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Keeping Nutrients in Manure

By Lupe Chavez
October 3, 2001

Manure-treating practices that reduce ammonia emissions and preserve nitrogen in the manure for plant use have been developed by Agricultural Research Service scientists. The treatments reduced ammonia release by more than 55 percent overall. Nitrogen is lost from manure when ammonia, a nitrogen-containing compound in the manure, escapes to the atmosphere through a process called volatilization. The loss of nitrogen makes the manure less useful as a fertilizer.

Alan Lefcourt and John Meisinger, colleagues at the ARS Animal and Natural Resources Institute in Beltsville, Md., conducted tests to improve the retention of manure nitrogen for organic use. They found that adding 2.5 percent alum or 6.25 percent zeolite to manure slurry by wet weight reduced ammonia loss by 60 and 55 percent, respectively.

Alum and zeolite, acidifying and sequestering agents, helped reduce the formation of ammonia gas and its volatilization, or release, into the air. Alum lowered the pH level of the tested dairy slurry below 5, a level that limits the amount of ammonia released from the manure. Zeolite, commonly used in kitty litter, acted as a cation-exchange medium, binding with the chemicals that would form ammonia and preventing volatilization.

To measure ammonia loss, the researchers utilized a canopy and wind-tunnel system. A variable-speed fan pulled air over the manure samples and ammonia gases were trapped in acid bottles as they passed through the system. Ammonia losses were measured over a period of 96 hours.

Lefcourt and Meisinger initiated their research in response to problems created by increased animal production on farms and dwindling land available for spreading manure as fertilizer. Crop plants can take up and use the nitrogen and phosphorus in the manure. However, when too much nitrogen escapes into the air, excess phosphorus is left in the manure and soil. By limiting ammonia losses from manure, the team of scientists can create better ratios of nitrogen to phosphorus for farm crops. Moreover, zeolite-treated slurries are also a nitrogen-rich, slow-release, fertilizer.

Treating dairy slurry with either alum or zeolite is cost-effective and safe. Slurries treated with alum would cost less than 50 cents a day per lactating cow. Zeolite costs should be similar, although volume pricing is not currently available.

ARS is the U.S. Department of Agriculture's chief scientific research agency. At the ARS Animal and Natural Resources Institute, Lefcourt works in the Instrumentation and Sensing Laboratory. Meisinger works in the institute's Environmental Quality Laboratory.