Rice Technology Bulletin

Transcription

1 Rice Technology Bulletin Philippine Rice Research Institute (PhilRice) ISSN No. 70 Reducing Methane Emissions from Irrigated Ricefields

2 For more information, text the PhilRice Text Center (0920) ; write, visit, or call: Agronomy, Soils, and Plant Physiology Division Philippine Rice Research Institute Maligaya, Science City of Muñoz, Nueva Ecija 3119 Tel. No. (044) ; -0113; local 212, 215 or 217. Readers are encouraged to reproduce the content of this bulletin with acknowledgment.

3 Foreword Rice production is greatly affected by global warming and climate change. However, rice production in return contributes to global warming. Irrigated rice cultivation, for one, is considered as one of the human-influenced sources of methane (CH 4 ). Methane is considered a greenhouse gas that contributes to the global warming and climate change owing to its greenhouse effect. In the Philippines, CH 4 emissions from rice fields are about 40% of the total emissions from agriculture sector. When the rice field is flooded, it cuts off atmospheric oxygen supply to the soil. Flooding leads to anaerobic (without oxygen) fermentation of organic matter in the soil, which produces a substantial amount of CH 4. This technology bulletin presents the factors affecting CH 4 emission and the measures to reduce CH 4 emission. It is hoped that through this publication, we can encourage farmers to help lessen the impact of rice production on climate change without affecting their yield by reducing CH 4 emission from irrigated rice fields.

4 METHANE- A GREENHOUSE GAS Methane (CH 4 ) is a colorless, odorless, and flammable gas. It is formed when organic matter decomposes in oxygen-poor environments, such as marshes, rice paddies, or digestive systems of ruminants, and when carbon-based fuels are burnt. Methane absorbs heat 21 times more than carbon dioxide (CO 2 ) and it has a 9 to 15-year life time in the atmosphere over a 100-year period. When CH 4 is released into the atmosphere, CH 4 traps significant amount of heat that would otherwise escape to space. Thus, CH 4 is considered a greenhouse gas that contributes to the global warming and climate change owing to its greenhouse effect. 1

5 The historical record shows that CH 4 is more abundant in the Earth s atmosphere now than at any time during the past 400,000 years. Methane levels in the atmosphere have more than tripled since pre-industrial times, accounting for around one-fifth of the human contribution to greenhouse gas-driven global warming. Until recently, the leveling-off of the CH 4 levels had suggested that the rate of its emission from the Earth s surface was approximately balanced by the rate of its destruction in the atmosphere. METHANE EMISSION FROM RICE FIELD In the agriculture sector, flooded rice fields are significant sources of atmospheric CH 4 with an annual global emission ranging from Tg (1 teragram=1 million tons) CH 4. When the rice field is flooded, it cuts off atmospheric oxygen supply to the soil. Flooding leads to anaerobic (without oxygen) fermentation of organic matter in the soil, which produces a substantial amount of CH 4. 2

6 Methane is emitted to the atmosphere from submerged soils through diffusion in its dissolved form, release of gas bubbles (ebullition), and aerenchyma (air channels) of the rice plants. Several studies showed that 60-90% of CH 4 emitted from rice fields to the atmosphere is transported through the aerenchyma rather than molecular diffusion across water-air interfaces or release of gas bubbles. The aerenchyma mediate the transport of air (oxygen) to the roots and CH 4 from the anaerobic soil to the atmosphere. IMPORTANCE OF REDUCING METHANE EMISSION FROM IRRIGATED RICE FIELDS Although rice production is greatly affected by global warming and climate change, rice production in return contributes to 3

7 global warming. Irrigated rice cultivation, for one, is considered as one of the human-influenced (antropogenic) sources of CH 4. Rice fields contribute about 10-15% to the global CH 4 emission. In the Philippines, CH 4 emissions from rice fields are about 40% of the total emissions from agriculture sector. Hence, ways should be developed to lessen the impact of rice production on climate change without affecting the yield through reduction of CH 4 emission from irrigated rice fields. FACTORS AFFECTING METHANE EMISSION The magnitude and pattern of CH 4 emissions from rice fields are determined mainly by the individual and interactive effects of the following factors: 1. Fertilizer application Applying chemical and organic inputs such as urea, rice straw, animal manure, and green manure generally in- 4

8 crease CH 4 emissions. The increase in CH 4 emissions depends on the quantity, quality, and timing of fertilizer application. Moreover, water management and temperature may reduce or amplify the effect of fertilizer inputs on CH 4 emission. 2. Water management Flooded soil is prerequisite to sustained emissions of CH 4. When water level fluctuates between oxidative (drained field) and reductive (submerged field) conditions, depending on water management, CH 4 emission also fluctuates. Thus, rice environments with unsteady supply of water, such as rainfed areas, have a lower CH 4 emission potential than with adequate irrigation. 3. Soil type 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. Infiltration is the process by which water on the ground sur- 5

9 face enters the soil. Floodwater cannot be retained longer in light-textured soils compared to heavy clay soils resulting in a high-oxygen input, which impedes CH 4 emissions even with high organic inputs. 4. Population of methanotrophic bacteria Biological consumption of CH 4 is critical to the regulation of almost all sources. Methane-oxidizing bacteria (methanotrophs) consume a significant but variable fraction of greenhouseactive CH 4 gas produced in wetlands and rice fields before it can be emitted to the atmosphere. 5. Rice cultivars Rice cultivars showed differences in emitting CH 4 gas from flooded rice field. Morphological properties such as root, biomass, number of tillers, dry matter weight of aboveground biomass, and root exudates (compounds released by different parts of root systems), and growth duration play a significant role in the variation of CH 4 emission among cultivars. 6. Temperature High temperatures in the weeks following the application of fertilizer and organic inputs result in a pronounced CH 4 emission peak. The higher the temperature, the faster is the decomposition of organic matter. 6

10 The variation of methane emission daily is correlated with temperature. Temperature and methane fluctuations are high in early rice growth stages and lower during the second half of the growing season when the soil is shaded by rice plants. MEASURES TO REDUCE METHANE EMISSIONS 1. Apply compost rather than fresh residue Methane emission is significantly lowered when rice straw compost is used rather than fresh straw. Therefore, fully decomposed organic inputs should be applied to aerobic soil to reduce CH 4 emission. 2. Use ammonium sulfate instead of urea Adding any electron acceptor to the soil, such as sulfate or nitrate, reduces CH 4 emissions. Results show a significant reduction of 25-36% in CH 4 emissions with the use of ammonium sulfate as nitrogen fertilizer source instead of urea. The addition of 6 t/ha of phosphogypsum to urea, however, has resulted in 72% reduction in CH 4 emissions. The 7

11 high sulfate levels inhibit CH 4 formation in anaerobic systems due to the substrate competition between sulfatereducing and methanogenic bacteria. Gypsum application is also beneficial to neutralize the ph of alkaline soils and reduce CH 4 emissions. 3. Adopting intermittent irrigation and midseason drainage Water management is one option to reduce CH 4 emissions from rice fields. Flooding of rice fields is prerequisite to high CH 4 emissions. The consequent alternative to reduce CH 4 emissions is to limit the anaerobic conditions of the soil through midseason drainage and alternate wetting and drying technology. Results showed that midseason drainage reduced CH 4 emissions by 43%, while intermittent irrigation resulted in 92% reduction without a significant effect on grain yield. Midseason drainage and intermittent irrigation temporarily keep soil conditions oxidative, thus, enhances root activity, but reduces the activity of methane-producing bacteria. However, there is a risk of increasing nitrous oxide emission when fertilizer is applied at a high rate. Therefore, the modification of water management should be coupled with efficient fertilizer application to reduce both greenhouse gas emissions and lessen irrigation and fertilizer costs. PhilRice had developed technologies and tools for nutrient and water management. 8

12 CI is a water-saving technology that makes use of observation wells to monitor the status of field water, which tells whether there is a need to irrigate the field and how much water is needed. MOET is a tool that is reliable, low-cost, and an easy alternative technique for diagnosing soil nutrient status. LCC, or the four-stripped plastic ruler is used in assessing the nitrogen status of rice plants. [Please refer to technology bulletins on Controlled Irrigation for water management and Minus-One Element Technique (MOET) or Leaf Color Chart (LCC) for nutrient management.] 4. Use low-methane-emitting rice cultivars The most promising strategy to reduce emission from rice fields is to select and plant high-yielding rice cultivars, which can reduce CH 4 transport capacity. The different abilities of rice cultivars in emitting methane gas are mostly related to their morphological properties. 9

13 The combination of various factors, such as the supply of organic matter, size of the root space, and oxidation rate in the rhizosphere (the narrow zone of soil immediately surrounding the root system), have also been identified to affect the CH 4 fluctuation from various rice cultivars. Development of new plant type cultivars that have minimum number of tillers but with higher proportion of productive tillers, and can induce less amount of CH 4 seems to be an economically sound and promising approach to mitigate CH 4 emission from rice fields. 5. Practice direct seeding instead of transplanting method of crop establishment Direct seeding could reduce CH 4 emission by 18% as compared to transplanting. The mitigation effect could be enhanced up to 50% when direct seeding is combined with midseason drainage. Direct-seeded rice has a higher root biomass,thus, may introduce more organic material into the soil. The additional substrate for methanogenic bacteria is more significant in a soil environment with low organic inputs. 10

14 Moreover, the distinct root structure of direct-seeded rice, which shows a concentration of root in the upper lower layer, may become the decisive trait determining emissions. 6. Integration of mitigating measures The different mitigating strategies from seed selection to nutrient and water management and crop establishment, should be integrated to reduce CH 4 emission by 83-93%. Mitigating Options to Reduce CH 4 Emissions Options Potential Methane Reduction Direct Seeding Technology 16-54% Mid-season Drainage 43% Fertilizer Management 25-72% 11

15 References Corton TM, Bajita JB, Grospe FS, Pamplona RR, Asis CA Jr, Wassmann R, Lantin RS, and Buendia LV Methane emission from irrigated and intensively managed rice fields in Central Luzon (Philippines). Nutrient Cycling in Agroecosystems 58: International Rice Research Institute Rice Today Magazine, Vol. 6 No. 3 Intergovernmental Panel on Climate Change Guidelines for national greenhouse gas inventories: Workbook, Chapter 4.3 Agriculture: Rice cultivation. OECD, Paris, France Majumdar D Methane and nitrous oxide emission from irrigated rice fields: Proposed mitigation strategies. Current Science 84: Neue HU Methane emission from rice fields: Wetland rice fields make a major contribution to global warming. BioScience 43: Wassmann R, Neue HU, Ladha JK, and Aulakh MS Mitigating greenhouse gas emissions from rice-wheat cropping systems in Asia. Environment, Development and Sustainability 6: 65-90

16 Notes

17 Subject Matter Specialists Constancio A. Asis Jr., PhD Jimmy P. Quilang, PhD Filomena S. Grospe Managing Editor/Desktop Artist Hanah Hazel Mavi M. Biag Editorial Advisers Ronilo A. Beronio Andrei B. Lanuza Charisma Love B. Gado

18 Rice Technology Bulletin Series No. 1 Released Rice Varieties ( ) 2 Pagpaparami at Pagpupuro ng Binhi sa Sariling Bukid 3 Paggawa ng Maligaya Rice Hull Stove 4 PhilRice Micromill 5 PhilRice Flourmill 6 PhilRice Drumseeder 7 PhilRice Rototiller 8 Rice Food Products 9 PhilRice-UAF Batch Dryer 10 Integrated Management of the Malayan Black Bug 11 SG800 Rice Stripper-Harvester 12 Dry-Seeded Rice-Based Cropping Technologies 13 Maligaya Rice Hull Stove Steps in Compost Production 15 Rice Tungro Virus Disease 16 The Philippine Rice Seed Industry and The National Rice Seed Production Network Hakbang sa Paggawa ng Kompost nga Addang ti Panagaramid iti Kompost 19 Characteristics of Popular Philippine Rice Varieties 20 Rice Stem Borers in the Philippines 21 Rice Food Products (revised edition) 22 Leaf Color Chart (English) 23 Leaf Color Chart (Ilocano) 24 Leaf Color Chart (Filipino) 25 Equipment for Rice Production and Processing 26 Use of 40kg Certified Seeds per Hectare 27 Rice Wine 28 Management of Field Rats 29 Controlled Irrigation: Saving water while having good yield 30 Minus-one Element Technique: Soil Nutrition Defi ciency Test Made Easy 31 Management of the Rice Black Bug 32 Management of Zinc-defi cient Soils 33 Management Options for Golden Apple Snail 34 Use of Evaporation Suppressant 35 Pagpaparami ng Purong Binhi ng Palay 36 Management of Sulfur- Defi cient Lowland Rice Soils 37 Management of Planthoppers and Leafhoppers 38 Management Options for Ricefield Weeds

19 39 Use of Indigo as Green Manure 40 Management of Salt-affected Soils for Rice Production 41 Wet-Seeded Rice Production 42 Matatag Lines 43 Hybrid Rice Seed Production 44 Metarhizium anisopliae: Microbial Control Agent for Rice Black Bug 45 Integrated Nutrient Management for Rice Production 46 Management of Armyworms/Cut worms 47 Carbonized Rice Hull 48 Rice-based Microbial Inoculant 49 Integrated Farm and Household Waste Management 50 Rice Postproduction Practices 51 Ecological Rice Farming 52 Modifi ed Dry Direct Seeding Technology 53 Palayamanan: Making the Most out of Rice Farms 54 Practical Guidelines in Predicting Soil 58 Management of Yellow and White Stemborers 59 The PhilRice Dapog Technology 60 Rice Straw-Based Nutrient Management in Irrigated Lowland Rice 61 Biofertilizer Production: Vesicular Arbuscular Mycorrhizae (VAM) 62 Trichoderma: Biofungicide for vegetables 63 Barayti ng Palay handog ng PhilRice Management of Zinc-deficient Soils (revised edition) 65 Soil Series: Improving Agricultural Productivity in Pampanga 66 Soil Series: Improving Productivity in Tarlac 67 Laboy tiller: Improving deep muddy and swampy rice lands 68 B&S Rice mini-combine harvester 69 Rice Disease Diagnostic Kit Fertility Status of Lowland Rice Soils 55 Bakanae: The Foolish Disease of Rice 56 Management of Rice Blast Disease 57 Root-knot Management in Rice-Onion Cropping System

20 Copyright 2011