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| 1 | 土壤、农作物中及家畜体内的微量营养元素(英文)显示文摘微量营养元素通常富集在表层土壤中,其含量随土层深度递减。尽管土壤中大多数微量元素的含量很高,但只有一小部分能被植物吸收。微量营养元素,也被称为痕迹元素,所需数量微小,但其缺乏会对农作物生产和动物健康造成严重影响。农作物对不同微量营养元素有着不同的反应。芸苔和豆类对Mo和B有较高的响应度,而玉米和其他谷类对Zn和Cu较为敏感。在温润和湿热地区,由于强降雨和强淋溶作用,微量营养元素缺乏较为普遍。土壤pH值是影响微量营养元素对植物有效性的重要因素之一。除Mo以外,微量营养元素的有效性随pH的增加而减小,Mo的有效性随pH的增加而增加。对于大多数植物来说,叶片中的微量营养元素含量高于植物的其他部分。因此,可以用叶片作为样品来测定农作物中微量营养元素的含量。大多数微量营养元素缺乏表现在植物顶部的新叶上,而过量则表现在老叶上。根据Deckers和Steinnes的结论,土壤较为贫瘠的发展中国家与土壤肥沃的欧洲及北美地区相比,微量营养元素缺乏现象较为普遍。许多营养元素缺乏区位于潮湿的热带地区,土壤极度贫瘠、高度风化和/或强淋溶,营养元素十分匮乏。此类其他土壤分部于半干旱及毗邻地区,这些地区的碱性和石灰性土壤条件严重限制了微量营养素对植物的供给。通常,可以满足草料作物生长的Cu、Fe、Mn、Zn、Se含量水平,却不能满足家畜的需要。Se是植物生长所不需要的微量元素,因此草料作物中Se的含量很少。然而,如果动物所食农作物和草料中Se含量偏低,会造成严重的肌肉异常和其他疾病。白肌病是最常见的由于Se缺乏造成的疾病,在牛犊和羔羊中都有发现。本文讨论了与动物需求相关的农作物微量营养元素充足度。 | Umesh C. Gupta Wu Kening Liang Siyuan | 2008 | 地学前缘2008，15，5： | 16 |
| 2 | Selenium in soils and crops, its deficiencies in livestock and humans: Implications for management显示文摘 | Umesh C. Gupta Subhas C. Gupta | 2000 | Communications in Soil Science and Plant Analysis (-)2000，，11： | 1 |
| 3 | Trace element toxicity relationships to crop production and livestock and human health: implications for management显示文摘 | Umesh C. Gupta Subhas C. Gupta | 1998 | Communications in Soil Science and Plant Analysis (-)1998，，11： | 1 |
| 4 | PERFORMANCE EVALUATION OF SUBMERGENCE RATIO OF A RECTANGULAR SUBMERGED VANE WITH A COLLAR显示文摘The vane induced strength of secondary flow in terms of dimensionless moment of momentum is maximum in the case of a rectangular vane with a collar at angle of attack 400 at different degrees of submergence (T/d) such as 0.60, 0.67 and 0.75. The same value of optimal angle of attack was found by Marelius and Sinha (1998) in the case of a rectangular vane without a collar. The vane induced strength of a vortex is insensitive to the submergence ratio (T/d). The vane induced strength of a vortex in terms of moment of momentum (MOM) depends on a wide range of variables, such as angle of attack, vane height, vane length, vane thickness flow depth, water density, median sediment size, velocity vector, acceleration due to gravity, water dynamic viscosity, vane shape, taper angle, etc. The optimal angle of attack is very close to 400. A dimensionless moment of momentum parameter has also been identified. Vane induced secondary flow is also related to linear momentum. The graphical plot of moment of momentum vs. different angle of attack shows a similar trend as that of the plot of dimensionless MOM such as MOM made non- dimensional by flow depth or by vane height vs. angle of attack. | Umesh P. GUPTA Nayan SHARMA C. S. P. OJHA | 2006 | International Journal of Sediment Research2006，21，1： | 0 |
| 5 | DIKE FORMATION WITH SUBMERGED VANE显示文摘Submerged vanes are submerged foils constructed in a river at an angle of attack to induce horizontal circulation in the downstream flow. The initial height of vanes is 0.2 – 0.4 times the local water depth (d) at the design stage. Its length expressed as a multiple of the height to length ratio (H/L) normally is 0.25 to 0.5. With the use of a submerged vane in straight channels, dikes (heaps of sediment) were formed downstream. At an optimal angle of attack of 40o and at a Froude number of 0.25, the formation of the dike starts at some distance from the trailing edge of the rectangular and trapezoidal submerged vanes with a collar. A significant scour hole results at the trailing edge of a vane with a collar. A typical dike formed along the vane on the suction side with a symmetric bell-shaped profile. The dike formation phenomenon triggered by a vane close to the bank-line at a flow with a relatively higher Froude number, such as 0.25, does not seem to follow a straight alignment, but has a sort of curvilinear shape bent towards the suction side. The dike formation process for a flow with a smaller Froude number, such as 0.13, is observed to not be appreciable. With the same installation height of H, a vane without a collar was dislodged by the flow at a Froude number of 0.25, whereas it was stable at a Froude number of 0.13. | Umesh P. GUPTA C. S. P. OJHA Nayan SHARMA | 2006 | International Journal of Sediment Research2006，21，3： | 0 |
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