Study looks at water quality issues that swirl around Iowa's growing poultry industry

By Laura Miller
Newsletter editor

Research shows that poultry manure is a viable crop nutrient -- if used with care. (Photo courtesy Carl Pederson.)

Iowa's newest feather in its agricultural cap -- as the nation's top producer of egg-laying chickens -- also comes with a predictable problem: what to do with all that manure.

According to the National Agriculture Statistics Service, Iowa's rapidly expanding poultry industry took over the top spot in February 2001, surpassing Ohio, California and Indiana in the number of egg layers. An estimated 30 million chickens produce about 7 billion eggs a year in Iowa -- and about 315,000 tons of manure.

In a unique intersection of interests, the Iowa Egg Council and the Leopold Center are both supporting a multi-year research project to better quantify the impacts on water quality when poultry manure is applied on cropland as a nutrient. This project, which began in 1998, is the first publicly-funded water quality study in Iowa related to poultry manure application on crop fields.

After three growing seasons on nine test plots in a corn/soybean rotation, Iowa State University researchers found that over-application of poultry manure can, indeed, result in high concentrations of nitrates, phosphates and bacteria in surface and subsurface drainge water. But when applied to the test plots at a lower rate, poultry manure resulted in the highest average corn yields (compared to liquid urea-ammonium-nitrate, or UAN fertilizer) and the lowest amount of pollutants in drainage water.

In other words, chicken manure is a viable crop nutrient in Iowa, but only when carefully managed.

Adion Chinkuyu, a former graduate student at Iowa State University, calibrates the amount of poultry manure to apply on ISU field test plots west of Ames. (Photo courtesy Carl Pederson.)

Careful management needed
"Our worry is that as the poultry industry grows in Iowa, land-application and other environmental problems can occur here as they have in other areas of the country where poultry manure is land-applied on a large scale," said Ramesh Kanwar, lead researcher and head of the ISU Department of Agricultural and Biosystems Engineering.

"We want to be prepared with the data to recommend the best management practices that can reduce or minimize any environmental effects these applications might have on our landscape," he added.

Kanwar conducted the research trials at ISU's Agronomy and Agricultural Engineering Research Center near Ames. Application was based on nitrogen content of liquid UAN and poultry manure. Two different rates were used: 150 lb. N/acre for both UAN and poultry manure applications, and 300 lb. N/acre for poultry manure applications. Water samples, collected from subsurface drains once a week and immediately after rainfall, were analyzed for NO3-N, PO4-P and three types of bacteria. Soil samples were taken before planting and after harvest.

Results show that use of poultry manure in field plots, compared to UAN applications, resulted in significantly higher corn yields with increased subsurface water quality. Poultry manure applications at a lower N rate of 150 lb./acre resulted in the highest yields and lowest concentrations of NO3-N, PO4-P and bacteria of all treatments in the study.

Research continues
The study has been extended so that researchers can repeat the experiments for a complete corn-soybean rotation. Kanwar said he also hopes to gather data helpful in establishing recommended practices for poultry manure application. During the first three years, the Leopold Center picked up 60 percent of the costs, or about $65,000, and the Iowa Egg Council the remaining 40 percent. Those expense splits will be reversed in the fourth year of the project.

A poultry manure profile
The manure from Iowa's largest egg-laying facilities has to go somewhere. Iowa State University agricultural engineer Jeff Lorimor said the poultry manure generated in the state is spread on neighboring farmland.

"Most is either sold or given away and is hauled up to 30 miles to the farmers who want to use it," said Lorimor, who works closely with poultry, cattle and hog producers to develop manure management plans. "Many of the layer operations have a waiting list of farmers who want the manure. It's dry and quite concentrated compared to liquid manure, and can be economically hauled farther than hog manure."

Poultry manure contains about 40 percent water, compared to hog manure, which is 96 percent water. Poultry manure is handled as a solid, and is less likely to contribute to odor problems than liquid manure.

The concern for poultry manure is its high phosphorus content relative to nitrogen. Unlike nitrogen, which can be carried away in water runoff, phosphorus most commonly clings to solid matter and can be carried into streams by soil erosion. Poultry manure also contains small amounts of heavy metals such as copper, selenium, nickel, lead and zinc.

Lorimor estimated that it would take about four tons of chicken manure (the amount produced by approximately 400 egg-laying chickens in a year) to fertilize an acre of corn at the recommended nitrogen rate.