A masked man walks past trees shrouded with pollution haze in Beijing, China. Andy Wong/AP hide caption
fertilizer fertilizer
A cereal rye cover crop grows (at left) in a field where corn was recently harvested. Cover crops can capture nutrients such as nitrate and prevent them from polluting nearby streams. Courtesy of Paul Jasa/University of Nebraska-Lincoln hide caption
The city of Des Moines, Iowa, sits on the Raccoon and Des Moines rivers. The city's water works says it will sue three neighboring counties for high nitrate levels in these waterways. iStockphoto hide caption
More than 170 volunteers in the Brattleboro, Vt., area have contributed urine to the Rich Earth Institute field trials. Mike Earley/Courtesy of Rich Earth Institute hide caption
A woman shops in the produce section at Whole Foods in New York City. The company recently announced it would prohibit produce farmed using biosolids in its stores. Stephen Chernin/Getty Images hide caption
Fertilizer runoff causes toxic algal blooms. This one covered a third of Lake Erie in 2011. © Peter Essick/National Geographic hide caption
Thick jets of processed sewage arc out 30 to 40 feet from giant moving spreaders at Birmingham Farm in Kansas City, Mo. Frank Morris for NPR hide caption
A tractor spreads fertilizer at a dairy farm in Morrinsville, New Zealand. Sandra Mu/Getty Images hide caption