(AP) — In this Aug. 29, 2013, photo research technician Kris Niemann hooks up equipment that will measure the amount of ammonia, carbon dioxide and other greenhouse gases coming off a barnyard lined with sand at the U.S. Dairy Forage Research Center in Prairie du Sac, Wis.
Scientists are looking at whether changing the surface of a barnyard from soil to sand or wood chips can help reduce the amount of gases that vaporize after cattle urinate. The information will be used to help farmers make their dairies more environmentally friendly. (AP Photo/M.L. Johnson)