Mitigating nitrogen pollution from global croplands with cost-effective measures

Cropland is one of the major sources of global nitrogen pollution1, 2. Mitigating nitrogen pollution from global croplands is a grand challenge because of the nature of non-point source pollution from millions of farms and the lack of financial resources and scientific knowledge of farmers3. Here we synthesize 683 studies worldwide and identify 11 key measures which can reduce 30-70% of nitrogen pollution while increasing crop yield and nitrogen use efficiency by 10-30% and 20-60%, respectively. Adoption of these measures would produce 14 million tonnes (Tg) more crop nitrogen with 28 Tg less nitrogen fertilizer and 27 Tg less nitrogen pollution to the environment in global croplands in 2015. However, to achieve these potentials, innovative policies such as a nitrogen credit system (NCS) should be implemented to incentivize and subsidize the adoption of these measures given the mismatch between benefits for the whole society while the abatement cost only for farmers. Full implementation of the best-fitted measures could achieve 306 billion USD benefits on ecosystem, human health and climate globally, with net mitigation costs of only 21 billion USD given 35 billion USD fertilizer saving cost has offset 2/3 of the total mitigation cost. The large benefit-to-cost ratio suggests the feasibility and urgency to implement the NCS and Tier approaches could help to implement the most cost-effective measures on regional and local scales.