The role of globalizing livestock supply chains in the disruption of global nitrogen cycles

Summary

The globalizing livestock sector has disrupted the nitrogen (N) cycle and flows leading to increased crop and animal-sourced food production, but also risks for the environment and human health. Previous researches have analyzed global N flows and losses from livestock systems focusing on animal production— including manure management and on-farm feed production — but excluding traded feed and animal products, transport, and post-farm activities, in which substantial N losses take place. Additional analyses considered the livestock as an aggregated component of food systems, without analyzing in details the sources and fate of N losses within the sector. Analyzing N flows and losses from the livestock is essential to understand their contributions to the transgression of the planetary boundaries. We filled this knowledge gap by assessing the contribution of globalized livestock supply chains to anthropogenic N losses on the global, regional and national scale for 2010. This study focused on 237 countries and territories grouped in 10 regions, using an updated version of the Global Livestock Environmental Assessment Model (GLEAM). GLEAM was coupled with an explicit indicator framework, which analyses N inputs (e.g. synthetic fertilizer, biological N fixation), N outputs (e.g. feed, animal products), N loss compounds (e.g. ammonia (NH3), nitrous oxide (N2O), nitrates (NO3-)) and N recycled (e.g. manure, crop residues) along the chain and reconnects geographically distant supply chain stages when examining the efficiency of N use. This study relied on the most detailed geo-referenced information on N flows, at a resolution circa 10 x 10 km at the equator. The results of this study provide a detailed analysis of the magnitude, sources and pathways of N to stimulate international efforts in designing improvement pathways and informing policy dialogue while supporting evidence-based decisions to shape the future of livestock sector.