Poultry manure, with proper application, is an environmentally friendly fertilizer, ISU researchers said.

Rameshwar Kanwar, professor and chairman of agricultural and biosystems engineering, along with professor Hongwei Xin and associate professor emeritus Jeffery Lorimor, recently finished the fifth year of a six-year study on the effects of using poultry manure as a fertilizer. They found that over-applying poultry manure does not significantly increase crop yields but negatively affects the water quality, Kanwar said.

“Some livestock producers, especially poultry, don’t have enough land to apply poultry manure at a given rate of 150 pounds per acre, and they have to over-apply the manure,” Kanwar said. “We were trying to understand what might be the consequences of over-application on water quality and crop yield.”

The study compared nitrate, phosphate and bacteria concentrations in subsurface and surface water samples at nine one-acre plots at an ISU research farm west of Ames. The researchers used nitrogen application rates of both 150 and 300 pounds per acre from poultry manure and 150 pounds per acre from a commercial urea-ammonium nitrate fertilizer.

“Crops need nitrogen, phosphorus and potassium, and all three are present in manure,” Kanwar said. “We look at nitrogen more critically because it is the one that can get into the ground water and has some negative impact on health.”

They found that poultry manure applied at 150 pounds per acre had lower subsurface water levels of nitrate, phosphate and bacteria than occurred with the same application rate of commercial nitrogen fertilizer, Kanwar said. A comparison of 150 and 300 pounds per acre of poultry manure showed the higher rate of application had a greater impact on water quality with insignificant increases in crop yields.

“Some crops, like soybeans, can fix their own nitrogen, but for corn, wheat, cotton and others, we need to apply some kind of fertilizer,” Kanwar said.

“We as humans need some nutrients that we get from food, and fertilizer is essentially a kind of food for plants.”

The poultry manure research is funded by the Leopold Center for Sustainable Agriculture and the Iowa Egg Council, Kanwar said.

“We want a better understanding of what’s happening as water moves through the soil and nutrients move through the system,” said Jeri Neal, program coordinator of the Leopold Center. “Knowing that helps you understand how to better manage agriculture on the landscape.”

Research on the environmental effects of poultry manure is needed because the Iowa poultry industry is expanding and thus producing more poultry manure, Kanwar said.

Iowa was the top egg production state during the 1940s and 1950s until it was passed in production by Ohio and Pennsylvania, according to the Iowa Egg Council’s Web site. In 2003 Iowa regained top egg production status.

“The amount of poultry manure we’re applying is relatively a change, and we need to know what is happening when we do this,” Neal said. “What kind of application rates are appropriate, what happens to the yield, what happens to the water quality — all those questions need to be answered about poultry manure for Iowa.”