Modeling Nutrient Flows in the Food Chain of China

Increasing nitrogen (N) and phosphorus (P) inputs have greatly contributed to the increasing food production in China during the last decades, but have also increased N and P losses to the environment. The pathways and magnitude of these losses are not well quantified Here, we report on N and P use efficiencies and losses at a national scale in 2005, using the model NUFER (NUtrient flows in Food chains, Environment and Resources use) Total amount of "new" N imported to the food chain was 48.8 Tg in 2005. Only 4 4 Tg reached households as food Average N use efficiencies in crop production, animal production, and the whole food chain were 26, 11 and 9%, respectively Most of the imported N was lost to the environment, that is, 23 Tg N to atmosphere, as ammonia (57%). nitrous oxide (2%), dinitrogen (33%), and nitrogen oxides (8%), and 20 Tg to waters The total P input into the food chain was 7.8 Tg The average P use efficiencies in crop production, animal production, and the whole food chain were 36, 5, and 7%, respectively This is the first comprehensive overview of N and P balances, losses, and use efficiencies of the food chain in China It shows that the N and P costs of food are high (for N 11 kg kg(-1). for P 13 kg kg(-1)) Key measures for lowering the N and P costs of food production are (i) increasing crop and animal production, (ii) balanced fertilization, and (iii) improved manure management.