(178c) Embodied Phosphorus in Interstate U.S. Food Transfers: Sustainability Implications for Food-Energy-Water Nexus

Authors: 
Vora, N., University of Pittsburgh
Khanna, V., University of Pittsburgh
Modern agriculture relies heavily on nitrogen, phosphorus, and potassium based fertilizers to reduce the yield gap and sustain current crop yields. Recently inorganic phosphorus fertilizers, an essential input to agriculture have garnered attention as they are primarily obtained from non-renewable and geographically concentrated rock phosphate sources. Phosphorus content in the soil is heavily skewed across the world with many regions facing water quality issues due to nutrient overloading in surface waters, while some face nutrient deficiency and soil degradation issues. Food trade is essential for supplying diverse and large quantities of food items to feed the growing population at global, national, and regional scale. Food trade also presents a pathway for transferring large volume of virtual nutrients and associated environmental impacts. The spatial heterogeneity of food production systems can increase or decrease the consumption based environmental impact of food trade in a particular region. At domestic level, vast quantities of food is traded between states resulting in a complex interstate food trade network. Although, estimates of United States (U.S.) centric domestic production and international trade of embodied phosphorus are available, we lack an understanding of interstate flux of embodied phosphorus for the U.S. To avoid unintended consequences and ensure optimal outcomes for a resilient food supply system, a holistic systems approach to studying interconnected resources is required. We model the origin and destination of food and embodied phosphorus flows to quantify trends in regional phosphorus use, identify hotspots, and propose interventions for enhancing the fertilizer use efficiency and overall environmental sustainability of the U.S. food system.

Using publicly available disparate datasets, we develop a food trade and associated virtual phosphorus model for the U.S. To this end, we evaluate over 60 crop items covering commodity groups of cereal grains, and fruits, nuts and vegetables. The interstate food trade network is translated to virtual phosphorus network by using crop yields and phosphate fertilizer application rates from estimates provided by the U.S. Department of Agriculture. Preliminary results indicate that over 655 million tons of food commodities were transferred across the U.S. in 2012 along with 61 million tons of embodied phosphorus fertilizer. Additionally, fruits and vegetables category contributed only 30% by mass for food trade but accounted for half of embodied phosphorus trade compared to cereal grains. We also evaluate virtual phosphorus savings for each individual item to identify phosphorus use efficiency in the US food production system. Additionally, we quantify the embodied energy flows associated with embodied phosphorus trade and discuss the inorganic phosphorus impact on water quality. Furthermore, we apply a network theory framework to understand the structure, robustness, and environmental sustainability of the considered trade networks. From a network perspective, our previous work has found that interstate food trade forms a well-connected, robust network with a majority of states participating in a high volume of trade. We characterize interstate virtual phosphorus network through series of higher order network measures to understand robustness and resilience patterns in virtual phosphorus trade. This will provide a necessary framework to evaluate series of interventions in a highly interconnected food trade system.