Inthe past 2 decades (1990–2009), 61% of
the world’s increase in N fertilizer production and 52% of the
increased N consumption occurred in China (4). In 2010, China
produced 37.1 terrogram (Tg) of N (Tg N; agricultural consumption of 28.1 Tg N, industrial use of 4.7 Tg N, and export of 4.3
Tg N). This accounted for>30% of world’s total and exceeded the
combined N fertilizer use in North America (11.1 Tg N) and the
European Union (10.9 Tg N) in 2009 (4). Furthermore, China’sN
fertilizer production and utilizationhave distinct characteristics. N
fertilizer relies heavily on coal as the main source of energy in its
production. Coal has a greater carbon footprint than other forms of
energy, such as natural gas (Table S1)