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RICE ECOSYSTEM AND METHANE EMISSIONS

INTRODUCTIONRice - 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

CLASSIFICATION OF RICE ECOSYSTEM

Rice Ecosystem can be classified into four categories:

IRRIGATED RICE FIELDSthe floodwater is fully controlledkept shallow

RAIN-FED RICE FIELDSprecipitation controls flooding of soilsAt times in the growing season, soils of rain-fed rice fields

may dry up or be flooded up to 50 cm.

CLASSIFICATION OF RICE ECOSYSTEM

DEEPWATER RICE FIELDSfloodwater rises to more than 50 cm during the growing

season, and it may reach several meters

UPLAND RICE FIELDSneither flooded nor does the topsoil become water

saturated at any significant period of time

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WHY IS FLOODING OF RICE FIELDS IMPORTANT?

Flooding of rice fields provides

ideal growth mediumsufficient water supply makes preparing the soils easyweed suppression

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RELATIONSHIP OF RICE ECOSYSTEM AND METHANE EMISSIONS

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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METHANOGENESISAlso referred to as biomethanationIt is the formation of methane by a group of microbes called

methanogenic bacteria or methanogensMethane 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

PROCESSES INVOLVED IN METHANE EMISSIONS

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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FACTORS RELATED TO METHANE EMISSIONS

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

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

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)

4. PLANT GROWTH STAGE:

Difference of methane emissions at different growth periods are significant

78% of the emissions occurs at the reproduction stage

5. TILLAGE

Tillage disturbs and releases stored CH4 from the soil

6. WATER REGIMEFlooded 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

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

8. RICE CULTIVARS

Morphological properties play a significant role in the variation of CH4 emission among cultivars such as:

rootbiomass number of tillersroot exudates (compounds released by different parts of

root systems), and growth duration

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

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EFFECT OF METHANE ON ENVIRONMENT

1. CLIMATE CHANGEMethane 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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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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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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4. OCEANIC CHANGESWhen water containing methane mixes with ocean it directly affects that climate and the life within that system.

5. VEGETATION CHANGESClimate changes due to methane also affects the

vegetation

MITIGATION OPTIONS FOR METHANE EMISSIONS FROM

RICE FIELDS

CONSIDERATIONS

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

THE OPTIONS CHOSEN MUST Reduce methane emissions

Be economically feasible

Be easy to implement

Be acceptable by farmer

MITIGATION OF RICE CULTIVATION RELATED METHANE EMISSIONS

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

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 reductionLimited to the rice paddy fields where the irrigation system is

well prepared

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

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%

4.USE RICE VARIETIES WITH LOW METHANE EMISSION POTENTIALRice 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)

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

BARRIERS TO MITIGATING RICE CULTIVATION METHANE EMISSIONS

1. Limited Applicability to Different Types of Rice Fields (e.g., Irrigated, Deepwater)

2. Technical Capacity3. Limited Measurement Techniques and Lack of

Detailed Baseline4. Increased Costs5. Reduced Yield and Field Fertility6. Cultural Diversity

CONCLUSIONInterdisciplinary 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

REFERENCES1. Bouman, A.F. (1991) Argonomic aspects of wetland rice cultivation and associated methane

emissions. Biochemistry. 15: 65-88. 2. U.S. Environmental Protection Agency (1991). Improving Ruminant Production and 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).5. Wang, Z.Y., Y.C. Xu, Y.X. Guo, R. Wassmann, H.U. Neue, R.S. Lantin, L.V. Buendia, Y.P. Ding, 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.

7. Seiler, W., A. Holzapfel-Pschorn, R. Conrad, and D. Scharffe. (1984). Methane emission from 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.

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