"In North Carolina, that started changing with industry consolidation in the 1980s. The number of small, diversified farms fell precipitously. Most of the farms that survived did so by going big—raising thousands of animals that spend their entire lives inside barns. Today, Duplin County, North Carolina, the top swine producer in the country, is home to 530 hog operations with a collective capacity of 2.35 million animals. According to a 2008 GAO estimate, hogs in five eastern North Carolina counties produced 15.5 million tons of manure in one year.
To handle all that waste, farmers in North Carolina use a standard practice called the lagoon and spray field system. They flush feces and urine from barns into open-air pits called lagoons, which turn the color of Pepto-Bismol when pink-colored bacteria colonize the waste. To keep the lagoons from overflowing, farmers spray liquid manure on their fields nearby."
Read the National Geographic article here.