AMES, Iowa — Iowa State University researchers recently revealed that poultry manure is an effective fertilizer that helps neutralize odor and gas emissions levels when properly applied.

“Nine years of data shows corn yields are the highest on the plots receiving 300 pounds of nitrogen from poultry manure," said Ramesh Kanwar, who chairs of the ISU agricultural and biosystems engineering department and lead researcher, specializing in drainage, irrigation, water quality and natural resource management.

“Yet the 150 pound nitrogen rate of poultry manure produces the second highest yields, and compares favorably to yields on plots that received commercial fertilizer,” he said of the research project, which will continue for another two years.

Started in 1998 and funded by the Iowa Egg Council, the study was created to evaluate the impact of poultry manure applications on crop production, and on surface and groundwater quality.

In the report, three nitrogen treatments were investigated: Both 150 and 300 pounds per acre of nitrogen from poultry manure, and 150 pounds per acre from a commercial fertilizer of urea-ammonium nitrate; control plots where no nitrogen was applied was also included in the project. The research team surveyed nine, one-acre field plots at an ISU research farm west of Ames, making all nitrogen applications in the spring during the nine-year trial. Both subsurface and surface water samples were collected and tested for nitrates and phosphates, and yields were determined.

Of the data gathered from the study, researchers discovered that when poultry manure was applied at the 150 pound per acre rate, lower nitrate and phosphate concentrations in subsurface drainage water resulted when compared with equivalent application rates of commercial nitrogen fertilizer.

The research also had shown that when poultry manure was applied at a higher rate than needed to meet a corn crop’s nitrogen needs – such as the application of poultry manure at the 300 pound rate - the impact on water quality was greater.

“This study shows that using poultry manure at lower rates reduces the nutrient losses to groundwater and gives some of the best crop yields under a corn-soybean system,” Kanwar said.

In a second study on odor and gas emissions emanating from livestock and poultry operations, ISU researchers also found that such smells could be reduced when a manure additive called zeolite was incorporated in poultry manure to help reduce odors and the release of ammonia, and some volatile organic compounds (VOCs).

A team of ISU agricultural engineers and chemists said zeolite – minerals that have a micro-porous structure – could be mined from abundant low-cost deposits.

Funded by the Midwest Poultry Research Program and a Special USDA-CSREES Air Quality Research Grant and published in the January-February issue of the Journal of Environmental Quality, researchers used a novel sampling and sample preparation technique to evaluate the effectiveness of zeolite as a manure additive.

In this approach, researchers simultaneously analyzed gases and the resulting odor. When compounds were isolated, an instrument was used that could identify different substances within a test sample, with an instrument that used special software and a sniff port.

“The software records odors caused by each chemical and records information about the odor intensity associated with each compound,” said Jacek Koziel, assistant professor in the ISU agricultural and biosystems engineering department and head of the study.

“The analysis allows olfactory responses from panelists to be measured compound-by-compound at the same time chemical compositions are evaluated,” he said.

Zeolite was topically applied in two trials on fresh laying-hen manure at three rates, with a top rate of 10 percent.

In a third trial, researchera applied zeolite applied at a 5 percent rate, placing each addition of fresh manure into the storage vessel simulating what Koziel called a periodic ‘layered’ application of zeolite, with more than 90 volatile compounds were identified as emitted from the manure. When researchers applied topical zeolite, data had shown the potential for reducing emissions of several compounds from manure storage, with the effectiveness of treatment proportional to the zeolite application rate, and the 10 percent zeolite application rate was the most effective.

“One sniff is better than a thousand words,” said Koziel, who specializes in air quality engineering and livestock odor. “With this simultaneous chemical-olfactometry analysis, we are finding links between specific chemicals released by manure and the overall offensive odor.

“That makes it possible to focus odor mitigation on compounds that really matter,” he said.