Nitrogen losses can be significant in conservation-tillage systems

Clemson University's new model to gauge ammonia nitrogen losses could change the way farmers think about nutrients and application methods in conservation-tillage in the Southeast.

Clemson University Extension Ag Engineer John Chastain and colleagues found that the current Clemson University estimates of ammonia-N loss differ from the new model by 2 percent to 95 percent.

In developing the new method to estimate ammonia-N losses, the researchers used literature and new data obtained at Clemson to develop the model that considers the organic nitrogen available to the plant, and loss of ammonia-N following application in a conservation-tillage system.

The long-term implications of the findings could lead to the need for new implements.

“The new model shows that farmers can literally blow off 1 percent to 51 percent of the ammonia N in manure or fertilizer to the air if simple broadcast applications are used. Losses from low-tech applications of granular ammonium N can be about 20 percent.

“This is a financial loss to the farmer who is trying to save soil using conservation-tillage,” Chastain said at the 27th annual Southern Conservation-Tillage Systems Conference held recently in Florence, S.C. “The loss of nitrogen to the atmosphere is also an environmental concern.”

Irrigation with a half an inch of water immediately following application of fertilizer or animal manure will wash ammonium N into the soil. As a result, ammonia N losses are minimal. If lagoon water is irrigated to provide 100 pounds of N per acre, the total ammonia N lost is only 0.4 pounds per acre, Chastain says.

“Our data shows that ammonia-N is not lost during the irrigation process. Losses occur after it strikes the ground,” Chastain says.

Chastain and his colleagues used the new model to estimate ammonia-N losses after application of granular fertilizer, lagoon effluent, broiler litter and dairy slurry to a no-till field.

He found that the application method played a huge role in how much ammonia N was lost.

For example, banding, banding with immediate soil coverage, direct injection, immediate incorporation and incorporation with irrigation can reduce ammonia-N losses by 51 percent to 94 percent. That's 51 percent to 94 percent of the nitrogen “volatilized” before the plant can use it.

The model indicates the time lag between application and incorporation is critical. “In most cases, incorporation within 24 hours isn't good enough,” he says.

“The time lag between application and incorporation should be no more than 24 hours for granular fertilizer, six hours for poultry litter and 12 hours for dairy manure to reduce N losses 50 percent.”

The type of manure also impacts the ammonia-N loss potential.

In the study, losses from broadcast application ranged from 0.4 pounds per acre for lagoon water to 48 pounds per acre for dairy slurry. About 25 pounds of ammonia-N can be lost per acre with the broadcast of granular fertilizer as opposed to 7.4 pounds of N per acre with the broadcast of poultry litter.

“That means people who buy fertilizer and simply broadcast on top of grass or crop residue can lose 20 percent of their fertilizer bill.

“These results also tell us that poultry litter performs better. The reason is the larger amount of organic N that cannot be lost as ammonia,” Chastain says.

The information gained from the new Clemson model indicates “the need to work on new implements, application techniques, and new spreading equipment,” for conservation tillage, Chastain says.

“It's coming,” Chastain says.

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