Food and feed trade as a driver in the global nitrogen cycle: 50-year trends

The alteration of the global nitrogen (N) cycle is creating severe environmental impacts. This paper analyses the increasing importance of the international trade of food and feed in the alteration of the N cycle at the global scale in two ways. First, using the information on food and feed trade across world countries, and assuming that N constitutes 16 % of proteins, we quantified the N annually traded in the period 1961-2010. We observed that in that period, the amount of N traded between countries has increased eightfold (from 3 to 24 TgN) and now concerns one-third of the total N in world crop production, with the largest part corresponding to animal feed. Secondly, we divided the world into 12 regions and studied the N transfer among them in two reference years: 1986 and 2009. The N flow among these regions has dramatically intensified during this period not only due to an increase in the population but also in the proportion of animal protein in the diet of some countries. Nowadays, in terms of proteins and N, a small number of countries (e.g., USA, Argentina and Brazil) are feeding the rest of the world. At the global scale the system is becoming less efficient because of the disconnection between crop and livestock production across specialised regions, increasing the environmental impacts. As human diet is an additional clear driver of the observed changes, the solutions must rely not only on the producers, but also on the consumers. The results of our study provide new insights into the food dependency relationships between the different regions of the world as well as the growing importance of international food and feed trade in the global N cycle.