Challenges for Global Sustainable Nitrogen Management in Agricultural Systems.

Nitrogen (N) losses from agricultural production contribute to detrimental impacts on water, soil, air, and human health. However, it is still lacking in evaluating global N budgets in agricultural systems. Hence, we conducted a global analysis on the current status of the N flows in the agricultural systems, explored the possible mitigation measures and challenges, and investigated the existing regulations on controlling N pollution. Globally, agricultural soils received a total of 73 kg of N ha-1 year-1 on average, including N fertilizer plus manure (61%), atmospheric N deposition (10%), and N litters and fixation (29%). The estimated global NH3 loss to total N inputs was 17%, which led to a loss of $15 billion year-1. The N use efficiency (NUE) in Eastern China (33%) was much lower than that in the Eastern United States (65%) or Western Europe (61%), leaving much room to enhance the NUE to increase agricultural food production. Meanwhile, higher NH3 losses from N fertilizers and manure were found in Eastern China (22%) than the Eastern United States (17%) and Western Europe (17%). We highlight the urgency to improve the NUE and decrease NH3 loss with lower environmental consequences. Our results showed high potentials to mitigate NH3 volatilization and enhance the NUE by various measures, such as substituting manure N for chemical fertilizer N, applying controlled release fertilizers, and urease inhibitors. These measures should be implemented in combination with the transfer of knowledge to farmers with new technologies and increasing the farm size to enhance the efficiency of agricultural production in the future.