Project brings latest data to help producers gain value from manure

Livestock manure is a rich source of fertility, and Iowa has abundant supplies from about 8,200 livestock farms. About 20% of cropped acres across the state are estimated to receive manure. 

“Farmers respect manure and want to get the most value from it, but that’s not easy. Manure management is complicated,” said Dan Andersen, professor of agricultural and biosystems engineering at Iowa State University andknown by many as “Dr. Manure.” 

As a result, manure is often underutilized as a resource to boost crop yields and soil health, according to Andersen. And when it is not managed well, manure can contribute to the state’s water quality problems.  

Studying multiverse of factors influencing management 
“We have to develop modern strategies for smarter use to encourage farmers to recycle this resource. A main goal of mine is to help make sure producers have good data to inform their decisions,” he said. 

During presentations, Andersen reviews results from test plots in northeast and central Iowa, where he studies a multiverse of factors that impact manure management. These include balancing manure application and its variable nutrient levels with diverse soils, crop fertility needs that change over the growing season, water quality concerns and economics. Adding to the challenges are tight schedules for application to accommodate retail applicators’ availability, regulations and uncertain weather. 

His current research focuses on fine-tuning the timing of manure applications when used with cover crops to optimize nitrogen use efficiency, protect crop yields and minimize environmental impacts. Several graduate and undergraduate students are working with Andersen on the project, funded initially by the Iowa Pork Producers Association and now by the Iowa Nutrient Research Center (INRC).
More specifically, the project’s multiple aspects include:
- Evaluating the performance of cover crops when spring manure is applied, comparing results to data collected in previous studies for early fall and late fall manure applications. 
- Assessing the effectiveness of split manure applications, such as fall-applying 100 pounds of nitrogen from manure and side-dressing 50 pounds of UAN (urea-ammonium nitrate) synthetic fertilizer at spring planting. 
- Fine-tuning recommended best practices for using manure with perennial cover crops. 

After the second year of the three-year project, the team’s findings show that a cereal rye cover crop regularly boosts soybean yields by about 5% and often results in minimal or no yield drag for the following corn crop, depending largely on careful management of cover crop height in the spring. The early results for water quality have been mixed but are especially positive for the perennial ground cover treatments.

Exploring new tools, broader outreach 
Andersen is also exploring the potential of precision agriculture tools to enhance effective use of livestock waste. These include global positioning and row-guidance technologies that can create unique placement zones for a cash crop, fertilizer and a cover crop in strip-tillage systems. 

“That’s really promising,” he says. 

Working with a farmer in north central Iowa, Andersen is helping evaluate a new precision irrigator that could also apply liquid manure. The highboy-type 360RAIN equipment could expand timing windows for manure application. At this point, it requires too much water, even when used with manure, which could be a disadvantage when soils are already wet. It would need some adjustments, and it is not economically viable yet, he said, “but there’s interest in its potential.” 

Always looking for creative ways to reach a wider group of farmers and ag retailers, Andersen hosts a monthly “Talkin’ Crap” podcast featuring advanced manure management advice from experts across the country. The tone can be light, but the topics are far from trivial.

“I want to help farmers succeed in making use of their manure resources, ideally benefiting their bottom line and the environment,” Andersen said.

“Manure is a critical resource for farmers in Iowa and improving management of manure has the potential to improve the bottom line for farmers and benefit the environment,” said INRC Director Matt Helmers. “We are fortunate to have Dr. Andersen working on these opportunities.”

Learn more by watching a recording online of Andersen discussing his research for an Iowa Learning Farms virtual field day (March 2026).  

Contacts for the project include Daniel Andersen, Agricultural and Biosystems Engineering, 515-294-4210, dsa@iastate.edu and Ann Y. Robinson, Iowa Nutrient Research Center, 515-294-3066, ayr@iastate.edu.