Rice Ecosystem and Methane Emissions!

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2.  Rice - World's most important wetland food crop
 The only major grain crop that is grown almost exclusively
as food
 Pressure to grow more rice accelerating with ever
increasing population
 >90% of the world's rice grown in Asia, 3.2% in Latin
America, 2.1% in Africa, and 2.5% in the rest of the world

3. Rice Ecosystem can be classified into four categories:
 IRRIGATED RICE FIELDS
the floodwater is fully controlled
kept shallow
 RAIN-FED RICE FIELDS
precipitation controls flooding of soils
At times in the growing season, soils of rain-fed rice fields
may dry up or be flooded up to 50 cm.

4.  DEEPWATER RICE FIELDS
floodwater rises to more than 50 cm during the growing
season, and it may reach several meters
 UPLAND RICE FIELDS
neither flooded nor does the topsoil become water
saturated at any significant period of time

5.  Flooding of rice fields provides
ideal growth medium
sufficient water supply
makes preparing the soils easy
weed suppression
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6.  The increasing population demands enhancement in
the production of rice. This has a direct effect on the
global environment since the rice cultivation is one of
the major contributors to the methane emissions
 Methane fluxes rising substantially as the rice
cultivation is intensified with the current practices
and technologies
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7.  Also referred to as biomethanation
 It is the formation of methane by a group of microbes called
methanogenic bacteria or methanogens
 Methane is produced as a terminal step of the anaerobic
breakdown of organic matter and is exclusively produced only
in the strict absence of free oxygen
 Methanogens rely on a plethora of other microorganisms to
provide them with the few substrates they can catabolize:
hydrogen, carbon dioxide, formate, acetate, methanol,
methylamines, and methysulfides
 This process is estimated to contribute about 25% of the total
budget of global methane emissions
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8.  Methane emissions from rice paddy result from these
processes:
A concentration gradient that causes diffussion through the
soil-water and water-air interfaces
The release of gas bubbles from soil surface to the
atmosphere
Soil methane enter into the plant through the roots, is
released to the atmosphere through the plant stomata

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10. 1. SOIL TYPE/FIELD
 Soil temperature (in the 0-15 cm layer)
 Soil water content
 Soil Characteristics
Methane emission is higher in heavy clay soils than in
porous soils (sandy, loamy sand, and sandy loam-
textured soils) because the latter have high infiltration
rates

11. 2. FERTILIZATION:
 Fertilizer quality
 Quantity applied
 Application practices
Applying chemical and organic inputs such as urea, rice
straw, animal manure, and green manure generally
increases methane emissions

12. 3. ORGANIC FERTILIZER:
 Addition of rice straw compost
(23-30% increase in methane emissions)
 Application of fresh rice straw
(162-250% increase in methane emissions)

13. 4. PLANT GROWTH STAGE:
 Difference of methane emissions at different growth
periods are significant
78% of the emissions occurs at the reproduction stage

14. 5. TILLAGE
 Tillage disturbs and releases stored CH4 from
the soil

15. 6. WATER REGIME
 Flooded soil is prerequisite to sustained emissions
of CH4. When water level fluctuates between
oxidative (drained field) and reductive (submerged
field) conditions, depending on water management,
CH4emission also fluctuates
 Thus, rice environments with unsteady supply of
water, such as rain fed areas, have a lower CH4
emission potential than irrigated rice

16. 7. TEMPERATURE:
 High temperatures in the weeks following the
application of fertilizer and organic inputs result in a
pronounced CH4emission peak
 The higher the temperature, the faster is the
decomposition of organic matter

17. 8. RICE CULTIVARS
Morphological properties play a significant role in the
variation of CH4 emission among cultivars such as:
 root
 biomass
 number of tillers
 root exudates (compounds released by different parts of
root systems), and
 growth duration

18. 9. POPULATION OF METHANOTROPHIC
BACTERIA
 Biological consumption of CH4 is critical to the
regulation of almost all sources
 Methane-oxidizing bacteria (methanotrophs)
consume a significant but variable fraction of
greenhouse-active CH4 gas rice fields

19. 1. CLIMATE CHANGE
Methane contributes to climate change- trap warm
air.
Methane also affects the degradation of the ozone
layer.
Methane's lifetime in the atmosphere is much
shorter than carbon dioxide (CO2),
CH4 is more efficient at trapping radiation than CO2
Methane is 23 times more potent than carbon
dioxide in trapping heat in our atmosphere.
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21. 2. WATER CONTAMINATION
Methane gas can seep into water supplies and
contaminate wells or surface water. Deaths have been
caused by contaminated drinking water systems
poisoned by this odorless, tasteless gas.
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22. 3. HUMAN PROBLEMS
RELATED TO EMISSIONS
• Methane emissions can seep up
through the ground and cause
problems for the environment and
humans in particular
• The emissions don't just propose a
danger for flammability but it also
cause headaches and dizziness in
humans as it replaces the oxygen. This
can result in suffocation
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23. 4. OCEANIC CHANGES
When water containing methane mixes with ocean it
directly affects that climate and the life within that
system.
5. VEGETATION CHANGES
Climate changes due to methane also affects the
vegetation
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25.  To implement mitigation -Understanding of the
emission mechanisms
 Interaction between rice plant, microbe, the
environmental condition in the soil, and the cultural
and economic condition of the farmer must be
considered

26.  Reduce methane emissions
 Be economically feasible
 Be easy to implement
 Be acceptable by farmer

27. Methane mitigation opportunities within the rice
cultivation sector include:
 Temporary drainage of rice fields
 Direct seeding
 Use of chemical fertilizers
 Use of different rice cultivars
 Improved tillage

28. 1. TEMPORARY DRAINAGE OF RICE FIELDS
 Midway drainage leads to higher yields and less methane
emissions- Chinese rice farmers- 1980
 Mid-season drainage: 43% emission reduction
 Limited to the rice paddy fields where the irrigation system is
well prepared

29. 2. DIRECT SEEDING (VS. TRANSPLANTING)
 Direct seeding of pre-germinated rice- Reduction in methane
emissions due to shorter flooding periods and decreased soil
disturbances
 Research in Pakistan- to assess water-saving potential through
alternative wheat and rice establishment and crop
management practices (e.g., direct seeding versus
transplanting). The research revealed that methane emission
reductions were an unintended benefit of direct seeding
 Direct seeding is faster and easier than transplanting and
requires less labor

30. 3. USE OF CHEMICAL FERTILIZERS
•The use of sulfate-containing
fertilizers such as ammonium
sulfate reduced methane emissions
by 25-36%
•Applying phosphogypsum in
combination with urea has been
determined to reduce methane
emission by more than 70%

31. 4.USE RICE VARIETIES WITH LOW
METHANE EMISSION POTENTIAL
 Rice varieties with small root systems produce less CH4 than
other varieties.
 This option is easily adopted with existing varieties but results
in less significant emission reductions than other techniques.
 In the Beijing region of China, for example, studies have shown
that the use of cultivar Zhongzhou (modern japonica) reduced
methane emissions by approximately 50 percent when
compared with Jingyou (japonica hybrid) and Zhonghua (tall
japonica)

32. 5.IMPROVED TILLAGE PRACTICES
 Methane emissions are very intense during the tilling
stage of rice field preparation, which can account for
more than 80 percent of total annual emissions.
 This option is easily implemented but requires
increased education and outreach

33. 1. Limited Applicability to Different Types of Rice
Fields (e.g., Irrigated, Deepwater)
2. Technical Capacity
3. Limited Measurement Techniques and Lack of
Detailed Baseline
4. Increased Costs
5. Reduced Yield and Field Fertility
6. Cultural Diversity

34.  Interdisciplinary research approach, including application of
socioeconomics and participation of farmers, to achieve the
knowledge needed to design feasible and effective mitigation
technologies.
 The opportunity to reduce methane emissions should not outweigh
the need to feed a growing population.
 With current cultivation technologies, methane emission from rice
fields is expected to increase, as rice production is increased by 50
to 100% within the next three decades.
 By using a combination of feasible mitigation technologies, however,
there is great potential to stabilize or even reduce methane
emission from rice fields while increasing rice production, without
dramatically changing culture practices

35. 1. Bouman, A.F. (1991) Argonomic aspects of wetland rice cultivation and associated methane
emissions. Biochemistry. 15: 65-88.
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Reducing Methane Emissions from Ruminants by Strategic Supplementation. Washington,
D.C. (EPA 1991a)
3. U.S. Environmental Protection Agency (2006). Global Anthropogenic Non-CO2 Greenhouse
Gas Emissions: 1990–2020. Washington, D.C. (EPA 2006a).
4. U.S. Environmental Protection Agency (June 2006) Global Mitigation of Non-CO2
Greenhouse Gases.. (EPA 2006b).
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and Z.Z. Wang.(November 2000) A four-year record of methane emissions from irrigated
fields in the Beijing region of China. Nutrient Cycling in Agroecosystems. 58 (1-3): 55-63.
6. International Water Management Institute (IWMI)(2007). Sustaining the Rice-Wheat
Production Systems of Asia. Online project overview and lessons/results.
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rice paddies.
8. Wang Zhaoqian. (1986). Rice based systems in subtropical China.
9. Holzapfel-Pschorn, A., R. Conrad, and W. Seiler. (1985). Production, oxidation and emission
of methane in rice paddies. FEMS Microbial. Ecol. 31: 343-351.