Reducing Phosphorus Runoff

Feeding phytase to swine, coupled with adding aluminum chloride to their manure, can cut phosphorus pollution by up to 70%, says an Agricultural Research Service study.

Douglas Smith, then a graduate student at the University of Arkansas at Fayetteville, conducted the study. The study focused on the effects of both practices, usually studied separately.

Adding aluminum chloride to manure reduced phosphorus in runoff by 53%, says Smith. Aluminum chloride binds with phosphorus to form an aluminum phosphate, which is less prone to losses in runoff.

Adding phytase to animal feed reduced phosphorus content in manure by 13%. Phytase allows livestock to digest more of the phosphorus in feed, lowering the amount excreted in manure.

In achieving those results, Smith and colleagues applied aluminum chloride-treated manure from phytase-fed pigs 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 didn’t exceed that of land to which no manure had been applied.

Also, treating manure with aluminum chloride would prevent nitrogen in the manure from turning into ammonia and escaping into the atmosphere. This would reduce atmospheric ammonia levels and help manure retain nitrogen, scientists said.