How China's nitrogen footprint of food has changed from 1961 to 2010

People have increased the amount of reactive nitrogen (Nr) in the environment as a result of food production methods and consumption choices. However, the connection between dietary choices and environmental impacts over time has not yet been studied in China. Here we combine a nitrogen footprint tool, the N-Calculator, with a food chain model, NUFER (NUtrient flows in Food chains, Environment and Resources use), to analyze the N footprint of food in China. We use the NUFER model to provide a detailed estimation of the amounts and forms of Nr released to the environment during food production, which is then used to calculate virtual nitrogen factors (VNFs, unit: kg N released/kg N in product) of major food items. The food N footprint consists of the food consumption N footprint and food production N footprint. The average per capita food N footprint increased from 4.7 kg N capita-1 yr-1 in the 1960s to 21 kg N capita-1 yr-1 in the 2000s, and the national food N footprint in China increased from 3.4 metric tons (MT) N yr-1 in the 1960s to 28 MT N yr-1 in the 2000s. The proportion of the food N footprint that is animal-derived increased from 37% to 54% during this period. The food production N footprint accounted for 84% of the national food N footprint in the 2000s, compared to 62% in the 1960s. More Nr has been added to the food production systems to produce enough food for a growing population that is increasing its per-capita food consumption. The increasing VNFs in China indicate that an increasing amount of Nr is being lost per unit of N embedded in food products consumed by humans in the past five decades. National N losses from food production increased from 6 MT N yr-1 in the 1960s to 23 MT N yr-1 in the 2000s. N was lost to the environment in four ways: ammonia (NH3) emissions and dinitrogen (N2) emissions through denitrification (each account for nearly 40%), N losses to water systems (20%), and nitrous oxide (N2O) emissions (1%). The average per capita foo