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Feedlots and the Environment

An experimental feedlot in Bushland, Texas, is one of a very few fitted with devices that measure runoff flow from the cattle pens and sample it for nitrogen, phosphorus and pathogens. Commercial feedlots store runoff in holding ponds that normally prevent it from contaminating waterways.

The study, by Agricultural Research Service animal scientist Andy Cole and colleagues at the ARS Conservation and Production Research Laboratory in Bushland and Texas A&M University, is aimed at finding ways to minimize the amount of nutrients in runoff and eliminate pathogens. The excess nutrients are a waste of money to feedlots and pose a risk if the holding ponds should fail. The scientists are also concerned that feedlot dust, runoff and manure might carry pathogens to nearby crops.

Cole is monitoring how much nitrogen is escaping from manure into the air as ammonia gas. Ammonia washed from the atmosphere in rain can harm natural ecosystems by overfertilizing them with nitrogen. Also, it can combine with others gases to produce particles small enough to be inhaled, potentially causing human health problems.

To study ammonia emissions from manure, ARS soil scientist Richard Todd of the Bushland lab simulates feedlot surfaces by packing manure in 8-inch-deep, 33-foot-diameter circles outdoors. He places a 10-foot-tall tower in the center of each circle, with collectors at various heights to capture ammonia.

Initial results show that decreasing the protein fed to cattle in feedlots from 13 to 11.5 percent might decrease daily ammonia emissions by about 20 percent. But that may be possible only near the end of animals' feedlot stay, to preserve weight gains.

Future studies will look at methane emissions from manure. The objective of the experimental feedlot is to find cost-effective ways to improve feedlots environmentally.

More information about this research can be found in the July 2003 issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.