“It’s time to curb global nitrogen pollution,” says Sutton, who led the UNEP study. Improving practices in agriculture — the biggest contributor of nitrogen pollution worldwide — should be a top priority, he says.
“Fertilizer overuse is a common problem, especially in developing countries,” agrees Zhang. In an earlier study, he and his colleagues found that Chinese farmers use an average of around 600 kilograms of nitrogen fertilizers per hectare per year, but that could be cut by up to two-thirds without affecting crop yields.
Furthermore, says Sutton, “80% of the nitrogen in crops grown globally goes to feed livestock,” says Sutton. Higher consumption of meat and diary products, especially in developed countries, has substantially increased global nitrogen pollution. “Recycling nitrogen from manure and sewage would increase the efficiency of nutrient use, while reducing pollution and improving crop production.”
To make a real difference, he adds, “governments should join forces to better manage the global nitrogen cycle.”