Broad leaf mustard(BLM)(Brassica juncea L.var.rugosa,Brassicaceae)is one of the most widely consumed vegetable crops in Nepal.The production of crop in open field is constrained by major pests like mustard aphid and f...Broad leaf mustard(BLM)(Brassica juncea L.var.rugosa,Brassicaceae)is one of the most widely consumed vegetable crops in Nepal.The production of crop in open field is constrained by major pests like mustard aphid and flea beetle.This study was aimed to determine the effects of pest exclusion net(PEN)on pest-infestation and yield of BLM cultivar“Khumal Broad Leaf”.The experiment was carried out in randomized complete block design(RCBD)with five treatments and four replications.The treatments included control(no mulch+no net+no pesticide spray),black plastic mulch only,reflective plastic mulch only,black plastic mulch+no net+pesticide spray,and PEN+black plastic mulch+no pesticide spray.Data were analyzed with RSTAT software package and means were separated by Duncan’s multiple range test(DMRT)at 5%level of significance.The result revealed that crop under PEN had highest plant height(38.99 cm),lowest number of aphid(0-0.86 per plant),flea beetle(0-1.07 per plant)and highest total marketable yield(77.50 ton/ha)while control had lowest plant height(20.06 cm),highest number of aphid(maximum 2.49 per plant),flea beetle(maximum 2.00 per plant)and lowest total marketable yield(13.75 ton/ha).Economic analysis revealed highest benefit-cost ratio in PEN(9.90).This study indicates that the use of PEN protect BLM against aphid and flea beetle,increases yield and can be considered as a viable technology for BLM production by smallholder growers of Nepal.展开更多
A starvation trial was conducted to determine compensatory growth of the juvenile golden pompano Trachinotus ovatus which were deprived of food for 1, 2, 5 and 7 days respectively. The results of tests in outdoor ceme...A starvation trial was conducted to determine compensatory growth of the juvenile golden pompano Trachinotus ovatus which were deprived of food for 1, 2, 5 and 7 days respectively. The results of tests in outdoor cement pools and net pens showed that, in the first 15 days and 30 days, the growth of 1 day and 2 days-deprived groups was probably the same with that of control group, which accorded with fully compensatory description. However, the weight of 5 days and 7 days-deprived fingerlings were lower than that of the control group, which accorded with the description of the partial compensatory growth. As the starvation prolonged, feed conversion efficiency of the starved groups increased and was higher than the control group. Meanwhile, feeding rate also increased, but the fish of 1 day and 2 days-deprived groups was lower than that of the control group, and feeding quantity reduced and was lower than that of the control group. It suggested that the mechanism of compensatory growth was mainly due to improving feed conversion efficiency. Fish biochemical composition was analyzed： the water content and ash of fish sample increased due to starvation, while the lipid and protein decreased. The loss of lipid was greater than that of the protein, and the biochemical composition of fish in each group was restored to the control level by the end of the experiment. It suggested that Trachinotus ovatus may mainly consume lipid during the period of starvation.展开更多
Numerous studies have been undertaken to improve the viability, durability and suitability of materials and methods used for aquaculture enclosures. While many of the previous studies considered macro-deformation of n...Numerous studies have been undertaken to improve the viability, durability and suitability of materials and methods used for aquaculture enclosures. While many of the previous studies considered macro-deformation of nets, there is a paucity of information on netting micro-deformation. When aquaculture pens are towed, industry operators have observed the motion described as ＂baffling＂ – the transverse oscillation of the net planes parallel and near parallel to the flow. The difficulty to observe and assess baffling motion in a controlled experimental environment is to sufficiently reproduce netting boundary conditions and the flow environment experienced at sea. The focus of the present study was to develop and assess experimental methods for visualisation and quantification of these transverse oscillations. Four netrig configurations with varied boundary conditions and model-netting properties were tested in a flume tank. While the Reynolds number was not equivalent to full-scale, usage of the pliable and fine mesh model netting that enabled baffling to develop at low flow velocities was deemed to be of a larger relevance to this initial study. Baffling was observed in the testing frame that constrained the net sheet on the leading edge, similarly to a flag attachment onto a pole. Baffling motion increased the hydrodynamic drag of the net by 35%–58% when compared to the previously developed formula for taut net sheets aligned parallel to the flow. Furthermore, it was found that the drag due to baffling decreased with the increasing velocity over the studied Reynolds numbers（below 200）; and the drag coefficient was non-linear for Reynolds numbers below 120. It is hypothesised that baffling motion is initially propagated by vortex shedding of the netting twine which causes the netting to oscillate; there after the restoring force causes unstable pressure differences on each side of the netting which excites the amplitude of the netting oscillations.展开更多
文摘Broad leaf mustard(BLM)(Brassica juncea L.var.rugosa,Brassicaceae)is one of the most widely consumed vegetable crops in Nepal.The production of crop in open field is constrained by major pests like mustard aphid and flea beetle.This study was aimed to determine the effects of pest exclusion net(PEN)on pest-infestation and yield of BLM cultivar“Khumal Broad Leaf”.The experiment was carried out in randomized complete block design(RCBD)with five treatments and four replications.The treatments included control(no mulch+no net+no pesticide spray),black plastic mulch only,reflective plastic mulch only,black plastic mulch+no net+pesticide spray,and PEN+black plastic mulch+no pesticide spray.Data were analyzed with RSTAT software package and means were separated by Duncan’s multiple range test(DMRT)at 5%level of significance.The result revealed that crop under PEN had highest plant height(38.99 cm),lowest number of aphid(0-0.86 per plant),flea beetle(0-1.07 per plant)and highest total marketable yield(77.50 ton/ha)while control had lowest plant height(20.06 cm),highest number of aphid(maximum 2.49 per plant),flea beetle(maximum 2.00 per plant)and lowest total marketable yield(13.75 ton/ha).Economic analysis revealed highest benefit-cost ratio in PEN(9.90).This study indicates that the use of PEN protect BLM against aphid and flea beetle,increases yield and can be considered as a viable technology for BLM production by smallholder growers of Nepal.
基金Supported by Ocean Public Welfare Scientific Research Project,State Oceanic Administration of the People's Republic of China(Grant No.201205028)Key Projects in the National Science&Technology Pillar Program during the Twelfth Five-year Plan Period(2011BD13B11)Hainan Scientific Operating Expense Projects and Major Project of Science and Technology(ZDZX2013009,ZDZX2013014)
文摘A starvation trial was conducted to determine compensatory growth of the juvenile golden pompano Trachinotus ovatus which were deprived of food for 1, 2, 5 and 7 days respectively. The results of tests in outdoor cement pools and net pens showed that, in the first 15 days and 30 days, the growth of 1 day and 2 days-deprived groups was probably the same with that of control group, which accorded with fully compensatory description. However, the weight of 5 days and 7 days-deprived fingerlings were lower than that of the control group, which accorded with the description of the partial compensatory growth. As the starvation prolonged, feed conversion efficiency of the starved groups increased and was higher than the control group. Meanwhile, feeding rate also increased, but the fish of 1 day and 2 days-deprived groups was lower than that of the control group, and feeding quantity reduced and was lower than that of the control group. It suggested that the mechanism of compensatory growth was mainly due to improving feed conversion efficiency. Fish biochemical composition was analyzed： the water content and ash of fish sample increased due to starvation, while the lipid and protein decreased. The loss of lipid was greater than that of the protein, and the biochemical composition of fish in each group was restored to the control level by the end of the experiment. It suggested that Trachinotus ovatus may mainly consume lipid during the period of starvation.
文摘Numerous studies have been undertaken to improve the viability, durability and suitability of materials and methods used for aquaculture enclosures. While many of the previous studies considered macro-deformation of nets, there is a paucity of information on netting micro-deformation. When aquaculture pens are towed, industry operators have observed the motion described as ＂baffling＂ – the transverse oscillation of the net planes parallel and near parallel to the flow. The difficulty to observe and assess baffling motion in a controlled experimental environment is to sufficiently reproduce netting boundary conditions and the flow environment experienced at sea. The focus of the present study was to develop and assess experimental methods for visualisation and quantification of these transverse oscillations. Four netrig configurations with varied boundary conditions and model-netting properties were tested in a flume tank. While the Reynolds number was not equivalent to full-scale, usage of the pliable and fine mesh model netting that enabled baffling to develop at low flow velocities was deemed to be of a larger relevance to this initial study. Baffling was observed in the testing frame that constrained the net sheet on the leading edge, similarly to a flag attachment onto a pole. Baffling motion increased the hydrodynamic drag of the net by 35%–58% when compared to the previously developed formula for taut net sheets aligned parallel to the flow. Furthermore, it was found that the drag due to baffling decreased with the increasing velocity over the studied Reynolds numbers（below 200）; and the drag coefficient was non-linear for Reynolds numbers below 120. It is hypothesised that baffling motion is initially propagated by vortex shedding of the netting twine which causes the netting to oscillate; there after the restoring force causes unstable pressure differences on each side of the netting which excites the amplitude of the netting oscillations.
