Vol. 3 No. 4 (2020): Vietnam Journal of Agricultural Sciences

Weed infestation has an adverse impact on the yield of vegetable corn. This study, therefore, aimed to investigate the effects of plant density and hand weeding on controlling weeds and yield of vegetable corn. The experiments were conducted in the field condition in a randomized complete block design with three replications. The planting densities were 79,365 plants ha-1 (D1); 92,593 plants ha-1 (D2); 111,111 plants ha-1 (D3); and 138,889 plants ha-1 (D4). The hand weeding treatments were no weeding (NW), hand weeding once at 3-4 leaf stage of vegetable corn (HW1), and hand weeding twice at 3-4 leaf and 8-9 leaf stages of vegetable corn (HW2). The results showed that the highest planting density combined with hand weeding was generally effective in controlling weeds. Furthermore, the increase in planting density combined with hand weeding significantly improved the physiological traits, which consequently increased the cob yield. The yield was optimum at D3 combined with hand weeding once. Thus, the results suggested that the optimum yield of vegetable corn could be obtained at a planting density of 111,111 plants ha-1 combined with hand weeding once at 3-4 leaf stage, an increase of the cob yield by 2.01 tons ha-1.

Despite significant contributions of vegetable and flower production to the improvement of the livelihoods of household producers in the Central Highlands of Vietnam, several challenges facing the development of this sector require a general evaluation. This study aimed at assessing the current situation and economic efficiency of flowers and vegetables and analyzing the application of production techniques on the cultivation of these crops. Based on secondary data sources combined with a primary survey of 144 vegetable farmers and 74 flower growers in all five provinces (Lam Dong, Dak Lak, Dak Nong, Kon Tum, and Gia Lai) of the area in 2018, descriptive statistics and economic values were applied to provide an overview of the development of vegetable and flower production of the region. Findings showed that there were large differences in yields and economic efficiencies of vegetables and flowers among the five provinces of the Central Highlands. Accordingly, the yields and economic efficiencies of vegetables and flowers in Lam Dong were two to five times higher than those in other provinces (Dak Lak, Dak Nong, Kon Tum, and Gia Lai). In addition, the applications of technological advances in vegetable and flower production remained limited. Major challenges for flower and vegetable development included the lack of irrigation water, weak capabilities of building flower and vegetable brands, and limitations in market access. Solutions to improve production technology implications, develop brands of high-quality products, and raise the ability to access market for all vegetable and flower stakeholders are highly recommended.

Resting egg production of rotifers provides critical advantages in larviculture of most fish species due to the reduction in the costs of labour and algae production. The study was conducted to investigate the effects of temperature on population growth and resting egg production of a freshwater rotifer, Brachionus calyciflorus, collected in Northern Vietnam. The rotifer was pre-cultured at 27ºC before being transferred to the cultures at 15 and 35ºC while the control was maintained at 27ºC. One-liter beakers filled with 500mL culture medium were used with three replicates for each temperature group. Stock rotifers were inoculated at an initial density of 200 ind ml-1 and fed with concentrated fresh algae. The results indicated that population growth rate (r) of rotifers cultured at 27 and 35ºC were significantly higher than that of rotifers at 15ºC while the highest density was attained from the treatment of 27ºC, at 608.3 ind mL-1, compared to 468.3 and 360.5 ind mL-1 at 35 and 15ºC, respectively. Transferring the cultures from 27 to 35ºC significantly increased the rate of resting egg carrying females with the maximum rate of 31.5% compared to 21.2 and 13.5% of the rotifers at 27 and 15ºC, respectively. The resting egg densities of the cultures at 35ºC were also significantly higher than those at 15 and 27ºC. The resting egg carrying females appeared and increased their rates in concurrence with increases in the population density. The present results are important information for resting egg induction and production of rotifer in larviculture.

The study aimed to investigate morphometric and meristic variability in the mud sleeper Butis koilomatodon (Bleeker, 1849) in the Mekong Delta. This species is a commercial fish species with a small-size and is mainly distributed in some coastal areas from Tra Vinh to Ca Mau provinces. In the present research, the parameters of morphometry and measurement, including the head length, body depth, eye diameter, distance of the two eyes, and the interrelationships among the morphometric variables, were determined. The results revealed that the total length and weight of the fish changed by sex, season, habitat, and the interaction between the seasons and habitats. Likewise, the meristic criteria were different between males and females, and the dry and wet seasons, but not by their interactions. The growth rate of males was faster than females. The outcomes also showed that the body size of this species was larger in the dry season and the largest fish were found in Duyen Hai and Tra Vinh provinces. The Findings would be useful not only for further effects of environmental factors on morphology but also for comparisons between  congeners Butis morphologically.

Land resources potential assessment is a valuable method for orienting land use planning in the world as well as in Vietnam.The objectives of the study are (1) to assess land suitability and (2) to orient the effective use of agricultural land in the study area. Results indicated that Ham Thuan Bac has 107 land mapping units (LMU), in which includes 11 land-use types (LUTs) such as rice, corn, cassava and sweet potato, sugarcane, grass for livestock, vegetables, green dragon fruit, rubber, coffee, and other fruit trees. Agricultural land with high suitability (S1) and moderately suitable (S2) for mostly LUTs is small, however, marginally suitable (S3) and not suitable land (N) are quite large. More than 50% of the LUTs for growing rice, rubber, coffee, other fruit are not suitable; the remaining LUTs have unsuitable land ranging from 10.76% to 25.16% of agricultural land in the district. Based on land suitability classification, we propose to keep 8550 ha with S1, S2, and a part of S3 area to be irrigated for cultivating rice; 9071.7ha of dragon fruit land including 694.67 ha of S1 and 8377.03 ha of S2 land; and only cultivate annual crops, fruit trees and grazing grass on the land with suitble levels from S1 to S3 of the current status.The remainingareas ofS3 and N for riceand areas of S2 and S3for green dragon fruit under S2, S3with active and semi-active irrigation regimeswill be converted to annual crops and fruit trees and grass for livestock.

Increases in pig farm densities have caused great pressures on waste management systems and produce massive manure and urine quantities in Vietnam. This study aimed to identify the role and contributions of biogas digesters to better manage the sources of greenhouse gas (GHG) emissions from pig wastes for different types of pig farms in the north of Vietnam. Four provinces, namely Thanh Hoa, Phu Tho, Thai Binh, Vinh Phuc, were identified. A total of 24 farms were purposively selected including 16 small-size farms and 8 larger-size farms. The findings showed that GHG emissions from small-size farms (154.8 t CO2-eq.yr-1) did not significantly differ from the amounts measured in larger-size farms (139.1 t CO2-eq.yr-1) in the four surveyed provinces. The sampling position did not significantly affect the GHG emission rates, with 173.9 t CO2-eq.yr-1 inside piggeries and 120.8 t CO2-eq.yr-1 outside the outlet of the biogas digesters (p-value=0.09). N2O emissions require further measurements at different farm sizes and sites. These results confirmed that the pig waste management of biogas digesters for both small-size and larger-size pig farms is not completely efficient and that efforts need to be invested in to mitigate GHG emissions in pig production. Reducing pig density per piggery is highly recommended. The application of other alternative aerobic or anaerobic digestion technologies like vermicompost, effective microorganisms, and composting should also be encouraged and promoted.

The effect of technological parameters such as gas pressure, cutting current, standoff distance, and cutting speed on the cutting surface quality of CNC plasma cutting process was investigated. The experiment was carried out by Bruco CNC plasma cutting machine for CT3 steel with different thicknesses. The quality characteristics examined included the ability to cut out samples, the slag formation on the surface, the surface roughness, and the cut angle. The analysis of the results was made using the Taguchi method in order to determine the contribution of each-individual parameter to the cutting quality, especially surface roughness. The obtained results show that the value of cutting current should be set up at a real value in order to cut out of the sample. The air pressure strongly affected the slag formation. The surface roughness was mainly affected by the standoff distance and air pressure, whereas the cutting speed and cutting current were the minor influencing parameters.

Longan ‘Huong Chi’ (Dimocarpus longan Lour.) is one of the most favorite and widely exported fruits in Vietnam, but the trading of longan faces considerable challenges due to rapid pericarp browning and decay. Our study aimed to determine the effects of modified atmospheres generated by low-density polyethylene (LDPE), polypropylene bag (PP), and LifeSpan L201 films on the quality and pericarp browning of ‘Huong Chi’ longan fruit pre-treated with 3.0 % citric acid and stored at 5oC. The results showed that LifeSpan L201 and LDPE packaging created an equilibrium atmosphere of 10.66 ± 0.78% O2, 4.44 ± 0.64% CO2, and 15.04 ± 0.89% O2, 2.96 ± 0.61% CO2,  respectively. The modified atmospheres generated by LifeSpan L201 and LDPE delayed pericarp browning, maintained the total soluble solids (TSS) and vitamin C content, and reduced decay in longan fruit. Meanwhile, the PP packaging resulted in an improperly modified atmosphere which led to severe decay and browning in cold storage conditions. 

The Optical Mark Recognition (OMR) is very popular with universities for the reading of multiple-choice questions. In this article, we presented a software system for processing surveys at the Vietnam National University of Agriculture based on digital image processing. This software was built using MATLAB and easy to use. The surveys were digitized using a scanner and sent to the software tool. In this study, we tested more than 170 surveys of nine different types. The software tool correctly detected all the valid answers. It was also able to detect all questions with no or multiple marks.

Along with socio-economic development, the volume of domestic solid waste in Vietnam is increasing by 12% annually. The current management model of domestic solid waste presents many limitations: low collection rate, lack of proper treatment, and low levels of recycling and reusing rates but high rates of buried waste and pollution. Published research and overviews of practical implementation of solid waste management models in typical countries around the world have shown the need to innovate domestic solid waste management in Vietnam following the circular economy model to increase the economic efficiency of resources and to minimize polluting the environment. Accordingly, state management of domestic solid waste needs to be reformed synchronously to ensure the development of a closed cycle of waste from identifying generators, classifying waste at sources, collecting, transporting, and treating waste, to the consumption of recycled waste.

This research was conducted to investigate the production efficiency of Ban pig production in northwest Vietnam between October 2016 and January 2017. Primary data obtained from 171 producers were analyzed by applying cost-benefit analysis and stochastic frontier production function. The benefit-cost ratio per litter was 1.24, indicating that the enterprise was profitable. Compared to other farms, the farms focused on farrow-to-finisher attained the highest net return (EUR 213.71/litter), while inputs were used most effectively by the mixed farms. The results from the Cobb-Douglas production function revealed that labour, feeding costs, stocking density, and pigpen structure had positive effects on the production output. Additionally, farms with the phase of farrow-to-nursery obtained less total revenue, while farms focused on the farrow-to-finisher phase achieved higher production outputs than the mixed farms. The level of technical efficiency for each farm ranged between 0.62 and 0.98, with a mean of 0.88. The number of live-born piglets and depreciation cost had positive effects, whereas the nursery interval had a negative impact on the technical efficiency. Ban pig producers could increase technical efficiency by efficiently utilizing available resources and improving managerial skills.

By reviewing worldwide literature, this paper aimed to systematically collate available information about the species Cunninghamia lanceolata. Based on the findings of the review, including the species’ floral characteristics; updated distribution; historical knowledge and heritage; growth and factors influencing its forests; soil nutrition and microbes; carbon storage; wood; and chemicals and essential oils, we have identified issues for consideration regarding the use of this species for big timber production in Vietnam. We propose that it is suitable for a range of applications: for small or large timber plantations, mono/mixed plantations, and agroforestry. If planted at lower altitudes or warmer temperatures, its growth is likely to be improved, but seed production may be less successful. Cultivation of this species for big timber production should be undertaken according to silviculture best practices, ensuring good seed quality, a suitable stand density, and appropriate fertilization thinning strategies, in support of government policies and in accordance with current science and technology.