苗木切根技术研究进展

精准培育的理念已经渗入到森林培育的各个环节。切根作为干扰根系最为重要的技术,也受到越来越多地重视。切根可以划分为芽苗切根、苗期切根和起苗后切根等3种类型,把平截、扭根、侧方修根、盒式修根等称为苗期切根,是狭义切根范畴。结合苗木形态指标、生理指标和造林效果,综述每一类型的切根对苗木质量和造林效果的影响。以辐射松为代表的主根发达树种,通过芽苗切根、苗期的平截和扭根,抑制根系顶端优势,从而降低苗木高生长,促进侧根发育,形成发达、紧凑的根系,调整苗木地上和地下比例,最终提高苗木造林效果。以花旗松为代表的慢生常绿树种,侧根较为发达,切根效果不一。苗木平截和扭根后,内源激素、矿质营养、碳水化合物、水分等均会发生变化,这种变化如何影响苗木质量的机制尚不明确。     

切根、截顶对湿地松裸根苗生长调控效果的研究

在江西景德镇和安徽泾县布置了１年生湿地松裸根苗生长后期切和截顶试验，研究其对苗木形态和造林表现的效应及其例题应用制度。两年的结果表明，切根苗的高、径及主根形态指标均低于未切根苗，而侧须根系增加，早切根多次切根处理效应最显著。     

基于插齿数值计算模型的非圆齿轮根切分析

提出了一种判断非圆齿轮任意齿廓是否发生根切的精确方法。该方法首先从非圆齿轮齿廓数值计算模型出发,计算出齿廓在节曲线法向等距线上的一系列点和形成这些点的对应插齿刀齿廓上的点,然后利用齿廓啮合基本定律对非圆齿轮齿廓根切进行理论分析,最后将插齿数字模型和根切产生的原理综合起来,得出判断各个齿是否发生根切的精确方法,并首次对齿廓的根切程度提出了量化计算方法。根据这些方法可以在设计阶段对非圆齿轮根切缺陷进行校验和评价。     

Effect of density control and undercutting on root morphology of 1+0 bareroot hardwood seedlings: five-year field performance of root-graded stock in the central USA

The Hardwood Quality Nursery Cooperative (bareroot forest nurseries in 5 midwestern states) initiated a series of studies in 1987 to evaluate red oak (Quercus rubra L.), and black walnut (Juglans nigra L.) seedling performance as a function of cultural treatments and seedling root system morphology.Seedlings were grown at three densities (32, 64, and 128 stems m^-2for red oak; 32, 64, and 96 stems m^-2for black walnut), and half of the density plots were undercut. Seedlings received fertilizer, weeding, and irrigation treatments customary to their respective nurseries. Seedlings were lifted, measured, and outplanted in their respective states as completely random individual tree plots during spring 1988. Survival, height, and diameter were evaluated annually through 1992.Seedling height, diameter, and number of permanent first-order lateral roots (FOLR) decreased with increasing bed density. At a given density, undercutting produced smaller seedlings (for both height and diameter) that had greater numbers of FOLR. Numbers of FOLR influenced seedling performance after outplanting. Red oak seedlings with at least 5 FOLR and black walnut with at least 7 FOLR had better survival and growth than seedlings with fewer roots.     

刀具半径补偿在数控铣床加工中的应用

刀具半径补偿指令是数控铣床编程与加工中应用最广最重要的指令,正确、合理地使用刀具半径补偿对于复杂零件简化编程计算和提高零件精度具有举足轻重的作用。介绍刀具半径补偿原理,以实例说明刀具半径补偿的过程。     

Northern red oak planting stock: 6-year results

A northern red oak plantation was established in 1988 in a recently clearcut mixed oak stand to evaluate outplanting performance relative to type of planting stock (1--0, 2--0, 1--1, 2--1, 2-year-old containerized, and direct-seeded) and other cultural factors (undercutting in the nursery, raising stock in an extended growing season in Alabama vs a local Pennsylvania nursery, top-clipping at planting time, and tree shelters). Six years after outplanting, seedlings grown from 2-year-old containerized stock were tallest (averaging 3.3 m) and had excellent survival. Among other treatments, 2--0 bareroot stock, especially if undercut in the nursery and top-clipped at planting, performed best and averaged 3.0 m height and 100% survival. Remaining treatments, especially 1--0, were smaller and had reduced survival. Seedlings from direct-seeding were as tall as most 1--0 treatments. Undercutting, top-clipping, nursery transplanting, raising stock in different nurseries, and tree shelters minimally affected the height or survival of seedlings. Seedlings above average in height 3 years after outplanting when fencing was removed and herbiciding ceased, were most likely to survive after 6 years.