Each year, more than 14 million tons of chicken litter is generated in the U.S., a portion of which is used to fertilize crops, such as cotton. A new study by the USDA Agricultural Research Service has now calculated how much litter farmers need to apply to cotton crops to maximize profits.

“Most research focuses on the amount of poultry litter needed to maximize crop yields,” says agronomist Haile Tewolde, lead author of the study. “We wanted to know if aiming for maximum yield always makes economic sense for farmers.”

Chicken litter applications over a certain level did not result in net economic gains, even though cotton yields were somewhat higher. Image credit: Carol M. Highsmith/Library of Congress.Chicken litter applications over a certain level did not result in net economic gains, even though cotton yields were somewhat higher. Image credit: Carol M. Highsmith/Library of Congress. Tewolde and his colleagues found that it doesn't. Using less chicken litter than what is needed to maximize crop yields actually increased profits for farmers.

The study was conducted on two farms in Mississippi, where the researchers applied varying amounts of chicken litter as fertilizer on seven replicated farm plots. They compared yield and profitability among the plots, as well as the use of synthetic fertilizers versus chicken litter.

They found that chicken litter applications over a certain level did not result in net economic gains. Instead, they led to economic losses even though yields were somewhat higher.

Maximum cotton yields were achieved by applying between 9,000 and 12,000 pounds of chicken litter annually per acre. However, applying about 7,000 pounds of chicken litter per acre was the level at which profits were maximized.

Poultry litter contains high levels of nitrogen, an important nutrient for plants. It also contains other minerals needed by crops, including phosphates and potash. Using poultry litter as manure also recycles a waste product and can benefit the environment.

However, using too much poultry litter can cause environmental pollution, the researchers note. Nitrogen and phosphorus in the litter can dissolve in runoff from storms, and these dissolved nutrients can pollute surface and ground waters. If farmers can use less poultry litter to maximize profits, such pollution can be managed more effectively, according to the researchers.

“We are the first to identify ways to calculate optimal rates of applying chicken litter manure and maximize earnings at this scale of farming,” says Tewolde, who adds that the study has wider implications beyond Mississippi. “The approach we use to determine optimal rates of chicken litter application will be applicable in other cotton-growing areas around the country,” he says.

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