Environmental damage caused by reactive nitrogen is not just a European problem (Nature 472, 159–161; 2011). China must also rein in its overuse of nitrogen fertilizers — which accounts for 40% of global production since 2006 — to balance food-security requirements with the protection of human health and the environment.

Despite China's nitrogen consumption almost doubling between 1990 and 2009, its grain production increased by just 22%. Although the research community widely recognizes the problem of fertilizer overuse, farmers in China continue the practice, which is promoted by some agricultural-extension advisers and by sellers of fertilizer.

Chinese farmers need to be taught how, when and in what quantities fertilizer should be applied. The existing agricultural-extension system must revert to its role of assisting farmers by methods other than promoting fertilizer sales. Establishing an environmental-extension system at the township level could also help to prevent overuse of fertilizers and pesticides.