ISU Poultry Manure Research Helps Growers Manage Crop, Environmental Quality

December 3rd, 2009

AMES, Iowa - As the nation's top egg-producing state, Iowa has had a plentiful supply of nutrient-rich poultry manure as a resource for growing crops.

Amid continued growth of the egg industry, interest in improving poultry manure management has increased. Just as Iowa farmers have long used poultry manure as a source of nutrients for crops, Iowa State University has had a long-standing poultry manure research program to help address key agronomic and environmental issues.

ISU research has examined how manure nutrients compare to commercial fertilizers; the value to crops and longevity in soil; effects of application on runoff; and ideal application rates to protect both crop yields and water quality.

Data from recent and current research are helping fill critical gaps in knowledge of manure use in Midwestern agronomic and climatic systems. They also are helping growers make more informed decisions on post-harvest applications, when most poultry manure is applied.

Considerable poultry manure research has been conducted with pasture systems in the South, said John Sawyer, professor of agronomy and extension soil fertility specialist.

"Crop nutrient needs and runoff are different with Midwest row crop production," Sawyer said. "That's why we need research addressing Iowa cropping systems, soils and climatic conditions."

A three-year agronomic demonstration and research study, completed in 2007, was the first effort of its kind in Iowa to get comprehensive data on poultry manure's value to crops in producer fields, its nutrient content, how the resource ranks with commercial fertilizers and effects of land application on runoff. The work was funded by the Integrated Farm and Livestock Management Demonstration Program of the Iowa Department of Agriculture and Land Stewardship and the Iowa Egg Council.

While already known to be rich in phosphorus, the researchers found that poultry manure contained much higher crop-available levels than previously thought. Nitrogen levels were found to be lower, with most nitrogen available for just the first crop year.

In 2008, that study helped spur a major revision of an ISU Extension publication that offers guidelines on use of poultry and other animal manures and outlines their crop availability. Since its release, more than 1,000 copies of "Using Manure Nutrients for Crop Production" (PMR-1003)have been downloaded or distributed.

"We now have the most up-to-date extension publication for poultry manure nitrogen and phosphorus," said Antonio Mallarino, professor of agronomy and extension soil fertility specialist. "The guidelines we had before said that the value of phosphorus was 60 percent that of fertilizer under equal conditions. Now we're saying it's 90 to 100 percent. And first-year nitrogen availability to corn is 50 to 60 percent."

The research has helped producers ensure they have an adequate nutrient supply for their crops. It also has reduced the potential for over-application or under-application and the effects on soil and water quality.

Understanding the environmental effects of short- and long-term use of poultry manure has been another ongoing focus of Iowa State studies.

A 10-year study tracked water quality effects of poultry manure applied at different rates to cropland. It was the first study in Iowa to look at water quality related to poultry manure, and was funded by the Iowa Egg Council and ISU's Leopold Center for Sustainable Agriculture.

"We found that if you apply poultry manure at the recommended 150 pounds per acre crop-available nitrogen rate, you can maintain water quality and crop yields," said Ramesh Kanwar, who led the study. Kanwar is a Charles F. Curtiss Distinguished Professor of Agriculture and Life Sciences and chair of the agricultural and biosystems engineering department.

While Kanwar studied transport of nitrate to subsurface tile drains — the underground plumbing that helps siphon excess water from fields — Mallarino collaborated by testing soil phosphorus levels and tracking the nutrient's flow through the drains.

After that study, Mallarino realized a need to focus more on phosphorus surface runoff from poultry manure. Unlike nitrogen, phosphorus doesn't change to a form easily leached to subsurface drainage or groundwater. "This is important for management, because controlling surface runoff will help minimize phosphorus loss as well as effects on surface water quality," he said.

He conducted two collaborative studies with Sawyer looking at how nitrogen and phosphorus react in soils and how rainfall shortly after application affects runoff of these nutrients. Independently, Mallarino studied phosphorus runoff from poultry manure relative to other manures and inorganic phosphorus, and whether manure additives can lower phosphorus losses.

The studies, many of which are ongoing, have included laboratory and large-plot research, as well as smaller field rainfall simulations, with many receiving funds from the Iowa Egg Council.

"There will always be questions of how to best use poultry manure as poultry production and crop production continue to change," Sawyer said. "Future and on-going research will help address questions related to manure nutrient use, which is the key. We need to manage manure as a nutrient resource and get the best utilization of that resource for crop production as well as minimizing environmental effects."


John Sawyer, Agronomy, (515) 294-7078,

Antonio Mallarino, Agronomy, (515) 294-6200,

Ramesh Kanwar, Agricultural and Biosystems Engineering, (515) 294-1434,

Tamsyn Jones, Agriculture and Life Sciences Communications, (515) 294-7192,