(EOCAY 1991). The second phase (1991–1996) saw the most rapid increase in
emissions, and the growth rate rose to 10% between the years 1994 and 1995. In
1992, China began to implement a reform of the socialist market economic system,
which had previously driven livestock production (CAAA 2009), and accordingly,
more NH 3 emissions from livestock waste were emitted. However, in 1997, there
was a 0.5 Tg decrease in livestock emissions, compared to the those in 1996. This
observed decline could be attributed to the Asian financial crisis, which started in
1997 and had a detrimental effect on the development of the Chinese livestock
industry. From 1998 to 2005, as the third phase, NH 3 emissions continually rose in
conjunction with an increase in livestock production due to improvements in cultivation technique and increases in market demand (Zhang et al. 2003). After a peak in
2005, there was a marked decrease, and emissions fluctuated around 5.0 Tg in the
fourth phase, significantly lower than those in the mid-2000s, which can be
explained by a decrease in several major livestock classes, including cattle and
sheep. A rural labor shortage, increased feeding costs for farmers, and market
price fluctuations of meat products inhibited livestock production during this period
(Pu et al. 2008). In contrast to the free-range and intensive systems, in recent decades
NH 3 emissions from grazing systems have demonstrated slight growth, from 0.13 Tg
(1980) to 0.20 Tg (2012), without significant changes.
Temperature is dominant in determining the seasonal pattern of NH 3 emission
from livestock animal wastes. The major emissions occur in warmer months (May to
September), accounting for more than 45% of the annual livestock emissions due to
enhanced NH 3 volatilization related to a substantial increase in ambient temperature.
The lowest emissions were always estimated in wintertime with relatively smaller
EFs linked to lower temperature.
Synthetic fertilizer application is another major source of NH 3 emissions across
China. Figure 2.7 shows estimates of NH 3 emissions for the period 1980–2012. The
annual levels consistently increased from 1980 (2.1 Tg) to 1996 (4.7 Tg) and then
declined from 1996 to 2012 (2.8 Tg). The ABC and urea application were the two
major contributors, while NH 3 release from other synthetic fertilizers, such as AS
and AN, made a negligible contribution to emissions (<0.1%). Since the 1990s,
Chinese farmers have gradually replaced ABC in fertilizer application with urea that
has higher N efficiency and lower NH 3 loss. In 1980, 3.0 million and 5.1 million tons
of urea-N and ABC-N, respectively, were produced; by 2012, these values had
changed to approximately 28.8 million and 3.4 million tons, accounting for approximately 66.7% and 7.9% of total synthetic fertilizer production in China, respectively. Because the NH 3 volatilization rate from ABC is more than twofold that from
urea (Roelcke et al. 2002; Cai et al. 1986), the increasing proportion of urea
application relative to that of ABC has caused the decrease in total synthetic fertilizer
emissions observed from the mid-1990s onward. As shown in Fig. 2.7, although
emissions from urea application increased by 1.0 Tg from 1996 to 2012, those from
ABC fell by nearly 3.0 Tg.
There have been distinct seasonal disparities in NH 3 emissions from synthetic
fertilizers, caused by variation in both the temperature and timing of fertilizer
application for different crops. Generally, NH 3 volatilization began to rise in April
with increasing temperatures, and the highest emissions occurred in summer (June–
28
Q. Zhang et al.
emissions, and the growth rate rose to 10% between the years 1994 and 1995. In
1992, China began to implement a reform of the socialist market economic system,
which had previously driven livestock production (CAAA 2009), and accordingly,
more NH 3 emissions from livestock waste were emitted. However, in 1997, there
was a 0.5 Tg decrease in livestock emissions, compared to the those in 1996. This
observed decline could be attributed to the Asian financial crisis, which started in
1997 and had a detrimental effect on the development of the Chinese livestock
industry. From 1998 to 2005, as the third phase, NH 3 emissions continually rose in
conjunction with an increase in livestock production due to improvements in cultivation technique and increases in market demand (Zhang et al. 2003). After a peak in
2005, there was a marked decrease, and emissions fluctuated around 5.0 Tg in the
fourth phase, significantly lower than those in the mid-2000s, which can be
explained by a decrease in several major livestock classes, including cattle and
sheep. A rural labor shortage, increased feeding costs for farmers, and market
price fluctuations of meat products inhibited livestock production during this period
(Pu et al. 2008). In contrast to the free-range and intensive systems, in recent decades
NH 3 emissions from grazing systems have demonstrated slight growth, from 0.13 Tg
(1980) to 0.20 Tg (2012), without significant changes.
Temperature is dominant in determining the seasonal pattern of NH 3 emission
from livestock animal wastes. The major emissions occur in warmer months (May to
September), accounting for more than 45% of the annual livestock emissions due to
enhanced NH 3 volatilization related to a substantial increase in ambient temperature.
The lowest emissions were always estimated in wintertime with relatively smaller
EFs linked to lower temperature.
Synthetic fertilizer application is another major source of NH 3 emissions across
China. Figure 2.7 shows estimates of NH 3 emissions for the period 1980–2012. The
annual levels consistently increased from 1980 (2.1 Tg) to 1996 (4.7 Tg) and then
declined from 1996 to 2012 (2.8 Tg). The ABC and urea application were the two
major contributors, while NH 3 release from other synthetic fertilizers, such as AS
and AN, made a negligible contribution to emissions (<0.1%). Since the 1990s,
Chinese farmers have gradually replaced ABC in fertilizer application with urea that
has higher N efficiency and lower NH 3 loss. In 1980, 3.0 million and 5.1 million tons
of urea-N and ABC-N, respectively, were produced; by 2012, these values had
changed to approximately 28.8 million and 3.4 million tons, accounting for approximately 66.7% and 7.9% of total synthetic fertilizer production in China, respectively. Because the NH 3 volatilization rate from ABC is more than twofold that from
urea (Roelcke et al. 2002; Cai et al. 1986), the increasing proportion of urea
application relative to that of ABC has caused the decrease in total synthetic fertilizer
emissions observed from the mid-1990s onward. As shown in Fig. 2.7, although
emissions from urea application increased by 1.0 Tg from 1996 to 2012, those from
ABC fell by nearly 3.0 Tg.
There have been distinct seasonal disparities in NH 3 emissions from synthetic
fertilizers, caused by variation in both the temperature and timing of fertilizer
application for different crops. Generally, NH 3 volatilization began to rise in April
with increasing temperatures, and the highest emissions occurred in summer (June–
28
Q. Zhang et al.