Environmental Impact of Poultry Manure as Fertilizer Studied

April 22nd, 2002

AMES, Iowa — Iowa is one of the nation's top poultry producers, ranking first in the egg laying industry and ninth in the turkey industry. The recent expansion of poultry production in the state has raised questions about the environmental impact of the industry.

Three years of preliminary data from an Iowa State University research project is providing some answers. The key finding is that, when compared to equivalent application rates of commercial fertilizer, poultry manure applied at reasonable rates can result in less impact on water quality and higher crop yields.

The research involved nine field plots at an ISU research farm west of Ames. Poultry manure was applied to plots at two rates - some at 150 pounds of nitrogen per acre with others at 300 pounds per acre. For comparison, two plots received commercial liquid nitrogen applications of 150 pounds per acre.

Both subsurface and surface water samples were collected. The water samples were tested for nitrates, phosphates and bacteria.

"Poultry manure applications at the lower application rate resulted in the lowest levels of nitrates, phosphates and bacteria in subsurface drain water," says Ramesh Kanwar, chair of the ISU agricultural and biosystems engineering department and lead researcher on this project.

Kanwar says the field plots receiving poultry manure at the rate of 150 pounds of nitrogen per acre also produced corn and soybean yields that were significantly higher than fields that received the same rate of commercial fertilizer. "And application of poultry manure did not result in any significant effect on the quality of corn and soybean grains in terms of protein, oil and starch contents," he says.

Kanwar says the research also showed that when poultry manure and commercial nitrogen fertilizer is applied at the same rate, poultry manure may be the better option because it improves soil quality.

The research did show that when poultry manure was applied at the higher level, the impact on water quality was greater. Also, crop yields weren't any higher where the higher rate of poultry manure was applied. "That demonstrates responsible application of poultry manure is just as important as it is with any commercial fertilizer," Kanwar says.

This project, funded by the Leopold Center for Sustainable Agriculture and the Iowa Egg Council, will continue another three years.


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

Susan Thompson, Communications Service, (515) 294-0705