accounted for 12.5 Tg N year
À1 of N transferred from industry to human systems in
2015, and another 6.3 Tg N year
À1 of N was emitted to the atmosphere as NO x
during fossil fuel combustion.
Cropland was the second largest subsystem on the N input, followed by atmosphere. Three main forms of N inputs to croplands were synthetic fertilizers,
manures, and CBNF; all got increased from 1980 to 2015, and the contribution of
industrial fertilizer to total inputs increased from 50% to 64% during this period. It’s
fair to say that N inputs to croplands in China were primarily—and increasingly—
from industrial fertilizer although recycled Nr (human and animal manure, even
atmospheric deposition and irrigation water) made a meaningful contribution to total
N inputs to cropland. N losses and removals from cropping systems in 2015 included
reactive N trace gases (7.9 Tg N year
À1 for NH 3 and NO x ), denitrification to N 2
(7.6 Tg N year
À1 ), N 2 O emission (0.4 Tg N year
À1 ) to atmosphere, grain and straw
to livestock subsystem (9.0 Tg N year
À1 ), food (4.2 Tg N year
À1 ) and fuel (straw,
1.4 Tg N year
À1 ) to human subsystem, feed to the Others category (2.5 Tg N year
À1 ,
mostly to aquaculture), and losses to surface and groundwater (4.8 Tg N year
À1 ); all
of these (except the food and fuel transferred directly to human subsystem) increased
more than twofold from 1980 to 2015.
Livestock subsystem also saw an increased N input from 4.0 Tg N year
À1 in 1980
to 14.9 Tg year
À1 in 2015. Livestock production system receives both domestic and
imported sources of feed, while imported feed increased nearly tenfold in this
interval, reaching 3.1 Tg N year
À1 in 2015. Major outputs of N from the livestock
system elevated in 2015 compared with 1980, including manure returned to croplands (from 1.7 to 5.5 Tg N year
À1 ), food for the human subsystem (from 0.4 to
2.6 Tg N year
À1 ), volatilization of NH 3 (from 1.3 to 5.0 Tg N year
À1 ), and losses to
stream and groundwater (from 0.8 to 1.7 Tg N year
À1 ). However, the rate of manure
to field (the fraction of N that flowed into the livestock system and then returned as
manure to cropland) remained 23–25% through this period.
Human subsystem was the main consumer group. Inputs of Nr to the human
system substantially increased from 5.3 Tg N year
À1 in 1980 to 22.2 Tg N year
À1 in
2015. Food consumption from agricultural products, livestock, and aquaculture
increased from 3.1 to 7.4 Tg N year
À1 during the past 35 years, and the proportion
represented by animal-derived food increased from 14% to 44%, suggesting that
China is shifting to meat-rich diets. On the other hand, the Nr use in non-food goods,
including chemical (e.g., explosives and nylon) and agricultural (e.g., cotton and
leather) products, increased over 24-fold from 0.4 to 12.5 Tg N year
À1 , reflecting the
expansion of industrial N use with socioeconomic development in China. Although
the domestic use of agricultural residue (primarily as biofuel) decreased slightly over
the interval, household use of fossil fuel increased by emitting NO x to the atmosphere from 0.3 Tg N in 1980 to 0.8 Tg N in 2015. Losses of N from the human
subsystem to waste subsystem (combined in the Others category) increased dramatically from 0.3 Tg N in 1980 to 5.7 Tg N in 2015, whereas the amount of N returned
to cropping system shows a declining trend, from 2.2 to 1.4 Tg N year
À1 , reflecting a
substantial and increasing disconnect between the human and cropland subsystems.
5 Reactive Nitrogen Budgets in China
95
À1 of N transferred from industry to human systems in
2015, and another 6.3 Tg N year
À1 of N was emitted to the atmosphere as NO x
during fossil fuel combustion.
Cropland was the second largest subsystem on the N input, followed by atmosphere. Three main forms of N inputs to croplands were synthetic fertilizers,
manures, and CBNF; all got increased from 1980 to 2015, and the contribution of
industrial fertilizer to total inputs increased from 50% to 64% during this period. It’s
fair to say that N inputs to croplands in China were primarily—and increasingly—
from industrial fertilizer although recycled Nr (human and animal manure, even
atmospheric deposition and irrigation water) made a meaningful contribution to total
N inputs to cropland. N losses and removals from cropping systems in 2015 included
reactive N trace gases (7.9 Tg N year
À1 for NH 3 and NO x ), denitrification to N 2
(7.6 Tg N year
À1 ), N 2 O emission (0.4 Tg N year
À1 ) to atmosphere, grain and straw
to livestock subsystem (9.0 Tg N year
À1 ), food (4.2 Tg N year
À1 ) and fuel (straw,
1.4 Tg N year
À1 ) to human subsystem, feed to the Others category (2.5 Tg N year
À1 ,
mostly to aquaculture), and losses to surface and groundwater (4.8 Tg N year
À1 ); all
of these (except the food and fuel transferred directly to human subsystem) increased
more than twofold from 1980 to 2015.
Livestock subsystem also saw an increased N input from 4.0 Tg N year
À1 in 1980
to 14.9 Tg year
À1 in 2015. Livestock production system receives both domestic and
imported sources of feed, while imported feed increased nearly tenfold in this
interval, reaching 3.1 Tg N year
À1 in 2015. Major outputs of N from the livestock
system elevated in 2015 compared with 1980, including manure returned to croplands (from 1.7 to 5.5 Tg N year
À1 ), food for the human subsystem (from 0.4 to
2.6 Tg N year
À1 ), volatilization of NH 3 (from 1.3 to 5.0 Tg N year
À1 ), and losses to
stream and groundwater (from 0.8 to 1.7 Tg N year
À1 ). However, the rate of manure
to field (the fraction of N that flowed into the livestock system and then returned as
manure to cropland) remained 23–25% through this period.
Human subsystem was the main consumer group. Inputs of Nr to the human
system substantially increased from 5.3 Tg N year
À1 in 1980 to 22.2 Tg N year
À1 in
2015. Food consumption from agricultural products, livestock, and aquaculture
increased from 3.1 to 7.4 Tg N year
À1 during the past 35 years, and the proportion
represented by animal-derived food increased from 14% to 44%, suggesting that
China is shifting to meat-rich diets. On the other hand, the Nr use in non-food goods,
including chemical (e.g., explosives and nylon) and agricultural (e.g., cotton and
leather) products, increased over 24-fold from 0.4 to 12.5 Tg N year
À1 , reflecting the
expansion of industrial N use with socioeconomic development in China. Although
the domestic use of agricultural residue (primarily as biofuel) decreased slightly over
the interval, household use of fossil fuel increased by emitting NO x to the atmosphere from 0.3 Tg N in 1980 to 0.8 Tg N in 2015. Losses of N from the human
subsystem to waste subsystem (combined in the Others category) increased dramatically from 0.3 Tg N in 1980 to 5.7 Tg N in 2015, whereas the amount of N returned
to cropping system shows a declining trend, from 2.2 to 1.4 Tg N year
À1 , reflecting a
substantial and increasing disconnect between the human and cropland subsystems.
5 Reactive Nitrogen Budgets in China
95