Climate Change Mitigation - Climate Resilient Agriculture for Ensuring Food Security - page 288

13.1.4.1 Irrigation
CO 2 emissions can be reduced with effective
irrigation by increasing yields and crop residues
which can enhance carbon sequestration (Smith
et al. 2008 ). All types of irrigation, such as fl ood,
sprinkler, surface, and subsurface drip, can all
enhance crop yields with subsequent increases in
crop residues and enhanced carbon sequestration.
Eighteen percent of cropped areas are currently
irrigated. If additional areas can be put under
irrigation, then additional carbon sequestration
can occur.

• Adjusting the timing of organic residue
additions can also reduce methane emissions.
For instance, incorporating organic materials
in the dry period rather than in the fl ooded
periods reduces emissions.
• Composting the residues before incorporation
reduces methane emissions.
• By producing biogas for use as fuel for energy
production.
The US Environmental Protection Agency
(US EPA) concludes that the water management
system under which rice is grown is the most
important factor affecting methane emissions.
Also, the amount of available carbon susceptible
to decomposition is also considered critical by
the US EPA. In addition to water management,
other practices (e.g., tillage, fertilization, manure
amendments) will alter the soil environmental
conditions (e.g., temperature, moisture, pH) and
hence affect the soil carbon- and nitrogen-driving
processes such as decomposition, nitrifi cation,
and denitrifi cation. The changes in the soil bio-
geochemical processes will fi nally affect the
availability of soil nitrogen and water to the crops
and hence alter the crop yields. Because crop
residue is the major source of soil organic carbon,
the change in crop yield and litter will redefi ne
the soil organic matter balance, which is one of
the most important factors determining the CH 4 ,
soil CO 2 , and N 2 O emissions.
Soil temperature is also known to be an impor-
tant factor regulating the activity of methano-
genic bacteria and, therefore, the rate of CH 4
production.
Rice cultivation is responsible for 10 % of
GHG emissions from agriculture. In developing
countries, the share of rice in GHG emissions
from agriculture is even higher, e.g., it was 16 %
in 1994. A variety of technologies are presented
for reducing emissions from rice cultivation.
The following rice-related mitigation technol-
ogies are described:
• Fertilizer, manure, and straw management
• Water management: mid-season drainage
• Water management: alternate wetting and
drying

13.1.5 Rice Production Technologies

Most rice is grown in fl ooded paddy fi elds. When
fi elds are fl ooded, the decomposition of organic
material depletes the oxygen present in the soil
and fl ood water which results in anaerobic condi-
tions in the soil. Anaerobic decomposition of soil
organic matter by methanogenic bacteria results
in methane emissions. While part of the methane
is oxidized by aerobic methanotrophic bacteria in
the soil and part is leached away as dissolved
methane in the fl ood water, the remaining unoxi-
dized methane is emitted from the soil to the
atmosphere.
As such, cultivated rice production results in
signifi cant emissions of methane by the soil. These
emissions can be reduced by various practices:
• Draining wetland rice once or several times
during the growing season reduces methane
emissions. If water is drained and soils are
allowed to dry suffi ciently, CH 4 emissions
decrease or stop entirely. However, this benefi t
may be partly offset by increased N 2 O emis-
sions, and the practice may be constrained by
water supply.
• Rice cultivars with low exudation rates could
also offer an important methane mitigation
option. In the off-season rice, methane emis-
sions can be reduced by improved water man-
agement. Methane emissions are reduced by
keeping the soil as dry as possible and avoid-
ing water logging.
• Increasing rice production can enhance soil
organic carbon stocks.

• Potassium fertilizer application

• Agricultural biotechnology