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Nguyen Van C.,Can Tho University | Tran Tan H.,Cuu Long Delta Rice Research Institute
Key Engineering Materials | Year: 2015

Microwave vacuum drying is one of innovative drying techniques that is today used in drying of foods, medical products and other high quality products. In this drying technology, heat is generated by directly transforming the electromagnetic energy into kinetic molecular energy of water, thus the heat is produced deep within the material to be dried under vacuum environment. This paper presents the results of research on microwave vacuum drying of "Cat Chu" mango in Mekong Delta - Vietnam. "Cat Chu" mango, with moisture content of (80 ± 1) % (wet basis - wb), was sliced into 5 cm thickness, and was dried in μWaveVac0150-lc dryer (Püschner - Germany). The drying vacuum was from 60 to 120 mbar. Three levels of microwave power were established: the first phase from 600 to 800 W, the second phase from 300 to 500 W, the last one from 150 to 250 W. The control sample was dried by convective drying method at 60 °C; and vacuum drying at 70 mbar, 60 °C. The results of this research showed that high quality product in terms of color, surface shrinkage and structure was obtained by microwave vacuum drying. The drying time was about 45 min, 450 min and 870 min with microwave vacuum drying, vacuum drying and convective hot-air drying, respectively. In addition, Fick's equation and Crank's solution were applied to analyze and calculate the accessibility and diffusion coefficient of microwave vacuum drying process. Starting accessibility of process was significantly increased; the diffusivity obtained was within a range from 6.44∗10-10 m2/s to 16.16∗10-10 m2/s. The results also indicated that there was a higher exchange in surface and a greater internal diffusion of experimental microwave vacuum drying samples compared to the control vacuum and hot-air drying samples. © (2015) Trans Tech Publications, Switzerland. Source

Watanabe T.,Japan International Research Center for Agricultural science | Watanabe T.,Chiba University | Luu H.M.,Cuu Long Delta Rice Research Institute | Nguyen N.H.,Cuu Long Delta Rice Research Institute | And 2 more authors.
Japan Agricultural Research Quarterly | Year: 2013

We conducted a 12-year field experiment to study the combined effects of rice straw compost and chemical fertilizer application on a double rice cropping system in the Mekong Delta, Vietnam and established 7 treatments using a randomized block design with 3 replications. We calculated the yields of treatments relative to those of conventionally fertilized plots (i.e. with no added rice straw compost), and analyzed their annual trends. In the plots with rice straw compost, we observed a positive trend over 12 continuous wet cropping seasons. In comparison with conventional fertilization, the application of rice straw compost with reduced chemical fertilizer can maintain rice productivity over a longer period. We analyzed the nutrient status of the rice straw at harvest over 4 cropping seasons and observed that the Si concentration of the rice straw in conventionally fertilized plots was significantly lower than that in the plots where rice straw compost was applied. The N, P and Mg concentrations of the rice straw increased with the fertilizer application rate, while the concentrations of K, Ca, Mn, Fe, Zn, and Cu did not differ significantly among treatments. Our results suggest that continuous removal of rice straw may reduce the Si availability in soil, thereby decreasing rice productivity. In addition, we verified that rice straw compost can be an effective source of silicon for paddy rice. Source

Dong N.M.,Copenhagen University | Brandt K.K.,Copenhagen University | Sorensen J.,Copenhagen University | Hung N.N.,Can Tho University | And 3 more authors.
Soil Biology and Biochemistry | Year: 2012

Alternate wetting and drying (AWD) irrigation is projected to replace continuous flooding (CF) irrigation for rice production in parts of the Mekong delta area during the dry season. A dry season field experiment was conducted in Mekong delta alluvial soil to compare N cycle processes and agronomic parameters under AWD and CF water management schemes. 15N-labeled urea was applied in microplots to follow the fate of fertilizer N. The major loss of fertilizer N occurred through ammonia volatilization amounting to 21% and 13% of the applied N in the AWD and CF treatments, respectively. Ammonia volatilization was largely controlled by soil and floodwater pH which determined the NH3/NH4+ ratio.Irrespective of water management, 10-12% of the fertilizer N could be recovered from the top soil (0-15cm) after harvest, whereas 10% of fertilizer N accumulated in deeper soil horizons (15-50cm). Even though the loss of fertilizer N through nitrification-denitrification was 6 fold higher under AWD than CF (0.22 versus 0.04gNm -2) it only removed 2.5% of the applied fertilizer and was thus quantitatively insignificant. Overall, net N mineralization and potential nitrification in the top soil were stimulated by the AWD treatment, whereas the difference in water management practice did not affect N uptake by the plants, aboveground biomass, or grain yield. Fertilizer N contributed only around 20% of the N uptake by the plants probably because the soil was rich in N, which was deposited during the preceding flooding season. Although based on data from one dry season crop only, our study indicates that future implementation of AWD irrigation is unlikely to adversely affect crop yields by loss of fertilizer N in intensive rice production systems in the Mekong delta. © 2012 Elsevier Ltd. Source

Chen Y.H.,University of Vermont | Langellotto G.A.,Oregon State University | Barrion A.T.,University of the Philippines at Los Banos | Cuong N.L.,Cuu Long Delta Rice Research Institute
Annals of the Entomological Society of America | Year: 2013

Although it is well established that biodiversity plays an important role in pest control, there is limited knowledge on how the origins of agriculture may shape arthropod biodiversity. Arthropod food webs likely have coevolved with wild crop relatives before domestication, but not all arthropod taxa may be able to inhabit cultivated habitats. We sampled wild and cultivated rice fields in the Mekong Delta of Vietnam to determine how season (dry versus wet) and rice cultivation influenced arthropod diversity and community composition. We found that cultivated rice fields supported ≈50% fewer taxa than wild rice fields, and that there were widespread losses in taxonomic richness within all of the major orders. Wild rice fields supported 173 unique taxa that were not found in any cultivated rice fields, whereas cultivated rice (Oryza sativa L.) supported only 23 unique taxa. Furthermore, wild and cultivated rice supported different arthropod communities. Predators and parasitoids were the most abundant in wild rice during the dry season. Herbivore densities were similar in wild and cultivated rice, but were reduced in wild rice (Oryza rugipogon L.) during the wet season. Neither season nor habitat influenced the densities of detritivores, but aquatic predators were more abundant during the dry season. This study provides empirical evidence that large-scale losses of species richness and changes in arthropod community structure are associated with the cultivation of domesticated rice. © 2013 Entomological Society of America. © 2013 Entomological Society of America. Source

Lang N.T.,Cuu Long Delta Rice Research Institute | Tam B.P.,Cuu Long Delta Rice Research Institute | Van Hieu N.,Cuu Long Delta Rice Research Institute | Nha C.T.,Cuu Long Delta Rice Research Institute | And 3 more authors.
Sabrao Journal of Breeding and Genetics | Year: 2014

Information on genetic diversity among traditional varieties is critical in breeding programs as this influences parental selection in varietal development. A total of 100 traditional varieties in the genebank of the Cuu Long Delta Rice Research Institute (CLRRI), Vietnam, were used to explore this diversity using SSR markers. The study aims to evaluate the genetic diversity of traditional rice varieties and involves molecular diversity analysis using 55 polymorphic SSR markers revealed among the 100 varieties. The Vietnam varieties generated four clusters at 0.60 similarity coefficient. Some varieties with similar names were grouped into different clusters as molecular analysis showed that they were actually genetically different. The 100 landrace varieties collected were evaluated phenotypically. In the analysis of quantitative traits, the range of coefficients of variability was high. It varied from 94.38-80.3% (filled grain) to 60.02-5.63% (unfilled grain). This shows that these traits can be considered most stable as exemplified by their coefficients of variability. The highest values seen in unfilled grain indicate that this character is more affected by the environment and farmers' cultural management practices. The mean values of quantitative trait measurements were higher (78.75-139.75 cm). The highest values noted in yield (3.10-105.16 g) and survival (21-30 days) show good prospects to plant breeders. It has remained one of the major breeding objectives in developing rice varieties. Looking at agro-morphology, ANOVA showed highly significant differences among the 100 traditional rice varieties. The standardized Shannon-Weaver diversity indices for the quantitative morphological characters ranged from 0.68 to 0.95 with a mean of H' = 0.79. Cluster analysis using UPGMA grouped the 100 traditional varieties into 3major clusters. Varieties collected from the same site were grouped together in the same cluster. © Society for the Advancement of Breeding Research in Asia and Oceania (SABRAO) 2013. Source

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