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81.
为探明不同滴灌施肥策略对苹果树细根直径的调控效应,于2019—2021年开展二因素二水平完全组合设计田间试验,毛管布设方式设置一行一管和一行两管,施肥周期设置15 d和30 d,采用微根管原位监测技术,分苹果树正南、正西及东北3个方位和0~19、19~38、38~57、57~76 cm不同深度土层,持续观测苹果树活跃生长期内细根直径的动态变化,分析了苹果树细根直径对毛管布设方式和施肥周期的响应。结果表明:细根直径主要集中在0.5~1.5 mm范围内,约占90%,0~0.5 mm和1.5~2.0 mm直径的细根占比很少。在夏季之前,直径≤1.0 mm的细根增多;夏季之后,细根直径加粗,直径>1.0 mm的细根迅速增加。相较于施肥周期15 d,施肥周期30 d在2020年6—11月和2021年4—7月均能增加细根直径;在大部分土层中,施肥周期30 d会增加细根直径,施肥周期15 d会减小细根直径;在2020年正南和东北方向上,施肥周期15 d会减小细根直径,施肥周期30 d会增加细根直径。一行一管较一行两管在2020年和2021年8月均能增加细根直径;在浅中层土壤(0~38 cm土层... 相似文献
82.
以陕西长武旱塬为例,分别对研究区农地和5个不同林龄(9、12、16、19 a和23 a)苹果园的土壤剖面氢氧稳定同位素进行测定,利用Craig-Gordon模型定量估算其土壤平均蒸发量,并基于“空间换时间”方法分析果园种植及生长对土壤蒸发的影响。结果表明:农地及9、12、16、19、23 a林龄苹果园的土壤蒸发量均随苹果树的种植及生长呈现先减少再增大的趋势,年均蒸发量分别为129、104、89、119、128、136 mm;苹果园的土壤蒸发量变化与叶面积指数呈显著负相关(R=-0.713);苹果园种植的前中期(9~12 a)土壤蒸发量随叶面积指数增加逐渐减小,而在中后期(12~23 a)深层土壤水被大量消耗造成的干旱胁迫使得果树叶面积减少,从而导致林下土壤蒸发量又逐渐增大。 相似文献
83.
The cavity induced by top-blow gas jets impinging on the bath surface is one of most important parameters, which has overwhelming influence on the rate of slag formation and metallurgical performance. Water model experiments are conducted through a 1/10 scaled-down top-blown convertor. Effects of lance height and gas flow rate on penetration behavior are studied, and also the influence mechanism of liquid surface tension on penetration depth is addressed based on the experiments and theory analysis. An energy utilization index (EUI) is defined to reflect how much the impinging kinetic energy of gas jets are transferred into bath for formation of cavity, and an improved model is proposed to predict penetration depth of jets. The results show that penetration depth increases with lowering lance height and increasing gas flow rate, and impact diameter increases with increasing lance height, but is little affected by gas flow rate. Influence of liquid surface tension on penetration depth is enhanced with increasing surface tension and penetration depth. The EUI increases with increasing lance height, and a function relationship of it with lance height is obtained based on the experiments. 相似文献
84.
Considering the character of slope resistant engineering invest benefit, in line with security and economy balmaced, combining initial investment and anticipated hazard loss, disaster resistant engineering should be satisfied with the criterion of minimum cost. Decision tree model is adopted as analyzing means, and risk decision-making of slope design is carried out. Project input-output radio adopting dynamic analysis can reflect project investment benefit more accurately. At last this paper analyzes some questions in process of slope resistant engineering with benefits enumerate. 相似文献
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86.
针对国内汽车企业不具备整车齐全的三维CAD模型的实际情况,提出一种基于动态装配图热点和产品结构树结点双向驱动的备件数据可视化管理方案,在Delphi开发平台上将Action Script技术和ActiveX技术集成到可视化备件管理系统中。详细阐述了图热点驱动和树结点驱动的程序实现流程.给出了动态装配图、装配结构树和界面数据窗三者之间的联动关系,实现两种驱动的等效性。为了便于用递归算法遍历结构树,对复杂网状结构的零部件从属依赖关系进行规范化处理.使之成为树形结构。采用约束递归迭代,对一次性加载零部件的层数和范围进行约束,用统一的虚拟临时结点代替当前非叶子结点的子结点,实现整车装配关系结构树构造过程的优化。 相似文献
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Three trickle irrigation schedules, two of which were scheduled according to soil water potential ( soil) (tensiometer method) and daily stem contraction (DSC) (dendrometer method) respectively and the other one was a schedule of restricted water supply, were applied to a mature peach orchard.The annual water application based on soil was greater than that based on DSC. However, tree growth, fruit size and leaf water potential (leaf) on the trees in the dendrometer scheduling plot did not differ from those in the tensiometer scheduling plot while the premature fruit drop and fruit bud initiation were greatly different. The restricted water supply treatment limited significantly both tree and fruit growth. In addition, the lower leaf was observed on the trees in this plot.Further study shows that use of the dendrometer method for scheduling irrigation satisfies the water needs of the plant and that the tensiometer method is less accurate.Abbreviations leaf
leaf water potential
- soil
soil water potential
- DSC
daily stem contraction
- LVDT
linear variable displacement transducer
- PET
potential evapotranspiration 相似文献
90.
Although there has been increasing research on the adoption of agroforestry technologies over the last decade, few such studies have assessed uptake over a long period and many are based on a single snapshot in time. Furthermore, most of these studies have mainly looked at non-adopters and adopters: only recently have social scientists considered testers. A further category of users neglected in adoption studies has been re-adopters of technologies. Studying this group provides an interesting and more nuanced understanding of adoption and re-adoption. Methodologically, most adoption studies use quantitative methods and fail to link their findings to wider socio-economic, political and institutional settings. This paper presents a study of the dynamics of improved tree fallow use by farmers in Siaya and Vihiga districts of western Kenya over a period of eight years. It uses both qualitative and quantitative data to critically discuss the motivations of adopters, testers/rejecters and re-adopters. The results show that the process of adoption is highly dynamic and variable with farmers planting improved fallows and discontinuing or re-adopting them due to a whole range of factors, of which soil fertility improvement is just one. These factors included incentives from projects, the tying of adoption to credit programmes, prestige, participation in seminars/tours and the availability of a seed market from projects promoting improved fallows. Farmers planting improved fallows for such reasons may be termed ‘pseudo-adopters’. There were significant differences in adoption between the two districts, with more farmers in Siaya planting improved fallows than in Vihiga. A majority of farmers in Vihiga (53%) who were given seed never planted improved fallows, even though they had been exposed to the technology. Some 40% of farmers in Siaya and 38% in Vihiga planted improved fallows but later rejected them. This has some important implications for research and development. For improved fallow technologies to be attractive to farmers, they must provide other tangible economic benefits besides soil fertility improvement. This presents a challenge to researchers who must better attune themselves to the needs and demands of farmers if they wish to see their research findings widely adopted. 相似文献