
Keeping
Nutrients in ManureBy Lupe Chavez October 3, 2001Manure-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. U.S. Department of Agriculture |