Treating Both 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 and cooperators.

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 percent.

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.