funk noted that it can be dangerous even at low levels. That could pose a danger for humans and livestock if they are still in the building or don’t have proper ventilation.

“It’s like shaking up a bottle of Coke quick and then taking your finger off the cap,” he said. “You are going to have a whole lot of gas.”