Search

Background: Globally, rice systems are a major source of atmospheric CH4 and for major rice-producing countries, such as Vietnam, CH4 as well as N2O emissions from agricultural land used for rice production may represent about one-fourth of total national anthropogenic greenhouse gas (GHG) emissions. However, national-scale estimates of GHG emissions from rice systems are uncertain with regard to its magnitude, spatial distribution, and seasonality. Aims: Here, we used the biogeochemical model LandscapeDNDC to calculate emissions of CH4 and N2O from rice systems in Vietnam (Tier 3 IPCC approach). Our objectives were to identify hotspot regions of emissions and to assess the contribution of N2O to the total non-CO2 (CH4+N2O) GHG balance of rice systems as well as the seasonal and interannual variability of fluxes in dependence of uncertain input data on field management. Methods: The biogeochemical model LandscapeDNDC model was linked to publicly available information on climate, soils, and land management (fertilization, irrigation, crop rotation) for calculating a national inventory in daily time steps of CH4 and N2O emissions from rice systems at a spatial resolution of 0.083° × 0.083°. Uncertainty in management practices related to fertilization, use of harvest residues or irrigation water, and its effects on simulated CH4 and N2O fluxes was accounted for by Latin Hypercube Sampling of probability distribution functions. Results: Our study shows that CH4 and N2O fluxes from rice systems in Vietnam are highly seasonal, with national CH4 and N2O emissions totaling to about 2600 Gg CH4 year–1 and 42 Gg N2O year–1, respectively. Highest emissions were simulated for double and triple rice cropping systems in the Mekong Delta region. Yield-scaled emissions varied largely in a range of 300–3000 kg CO2-eq Mg–1 year–1, with CH4 emissions during the rice season(s) dominating (>82%) the total annual non-CO2 GHG balance of rice systems. In our study, uncertainty in field management information (nitrogen fertilization, ratio synthetic to organic fertilization, residue management, availability of irrigation water) were major drivers of uncertainty of the national CH4 and N2O emission inventory. Conclusions: Our study shows that Tier 3 approaches, that is, process-oriented model approaches combined with GIS databases, for estimating national-scale GHG emissions from rice systems are ready to be applied at national scale. Generally, this approach is powerful as it allows to identify regions with elevated emissions, thereby accounting not only for CH4, but as well for N2O emissions. However, our study also shows that specifically better information on land management is required to narrowing uncertainties.

This study estimates the sensitivity of parameters to serve the adjustment and construction of standard parameters in the Decomposition - Denitrification (DNDC) model when calculating greenhouse gas emissions from rice cultivation on alluvial, alkali, acid-sulfate, and bleached soils of Red river delta, Vietnam. The research results show that the following parameters: bulk density, clay fraction, microbial activity index, soil organic carbon (SOC), temperature, conductivity, fertilization of urea, and porosity have a high sensitivity for the calculation of CH4 emissions; the following parameters: pH, drainage efficiency, depth of water retention layer, field capacity, initial nitrate and ammonium concentrations at surface soil, and rainfall have low sensitivity and less influence for the calculation of CH4 emissions; the wilt moisture and salinity index have no effect on CH4 emissions. In case of N2O emissions, the following parameters: amount of manure, clay fraction, microbial activity index, pH, initial nitrate concentration at surface soil, bulk density, SOC, field capacity, porosity and depth of water retention layer have a high sensitivity and more influence to N2O emissions; the following parameters: drainage efficiency, conductivity, initial ammonium concentration at surface soil, temperature, fertilisation of urea and rainfall have low sensitivity and less influence to N2O emissions; the wilting point and soil salinity index have no effect on N2O emissions. The results of model calibration show a good correlation between observed and simulated values in both spring and summer crops in 2018. The R2 of the spring and summer crops reach 0.86 and 0.79, the Nash-Sutclitffe efficiency index reaches 0.82 and 0.77 for CH4 emission; meanwhile, for N2O emission, these values are 0.62, 0.69, and 0.76, respectively. The study also found a model calibration parameter used to calculate greenhouse gas emissions from rice cultivation on alluvial, alkali, acid-sulfate, and bleached soils.

Rice production is a significant source of greenhouse gas (GHG) emissions in the national budget of many Asian countries, but the extent of emissions varies strongly across agro-environmental zones. It is important to understand these differences in order to improve the national GHG inventory and effectively target mitigation options. This study presents a meta-analysis of CH4 database emission factors (EFs) from 36 field sites across the rice growing areas of Vietnam and covering 73 cropping seasons. The EFs were developed from field measurements using the closed chamber technique. The analysis for calculating baseline EFs in North, Central and South Vietnam in line with the Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology was specified for the three cropping seasons being early-(E), mid-(M) and late-year (L) seasons. Calculated average CH4 EFs are given in kg ha&ndash, 1 d&ndash, 1 and reflect the distinct seasons in North (E: 2.21, L: 3.89), Central (E: 2.84, M+L: 3.13) and South Vietnam (E: 1.72, M: 2.80, L: 3.58). Derived from the available data of the edapho-hydrological zones of the Mekong River Delta, season-based EFs are more useful than zone-based EFs. In totality, these average EFs indicate an enormous variability of GHG emissions in Vietnamese rice production and represent much higher values than the IPCC default. Seasonal EFs from Vietnam exceeded IPCC defaults given for Southeast Asia corresponding to 160% (E), 240% (M) and 290% (L) of the medium value, respectively.

The authors wish to make the following corrections to this paper [...]

The reduction of CH4 and N2O emissions from rice paddies is of utmost importance in minimizing the impact of rice production on global warming. A field experiment was therefore conducted in farmers' field in Hanoi, Vietnam to examine whether the use of straw compost or straw biochar, in combination with the safe alternate wetting and drying (AWD) has the potential to suppress both CH4 and N2O emissions from rice paddies while maintaining the rice yield. The study compared the proposed strategies with local farmers' practice of permanent flooding (PF) and farmyard manure (FYM) incorporation, respectively. A control treatment without organic matter incorporation in both AWD and PF water regimes was also included in the study; all treatments received equal amounts of mineral fertilizer. Gas emissions were monitored using the closed chamber method at seven-day intervals during the first 50 days and at 15-day intervals thereafter. Addition of FYM, straw compost and biochar increased CH4 emissions by 230%, 150% and 38%, respectively, when compared with the control treatments in both the AWD and PF water regimes. Within AWD, FYM increased N2O emissions by 30%, straw compost and biochar displayed similar amount of N2O emissions as the control treatment. Within PF, N2O emissions under FYM and straw compost were 40% and 35% higher than the control treatment, respectively, and biochar once again displayed similar amount of N2O emissions as the control treatment. Yield difference was not significant (p > 0.05) between any of the treatments. These results indicated that the straw compost incorporation might not reduce the global warming potential (GWP) and yield-scaled GWP of rice production, whereas biochar in combination with AWD has the potential to maintain the GWP and yield-scaled GWP of rice production at lower level than the farmers' practice.

Passive compliant prosthetic ankles have the advantage of energy saving, light weight, simple structure and competitive cost compared to powered devices. Despite of the variety of commercial products, these designs do not provide adequate degree-of-freedom during amputees' movement. It hampers them from walking comfortably especially on undulating and rough terrains. This paper presents a novel design of a multiaxis fully compliant prosthetic ankle. Finite element analyses are carried out to evaluate the mechanical behaviors of the design obtained by an optimization procedure. The designed prosthesis not only has a capability of bending and compression to store elastic energy and release it to assist in forward propulsion of the body but can also facilitate eversion motion when persons with disability move on rough road by integrating a circular flexure hinge. These characteristics make it more versatile and reduce the impact force on residual limbs.

Soil erosion is the main cause of soil degradation in northern Vietnam. In this study, soil erosion was measured in 2 m2 field plots, a 19.1-ha sub-watershed, and a 248.9-ha main watershed in Tam Quan commune, Tam Duong district, northern Vietnam during 2 years, i.e., 2004–2005. The main watershed includes lowland paddy fields, and is representative for watersheds in the northern Vietnamese landscape. Soil erosion was measured for eight events, at all the three scales to increase our understanding of erosional processes and to assess the effects of paddy fields within the main watershed. The results show that total discharge and sediment yield in both sub-watershed and main watershed were much lower than those in the field plots. Total discharge per unit area in the main watershed was higher than in the sub-watershed, because during the growing season, the paddies are filled with water and any rainfall on them therefore becomes runoff. Sediment yield in the main watershed fluctuated, depending on the soil erosion contribution from many sub-watersheds. Annual rainfalls in 2004 and 2005 were 1,172 and 1,560 mm, respectively, resulting in corresponding total discharges of 54 and 332 mm and total soil losses of 163 and 1,722 kg ha-1 year-1. High runoff volumes occurred in July, August, and September, but April, June, the last 10 days of September and October, were the susceptible periods for soil erosion in the study area because of low plant cover and many agricultural activities during these periods.

Urbanization, Water Quality Degradation and Irrigation for Agriculture in Nhue River Basin of Vietnam

A single-walled carbon nanotubes (SWNTs)-based gas sensor, fabricated by screen-printing method, was employed for ammonia (NH/sub 3/) detection at room temperature. Upon exposure to NH/sub 3/ gas, the resistance of the sensor positively increased. The sensor could detect NH/sub 3/ at a concentration as low as 5 ppm at room temperature with a response time of 10 minutes. When the NH/sub 3/ concentration increased, a saturation of the sensor sensitivity seemed to reach at 40ppm. Exceeding to 40ppm concentration, the sensitivity continued to rapidly increase. The effect of various operation conditions on the behavior of the SWNT-based gas sensor was reported. When the sensor was heated from room temperature up to 400/spl deg/C, a transition from semiconducting into metallic behavior eventually took place. The sensor sensitivity was affected by operating temperature. The higher temperature the sensor operated at, the lower sensitivity it exhibited. By choosing a suitable regime of operation, in which the carrier gas flux, the heating temperature and heating time were appropriately controlled, the performance of the sensor was significantly improved in comparison with other sensors at the same type.