J.G. Conijn1, J.J. Schröder1, P.S. Bindraban2
1 Wageningen University and Research centre, Droevendaalsesteeg 4, 6708 PB, Wageningen, the Netherlands, http://www.wageningenur.nl. Email address of corresponding author: firstname.lastname@example.org.
2 VFRC-IFDC, 1901 Pennsylvania Ave., NW. Washington, DC 20006. USA.
Food production causes losses of reactive nitrogen (N) to the detriment of the environment but the current level of losses per unit food leaves room for improvement. Due to feedback mechanisms a comprehensive analysis is needed and we developed a quantitative model of the whole food system to assess the effects of improvement measures on the required amount of N fertilizer and resulting N losses as function of food demand. For 2010 we calculate a total N loss from agricultural soils and ammonia volatilization of 172 Mt N y-1 and an amount of 32 Mt N y-1 entering households in food items. This implies a N loss ratio of 5.4 kg N lost per kg N purchased by households. Due to higher food demand and changed diet as projected for 2050, the N loss ratio increases to almost 6.0 if equal N use efficiencies are used as in 2010 and the total N loss amounts to 293 Mt N y-1. The effects of a number of improvement measures are explored, such as less animal-based products in the human diet and reduced N loss from agricultural soils. Single measures can reduce this ratio to as low as 3.8 but when all measures are combined, the ratio drops to 2.0 with a total N loss of 84 Mt N y-1 without affecting the projected food demand for 2050. Our results clearly illustrate that the effectiveness of measures cannot be realistically estimated without taking the whole system into account and that the N loss ratio is a better indicator to estimate environmental impacts of N use than N use efficiency.