排序方式： 共有44条查询结果，搜索用时 15 毫秒
21.
Standardized method for the Holmen pellet tester (NHP100) as a tool for evaluating the physical quality of fish feed 
下载免费PDF全文
下载免费PDF全文 The fish feed production industry requires reliable methods measuring the physical quality of feed before it is being released to the customer. The Holmen pellet tester (NHP 100) could be adapted for this purpose, but the special characteristics of fish feed require particular care during testing. The aim of the study was to determine the standardized conditions for using the Holmen tester as a tool measuring the durability of fish feed. Screening tests were performed on commercial fish feed samples to assess the effects of temperature, pressure and cleaning the instrument between runs. The operating pressure was found to be the most important factor that can influence the results. The temperature of the operating air can also alter the results; increased temperatures can cause oil to melt and leak from the pellets. Cleaning the instrument between analyses can also affect the results. This study shows that when these factors are maintained at a standardized level, the Holmen pellet tester is a valuable tool for assessing the physical quality of fish feed giving additional information on the quality of feed pellets compared to other durability tests like DORIS. 相似文献
22.
23.
In 2010, the first, and so far only, infestation of the Hungarian spruce scale (Physokermes inopinatus) and accompanying sooty mould occurred in Scania, southernmost Sweden. About 1000?ha of Norway spruce (Picea abies) were affected, and the trees suffered from the sucking of the insects as well as from the dense sooty mould that covered the needles. Salvage cuttings were carried out in many of the massively attacked forest stands, both in response to the fear that the trees otherwise would die, e.g. from secondary bark beetle attacks and to prevent spreading of the infestation. The aim of this study was to provide basic, quantitative knowledge on the aftermath response of trees that were heavily infested, but not exposed to salvage cutting. Growth characteristics, in terms of needle weight, shoot length and tree-ring size were measured on infested and uninfested trees to compare and contrast the spruce growth before, during and after the scale outbreak. The infestation resulted in dwarf annual shoots, stunted needles and thin tree rings. The needle weight returned to normal the following year, whereas shoot length and tree rings required one growing season before full recovery. 相似文献
24.
靖远松叶蜂性信息素的初步研究 总被引：10，自引：0，他引：10
试验结果表明，靖远松叶蜂雄蜂对处女雌蜂的昼夜趋性反应发生在白天，每天有两个高峰，强峰为９：００～１３：００，弱峰为１７：００～１９：００，晚２０：００～早８：００之间未见趋性反应；雄蜂对不同日龄处女雌蜂的反应不同，随着雌蜂日龄的增加，诱捕器诱到雄蜂的数量逐渐下降，１日龄雌蜂诱到雄蜂的数量最多，其诱捕率为５１．６４％；含有１头处女雌蜂的诱捕器在５０～１５００ｍ之间，均能诱到雄蜂；雄蜂对７种不同的人工合成性信息素反应表明，只有（２Ｓ，３Ｒ，７Ｒ）－３，７－二甲基－２－十三碳醇丙酸酯对雄蜂有引诱作用。 相似文献
25.
26.
27.
Margit Olle Ingrid H. Williams 《The Journal of Horticultural Science and Biotechnology》2017,92(3):223-230
Tomato can be injured by two very important physiological disorders, namely blossom end rot (BER) and fruit cracking (FC). The purpose of this review is to describe these physiological disorders and to assess whether cultivar and cropping system can minimise their symptoms. Physiological Ca deficiency is usually related to the inability of the plant to translocate adequate Ca to the affected plant part, rather than to insufficient Ca levels in the growing medium. The first visible symptom of BER is a small darkened or water-soaked area around the blossom end of the fruit, appearing about the time the fruit begins to ripen. The spot darkens, enlarges, and becomes sunken as the fruit matures. Large lesions may show in concentric rings. FC is the splitting of the epidermis around the calyx or stem scar. FC is a physiological disorder, which mainly occurs when there is a rapid net influx of solutes and especially water into the fruit, while at the same time ripening or other factors reduce the strength and elasticity of the tomato skin. This review article gives an overview of the causes of BER and FC and summarizes growing methods aimed at reducing these physiological disorders of tomatoes. 相似文献
28.
Migratory delay leads to reduced passage success of Atlantic salmon smolts at a hydroelectric dam 下载免费PDF全文
下载免费PDF全文 Daniel Nyqvist Larry A. Greenberg Elsa Goerig Olle Calles Eva Bergman William R. Ardren Theodore Castro‐Santos 《Ecology of Freshwater Fish》2017,26(4):707-718
Passage of fish through hydropower dams is associated with mortality, delay, increased energy expenditure and migratory failure for migrating fish and the need for remedial measures for both upstream and downstream migration is widely recognised. A functional fish passage must ensure safe and timely passage routes that a substantial portion of migrating fish will use. Passage solutions must address not only the number or percentage of fish that successfully pass a barrier, but also the time it takes to pass. Here, we used radiotelemetry to study the functionality of a fish bypass for downstream‐migrating wild‐caught and hatchery‐released Atlantic salmon smolts. We used time‐to‐event analysis to model the influence of fish characteristics and environmental variables on the rates of a series of events associated with dam passage. Among the modelled events were approach rate to the bypass entry zone, retention rates in both the forebay and the entry zone and passage rates. Despite repeated attempts, only 65% of the tagged fish present in the forebay passed the dam. Fish passed via the bypass (33%), via spill (18%) and via turbines (15%). Discharge was positively related to approach, passage and retention rates. We did not detect any differences between wild and hatchery fish. Even though individual fish visited the forebay and the entry zone on multiple occasions, most fish passed during the first exposures to these zones. This study underscores the importance of timeliness to passage success and the usefulness of time‐to‐event analysis for understanding factors governing passage performance. 相似文献
29.
Gun Lövblad Peringe Grennfelt Olle Westling Harald Sverdrup Per Warfvinge 《Water, air, and soil pollution》1995,85(4):2431-2436
Critical loads for sulphur and nitrogen are defined to produce effective control strategies over Europe, such as those of the new sulphur protocol. To determine the critical load exceedances on the European scale it is necessary to simplify and generalize. The spatial variation on a scale smaller than the 150 × 150 km EMEP grid squares is considered for critical loads, via a cumulative frequency distribution and the 95 percentile for the grid square is determined. The deposition is assumed to be uniform over the area and the exceedance over the 95 percentile critical load is determined. In reality, the spatial variation is considerable for critical loads as well as for deposition. Calculations based on the frequency of local critical load exceedances have been made for two grid squares in southern Sweden. Local critical loads for acidity are compared to local deposition. Deposition variations due to pollution gradients within the square and to ecosystem structure have been considered. The results are similar for the two squares. The calculations based on local exceedances on 50×50 km grid squares and consideration to landuse variability, indicate that in order to protect 95% of the ecosystems in the square, emission reductions 25% greater than the large-scale European approach are needed. The effect of enhanced deposition at forest edges is of relatively small importance for the total exceedance. 相似文献
30.
Biological feedback mechanisms regulate fundamental ecosystem processes and potentially regulate ecosystem productivity. To date, no studies have documented the down-regulation of terrestrial nitrogen (N) fixation via an ecosystem-level feedback mechanism. Herein, we demonstrate such a feedback in boreal forests. Rapid cycling of N in early secondary succession forests yielded greater throughfall N deposition, which in turn decreased N fixation by cyanobacterial associates in feather moss carpets that reside on the forest floor. The forest canopy exerts a tight control on biotic N input at a period of high productivity. 相似文献