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The above- and below-ground parts of rice plants create specific habitats for various microorganisms. In this study, we characterized the phyllosphere and rhizosphere microbiota of rice cultivars using a metaproteogenomic approach to get insight into the physiology of the bacteria and archaea that live in association with rice. The metaproteomic datasets gave rise to a total of about 4600 identified proteins and indicated the presence of one-carbon conversion processes in the rhizosphere as well as in the phyllosphere. Proteins involved in methanogenesis and methanotrophy were found in the rhizosphere, whereas methanol-based methylotrophy linked to the genus Methylobacterium dominated within the protein repertoire of the phyllosphere microbiota. Further, physiological traits of differential importance in phyllosphere versus rhizosphere bacteria included transport processes and stress responses, which were more conspicuous in the phyllosphere samples. In contrast, dinitrogenase reductase was exclusively identified in the rhizosphere, despite the presence of nifH genes also in diverse phyllosphere bacteria.

70% of the world's freshwater is used for irrigated agriculture and demand is expected to increase to meet future food security requirements. In Asia, rice accounts for the largest proportion of irrigated water use and reducing or conserving water in rice systems has been a long standing goal in agricultural research. The Alternate Wetting and Drying (AWD) technique has been developed to reduce water use by up to 30% compared to the continuously flooded conditions typically found in rice systems, while not impacting yield. AWD also reduces methane emissions produced by anaerobic archae and hence has applications for reducing water use and greenhouse gas emissions. Although AWD is being promoted across Asia, there have been no attempts to estimate the suitable area for this promising technology on a large scale. We present and demonstrate a spatial and temporal climate suitability assessment method for AWD that can be widely applied across rice systems in Asia. We use a simple water balance model and easily available spatial and temporal information on rice area, rice seasonality, rainfall, potential evapotranspiration and soil percolation rates to assess the suitable area per season. We apply the model to Cagayan province in the Philippines and conduct a sensitivity analysis to account for uncertainties in soil percolation and suitability classification. As expected, the entire dry season is climatically suitable for AWD for all scenarios. A further 60% of the wet season area is found suitable contradicting general perceptions that AWD would not be feasible in the wet season and showing that spatial and temporal assessments are necessary to explore the full potential of AWD.

PurposeIn recent years, climate-smart agriculture (CSA) was introduced to Vietnam to enhance farmers’ resilience and adaptation to climate change. Among the climate-smart agricultural technologies (CSATs) introduced were water-saving techniques and improved stress tolerant varieties. This study aims to examine the determinants of farmers’ adoption of these technologies and the effects of their adoption on net rice income (NRI) in three provinces as follows: Thai Binh (North), Ha Tinh (Central) and Bac Lieu (South).Design/methodology/approachDeterminants of adoption of CSATs and the adoption effects on NRI are analyzed by using a multinomial endogenous switching regression framework.FindingsThe results showed that gender, age, number of family workers, climate-related factors, farm characteristics, distance to markets, access to climate information, confidence on the know-how of extension workers, membership in social/agricultural groups and attitude toward risk were the major factors affecting the decision to adopt CSATs. However, the effects of these factors on the adoption of CSATs varied across three provinces. These technologies when adopted tend to increase NRI but the increase is much greater when these are combined.Practical implicationsIt is important to consider first the appropriateness of the CSA packages to the specific conditions of the target areas before they are promoted. It is also necessary to enhance the technical capacity of local extension workers and provide farmers more training on CSATs.Originality/valueThis study is the first attempt to identify key determinants of adoption of CSATs either singly or in combination and the adoption effects on NRI in Vietnam.

This study comprises field experiments on methane emissions from rice fields conducted with an Eddy-Covariance (EC) system as well as test runs for a modified closed chamber approach based on measurements at nighttime. The EC data set covers 4 cropping seasons with highly resolved emission rates (raw data in 10 Hz frequency have been aggregated to 30-min records). The diel patterns were very pronounced in the two dry seasons with peak emissions at early afternoon and low emissions at nighttime. These diel patterns were observed at all growing stages of the dry seasons. In the two wet seasons, the diel patterns were only visible during the vegetative stages while emission rates during reproductive and ripening stages remained within a fairly steady range and did not show any diel patterns. In totality, however, the data set revealed a very strong linear relationship between nocturnal emissions (12-h periods) and the full 24-h periods resulting in an R2-value of 0.8419 for all data points. In the second experiment, we conducted test runs for chamber measurements at nighttime with much longer deployment times (6 h) as compared to measurements at daylight (typically for 30 min). Conducting chamber measurements at nighttime excluded drastic changes of temperatures and CO2 concentrations. The data also shows that increases in CH4 concentrations remained on linear trajectory over a 6h period at night. While end CH4 concentrations were consistently >3.5 ppm, this long-term enclosure represents a very robust approach to quantify emissions as compared to assessing short-term concentration increases over time near the analytical detection limit. Finally, we have discussed the potential applications of this new approach that would allow emission measurements even when conventional (daytime) measurements will not be suitable. Nighttime chamber measurements offer an alternative to conventional (daytime) measurements if either (i) baseline emissions are at a very low level, (ii) differences of tested crop treatments or varieties are very small or (iii) the objective is to screen a large number of rice varieties for taking advantage of progress in genome sequencing.

Reducing methane (CH4) emission from paddy rice production is an important target for many Asian countries in order to comply with their climate policy commitments. National greenhouse gas (GHG) inventory approaches like the Tier-2 approach of the Intergovernmental Panel on Climate Change (IPCC) are useful to assess country-scale emissions from the agricultural sector. In paddy rice, alternate wetting and drying (AWD) is a promising and well-studied water management technique which, as shown in experimental studies, can effectively reduce CH4 emissions. However, so far little is known about GHG emission rates under AWD when the technique is fully controlled by farmers. This study assesses CH4 and nitrous oxide (N2O) fluxes under continuous flooded (CF) and AWD treatments for seven subsequent seasons on farmers’ fields in a pumped irrigation system in Central Luzon, Philippines. Under AWD management, CH4 emissions were substantially reduced (73% in dry season (DS), 21% in wet season (WS)). In all treatments, CH4 is the major contributor to the total GHG emission and is, thus, identified as the driving force to the global warming potential (GWP). The contribution of N2O emissions to the GWP was higher in CF than in AWD, however, these only offset 15% of the decrease in CH4 emission and, therefore, did not jeopardize the strong reduction in the GWP. The study proves the feasibility of AWD under farmers’ management as well as the intended mitigation effect. Resulting from this study, it is recommended to incentivize dissemination strategies in order to improve the effectiveness of mitigation initiatives. A comparison of single CH4 emissions to calculated emissions with the IPCC Tier-2 inventory approach identified that, although averaged values showed a sufficient degree of accuracy, fluctuations for single measurement points have high variation which limit the use of the method for field-level assessments.

The contribution of West African savanna ecosystems to global greenhouse gas budgets is highly uncertain. In this study we quantified soil‐atmosphere CH4 and CO2 fluxes in the southwest of Burkina Faso from June to September 2005 and from April to September 2006 at four different agricultural fields planted with sorghum (n = 2), cotton, and peanut and at a natural savanna site with termite (Cubitermes fungifaber) mounds. During the rainy season both CH4 uptake and CH4 emission were observed in the savanna, which was on average a CH4 source of 2.79 and 2.28 kg CH4‐C ha−1 a−1 in 2005 and 2006, respectively. The crop sites were an average CH4 sink of −0.67 and −0.70 kg CH4‐C ha−1 a−1 in the 2 years, without significant seasonal variation. Mean annual soil respiration ranged between 3.86 and 5.82 t CO2‐C ha−1 a−1 in the savanna and between 2.50 and 4.51 t CO2‐C ha−1 a−1 at the crop sites. CH4 emission from termite mounds was 2 orders of magnitude higher than soil CH4 emissions, whereas termite CO2 emissions were of the same order of magnitude as soil CO2 emissions. Termite CH4 and CO2 release in the savanna contributed 8.8% and 0.4% to the total soil CH4 and CO2 emissions, respectively. At the crop sites, where termite mounds had been almost completely removed because of land use change, termite fluxes were insignificant. Mound density‐based upscaling of termite CH4 fluxes resulted in a global termite CH4 source of 0.9 Tg a−1, which corresponds to 0.15% of the total global CH4 budget of 582 Tg a−1, hence significantly lower than those obtained previously by biomass‐based calculations. This study emphasizes that land use change, which is of high relevance in this region, has particularly affected soil CH4 fluxes in the past and might still do so in the future.

The impact of root exudates, collected from five rice cultivars, on methane (CH₄) production was studied in a paddy soil under anaerobic conditions. Root exudates of the cultivars Dular, IR72 and IR65598 collected at four growth stages and of B40 and IR65600 collected at two growth stages showed that (a) CH₄ production was commenced rapidly within 2 h upon exúdate addition and reached a maximum within a day of addition, and (b) 7-d incubation periods were sufficient to study exudate-induced CH₄ production potentials. Among different cultivars, high C releases from roots, increased the methanogenic source strength of the soil, which finally controlled CH₄ production. The relationship of the amount of CH₄ produced was stronger for the amount of total organic C (r = 0.920) than for the amount of organic acids (r = 0.868) added through exudates. Apparently, CH₄ production and CH₄ emission are more closely related to the release pattern of root exudate-C than to its individual components. The proportion of exudate-C converted to CH₄ ranged between 61 and 83% and remained unaffected by cultivars and growth stages suggesting that the majority of exudate-C served as a methanogenic substrate in the anoxic rice soils. These observations indicate that the use of high-yielding cultivars with lowest excretion (for example IR65598, IR65600) would result in lowest exudate-induced CH₄ production. Therefore, cultivar choice could greatly influence regional and global CH₄ emissions and screening/selection of exiting rice cultivars, and/or breeding new cultivars with low exudation rates could offer an important methane mitigation option as long as yields are not compromised.

Tropical soils are important sources and sinks of atmospheric methane (CH4) and major sources of oxides of nitrogen gases, nitrous oxide (NM2O) and NOx (NO+NO2). These gases are present in the atmosphere in trace amounts and are important to atmospheric chemistry and earth's radiative balance. Although nitric oxide (NO) does not directly contribute to the greenhouse effect by absorbing infrared radiation, it contributes to climate forcing through its role in photochemistry of hydroxyl radicals and ozone (O3) and plays a key role in air quality issues. Agricultural soils are a primary source of anthropogenic trace gas emissions, and the tropics and subtropics contribute greatly, particularly since 51% of world soils are in these climate zones. The soil microbial processes responsible for the production and consumption of CH4 and production of N-oxides are the same in all parts of the globe, regardless of climate. Because of the ubiquitous nature of the basic enzymatic processes in the soil, the biological processes responsible for the production of NO, N2O and CH4, nitrification/denitrification and methanogenesis/methanotropy are discussed in general terms. Soil water content and nutrient availability are key controls for production, consumption and emission of these gases. Intensive studies of CH4 exchange in rice production systems made during the past decade reveal new insight. At the same time, there have been relatively few measurements of CH4, N2O or NOx fluxes in upland tropical crop production systems. There are even fewer studies in which simultaneous measurements of these gases are reported. Such measurements are necessary for determining total greenhouse gas emission budgets. While intensive agricultural systems are important global sources of N2O and CH4 recent studies are revealing that the impact of tropical land use change on trace gas emissions is not as great as first reports suggested. It is becoming apparent that although conversion of forests to grazing lands initially induces higher N-oxide emissions than observed from the primary forest, within a few years emissions of NO and N2O generally fall below those from the primary forest. On the other hand, CH4 oxidation is typically greatly reduced and grazing lands may even become net sources in situations where soil compaction from cattle traffic limits gas diffusion. Establishment of tree-based systems following slash-and-burn agriculture enhances N2O and NO emissions during and immediately following burning. These emissions soon decline to rates similar to those observed in secondary forest while CH4 consumption rates are slightly reduced. Conversion to intensive cropping systems, on the other hand, results in significant increases in N2O emissions, a loss of the CH4 sink, and a substantial increase in the global warming potential compared to the forest and tree-based systems. The increasing intensification of crop production in the tropics, in which N fertilization must increase for many crops to sustain production, will most certainly increase N-oxide emissions. The increase, however, may be on the same order as that expected in temperate crop production, thus smaller than some have predicted. In addition, increased attention to management of fertilizer and water may reduce trace gas emissions and simultaneously increase fertilizer use efficiency. [PUBLICATION ABSTRACT]

Background and aims Replacing paddy rice by upland systems such as maize cultivation is an on-going trend in SE Asia caused by increasing water scarcity and higher demand for meat. How such land management changes will feedback on soil C and N cycles and soil greenhouse gas emissions is not well understood at present. Methods A new LandscapeDNDC biogeochemical module was developed that allows the effect of land management changes on soil C and N cycle to be simulated. The new module is applied in combination with further modules simulating microclimate and crop growth and evaluated against observations from field experiments. Results The model simulations agree well with observed dynamics of CH 4 emissions in paddy rice depending on changes in climatic conditions and agricultural management. Magnitude and peak emission periods of N 2 O from maize cultivation are simulated correctly, though there are still deficits in reproducing day-to-day dynamics. These shortcomings are most likely related to simulated soil hydrology and may only be resolved if LandscapeDNDC is coupled to more complex hydrological models. Conclusions LandscapeDNDC allows for simulation of changing land management practices in SE Asia. The possibility to couple LandscapeDNDC to more complex hydrological models is a feature needed to better understand related effects on soil-atmosphere-hydrosphere interactions.

AIMS: Two pot experiments in a “walk-in” growth chamber with controlled day and night temperatures were conducted to investigate the influence of elevated temperatures along with rice straw incorporation on methane (CH₄) and nitrous oxide (N₂O) emissions as well as rice yield. METHODS: Three temperature regimes–29/25, 32/25, and 35/30 °C (Exp. I) and 29/22, 32/25, and 35/28 °C (Exp. II), representing daily maxima/minima were used in the study. Two amounts of rice straw (0 and 6 t ha⁻¹) were applied with four replications in each temperature regime. CH₄ and N₂O emissions as well as soil redox potential (Eh) were monitored weekly throughout the rice-growing period. RESULTS: Elevated temperatures increased CH₄ emission rates, with a more pronounced effect from flowering to maturity. The increase in emissions was further enhanced by incorporation of rice straw. A decrease in soil Eh to <−100 mV and CH₄ emissions was observed early in rice straw–incorporated pots while the soil without straw did not reach negative Eh levels (Exp. I) or showed a delayed decrease (Exp. II). Moreover, soil with high organic C (Exp. II) had higher CH₄ emissions. In contrast to CH₄ emissions, N₂O emissions were negligible during the rice-growing season. The global warming potential (GWP) was highest at high temperature with rice straw incorporation compared with low temperature without rice straw. On the other hand, the high temperature significantly increased spikelet sterility and reduced grain yield (p < 0.05). CONCLUSIONS: Elevated temperature increased GWP while decreased rice yield. This suggests that global warming may result in a double negative effect: higher emissions and lower yields.