Agriculture Reference
In-Depth Information
Table 13.6
Reductions in methane emissions due to various water management practices compared to continuous
fl ooding (with organic amendments) (Wassmann et al.
2000
)
Mitigation practices
Seasonal emissions (kg/ha)
Relative reduction (%)
Experiment location
Mid-season drainage
385
23
a
Beijing 1995
312
44 ns
Hangzhou 1995
51
43
a
Maligaya 1997 DS
25
7 ns
Maligaya 1997 WS
Alternate fl ooding/drainage
216
61
a
Hangzhou 1995
207
59
a
Beijing 1995
Mid-season drainage and
no organic matter
26
95
a
Beijing 1995
239
57
a
Hangzhou 1995
a
Statistically signifi cant
WS
wet season,
DS
dry season,
ns
not signifi cant
methane emission was offset by increasing N
2
O
emissions. Little N
2
O emission occurred when
fi elds were continuously fl ooded (Zou et al.
2005
). Mid-season drainage, however, caused
intense emissions of N
2
O, which contributed
greatly to the seasonal amount. After the mid-
season drainage, on the other hand, no recogniz-
able N
2
O was observed when the fi eld was
frequently waterlogged by the intermittent irriga-
tion. In contrast, large N
2
O emissions were
observed when the fi eld was moist but not water-
logged by the intermittent irrigation. Thus, N
2
O
emissions during intermittent irrigation periods
depended strongly on whether or not water log-
ging was present in the fi elds. Different water
regimes cause changes to N
2
O emissions from
rice paddies (Zou et al.
2005
).
(i)
Advantages
• Methane emission reductions associated
with mid-season drainage in rice fi eld
range from about 7 to 95 % (Table
13.6
)
with little effect on rice grain yield.
• Draining stimulates root development and
accelerates decomposition of organic
materials in the soil making more miner-
alized nitrogen available for plant uptake.
• Mid-season drainage saves water, which
could be used for other purposes.
• Mid-season drainage inhibits ineffective
tillers and improves root activities.
(ii)
Disadvantages
• Drainage has the unintended effect of
increasing N
2
O emissions. However, mid-
season drainage can help mitigation of
N
2
O if a fi eld was frequently waterlogged
by intermittent irrigation.
• Intermittent drying or drainage of soil is
not feasible on terraced rice fi elds because
drying could cause cracking of the soil
leading to water losses or, in extreme
cases, complete collapse of the terraced
construction.
• Field drainage also induces weeds and
thereby reduces the rice grain yield.
• Mid-season drainage delays the develop-
ment of crop. Flowering is generally
delayed by 3-4 days, and harvest/matu-
rity may be delayed by 7-10 days.
• Mid-season drainage may increase plant
height, and this will make the crop more
prone to lodging especially when grain
yield is high.
According to Wassmann and Pathak (
2007
),
mid-season drainage is a profi table mitigation
technology due to low labor cost and low yield
risk. The cost of the technology was around
US$20 per t CO
2
e saved. Nelson et al. (
2009
)
observed that by one mid-season drying, net rev-
enue dropped less than 5 % while GHG emis-
sions dropped by almost 75 million metric tons of
CO
2
e (approximately 4,000 t CO
2
e ha
−1
).
13.1.5.3 Alternate Wetting
and Drying
The International Rice Research Institute (IRRI)
in the Philippines has developed a new mitigation
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