Managing Nitrogen in the anthropocene: integrating social and ecological science

Abstract:

Human alteration of the global nitrogen cycle by agricultural activities has provided nutritious food to society, but also poses increasing threats to human and ecosystem health through unintended pollution. Managing nitrogen more efficiently in crop production is critical for addressing both food security and environmental challenges.

Technologies and management practices have been developed to increase the uptake of applied nitrogen by crops. However, nitrogen use efficiency (NUE, yield per unit nitrogen input) is also affected by social and economic factors. For example, to maximize profit, farmers may change crop choice or their nitrogen application rate, both of which lead to a change in NUE. To evaluate such impacts, we use both theoretical and empirical approaches on micro (farm) and macro (national) scales:

1) We developed a bio-economic model (NUE³) on a farm scale to investigate how market signals (e.g. fertilizer and crop prices), government policies, and nitrogen-efficient technologies affect NUE. We demonstrate that if factors that influence nitrogen inputs (e.g. fertilizer-to-crop price ratios) are not considered, NUE projections will be poorly constrained. The impact of nitrogen-efficient technologies on NUE not only depends on how technology changes the production function, but also relies on the prices of the technologies, fertilizers, and crops.

2) We constructed a database of the nitrogen budget in crop production for major crops and major crop producing countries from 1961 to 2010. Using this database, we investigate historical trends of NUE and its relationship to agronomic, economic, social, and policy factors. We find that NUE in most developed countries follows a “U-shape” relationship with income level, consistent with the Environmental Kuznets Curve theory. According to the dynamics revealed in the NUE³ model, we propose three major pathways by which economic development affects NUE, namely consumption, technology, and public policy.

Overall, our research suggests that it is critical to include social and economic processes when studying perturbations of the global nitrogen cycle and crafting environmental and food security policy. Better collaboration across disciplines is essential to improve nitrogen management in the anthropocene.