Food-Nutrient Nexus: Quantifying Embodied Phosphorus in Interstate U.S. Food Transfers

Food production relies heavily on inorganic fertilizer inputs such as nitrogen, phosphorus, and potassium for maintaining soil fertility and sustaining crop yields. In particular, inorganic phosphorus fertilizers have garnered... [ view full abstract ]

Food production relies heavily on inorganic fertilizer inputs such as nitrogen, phosphorus, and potassium for maintaining soil fertility and sustaining crop yields. In particular, inorganic phosphorus fertilizers have garnered attention as they are primarily obtained from non-renewable and geographically concentrated rock phosphate resource. Phosphorus as a soil nutrient is also heavily skewed across the world with many regions facing water quality issues due to nutrient overloading in surface waters, while some remain phosphorus deficient and face soil degradation problems. Food trade plays a significant role in supplying diverse and large quantities of food items to feed the growing population at global, national, and regional scales. Simultaneously, food trade also presents pathways for transfer of large quantities of virtual nutrients and associated life cycle environmental impacts. In addition, the spatial heterogeneity in food production systems can result in large differences in environmental impacts of food consumption patterns. At a domestic level, vast quantities of food items are traded between states resulting in a complex interstate food trade network. While aggregate estimates of U.S. centric domestic food production and international trade of embodied phosphorus are available, there is a significant gap in our understanding of interstate fluxes of embodied phosphorus. Understanding and quantifying the origin and destination of food and embodied phosphorus flows is critical for capturing trends in regional phosphorus use, identifying hotspots, and proposing interventions for enhancing the phosphorus use efficiency and overall environmental sustainability of the U.S. food system. To this end, a holistic systems approach is needed for understanding the sustainability and resilience of the food-nutrient nexus, identifying improvement opportunities, and minimizing unintended consequences. 

Using publicly available data, we present a network model of interstate food trade for the U.S. The interstate food trade network is translated into embodied phosphorus network by using crop yields and phosphorus fertilizer application rates. The resulting models are utilized to understand the structure, robustness, and environmental sustainability of the food trade and embodied phosphorus networks. Specifically, we focus on two primary commodity groups: cereal grains, and fruits and vegetables covering over 50 crop items. Preliminary results indicate that over 650 million tons of food items in these commodity groups were transferred across the U.S. in 2012 along with 60 million tons of embodied phosphorus fertilizer. Additionally, fruits and vegetables category contributed 30% by mass of analyzed food trade but accounted for 50% of embodied phosphorus trade compared to cereal grains. From a network perspective, the interstate food trade network has a well-connected and robust structure with a majority of states participating in food trade. The weighted food trade network is controlled by a core group of states such as Texas, Louisiana, and California. Additionally, the results highlight significant variations in phosphorus application rates and embodied phosphorus flows. A series of higher order network measures are also utilized to understand robustness and resilience patterns in embodied phosphorus trade. The implications of these findings for sustainable phosphorus use and management will be described.