森林覆盖率计算标准的变化对云南省宏观规划目标的影响

森林覆盖率是宏观规划的重要指标之一,国家林业局在2003年颁布了新的森林覆盖率计算方法,由于标准的变化,导致森林覆盖率宏观规划目标值的变化．文章阐述了新旧森林覆盖率标准的变化和关系,以云南为例,计算不同时期森林覆盖率的同标准指标,分析云南省森林覆盖率的规划目标,2015年宜为53％,2020年宜为57％,极限目标为63％．     

森林资源连续清查进界木与漏测木确定标准的研究

对森林资源连续清查中进界木和漏测木传统确定方法进行分析，指出其存在的随意性和缺乏科学性、明确性；提出应用数理统计方法，通过对已往取得数据的分析，制定出科学、合理、明确的标准。并以云南省2002年森林资源连续清查中楚雄州云南松检尺数据对这一方法进行了具体分析。     

基于NAPA软件的渔业船舶完整稳性分析

为验证NAPA软件在渔业船舶应用上的可行性和采用船舶静力学原理计算完整稳性的精确性,根据南海海域49.5 m金枪鱼延绳钓船的特定作业工况,分别采用NAPA软件和表格进行计算。计算结果表明,两种计算方法的偏差在2%左右,能够满足工程应用的精度要求。对气象衡准计算,分别采用了渔业船舶规则和国际海事组织(IMO)规则,由于算法不同,其偏差较大。通过比较发现,渔业船舶规则对气象衡准的要求高于IMO规则的要求。在没有条件使用大型船舶计算软件,且船舶处于平浮状态时,采用船舶静力学原理的计算结果是精确的。采用了船舶静力学原理并建立了NAPA计算模型,通过实例计算表明,NAPA软件具有在渔业船舶应用上的可行性和采用船舶静力学原理计算完整稳性的精确性,该结论可为船舶设计人员选取不同计算方法时提供参考依据。     

基于模态置信度准则的插秧机支撑臂模态分析与结构优化

针对高速插秧机栽插机构动力传输过程中的振动问题,该文以2ZG-6DK插秧机为研究对象,分析了栽插系统动力传输方式及工作原理;利用Solid Works软件对插秧机动力传输系统中关键部件支撑臂进行建模,将模型导入ANSYS Workbench并结合Lanczos Method解算方法求解模态固有频率和振型,在此基础上开展基于MAC(modal assurance criterion)准则优化的模态试验,验证了有限元理论分析的准确性。为使支撑臂固有频率避开外部激振频率,在分析外部频率激振特点的基础上,基于ISIGHT多学科软件平台,采用序列二次规划法对支撑臂结构参数进行优化。研究结果表明:优化后支撑臂侧壁腔体厚度5.7 mm、横梁宽度42.0 mm、臂长497.0 mm,前4阶模态频率分别调整至135.17、204.23、483.14和702.32 Hz,均可避开插秧机汽油发动机激振频率范围86.67~120 Hz。优化后1阶频率下振动幅度衰减最为明显,振动幅值最高下降9.4%,支撑臂低频振动特性得到明显改善。研究结果可为插秧机的振动特性分析与减振设计提供参考。     

油茶幼林土壤养分限制因子的研究

利用土壤养分状况系统研究法，对江西宜春油茶幼林土壤进行了养分限制因子的研究。结果表明：宜春油茶幼林土壤养分限制因子为N、P、Ca，盆栽不施N、P、Ca作物分别减产63．97％、61．32％和19．08％。     

根—土复合体强度及其非线性特性试验研究

[目的]研究根—土复合体的非线性破坏准则,并结合不同含根量(G=0.12%,0.24%,0.36%)、不同含水率(w=13.22%,16.22%,19.22%)条件下根—土复合体强度,开展根—土复合体非线性特性研究,为生态水土防治工作提供科学参考。[方法]采用GDS三轴仪开展了根—土复合体的固结不排水三轴试验,获得根—土复合体应力—应变曲线及抗剪强度指标。[结果]素土与根—土复合体应力—应变关系曲线为硬化型。含根量与根—土复合体峰值强度成正比关系,但含水率对其峰值强度的影响表现出反比关系。当G=0.36%时,根—土复合体峰值强度的最大增幅为70.1%;当w=13.22%时,根—土复合体峰值强度最大增幅为86.7%。根—土复合体非线性破坏准则在正应力低于临界应力时呈非线性,在正应力高于临界应力时呈线性。c,k为根—土复合体非线性破坏准则中描述根系作用的关键参数,其中c与含根量和含水率均成正比关系,c越大,根系对根—土复合体强度的贡献程度越大;k与含根量成反比,与含水率成正比,k越小,根—土复合体强度包线的非线性化特征越明显。[结论]含根量(G)和含水率(w)对根—土复合体强度有显著影响。...     

冀东平原水稻大田生产营养元素限制因子研究

通过冀东平原水稻土壤氮、磷、钾、锌、硼等大量和微量元素对水稻产量的影响进行研究,阐明了养分限制因子,提出了增产措施。按照NY/T 497—2002《肥料效应鉴定田间试验技术规程》,采用田间小区肥料试验方法,对氮、磷、钾、铜、铁、锰、锌、硼、钼九种营养元素进行缺素对比,找出限制因子。施用氮肥比对照增产明显,产量差异极显著,说明氮肥是影响水稻产量的主要限制因子;除氮肥外,其他肥料作用与全素比较差异不显著,说明还不是限制因子;缺氮处理与对照比产量差异不显著,说明在氮素缺失情况下,其他肥料综合作用不明显。通过对水稻营养元素限制因子的研究,初步了解了水稻生产中各种营养元素对产量的影响,为今后水稻科学施肥奠定了基础。     

Comparison of critical limits for crop plant growth based on different indicators for the state of soil compaction

Soil compaction affects physical soil condition, in particular aeration, soil strength, and water availability and has adverse effects on plant growth. Bulk density is the most frequently used indicator to describe the state of compaction of a soil. However, this parameter lacks a direct functional relationship with plant growth. Various indicators have been proposed to simultaneously characterize the state of compaction of agricultural soil and its suitability for plant growth. This paper examines and compares the critical limits for crop plant growth based on three of these indicators: packing density, least limiting water range, and S parameter (the latter is the slope of the soil water‐retention curve in the inflexion point). In a first step, we reviewed the literature for published optimum and limiting values of bulk density and found that these values were highly dependent on clay and silt content. Converting them into corresponding values of packing density (composite index of bulk density and clay content), a value of 1.70 was found to effectively distinguish between optimum and limiting soil conditions for plant growth. In a second step, the packing density of 59 soil horizons sampled in N Switzerland was compared with the least limiting water range and the S parameter of these soil horizons (both determined by means of pedotransfer functions taken from the literature). A linear relationship between the three parameters was found, which allowed for a comparison of the published critical limits for plant growth based on these parameters. The critical limits of the three indicators, which had been postulated independently of each other in the literature, were found to agree well with each other. This means that all of them could equally be used to describe the compaction state of a soil and its physical suitability for plant growth. However, the proposed critical limits of packing density, least limiting water range, and S parameter still need further validation by field studies relating plant growth to soil compaction.     

Root growth conditions in the topsoil as affected by tillage intensity

Many studies have reported impeded root growth in topsoil under reduced tillage or direct drilling, but few have quantified the effects on the least limiting water range for root growth. This study explored the effects of tillage intensity on critical soil physical conditions for root growth in the topsoil. Samples were taken from a 7-year tillage experiment on a Danish sandy loam at Foulum, Denmark (56°30′ N, 9°35′ E) in 2008. The main crop was spring barley followed by either dyer's woad (Isatis tinctoria L.) or fodder radish (Raphanus sativus L.) cover crops as subtreatment. The tillage treatments were direct drilling (D), harrowing 8-10 cm (H), and ploughing (P) to 20 cm depth. A chisel coulter drill was used in the H and D treatments and a traditional seed drill in the P treatment. Undisturbed soil cores were collected in November 2008 at soil field moisture capacity from the 4-8 and 12-16 cm depths.We estimated the critical aeration limit from either 10% air-filled porosity (ε_a) or relative gas diffusivity (D/D₀) of 0.005 or 0.02 and found a difference between the two methods. The critical limit of soil aeration was best assessed by measuring gas diffusivity directly. Root growth was limited by a high penetration resistance in the D and H soils (below tillage depth). Poor soil aeration did not appear to be a significant limiting factor for root growth for this sandy loam soil, irrespective of tillage treatment. The soil had a high macroporosity and D/D₀ exceeded 0.02 at field capacity. Fodder radish resulted in more macropores, higher gas diffusivity and lower pore tortuosity compared to dyer's woad. This was especially important for the H treatment where compaction was a significant problem at the lower depths of the arable layer (10-20 cm depth). Our results suggest that fodder radish could be a promising tool in the amelioration of soil compaction.     

Integrating effects of hunting policy, catastrophic events, and inbreeding depression, in PVA simulation: the Scandinavian wolf population as an example

Focusing on the wolf Canis lupus in Scandinavia as an example, criteria are proposed and an analysis performed to assess the effect on extinction risk of various control policies, while accounting simultaneously for effects of inbreeding depression and potential catastrophic events. Each control policy is characterized by a hunting pressure (the increase caused by hunting of annual mortality rates) combined with a hunting threshold (the population size below which hunting is not permitted). Catastrophes are taken into account by including the persistence of a severe catastrophe in the criterion for population viability. Based on these criteria, the results suggest that only a very limited amount of hunting should be permitted at low population sizes. The results also illustrate the importance of including a long-term perspective in modelling threatened populations.