Evaluation of Soil Organic Matter Content under Topographic Influences in Agroforestry Ecosystems: a Study in Central Vietnam

Eurasian Soil Science - We investigate the key predictors that influence the soil organic matter (SOM) content in higher altitude plantations. This is to study the potential of carbon sequestration...     

Preparation of oligoalginate plant growth promoter by γ irradiation of alginate solution containing hydrogen peroxide

Degraded alginate compounds with molecular weights of 7-26, 40-77, or 11-26 kDa were obtained by γ irradiation, hydrogen peroxide (5% H(2)O(2)) treatment, or a combination treatment involving ionizing radiation and H(2)O(2), respectively. The 14 kDa oligoalginate, prepared by the combined method, promoted the growth of mustard greens and lettuce at an optimal concentration of 75 mg/L. The growth promotion effects of the oligoalginate prepared by γ irradiation in the presence of H(2)O(2) were statistically equivalent to those of the oligoalginate prepared by γ irradiation only. The combination of γ irradiation and H(2)O(2) reduced the required irradiation dosage by a factor of 9 relative to the oligoalginate produced by γ irradiation only. The combination treatment (γ irradiation/H(2)O(2)) may be carried out on a large scale at low cost to produce oligoalginate for use as a plant growth promoter in agricultural industries.     

A new flavonoid glycoside from the leaf of Cephalotaxus koreana

A new flavone glycoside, apigenin 5-O-alpha-L-rhamnopyranosyl-(1-->3)-beta-D-glucopyranoside (1), along with four known flavonol glycosides (2-5), were isolated from the leaf of Cephalotaxus koreana. The new glycoside 1 showed inhibitory activity in superoxide radical scavenging assay with IC(50) value of 13.0 microM, while it showed weak activity in 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay. Compounds 2-5 exhibited antioxidant activity in scavenging DPPH and superoxide radicals with IC(50) values ranging from 5.7 to 22.3 microM.     

Bioeconomic Analysis of Improved Diets for Lobster,Panulirus ornatus,Culture in Vietnam

Culture‐based growout of tropical spiny lobster, Panulirus ornatus, is a nascent and unique industry that faces a number of challenges and opportunities. Of particular interest to this study is the imminent development of pelleted diets for lobster (probably within 3 yr) that will potentially reduce the industry's dependence on bycatch for feed (with benefits to wild stocks of fish and reduced downstream environmental impacts). The aim of this paper is to conduct a bioeconomic analysis of lobster growout farming in Vietnam and analyze the cost‐effectiveness of potential manufactured feed diets for these farms. Growout lobster farming is found to be a high‐cost and high‐return industry, with a benefit cost ratio of approximately 1.44. Approximately 60% of the total costs are feed related, with the quantity of feed being the production parameter with the highest variability. Hence, reducing the cost and increasing the efficiency of feeding will have a significant impact on the level and variability of profit. It is expected that manufactured diets will improve the profitability by approximately 267 million VND/yr for an individual farmer (15,000 USD) and approximately 435 billion VND/yr for the industry (24 million USD). This is expected to double again if the diets have the added benefit of reducing mortality through the inclusion of vitamins and other additives.     

Effects of size and nitrite exposure on respiration,oxygen partitioning,and growth of obligate air-breathing fish Channa striata

The effects of fish size and nitrite level on metabolic rate and growth were investigated in the obligate air-breathing snakehead Channa striata, which is an important aquaculture species in Vietnam. Channa striata displayed respiratory size dependence, whereby the standard metabolic rate (SMR) and routine metabolic rate (RMR) decreased progressively in an exponential manner as fish size increased from 50 to 200 g. A mildly elevated nitrite level of 5% of the LC₅₀ 96 h (12 mg NO₂^?/L or safe concentration) induced significant increases in Channa striata SMR and RMR, which were almost double that of the control at the same size. At mild elevation, nitrite caused no significant effect on fish growth and survival during 3 months of rearing. However, both growth and survival rates of fish reared at severely elevated nitrite levels were significantly lower than those of the control; in particular, survival rates were under 50%. While changes in size reduced SMR and RMR, the percentage of air oxygen partitioning remained unchanged. Channa striata upregulation of SMR and RMR and air-breathing regulation were not significantly proven in this study. In summary, maintaining water environments at levels lower than 12 mg NO₂^?/L with ample oxygenation will not affect the growth and survival rate of snakeheads.

     

Production and economic efficiencies of intensive black tiger prawn (<Emphasis Type="Italic">Penaeus monodon</Emphasis>) culture during different cropping seasons in the Mekong delta,Vietnam

Production management of intensive prawn farming strongly differs between dry and wet season in terms of availability and quality of prawn seeds and water quality. Secondary data implied that prawn seed batches from the market had a total pathogen infection rate of 53%, predominantly caused by 37% white spot syndrome virus (WSSV), 19% monodon baculovirus (MBV) and 4% yellow head virus (YHV). Pathogen-free seed batches averaged to 52% during the dry season compared to the wet season (42%). Survey revealed average stocking density of 17 PL m⁻² with a survival rate of 55%, a crop yield of 2,470 kg ha⁻¹ crop⁻¹ and a net income of 6,768 USD ha⁻¹ crop⁻¹. Average production cost amounted to 3.4 USD kg⁻¹, and feed cost accounted for 58% of the production cost. Technical efficiency with respect to prawn yield and survival rate was higher during the dry season than the wet season. The probability of yield loss was 15.6 times higher in the wet than in the dry season. A positive net income can be generated for farms operating in the dry season using new ponds and performing pathogen laboratory tests on prawn seeds before stocking.     

River pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) in southern Vietnam

A technical and socio‐economic survey conducted in the Dong Thap province of Vietnam to assess the current status of river pen culture of giant freshwater prawn Macrobrachium rosenbergii (De Man) showed that pen culture, which has been developed and operated by farmers' indigenous knowledge, requires more study in order to optimize stocking density and to assess its environmental impacts. In this study, the prawn pens were of rectangular shape, with an average size of 209 m². Prawns were stocked in June at an average density of 62 pieces m^?2 and fed on farm‐made feed and were harvested 2–4 times starting from 4 months after stocking until late December or the following January. The average prawn yield was 0.52 kg m^?2 year^?1, ranging from 0.14 to 1.6 kg m^?2 year^?1. The average net return was US$0.71 m^?2 year^?1, ranging from US$1.24 to 4.37 m^?2 year^?1. About 73% of the farmers achieved positive net returns. The top five constraints for prawn pen culture were lack of knowledge of culture technologies, poor water quality, disease problems, poor quality of wild seed and lack of capital. Almost all farmers have no environmental awareness, and environmental regulations for prawn pen culture have not been established. Field measurements showed that all measured water quality parameters were within the range for good growth of giant freshwater prawns, and indicated that there was no significant accumulation of nutrients and organic matter at the bottoms of rivers or canals.     

Pond production of the mud crabs Scylla paramamosain (Estampador) and S. olivacea (Herbst) in the Mekong Delta, Vietnam, using two different supplementary diets

The production performance of Scylla paramamosain and S. olivacea reared together in ponds and provided with different supplementary diets (crustaceans or trash fish) were evaluated with that of an unfed control group relying only on natural food available within the pond. Each treatment was conducted in triplicate. The aim was to evaluate two production strategies over a 130‐day grow‐out trial: (1) production to 200 g crab^?1, which is the minimum preferred marketable size in the Lower Mekong Delta (LMD) and (2) production to 300 g crab^?1, the size that fetches the highest market price. Growth production models were estimated which revealed that the rearing period required to produce crabs of 200 g was 102 days with supplementary feeding, compared with 120 days for the unfed control group. The rearing period needed to produce 300‐g‐sized crabs was estimated to be 144 days and 186 days for the supplementary fed and unfed groups respectively. The additional risk involved in rearing mud crabs to 300 g is not considered worthwhile, under similar culture conditions as observed in this trial, as a decrease in pond water quality and higher mortality rates were observed in the final month of culture needed to achieve this larger size.