Incorporating nitrogen in the water-energy-food nexus: An optimization approach

Abstract

Growing populations and improved standards of living are increasing the global demand for food. Having to meet these demands, agricultural systems imposed unprecedented stress on water, land, energy and nutrient cycling on all scales. With nitrogen being a limiting factor for plant growth, intensified application of nitrogen fertilizers was necessary to meet the growing crop yield targets in food production, causing excessive quantities of reactive nitrogen to enter our ecosystem resulting in detrimental effects on the environment and human health. As such, this work develops a mathematical optimization model for nitrogen allocation under sustainable water, food and energy security targets, with nitrogen use efficiency as a primary indicator, and the nitrogen planetary boundary as a primary environmental constraint. Additional nutritional, socioeconomic and natural resources constraints are included. The model incorporates the nitrogen cycle within the land-crop-food continuum and optimizes the nitrogen footprint required to meet food demands, while accounting for water, energy and carbon footprints. A hypothetical case study validates the model and examines the sensitivity of the nexus to nitrogen input and nitrogen use efficiency, under different nitrogen, water and land availability scenarios and different nitrogen use efficiency and nitrogen input policy targets. The results indicate that the dynamics of the water-energy-food (WEF) nexus are highly sensitive to nitrogen. This work emphasizes the potential role of nitrogen as a primary decision factor when addressing WEF security and sustainability in agricultural systems, particularly when setting agricultural policies. © 2023 The Authors