Swine Diets and Manure Can Slash Phosphorus Runoff
By Don Comis
July 28, 2004
Feeding phytase to swine, combined with
adding aluminum chloride to their manure, can cut phosphorus pollution of water
by as much as 70 percent, according to a study by
Agricultural Research Service scientists
Douglas Smith, now a soil scientist at the ARS
National Soil Erosion
Research Laboratory in West Lafayette, Ind., conducted the study while he
was a graduate student at the University of
Arkansas at Fayetteville. The study focused on the effects of combining
both practices, which have usually been studied separately. Smith worked with
soil scientist Phillip Moore at the ARS Poultry Production and Product Safety
Research Unit in Fayetteville, and with University of Arkansas scientists.
Simply adding aluminum chloride to the manure reduced phosphorus in runoff
by 53 percent. Aluminum chloride binds with phosphorus to form an aluminum
phosphate, which is less susceptible to losses in runoff. Such a reduction
could significantly reduce the amount of phosphorus reaching rivers, lakes and
bays, where it can cause harmful algal blooms.
Adding phytase, an enzyme, to animal feed reduced phosphorus in manure by 13
Phytase allows livestock to digest more of the phosphorus that is in feed,
lowering the amount excreted in manure.
Smith and colleagues applied aluminum chloride-treated manure, from pigs fed
the added phytase, to a pasture at a rate commonly used by farmers. Then they
used sprinklers to simulate rainfall and analyzed the runoff.
The scientists found that phosphorus runoff from the combined practices was
no more than that from land to which no manure had been added.
As swine operations become more concentrated, less land is available for
manure spreading. Using this combination of practices might allow swine
producers to apply more manure without increasing the risk of pollution. The
addition of aluminum chloride also would prevent nitrogen in the manure from
turning into ammonia and escaping into the atmosphere. This benefit would
reduce atmospheric ammonia pollution and leave the manure with a higher
nitrogen content. Poultry producers are already enjoying these benefits as a
result of earlier work by Moore and colleagues.
Smith's study was published in the May-June issue of the Journal of Environmental Quality.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.