A biogeochemical view of the global agro-food system: Nitrogen flows associated with protein production, consumption and trade

Through a detailed analysis of the FAO database, we propose a generalised representation of the world׳s agro-food systems in 2009, based on the description of nitrogen (i.e. proteins) fluxes from fertilisers to crops and from crops to livestock and human nutrition. This description also includes the resulting environmental losses of nitrogen at each stage of the chain. Current trade and production fluxes of food and feed differentiate 12 macro-regions, strongly contrasted in terms of N transfer patterns. Three major factors determining the performance of the agro-food system are highlighted: (i) the cropland yield-fertilisation relationship, (ii) vegetal to animal protein conversion efficiency in the livestock farming system, as well as its connection to either semi-natural grassland or cropping systems, and (iii) total protein consumption and proportion of animal protein in the human diet.