Multiple Aeration Research Articles

Site-specific feasibility of alternate wetting and drying as a greenhouse gas mitigation option in irrigated rice fields in Southeast Asia: a synthesis

ABSTRACTThis study comprises a comprehensive assessment, integration, and synthesis of data gathered from a 3-year field experiment conducted at four sites in Southeast Asia, namely Hue, Vietnam; Jakenan, Indonesia; Prachin Buri, Thailand; and Muñoz, Philippines, to assess the site-specific feasibility of alternate wetting and drying (AWD) as a greenhouse gas (GHG) mitigation option in irrigated rice fields. AWD effectively reduced water use compared to continuous flooding (CF) but did not significantly reduce rice grain yield and soil carbon content in all sites. Methane (CH4) emissions varied significantly among sites and seasons as affected by soil properties and water management. AWD reduced CH4 emissions relative to CF by 151 (25%), 166 (37%), 9 (31%), and 22 (32%) kg CH4 ha−1 season−1 in Hue, Jakenan, Prachin Buri, and Muñoz, respectively. In Prachin Buri and Muñoz, AWD reduced CH4 emissions only during the dry season. Site-specific CH4 emission factors (EFs) ranged 0.13–4.50 and 0.08–4.88 kg CH4 ha−1 d−1 under CF and AWD, respectively. The mean AWD scaling factors (SFs) was 0.69 (95% confidence interval: 0.61–0.77), which is slightly higher than the Intergovernmental Panel on Climate Change (IPCC)’ SF for multiple aeration of 0.52 (error range: 0.41–0.66). Significant reductions in the global warming potential (GWP) of CH4+nitrous oxide (N2O) by AWD were observed in Hue and Jakenan (27.8 and 36.1%, respectively), where the contributions of N2O to the total GWP were only 0.8 and 3.5%, respectively. In Muñoz, however, CH4 emission reduction through AWD was offset by the increase in N2O emissions. The results indicate that the IPCC’s SF for multiple aeration may only be applied to irrigated rice fields where surface water level is controllable for a substantial period. This study underscores the importance of practical feasibility and appropriate timing of water management in successful GHG reductions by AWD.

Prediction of future methane emission from irrigated rice paddies in central Thailand under different water management practices

There is concern about positive feedbacks between climate change and methane (CH4) emission from rice paddies. However, appropriate water management may mitigate the problem. We tested this hypothesis at six field sites in central Thailand, where the irrigated area is rapidly increasing. We used DNDC-Rice, a process-based biogeochemistry model adjusted based on rice growth data at each site to simulate CH4 emission from a rice-rice double cropping system from 2001 to 2060. Future climate change scenarios consisting of four representative concentration pathways (RCPs) and seven global climate models were generated by statistical downscaling. We then simulated CH4 emission in three water management practices: continuous flooding (CF), single aeration (SA), and multiple aeration (MA). The adjusted model reproduced the observed rice yield and CH4 emission well at each site. The simulated CH4 emissions in CF from 2051 to 2060 were 5.3 to 7.8%, 9.6 to 16.0%, 7.3 to 18.0%, and 13.6 to 19.0% higher than those from 2001 to 2010 in RCPs 2.6, 4.5, 6.0, and 8.5, respectively, at the six sites. Regionally, SA and MA mitigated CH4 emission by 21.9 to 22.9% and 53.5 to 55.2%, respectively, relative to CF among the four RCPs. These mitigation potentials by SA and MA were comparable to those from 2001 to 2010. Our results indicate that climate change in the next several decades will not attenuate the quantitative effect of water management practices on mitigating CH4 emission from irrigated rice paddies in central Thailand.

Analysis of Agricultural Commodities Value Chains and Greenhouse Gas Emission in Rice and Maize in West Africa: Impact on Food Security

This paper analyses the greenhouse gas (GHG) emission along the value chains of two strategic commodities in West Africa (rice and maize) in four pilot countries: Ghana, Senegal Benin and Cote D’Ivoire. The Value Chains Analysis and Greenhouse model used in this study, provides insight into the relationship between output maximization and GHG emissions to help define optimal intervention approaches that minimize emissions while maximizing the potential yield, hence boost food security. It highlights intervention measures for improvement of production and productivity along with the identification of mitigation measures to reduce GHG emissions. It also revealed that the largest GHG emission factor from maize farming in the selected countries is from the application of nitrogen fertilizers (NO2), and for rice farming, depending on the systems, e.g. rain fed, irrigated or multiple aeration, the emission is mostly due to anaerobic decomposition of methane (CH4) which increases with flooding practice.

Estimation of methane and nitrous oxide emissions from paddy fields in Taiwan

To investigate the greenhouse gases emissions from paddy fields, methane and nitrous oxide emissions were estimated with the local measurement and the IPCC method during 1990–2006 in Taiwan. Annual methane emission ranged from 9001 to 14,980 ton in the first crop season for 135,314–242,298 ha of paddy fields, and it was between 16,412 and 35,208 ton for 101,710–211,968 ha in the second crop season with the local measurement for intermittent irrigation. The value ranged from 31,122 to 55,729 ton of methane emission in the first crop season, and it was between 29,493 and 61,471 ton in the second crop season with the IPCC guideline for continuous flooding. Annual nitrous oxide emission from paddy fields was between 371 and 728 ton in the first crop season, and the value ranged from 163 to 365 ton in the second crop season with the local measurement. Methane emission from paddy fields in Taiwan for intermittent irrigation was only 26.72–28.92%, 55.65–57.32% and 41.19–43.10% with the IPCC guidelines for continuous flooding and mean temperature of transplanting stage in the first crop, the second crop and total paddy fields, respectively. The values were 53.44–57.84%, 111.29–114.55% and 82.38–86.20% with the IPCC guidelines for single aeration and mean temperature of transplanting stage, respectively; and the values were 133.60–144.61%, 282.56–286.62% and 205.96–215.49% with the IPCC guidelines for multiple aeration and mean temperature of transplanting stage, respectively. Intermittent irrigation in paddy fields reduces methane emission significantly; appropriate application of nitrogen fertilizer and irrigation in paddy fields also decreases nitrous oxide emission.

Development of methane emission factors for Indian paddy fields and estimation of national methane budget

A state-wise assessment of methane (CH 4) budget for Indian paddies, based on a decadal measurement data across India is presented for the calendar year (CY) 1994, the base year for India’s Initial National Communication (NATCOM) to the United Nations Framework Convention on Climate Change (UNFCCC), along with national trend from CY 1979 to 2006. The NATCOM CH 4 emission factors (EFs) for Indian paddy cultivation areas, generally having less than 0.7% of soil organic carbon (SOC), have been estimated as 17.48 ± 4 g m −2 for irrigated continuously flooded (IR-CF), 6.95 ± 1.86 g m −2 for rain-fed drought prone (RF-DP), 19 ± 6 g m −2 for rain-fed flood prone (RF-FP) and deep-water (DW), 6.62 ± 1.89 g m −2 for irrigated intermittently flooded single aeration (IR-IF-SA) and 2.01 ± 1.49 g m −2 for IR-IF multiple aeration (MA) paddy water regimes. The state-wise study for 1994 has indicated national CH 4 budget estimate of 4.09 ± 1.19 Tg y −1 and the trend from 1979 to 2006 was in the range of 3.62 ± 1 to 4.09 ± 1.19 Tg y −1. Four higher emitting or “hot spot” states (West Bengal, Bihar, Madhya Pradesh and Uttar Pradesh) have accounted for 53.9% of total CH 4 emission with RF-FP paddy water regime as the major contributor. CH 4 emissions were enhanced by factors such as SOC (∼1.5 times due to increase in SOC by ∼1.8 times), paddy cultivars (∼1.5 times), age of seedlings (∼1.4 times), and seasons (∼1.8 times in Kharif or monsoon than in Rabi or winter season).

Simulation of oxygen regime of tree substrates

The oxygen regime of urban tree-growing sites may be sub-optimal for tree growth and the related ornamental value of trees. Problems may especially occur in situations where the substrate is covered by pavement and/or where the water table is very shallow. The stability (oxygen consumption rate) of the organic components of the substrate (peat, green waste compost, etc.) and the design of the growing site also play an important role. The oxygen regime of a number of designs (wide strip of substrate; narrow strip; wide strip with multiple aeration pipes; narrow strip with one aeration pipe) was simulated for a range of substrates with the computer program “Matlab, pde toolbox”. The program computed equilibrium distributions of oxygen in the substrates from gas diffusion coefficients of the different parts of the growing site constructions and from the specific oxygen consumption rate of the substrate. The simulation results were compared with measurements on an experimental substrate strip. The simulation results clearly showed the importance of organic matter stability and growing site design. On wide strips the presence of aeration pipes may be very advantageous, or even necessary.

Estimation of methane and nitrous oxide emission from paddy fields and uplands during 1990–2000 in Taiwan

To investigate the greenhouse gases emissions from paddy fields and uplands, methane and nitrous oxide emissions were estimated from local measurement and the IPCC guidelines during 1990–2000 in Taiwan. Annual methane emission from 182 807 to 242 298 ha of paddy field in the first crop season ranged from 8062 to 12 066 ton, and it was between 16 261 and 25 007 ton for 144 178–211 968 ha in the second crop season with local measurement. The value ranged from 12 132 to 17 465 ton, and from 16 046 to 24 762 ton of methane in the first and second crop season with the IPCC guidelines for multiple aeration treatments, respectively. Annual nitrous oxide emission was between 472 and 670 ton and between 236 and 359 ton in the first and second crop season, respectively. Methane and nitrous oxide emissions from uplands depend on crop, growth season, fertilizer application and environmental conditions. Annual methane emission from upland crops, vegetable, fruit, ornamental plants, forage crops and green manure crops was 138–252, 412–460, 97–100, 3–5, 4–5 and 3–51 ton, respectively. Annual nitrous oxide emission was 1080–1976, 1784–1994, 2540–2622, 31–54, 43–53 and 38–582 ton, respectively. Annual nitrous oxide emission ranged from 91 to 132 ton for 77 593–112 095 ton of nitrogen-fixing crops, from 991 to 1859 ton for 3 259 731–6 183 441 ton of non-nitrogen-fixing crops, and from 1.77 to 2.22 Gg for 921 169–1 172 594 ton of chemical fertilizer application. In addition, rice hull burning emitted 19.3–24.2 ton of methane and 17.2–21.5 ton of nitrous oxide, and corn stalk burning emitted 2.1–4.2 ton of methane and 1.9–3.8 ton of nitrous oxide. Methane emission from the agriculture sector was 26 421–37 914 ton, and nitrous oxide emission was 9810–11 649 ton during 1990–2000 in Taiwan. Intermittent irrigation in paddy fields reduces significantly methane emission; appropriate application of nitrogen fertilization and irrigation in uplands and paddy fields also decreases nitrous oxide emission.

Scientific basis for establishing country greenhouse gas estimates for rice-based agriculture: An Indian case study

A comprehensive scientific assessment of CH4 budget estimation for Indian rice paddies, based on a decade of measurements in India, is presented. Indian paddy cultivation areas contain soils that have low to medium levels of soil organic carbon. The average seasonally integrated CH4 flux (Esif) values calculated from these measurements were 15.3 ± 2.6 g m−2 for continuously flooded (CF), 6.9 ± 4.3 g m−2 for intermittently flooded (IF) single aeration (SA) and 2.2 ± 1.5 g m−2 for IF multiple aeration (MA) rice ecosystems. For CF and IF (MA) rice ecosystems having high soil organic carbon, without organic amendments, the CH4 flux (Esif) may be increased by 1.7 times relative to low soil organic carbon, whereas it may enhance by 5.3 for CF if amended organically. Organic amendment and high soil organic carbon paddy areas do not alter the methane budget estimates for India (3.6±1.4 TgY−1) much, due to their small paddy harvested area. Methane estimated using average emission factors (Esif) for all paddy water regimes, which include harvested areas having soils with high organic carbon and organic amendments, may give a budget of 5 TgY−1 for India.

Refinement in methodologies for methane budget estimation from rice paddies

To reduce the involved uncertainties in the methane budget estimation from rice paddy fields, the methodologies of methane budget estimation have been revised mainly on the basis of measurements undertaken in the Methane Asia Campaign (MAC-98). Studies from other continuous measurements of methane emission from rice paddy fields over last few years in other Asian countries were also used. The Asian Development Bank (ADB) sponsored Methane Asia Campaign (MAC-98) in which India, China, Indonesia, Philippines, Vietnam and Thailand participated during 1998–99.The resulting CH4 measurements have shown that apart from water management, soil organic carbon also plays a significant role in determination of methane emission factors from rice paddy fields. The available data from participating countries reveal that paddy soils can be broadly classified into low soil organic carbon ( 0.7% C) classes which show average methane emission factors of 12 (5–29) and 36 (22–57) g m−2 respectively for continuously flooded (CF) fields without organic amendments compared to the IPCC–96 emission factor of 20 g m−2. Similarly for irrigated paddy fields with intermittently flooded multiple aeration (IF-MA) without organic amendments, the MAC-98 gives average emission factors of 2 (0.06–3) and 6 (0.6–24) g m−2, respectively, for low and high organic carbon soils compared to IPCC–96 emission factor of 4 (0–10) g m−2. Incorporation of soil organic carbon along with classification based on water management and organic amendments in the estimation of CH4 emissions from rice paddy fields yields more characteristic emission factors for low and high organic carbon soils and is, therefore, capable of reducing uncertainties.

Functional and structural response of a cellulose-degrading methanogenic microbial community to multiple aeration stress at two different temperatures.

Two cellulose-fermenting methanogenic enrichment cultures originating from rice soil, one at 15 degrees C with Methanosaeta and the other at 30 degrees C with Methanosarcina as the dominant acetoclastic methanogen, both degraded cellulose anaerobically via propionate, acetate and H2 to CH4. The degradation was a two-stage process, with CH4 production mainly from H2/CO2 and accumulation of acetate and propionate during the first, and methanogenic consumption of acetate during the second stage. Aeration stress of 12, 24, 36 and 76 h duration was applied to these microbial communities during both stages of cellulose degradation. The longer the aeration stress, the stronger the inhibition of CH4 production at both 30 degrees C and 15 degrees C. The 72 h stressed culture at 30 degrees C did not fully recover. Aeration stress at 30 degrees C exerted a more pronounced effect, but lasted for a shorter time than that at 15 degrees C. The aeration stress was especially effective during the second stage of fermentation, when consumption of acetate (and to a lesser extent propionate) was also increasingly inhibited as the duration of the stress increased. The patterns of CH4 production and metabolite accumulation were consistent with changes observed in the methanogenic archaeal community structure. Fluorescence in situ hybridization showed that the total microbial community at the beginning consisted of about 4% and 10% archaea, which increased to about 50% and 30% during the second stage of cellulose degradation at 30 degrees C and 15 degrees C respectively. Methanosarcina and Methanosaeta species became the dominant archaea at 30 degrees C and 15 degrees C respectively. The first round of aeration stress mainly reduced the non-Methanosarcina archaea (30 degrees C) and the non-Methanosaeta archaea (15 degrees C). Aeration stress also retarded the growth of Methanosarcina and Methanosaeta at 30 degrees C and 15 degrees C respectively. The longer the stress, the lower was the percentage of Methanosarcina cells to total microbial cells after the first stress at 30 degrees C. A later aeration stress decreased the population of Methanosarcina (at 30 degrees C) in relation to the duration of stress, so that non-Methanosarcina archaea became dominant. Hence, aeration stress affected the acetotrophic methanogens more than the hydrogenotrophic ones, thus explaining the metabolism of the intermediates of cellulose degradation under the different incubation conditions.

Methane emission from rice fields: The effect of floodwater management

Rice fields emit methane and are important contributors to the increasing atmospheric CH4 concentration. Manipulation of rice floodwater may offer a means of mitigating methane emission from rice fields without reducing rice yields. To test methods for reducing methane emission, we applied four water management methods to rice fields planted on silty‐clay soils near Beaumont, Texas. The four water treatments investigated were: normal permanent flood (46 days post planting), normal flood with mid‐ season drainage aeration, normal flood with multiple drainage aeration, and late flood (76 days post planting). Methane emission rates varied markedly with water regime, showing the lowest seasonal total emission (1.2 g m−2) with a multiple‐aeration treatment and the highest (14.9 g m−2) with a late flood. Although the multiple‐ aeration water management treatment emitted 88% less methane than the normal irrigation treatment and did not reduce rice yields, the multiple‐aeration treatment did require 2.7 times more water than the 202 mm required by the normal floodwater treatment. A comparison of measured methane emission and production rates obtained from incubated soil cores indicated that, depending on time of season and flood condition, from zero to over 90% of the methane produced was oxidized. The average amount of methane which was oxidized during times of high emission was 73.1 ± 13.7 percent of that produced.