Đánh giá phát thải khí nhà kính (n2o và CH4) trên hai mô hình canh tác lúa tt tiếng anh

MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY SUMMARY OF PhD THESIS Specialization: Soil science Code: 9620103 NGUYEN KIM THU EVALUATION OF GAS EMISSION (N2O AND CH4) ON TWO MODELS OF RICE CULTIVATION Can Tho, 2019 THIS STUDY WAS COMPLETED AT CAN THO UNIVERSITY Scientific supervisor: Dr Cao Van Phung Co-supervisor: Dr Tran Thi Ngoc Son The Doctoral thesis was defended at the defence committee of Can Tho University Venue: Room of docteral dissertation (Room 3), The Second Floor - Admisnistration House Time: 14:00 23th November, 2018 Reviewer 1: Assoc Prof Dr Tran Kim Tinh Reviewer 2: Assoc Prof Dr Truong Thanh Canh The thesis is available at: Learning Resource Centre, Can Tho University, Vietnam National library of Vietnam PUBLISHED PAPERS Nguyen Kim Thu, Cao Van Phung, Tran Van Dung, Vu Ngoc Minh Tam, Ho Nguyen Hoang Phuc, 2017 Effect of straw treatments on methane emission and rice yield on alluvial soil in Thoi Lai district, Can Tho city, Journal of Vietnam Agricultural Science and Technology- 6(79)/2017 Nguyễn Kim Thu, Tran Van Dung, Cao Van Phung, Ho Nguyen Hoang Phuc, Huynh Ngoc Huy, 2018 Study on methane emission on rice-based from rotation and intensive models, Journal of Vietnam Agricultural Science and Technology- 03(88)/2018 Nguyen Kim Thu, Cao Van Phung, Duong Nguyen Thanh Lich, Ho Nguyen Hoang Phuc, 2018 Effect of sowing density and transplanting distance on greenhouse gas emissions, Vietnam soil science Journal No.53/2018 i Chapter I Introduction 1.1 Necessity of the thesis Nowadays, climate change (CC) due to global warming is one of the most problems by a scientist Climate change has been seriously impacting production, life and environment all over the world The Mekong Delta (Mekong Delta) of Vietnam is considered to be the most heavily impacted of the five regions suffering the most serious consequences of climate change Greenhouse gas (GHG) is known to be the main cause of this phenomenon GHG emissions mainly through human activities, agricultural production accounts for 14% of which paddy rice accounts for a large proportion (nearly 60% of agricultural emissions) due to Methane (CH4) and Nitrogen Oxide (N2O) from field emissions increase the GHG concentration CH4 and N2O are two important gases causing global warming and emissions of these two gases from agricultural land account for about 50% and 60% of green house gas emissions (WeiWang et al., 2016) According to FAO (1981), N2O gas accounts for 6% while the amount of CH4 emissions from fields accounts for 5-20% (IPCC, 1995) One example, rice area of 232,336 of Can Tho city, accounting for 99.6% of the area of grain crops (total area of 233,385 ha) shows that the majority of people still live on agriculture associated with rice cultivation as the main The 2-3 crops per year has less balanced the nutrient source in the soil, The most farmers are to burn or dip a fresh straw into the soil to reduce investment costs and shorten the time between long-term crops These actions are affected organic soil sources, or cause organic poisoning, especially in fields where a period of off-land between two rice seasons is too short In addition to chemical-physical characterization, soil changes also lead to productivity effects High production costs due to the investment of many inorganic fertilizers, especially N fertilizer and agro-chemicals to help high yield of crops In addition, rice cultivation in frequent flooding condition is also a concern due to scarcity of freshwater resources and increasing salinity intrusion Currently, Can Tho has many rice-based cultivation models such as rotational crops with (sesame, soybean, watermelon), or rice-fish or rice-shirmp etc These models to reducing risks crop productivity of season and season which is often low, due to wet season cultivation These rice models also play a big role in improving physical and chemical properties of soil Therefore, in the context of current climate change with the above mentioned problems, the research hypotheses are set up: – How to manage water appropriately to both reduce N2O emissions effectively but rice productivity is not affected How much water is in the field is still a problem argued by many researches, lead to will reduce CH4 emissions but increase N2O emissions and vice versa – Farmers practices to burn or bury fresh rice straws such as CH4 and N2O emissions on these farming models – The model of crop rotation on rice land has little benefit but the GHGs (CH4 and N2O) emission potential compared to the rice mono model In order to cope with practical issues in rice cultivation and climate change today, the study "Evaluation of greenhouse gases emission (N2O and CH4) on two models of rice cultivation" is done to evaluate potential of GHG emissions on rice farming models Based on that study to transfer technology management for rice production in order to contribute reducing GHG emissions in agriculture producing and ensuring national food security 1.2 Research subjects and scope of the study - Determining appropriate water management measures to reduce CH4 and N2O emissions in rice producing - Evaluate the potential of CH4 and N2O emissions between the straw treatments after harvest - Determine suitable rice models to reduce CH4 and N2O emissions on the system of crops rotation and rice seasons on rice land - Determine the rice model with the potential of low greenhouse gas emissions but the rice yield is still stable on the system of crops rotation and rice seasons on rice land In order to the recommendation in rice producing to reduce greenhouse gas emissions, contributing to minimizing potentials of global warming 1.3 The scientific and practical significance of the topic 1.3.1 Scientific significance The results of the thesis need to recommend for rice producing that can ensure productivity and reduce greenhouse gas emissions not only in Can Tho City but also the environments have conditions similar The results of the project are also used to supplement materials for teaching, studying and researching in universities and research institutes based on rice models and the relationship between rice production, water and greenhouse gas emissions 1.3.2 Practical significance Contribute to the recommendation of models of safely rice cultivation with an ecological environment in Can Tho province and ecological regions with similar conditions Contribute to raise people's awareness of GHG emission, response to climate change in rice production in Can Tho province in particular and rice cultivation in general 1.4 Research scope of the topic The project focuses on research and evaluate of the potential of CH4 and N2O emissions on water management models, post-harvest straw treatment model, cultivation model on the rotation and monorice system Recommendations on rice production towards reducing greenhouse gas emissions and cope with climate change Water management models, postharvest straw models, cultivation models on mono-rice and monoculture systems This study was carried out Thoi Phong A- Thoi Lai Town and Cuu Long Delta Rice Institute (Tan Thanh Commune-Thoi Lai District - Can Tho city in the 2015 2016 dry seasons, Spring-Summer 2016, wet season- 2016 and dry season 2016 - 2017 1.5 New contributions of the thesis The results of the study have determined that the water management at level (0 - cm) not only reduce CH4 emissions (kg/ha/ day) in the range of 28.3 - 38.0% but also not increases N2O emissions in rice fields In general, the total greenhouse gas emissions (CO2 kg/ ha/year) decreased by 27.9% compared to farmers method to allow the level of water to flood regularly in the field The results of the study determined on CH4 emission on the incorporation of stubble model was 2.02 kg/ha/day, Incorporation of rice straw treated with Trichoderma was 1.99 kg/ha/day and burning rice straw was 1.90 kg/ha/day Total emissions of kg CO2e/ha/year are almost no difference between rice straw treatments in the field Research results have been determined on the models of water management and rice straw treatment, amount N2O emissions after fertilizing are 2.50 to 3.00 times higher than the daily emissions, and accounting for 36.9 - 45.1% of total N2O emissions/season The study results also showed that the total N2O emissions after fertilization through crop seasons ranged from 25.1 to 65.6% in the rotation model and 18.3 - 37.4% in the mono-rice model The global warming potential (kgCO2e/ha) are statistically significant differences between the two models through the every season The global warming potential (kgCO2e/ha/year) in the rotation model lower than mono-rice model is 20.6% Thus, with the total area of rice cultivation in the Mekong Delta of about million ha/year Assuming that, if water management measures (0-5 cm) and crops rotational are applied, about 12.03 million tons of CO2e/ha will be reduced The results are great importance to contribute to the agricultural production goals Chapter 2: Overview document According to the IPCC (2001) report, temperatures worldwide increased by more than 0.60C and it is estimated that by 2010 average temperature will increase from 1.4 to 5.80C (FAO, 2002) More than 90% of paddy land is at least occasionally flooded or flooded regularly The flooding regime leads the prerequisites for major GHG emissions especially CH4 Farming land emits about 2.8 million tons of N2O gas per year, about 42% of N2O by humans or about 16% of global N2O emissions Initial research shows that N2O emissions from rice fields are not significant (Smith et al., 1982) In 2010, the total GHG emissions of the agricultural sector were 88,354.8 thousand tons of CO2, which emissions from rice cultivation accounted for 50.5%, the digestion of food was 10.7%, from fertilizer management was 9.69%, and from agricultural products was 2.15% (Ministry of Natural Resources and Environment, 2014) Global warming potential (GWPs) is a useful measure for comparing the impact of different GHG emissions such as CH4 and N2O on CO2 equivalents The global warming potential of N2O is 298 times, while that of CH4 is 25 times that of CO2 Emissions can also be reduced by adopting a monoculture system, reducing apply pesticides and other inputs (Paustian et al., 2004), for example rotations with Legumes (Izaurralde et al., 2001; West and Post, 2002) Agricultural activities cause emissions of 6.7 million tons of N2O per year, of which emissions from an agricultural land account for 42% of this amount (Denman et al., 2007) In 2030, the amount of N2O emissions from agriculture will increase by 30-60% due to the use of N fertilizers and animal fertilizer If the demand for food increases and the culture changes, the N2O emissions will increase further If improved techniques for agricultural production management will result in lower N2O emissions into the atmosphere (Smith et al., 2007a) The potential of N2O emission on rice soil is much lower than that of CH4 (Cai et al., 1997) Use balance N fertilizer and crop rotation can lead to smaller N2O emissions Applying some legume cover crops increases the easy-to-digest nitrogen in the soil and is likely to cause N2O emissions, but in an organic system lacking inorganic fertilizer nitrogen sources is expected to reduce N2O emissions when increasing the amount Inorganic nitrogen fertilizer is applied, because the source of legumes is legume so there is less organic protein available than inorganic nitrogen (Snyder et al., 2007) Many studies showed N2O emissions which are affected by the irrigation water management (Cai et al., 1999; Zou et al., 2005) Besides, the drying of soil between crops also contributed to the increase of N2O emissions into the environment (Cai et al., 1997; Zou et al., 2007) According to research by Sander et al (2014) showed that the total amount of N2O emitted when irrigated dry was alternately lower than to dry soil Zou et al (2005) found in the field in China N2O content was limited when the field was flooded continuously (0.04 kg N2O/ha), but when the field was drained, the N2O content increased (1.7 kg N2O/ha) Water saving methods reduce the amount of CH4 gas but increase N2O emissions in the period of tillering (To Lan Phuong et al., 2012) so to harmonize these two sources of emission Therefore, to harmonize these two emission sources, it is necessary to have appropriate water management regime (Lagomarsino et al., 2016) However, the alternative wetting and drying (AWD) managermnet are recommended by IRRI (International Rice Research Institute), this method helps to save 15-20% of water without reducing productivity (Bouman et al., 2007) According to Ngo Thi Nhang (2013), when burying fresh straw and applying AWD measures, the intensity of CH4 emission is higher than the AWD model and the control over the periods and the highest is at weeks after sowing Saving irrigation reduces CH4 emissions by 52 - 61%, increasing N2O emissions by 58 - 76% Incubation of fresh straw increased the amount of CH4 gas emissions by 150% compared to not burping straw (Nguyen Quoc Khuong and Ngo Ngoc Hung, 2014) The CH4 gas emitted from rice fields is mainly affected by water and organic matter regimes, CH4 emissions are less dependent on soil type, weather, soil preparation, fertilizers use and rice varieties Inadequate water-supply rice growing environments (such as in areas where water scarcity is present) have less potential for CH4 emissions than where adequate water is supplied Flooded rice fields continuously create anaerobic conditions in the soil, these conditions increase the ability to release CH4 The flooded fields are not frequently, reducing the ability to release CH4, the rate of CH4 emissions is affected by irrigation (Wassmann et al., 2000) Chapter Methods and materials 2.1 Time and location of study - The experiments were conducted from 2015 - 2017 - Study location: Cuu Long Delta Rice Institute and Thoi Lai town, Thoi Lai District, Can Tho City 2.2 Materials and research methods * The research materials: Rice variety such as OM5451, IR50404, gas chromatography (Gas Chromatography) Model SRI 8610C * Research methods: The greenhouse gas emissions CH4 and N2O in rice cultivation with treatment on: (1) Water management measures; (2) rice straw treatment; (3) The system of crop rotation and rice crops/season The thesis has experiments as follows: Experiment 1.1: Effect of the level of water management measures on the N2O and CH4 emissions in rice cultivation The experiment was arranged in a completely randomized block with different water management treatment measures and repetitions with the following treatments: (i) Control (keep water continuously 15 cm); (ii) Keep water continuously flooding cm (5 cm); (iii) Alternative Wetting and Drying - AWD; (iv) SS: saturated soil Experiment 1.2 & 1.3: Model to verify the impact of water management on the potential of CH4 and N2O emissions in rice cultivation carried out in the wet season (WS) 2016 and dry season (DS) 2016 - 2017 The study was carried out with inheritance results from net houses, models are arranged in large areas in the field (1,500 m2 /model), samples/models, 80 N fertilizer formulas (DS); 60 N (WS) 40 P2O5 - 30 K2O kg/ha with water control managements: Model control after sowing days, putting water in the field and keeping flooding higher than cm, draw water before harvesting 10 days; The model manages shallow submerged water (0 - cm) after sowing for days, allowing water to flow from - cm depending on the growth stage of rice in the field and adjusting the water to the field Managing water level by placing PVC pipe, when water is cm, cross section of plastic pipe and equal to field surface, water will be put into field up to cm then stop and continue to monitor water level until about cm Experiment 1.4: Effect of organic fertilizer and straw treatment measures on N2O and CH4 emissions in rice cultivation (Result of CLUES project) The experiment was arranged in a completely randomized block, with treatments and replications, fertilizer formula 80N - 40P2O5 - 30K2O kg/ha T1: incorporation of stubble; T2: Organic fertilizer supplement (2.00 t/ha); T3: incorporation of rice straw treated (5.20 t/ha) with Trichoderma; T4: Burning rice straw For T3, spray Trichcoderma (4 kg inoculant/ha doses) directly onto rice straw, and then plow it into the soil Experiment 1.5 & 1.6: This model to verify the effect of straw management measures on N2O and CH4 in rice cultivation during in the WS 2016 and DS 2016-2017 The study was carried out to inherit experimental results 1.4, large area in the field (1,500 m2/ model) was conducted, collecting samples/model, 80 N fertilizer formula (DS); 60 N (WS) - 40 P2O5 - 30 K2O kg/ha with models: (1) incorporation of stubble; (2) incorporation of rice straw treated with Trichoderma and (3) burning rice straw The protocol was conducted similarity of experiment 1.4 Experiments 1.7, 1.8 and 1.9: Evaluate the potential of N2O and CH4 gas emissions on the crop rotation system and the mono-rice cultivation system Models are monitored in fields planted with sesame on the rice field through planting seasons: spring summer (SS) 2016 sesame - WS 2016 rice - DS 2016 - 2017 rice and mono-rice of crops: SS 2016 WS 2016 - DS 2016 - 2017 For rotationa crop model: After the DS rice harvest in 2015–2016 The SS sesame season is carried out SS: 120 N – 80 P2O5 – 30 K2O, WS rice crop: 90 N – 50 P2O5 – 25 K2O and DS rice crop: 120 N – 60 P2O5 – 40 K2O kg/ha fomular For mono-rice model, SS: 90 N – 60 P2O5 – 60 K2O, WS: 100 N – 60 P2O5 – 30 K2O and 120 N – 60 P2O5 – 60 K2O kg/ha fomular Rice is sowing by hand with a density is 192 kg/ha (SS and WS) and 231 kg/ in DS on both models The density for sesame is 75 kg/ha 2.3 Sample collection, measurement and analysis N2O and CH4 gas were collected time/week after sowing and finish the sampling process until week before harvesting Particularly, N2O gas in addition to the above sampling periods will be collected at different times after fertilizing 1, 2, 3, 4, days to calculate the amount of N2O emitted after fertilizing, the gas sample is collected at the time 8-11 am, using closed chamber and measuring CH4 gas by gas chromatography (Model GC- SRI 8610C); OC (%) is determined by Walkley - Black method; pHH2O determined by pH meter Total nitrogen in the soil is determined by the Kjeldahl method; components of 2frame capacity of 0.25 m2 cross-sectioned, rice yield samples collect 0.5 m2frame/site of gas sample 2.4 Data processing method Use Microsoft Excel software and STAR statistics program (Statistical Tool for Agricultural Research, IRRI) to analysis of soil analysis, rice yield and rate of N2O and CH4 emissions on differed at 5% significance level Comparing the potential of greenhouse gas emissions to convert equivalent CO2e in the scope of research models Global warming potential (GWPs) is calculated as CO2e converted from N2O (kg/crop/ha) and CH4 (kg/crop/ha) as follows formula: GWPs (kg CO2e/ha) = (CH4 x 25) + (N2O x 298) (IPCC, 2007) Chapter The results and discussion 4.1 Affect of water mangament CH4 and N2O emissions 4.1.1 Effect of water management on CH4 and N2O emission in rice cultivation in greenhouse conditions CH4 emission showed significantly greater in the treatment of continuously flooded water level at 15 cm (98.8 kg/ha) compare to others with flooding level of cm (80.2 kg/ha) and soil saturated (71.6 kg/ha) and lowest in AWD treatment (66.2 kg/ha) Flooded condition is known to increase methane emission throught anaerobic condition which results in high CH4 gas emissions This study shows CH4 emission increase 27.5 - 33.0% in the treatment with water level of 15 cm (that mean 98.8 kg/ha compare to 71.6 kg/ha and 66.2 kg/ha) while keeping the water level at cm only increased by 10.7 - 17.5%, respectively 80.2 kg/ha compared to 71.6 kg/ha and 66.2 kg/ha, compared to saturated soil and AWD treatments (Table 4.1) N2O emission in AWD treatment showed the highest value and statistically significant differences compared to treatments with flooding level at 15 cm, cm and saturated soil at 2.78 kg/ha vs 2.06 kg/ha; 1.72 kg/ha and 1,68 kg/ha, respectively The results of this study show that AWD has increased N2O emissions significantly from 38.1 – 39.6% compared to continuous flooding of - 15 cm and 25.9% increase compared to saturated soil condition (Table 4.1) GWP (kgCO2e/ha) showed lowest value (2,404 kg/ha) in saturated soil, AWD (2,483 kg/ha) and continuous flooding of cm water level (2,519 kg/ha) treatments which showed statistically significant diferent with condition of 15 cm flooded (2,970 kg/ha) (Table 4.1) Thus, the CH4 emission is not significantly different among treatments without control But on the other hand, AWD treatment has increase N2O emission statistically significant compared to cm and saturated soil treatments Table 4.1 Effect of water management on CH4 and N2O emissions in rice cultivation (Net house conditions) Unit: kg/ha Treat Control cm AWD SS F CV (%) CH4 N2O CO2e 98.8 a 80.2 b 66.2 b 71.6 b ** 12.3 1.68 c 1.72 c 2.78 a 2.06 b *** 5.79 2.970 a 2.519 b 2.483 b 2.404 b * 9.93 Compare to control (%) CH4 CO2e N2O compare to AWD (%) -39.6 -18.8 -33.0 -27.5 -15.2 -16.4 -19.1 -38.1 -25.9 Note: Different letters indicate significant treatment differences *: significant at p < 0.05; **: significant at p < 0.01; ***: significant at p < 0.001; AF: after fertilization; WM: water management Control: keep water continuously 15 cm; cm: keep water continuously flooding cm; AWD: Alternative wetting and drying; SS: saturated soil; Sign (-): reduce 4.1.2 Verification model of the impact of water management on the potential of CH4 and N2O emissions in rice cultivation * The amount N2O gas emits after days the fertilization, CH4 and N2O emissions after each crop: In the WS 2016: The amount daily N2O gas emits after days fertilizer application on two water management models was about 0.09 kg/ha/day, seasonal N2O emission was 0.03 kg/ha/day Thus, the amount daily N2O gas emits after days fertilizer application were times higher than the seasonal N2O emission CH4 emission in the control (without water management) control was 2.21 kg/ha/day and showed 38.0% lower which was significant difference compared to water management model (1.37 kg/ha/day) (Figure 4.1) 10 In the DS 2016 - 2017: For the amount N2O gas emits after days fertilizer application has decreased slightly and N2O emission of the whole crop little change compared to the WS 2016, 0.08 kg/ha/day and 0.03 kg/ha/day, respectively CH4 emission in the control model was 1.91 kg/ha/day and higher than the water management model 28.3% (1.37 kg/ha/day) (Figure 4.1) Thus, water management did not show effect on N2O emissions but CH4 emissions Specifically, the water management model at 0-5 cm has lower CH4 emissions 28.3 - 38.0% than the control model Control WM Control WM DS 2016-2017 kg/ha/day WS 2016 N2O-AF N2O-crop CH4-crop N2O-AF N2O-crop CH4-crop Figure 4.1 Effect of water management on amount N2O gas emits after days fertilization, CH4 and N2O emssisons in DS 2016 and WS 2016 – 2017 Note: WM: water management; AF: after fertilization * Total N2O emission after fertilizer application, CH4 and N2O emissions after each crop: Total N2O emissions after fertilizer application in WS 2016 and DS 2016 - 2017 ranged from 1.28 to 1.29 and 1.18 to 1.21 kg/ha, respectively Total N2O emissions of season ranged from 3.03 - 3.08 kg/ha and 2.85 - 2.87 kg/ha, respectively Total N2O emissions after fertilizer application showed fairly stable which accounts for 41.2 42.4% of the total N2O emission (Table 4.2) Total emission of CH4, N2O and GWP were highly in the control model between the two crop of WS 2016 and DS 2016 - 2017 (with 695 kg CO2e/ha different), while that value was 332 kg CO2e/ha in the water management model which is times lower The GWP in control model in both crops was higher and significantly different with water 11 management model Specifically, in WS, total emissions on the two models were respectively 5,869 vs 3,987 kg CO2e/ha; DS 2016-2017 is 5,174 vs 3,970 kg CO2e/ha (Table 4.2) Through crop studies on water management, the water management with 0-5 cm water flooded showed lower emission but still maintain rice productivity stable compared to condition with high water level continuously in the field Table 4.2 Effect of water management on total N2O emissions after fertilization, CH4 and N2O emssison in WS 2016 and DS 2016 - 2017 Unit: kg/ha Models Total N2O emission AF Control WM F CV (%) 1.29 1.28 ns Control WM F CV (%) 1.18 1.21 ns 10.1 8.87 N2O emission rate AF/crop (%) WS 2016 42.4 41.6 DS 2016 – 2017 41.2 42.0 - CH4 N2O CO2e 199 a 123 b *** 14.7 3.03 3.08 ns 4.46 5.869 a 3.987 b *** 12.3 174 a 125 b *** 10.2 2.87 2.85 ns 5.174 a 3.970 b *** 8.14 10.4 Note: Different letters indicate significant treatment differences ***: significant at p < 0.001; ns: non-significant.; AF: after fertilization; WM: water management * The total CH4, N2O emissions and convert to GWP (kgCO2e/ha/year) Total emissions of CH4, N2O and GWP was significantly different between two water management models, the total emission in the control model was 11,043 kgCO2e/ha/year and 7,957 kgCO2e /ha/year in the water management model - cm Greenhouse gas emission rates in the two crops ranged from 46.9 -53.1% compared to GWP (Table 4.3) In summary, the water management model of 0-5 cm water flooded in crops has significantly reduced the CH4 emissions but not 12 increased the N2O emissions compared to the conventional practices as stated by previous studies The water management model with 0-5 cm water flooded showed lower CH4 emission about 28.3 - 38.0% and GWP (kgCO2e/ha/year) decreases by 27.9% in conventional water management model (Table 4.3) Table 4.3 Effect of water managements on total CH4 and N2O emissions convert to GWP (kgCO2e/ha/year) in WS 2016 and DS 2016 - 2017 Model Control WM F CV (%) Total emission (kgCO2e/ha/year) 11,043 a 7,957 b *** 5.26 Emission rate crop/ha/year (%) WS 2016 53.1 50.1 - Compare to DS 2016-2017 control (%) 46.9 27.9 49.9 - Note: Different letters indicate significant model differences ***: significant at p < 0.001, WM: water management 4.2 Potential of CH4 and N2O emissions on rice straw managements 4.2.1 Effect of organic fertilizer and straw managements on CH4 and N2O emissions in rice cultivation CH4 emissions in all treatments ranged from 127 - 160 kg/ha The incubation of stubble treatment showed CH4 emissions increased 20.6% compared to burning rice straw, it’s 160 kg/ha vs 127 kg/ha (Table 4.4) Table 4.4 Effect of organic fertilizer and straw managements on total CH4 and N2O emissions Unit: kg/ha Treaments Incorporation of stubble Organic fertilizer Incorporation of rice straw treated with Tricho Burning rice straw F CV (%) CH4 160 159 138 127 ns 10,2 N2O 2,45 2,54 2,55 2,60 ns 9,46 CO2e 4.743 4.732 4.202 3.950 ns 7,42 Note: Different letters indicate significant treatment differences ***: significant at p < 0.001; ns: non-significant.; AF: after fertilization; WM: water management 13 Total GHGs emissions of incorporation of stubble was 4,743 kgCO2e/ha, organic fertilizer supplement was 4,732 kgCO2e/ha, incorporation of rice straw treated Trichoderma was 4,202 kgCO2e/ha and 3,950 kgCO2e/ha on burning rice straw treatment (Table 4.4) 4.2.2 Verification model of the effect of straw management on the potential of CH4 and N2O emissions in rice cultivation * The amount N2O gas emits after days fertilization, CH4 and N2O emissions after each crop: In the WS 2016: The amount daily N2O gas emits after fertilization on rice straw management models ranged from 0.08 to 0.10 kg/ha/day, while the seasonal emission was 0.03 – 0.04 kg/ha/day Therefore, the amount daily N2O emissions after fertilizer application were 2.50 - 2.57 times higher than the seasonal emission The highest CH4 emission on the incoperation of stubble and incorporation of rice straw treated with Trichoderma were 2.11 and 2.0 kg/ha/day, respecitively compared to burning rice straw with 1.72 kg/ha/day (Figure 4.2) In the DS 2016-2017, the amount N2O gas emits after fertilize application on straw management ranged from 0.07 to 0.08 kg/ha/day, higher than of total emissions 0.03 kg ha/day, ie 2.33 - 2.67 times Amount CH4 gas emits from incoperation of stubble was 2.02 kg/ha/day, treated with Trichoderma was 1.99 kg/ha/day and burning rice straw was 1.90 kg/ha/day (Figure 4.2) kg/ha/day IS IRST BRS IS IRST BRS WS 2016 N2O-AF N2O-crop DS 2016 - 2017 CH4-crop N2O-AF N2O-crop CH4-crop Figure 4.2 Effect of rice straw managements on amount N2O gas emits after days fertilization, CH4 and N2O emssisons in DS 2016 and WS 2016 – 2017 Note: IS: incoperation of stubble; IRST: incorporation of rice straw treated with 14 Trichoderma; BRS: Burning rice straw; AF: after fertilization * Total N2O emission after fertilizer application, CH4 and N2O emissions after each crop: The total N2O emission after fertilization about 1,02 – 1,41 kg/ha of models and ratio on the total N2O missions ranges from 41.4% 45.1% in WS 2016; from 36.9 - 41.3% in DS 2016-2017 The highest total of CH4 emissions in the incoperation of stubble in two seasons was 5,671 kg/ha and 5,345 kg/ha while the lowest in the burning rice straw with 4,807 kg/ha and 5,108 kg/ha (Table 4.5) Bảng 4.5 Effect of rice straw managements on total N2O emissions after fertilization, CH4 and N2O emssison in WS 2016 and DS 2016 - 2017 Unit: kg/ha Model IS IRST BRS F CV (%) Total N2O emissions AF Ratio N2O emissions AF/crop (%) WS 2016 1,34 1,25 1,41 ns 15,2 CH4 N2O CO2e 43,3 41,4 45,1 190 a 180 a 155 b * 8,85 3,09 3,02 3,13 ns 4,44 5.671 a 5.400 ab 4.807 b * 7,46 41,3 36,9 37,3 - 182 179 171 ns 11,6 2,68 2,75 2,77 ns 4,69 5.345 5.304 5.108 ns 9,16 DS 2016 - 2017 IS IRST BRS F CV (%) 1,11 1,02 1,03 ns 10,1 Note: Different letters indicate significant treatment differences *: significant at p < 0.05; ns: non-significant; IS: incoperation of stubble; IRST: incorporation of rice straw treated with Trichoderma; BRS: Burning rice straw * The total CH4, N2O emissions and convert to GWP (kgCO2e/ha/year) Although there are significant differences in total emissions converted to CO2e kg/ha in WS 2016 The calculation of CH4 and N2O 15 emissions is converted into CO2e kg/ha/year, there is no difference between straw managements Total emissions corresponding to fresh rice straw (vùi rạ tươi, Trichoderma treatment and burning rice strawmodels were 11,016 CO2 kg/ha/year; 10.708 kgCO2/ha/year and 9.915 kgCO2/ha/year, respectively Greenhouse gas emission rates in the two seasons ranged from 48.5 - 51.5% compared with the total converted CO2e kg/ha/year (Table 4.6) Table 4.6 Effect of rice straw managements on total CH4 and N2O emissions convert to GWP (kgCO2e/ha/year) in WS 2016 and DS 2016 - 2017 Models IS IRST BRS F CV (%) Total emission (kgCO2e/ha/year) Emission rate crop/ha/year (%) Wet season 2016 51.5 50.5 48.5 - 11,016 10,708 9,915 ns 6,08 Dry 2016-2017 48.5 49.5 51.5 - Note: Different letters indicate significant model differences ns: non-significant; IS: incoperation of stubble; IRST: incorporation of rice straw treated with Trichoderma; BRS: Burning rice straw 4.3 Evaluation of the potential of CH4 and N2O emissions on the rotation and mono-rice cultivation systems * The amount N2O gas emits after fertilization, CH4 and N2O emissions after each crop: The amount N2O gas emits after fertilizing in the SA 2016 on the sesame crop is 0.11 kg/ha/day (2.75 times higher) on the rice of 0.04 kg/ha/day The amount N2O emissions of the whole crop are 0.09 kg/ha/day The amount CH4 emissions on high mono-rice model are significantly different from the rotation model in all crops (Figure 4.3) 16 kg/ha/day Rotation Mono-rice Rotation Mono-rice Rotation Mono-rice SS 2016 WS 2016 DS 2016-2017 O-crop CH4-crop O-AF N CH44-vụ -crop 2O-AF N NN N22O-crop O-vụ CH CH44-crop -vụ N N22O-AF O-SBPN2N NN22O-SBP N22O-crop O-vụ CH 2O-SBP 2O-vụ CH 4-vụ Figure 4.3 Effect of rotation and mono-rice models on amount N2O gas emits after fertilization, CH4 and N2O emission in WS 2016 and DS 2016-2017 Note: AF: after fertilization * Total N2O emission after fertilizer application, CH4 and N2O emissions after each crop: The total N2O emission is highest in the SA 2016 on the rotation model, which the nitrogen vapor is very large At the time of increasing the potential of N2O emissions is very high, accounting for 65.6% of the total N2O/season emissions On mono-rice model, the emissions potential after the fertilizer application on the total N2O emissions are highest in the DS 2016-2017 and WS 2106, while the lowest in the SA 2016 (accounting of 37.4%; 25.7 % and 18.3%) On the contract, the total N2O emissions are on the highest on SA (7.19 kg/ha) (Table 4.7) The total N2O emissions were 7.19 kg/ha the highest in the SS 2016 on mono-rice model Total CH4 emissions in the SS 2016 was 47.2 kg/ha lower than WS 2106 was 116 kg/ha and DS 2016 - 2017 was 158 kg/ha on monorice model (Table 4.7) Total emission of CH4 and N2O gas when converted into total CO2e in 3-crop mono-rice model is significantly higher than the model of sesame crop rotation in the whole experimental cycle, respectively 3.325 - 4.873 kg CO2e/ha compared to 2,339 - 4,283 kg CO2e/ha (Table 4.7) 17 Table 4.7 Effects of rotation and mono-rice models on total N2O and CH4 emissions after fertilizcation Unit: kg/ha Models Total N2O emission AF Rotation Mono-rice F CV (%) 3.85 a 1.32 b *** 4,69 Rotation Mono-rice F CV (%) 1.01 b 1.13 a * 9.36 Rotation Mono-rice F CV (%) 1.02 b 1.17 a * 11,9 N2O emission rate AF/crop (%) SA 2016 65,6 18,3 WS 2016 25,1 25,7 DS 2016 -2017 41,0 37,4 - CH4 N2O CO2e 23,7 b 5.87 b 47,3 a 7.19 a *** *** 7,59 4,54 2.339 b 3.325 a *** 3,30 81,0 b 116 a *** 10,9 4.03 4.37 ns 11.6 3.227 b 4.212 a *** 7.97 142 b 2.49 b 158 a 3.13 a *** *** 5,72 4.283 b 4.873 a *** 4,79 Note: Different letters indicate significant treatment differences *: significant at p < 0.05; ***: significant at p < 0.001; ns: non-significant 4.3.2 Effect of rotation and mono-rice on the total CH4, N2O emissions and convert to GWP (kgCO2e/ha/year) Total emission of CH4 and N2O gas is converted into CO2e kg/ha/year on the rice monoculture model (3 rice crops per year) is 20.6% higher than the rotation model The gas emission rate is converted into CO2e kg/ha/year from 23.7- 43.5% on the rotation model and 26.8 - 39.3% 18 Table 4.8 Effects of rotation and mono-rice models on total CH4 and N2O emissions convert to GWP (kgCO2e/ha/year) in SA 2016, WS 2016 and DS 2016 - 2017 Models Rotation Mono-rice F CV (%) Total emission (kgCO2e /ha/year) 9.849 b 12.410 a *** 3,26 Emission rate crop/ha/year (%) SA 2016 23.7 26,8 - WS 2016 32,8 33,9 - DS 20162017 43,5 39,3 - Compare to control (%) 20,6 - Note: Different letters indicate significant treatment differences ***: significant at p < 0.001, ns: non-significant Chapter Conclutions and recommendations 5.1 Conclutions Water management models were daily N2O emissions after fertilizing are 2.67 - 3.00 times higher than daily N2O emissions The water management Total N2O emissions after fertilization ranged from 1.18 to 1.29 kg/ha and accounted for 41.2 to 42.4% of the total N2O gas emit of the whole crop The water management model (level of water 05 cm) decreased 32.1% total emission converted CO2e kg/ha by in WS 2016 and 25.7% in DS 2016-2017 The CH4 emissions (kg/ha/day) is 28.3 - 38.0% lower and the total emission of CO2e kg/ha/year is reduced by 27.9% compared to the farmer management model Rice straw management models were amount N2O emissions after days fertilization were 2.50 to 2.57 times higher and accounted for 36.9 - 45.1% the total N2O emissions per crop Through seasons total greenhouse gas (kgCO2e/ha) and total gas emissions converted from kg CO2e/ha/year are not different between rice straw management models The total N2O emissions after fertilization through crop seasons ranged from 25.1 to 65.6% in the rotation model and 18.3 - 37.4% in the mono-rice model Total gas emissions converted kgCO2e/ha are statistically significant differences between the two models through the 19 seasons and the total gas emissions kgCO2e/ha/year in the rotation model is 20.6% lower than mono-rice model Thus, the results adapted to the research objectives: Determining appropriate water management measures of shallow flood from - cm to significantly reduce CH4, N2O, and greenhouse gas emissions in rice cultivation; evaluated the potential of CH4 and N2O emissions between the straw treatments after harvest; sesame rotation model on rice land with the potential of lowest greenhouse gas emissions but the rice yield is still stable 5.2 Recommendations Water management model (0-5 cm) in the rice paddy field needs to be transferred into large scale rice production in order to reduce greenhouse gas emissions in rice cultivation The long-term study of spray Trichoderma to rice straw model needs to be examed to assess the potential of greenhouse gas emissions in rice fields This is a model to help improve organic and nutrient content in the soil Multiplication of the model rice- legumes rotation suitable for every local to contribute to improving the economy, safe environment and reducing greenhouse gas emissions under the current climate change conditions 20 ... 23th November, 2018 Reviewer 1: Assoc Prof Dr Tran Kim Tinh Reviewer 2: Assoc Prof Dr Truong Thanh Canh The thesis is available at: Learning Resource Centre, Can Tho University, Vietnam National... accounts for a large proportion (nearly 60% of agricultural emissions) due to Methane (CH4) and Nitrogen Oxide (N2O) from field emissions increase the GHG concentration CH4 and N2O are two important... rice cultivation and climate change today, the study "Evaluation of greenhouse gases emission (N2O and CH4) on two models of rice cultivation" is done to evaluate potential of GHG emissions on rice