Agriculture as a Source of GHGs - Climate Resilient Agriculture for Ensuring Food Security - page 32

Table 3.3 Methane emission coeffi cients from different rice ecosystems in the year 2000

Emission coeffi cient
(kg ha −1 )

Methane
emission (Gg)
Irrigated CF 6.85 162 1,138
SA 8.99 66 605
MA 9.49 18 144
Rainfed DP 8.66 66 550
FP 4.35 190 827
Deep water DW 1.37 160 217
Upland 4.8 0 0
Total 44.7 3,483
a CF continuously fl ooded, SA single aeration, MA multiple aeration, DP drought prone, FP fl ood prone, DW deep water

Water regime a Rice area (M ha)

Ecosystem

3.2.4 Rice Cultivation (CH 4 )

escapes into the atmosphere primarily by vascular
transport through the rice plants. The volume of
CH 4 emitted from a given area of rice is a func-
tion of the crop duration, water regimes, and
organic soil amendments. The CH 4 emissions are
estimated by multiplying the seasonal emission
factors by the annual harvested area. Harvested
area for each subunit (state) on multiplication
with the respective emission factor is the repre-
sentative of conditions that defi ne the subunit
(state). The total annual emissions are equal to
the sum of emissions from each subunit of har-
vested area (Table 3.3 ).

The anaerobic decomposition of organic matter in
fl ooded rice fi elds produces CH 4 . When fi elds are
fl ooded, aerobic decomposition of organic mate-
rial gradually depletes the oxygen present in the
soil and fl ood water, causing anaerobic conditions
in the soil to develop. Once the environment
becomes anaerobic, CH 4 is produced through
anaerobic decomposition of soil organic matter by
methanogenic bacteria. Several factors infl uence
the amount of CH 4 produced, including water
management practices and the quantity of organic
material available to decompose (US-EPA 2011 ).
￿ CH 4 emissions from rice production have
increased 6 % between 1990 and 2005, from
670 to 710 MtCO 2 e, corresponding to 11.6 %
of total agricultural emissions. Underlying
this trend has been a similar increase in the
land area of harvested rice (Table 3.2 ).
￿ From 2005 to 2030, CH 4 emissions from this
source are projected to increase 4 % from 710
to 739 MtCO 2 e (this projection assumes a fur-
ther increase in rice area harvested over the
projection period) (US-EPA 2011 ).

3.2.5 Manure Management

(CH 4 , N 2 O)

Manure management produces CH 4 and
N 2 O. CH 4 is produced during the anaerobic
decomposition of manure, while N 2 O is produced
by the nitrifi cation and denitrifi cation of the
organic nitrogen content in livestock manure and
urine (US-EPA 2011 ).
￿ Between 1990 and 2005, CH 4 and N 2 O emis-
sions from manure management decreased by
5 %, from 408 to 389 MtCO 2 e, corresponding
to 6.4 % of total agricultural emissions
(Table 3.2 ).
￿ From 2005 to 2030, global CH 4 and N 2 O
emissions from manure management are pro-
jected to increase by 17 %, from 389 to 455
MtCO 2 e (US-EPA 2011 ) .

3.2.4.1 Inventory of Methane Emission
from Rice Fields
Rice fi elds with anaerobic conditions in wetlands
as a result of soil submergence under water are
one of the major sources of methane emission.
Decomposition of organic material in fl ooded
rice fi elds produces methane (CH 4 ),

which