天然草场改良用振动式间隔松土机作业机理

为了提升草地振动式间隔松土机的作业性能,需要对机具的作业机理进行研究。通过对机具的工作单体进行运动仿真分析,探讨了松土部件在强迫振动作用下对草耕层土壤的破碎机理。通过分析得出松土部件的工作过程为切削土壤和抛起土壤两个交替作用的阶段,在松土作业过程中,松土部件既有挤压松土又有振动松土,土垡因受剪切、弯曲和拉伸等作用得到松碎,松土部件产生与松土铲切削方向呈一定角度的振动有利于土壤疏松和降低机具的牵引阻力。     

基于Fluent的叶片数对低比转速离心泵内部流场的影响

叶片数是影响泵性能的主要参数,不同比转速的离心泵有不同的选取准则。为研究低比转速离心泵的叶片数选取准则,选取IS50—32—200低比转速离心泵作为研究对象,通过Pro／e建立三维模型,在gambit中进行网格划分,导入Fluent中对三维流场进行数值模拟,计算出各个物理参数的分布。通过对不同叶片数的计算比较分析,得出低比转速离心泵叶片数对流量,扬程和性能的影响,揭示不同叶片数的低比转速离心泵内部流动规律,给出低比转速离心泵叶片数的选取原则,提高低比转速离心泵的优化设计。     

两种小麦对行免耕播种机的对比实验

对2BMD-12型小麦对行免耕播种机和美国JD1590型进行了对比实验,内容包括机具适应的地表秸秆覆盖情况、施肥能力以及性能价格比等。结果表明,JD1590型小麦对行播种机不适用于我国一年两熟地区的小麦免耕播种;2BMD-12型小麦对行免耕播种机是专门针对我国一年两熟地区免耕播种小麦而设计的,有较好的防堵性能,能在直立玉米秸秆覆盖地直接进行小麦播种,作业质量良好。     

番茄群体冠层形态结构三维模拟——基于实测数据

为了提供较精确的作物冠层几何模型进行作物冠层光分布计算研究,首先实际测量番茄器官、个体及群体的形态特征参数,进而基于实测数据对番茄器官、个体及群体进行三维重建,使用C++语言和OpenGL函数库,开发了番茄群体可视化软件,可实现番茄群体三维模型的快速生成。基于精确器官模型和实测数据建立的番茄群体三维模型,较好地反映了群体冠层结构的基本特征,为作物冠层生产力计算和评价建立了几何模型基础。     

开缝叶片低比转数离心泵空化性能的数值模拟

为了进一步提高低比转数离心泵的空化性能,对离心泵叶轮叶片进口附近的开缝进行研究.考虑开缝的3个参数,设计6组水力模型探究开缝对低比转数离心泵性能的影响.针对离心泵运行过程中产生空化的流动特点,基于Rayleigh-Plesset方程来描述空泡成长和溃灭过程的空泡动力学模型,采用RNG k-ε模型对在相同工况下的离心泵中两相流动进行数值模拟与分析.模拟结果表明:在叶片进口处开缝可以提高泵空化性能,其中第二组模型的空化性能提升比较明显,空化余量由4.447 m下降到3.910 m,降低了12.1%,水力效率由71.56%上升至76.46%;在相同工况下,开缝叶轮流道内的能量分布更加均匀,而扬程在额定流量下只有很小的变化.该模拟结果对研究低比转数离心泵内部流动特性及性能的提升具有一定的参考价值.     

基于自动导航的小麦精准对行深施追肥机设计与试验

针对冬小麦返青期地表追施氮肥使氮素挥发导致肥料利用率低的问题,结合目前在小麦追肥过程中缺少深施氮肥作业装备的现状,进行了基于拖拉机自动导航技术实现精准对行深施氮肥的技术研究,设计了小麦精准对行精量深施追肥机。追肥机采用安装有自动导航系统的拖拉机牵引实现精准对行,以RTK-GNSS接收机测取的作业速度为基准,通过液压系统驱动排肥机构工作,双圆盘开沟器开沟深施,采用PID控制排肥轴转速与车辆行驶速度实现实时匹配,达到精量控制追肥量的目的。田间试验结果表明:设置目标追肥量为200 kg/hm2,车辆行驶速度为5 km/h时,追肥机能完成对行深施追肥作业,机具对行作业误差在±6 cm以内,追肥量偏差小于9%,可满足实际生产需求;对照撒肥机表层撒肥作业,每公顷减施氮肥25 kg左右,小麦每公顷增产486.5 kg左右。     

Pathogenicity and Virulence of the Two Dutch VCGs of Verticillium dahliae to Woody Ornamentals

Two experiments were performed in two consecutive years to test whether isolates of different vegetative compatibility groups (VCGs) differ in their ability to cause disease in woody ornamentals, to study the host specificity of the isolates and to get an insight into disease development in woody hosts. A range of woody ornamental plant species, including Acer campestre, Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Cotinus coggygria, Robinia pseudoacacia, Rosa canina, Syringa vulgaris and Tilia cordata, were root-dip inoculated with six isolates of Verticillium dahliae, belonging to the two VCGs that occur in the Netherlands (VCG NL-1 and VCG NL-2). Isolates belonging to each VCG caused severe symptoms of verticillium wilt in most plant species tested. Disease progress differed between plant species, but was generally the same for the two VCGs. No overall differences in virulence were observed between the two VCGs for external wilt symptoms, number of dead plants, or shoot length. No significant VCG × plant species interactions were present for these characteristics. However, isolates of VCG NL-1 caused more vascular discolouration than did isolates of VCG NL-2. Isolates within VCGs often differed considerably in their virulence to certain hosts, as shown by highly significant isolate × plant species interactions. Isolates were more virulent on their original host. These findings imply that VCG identification does not contribute to disease prediction for a range of woody hosts.     

Identification of ALS inhibitor‐resistant Amaranthus biotypes using polymerase chain reaction amplification of specific alleles

Summary Polymerase chain reaction (PCR) amplification of specific alleles (PASA) was adapted as a molecular marker‐based method for the rapid detection of point mutations in Amaranthus retroflexus and Amaranthus rudis leading to ALS inhibitor resistance. Two pairs of primers were designed for the specific amplification of alleles of the ALS gene of susceptible and resistant biotypes. The allele‐specific primer matched the desired allele, but mismatched the different allele at its 3′ end. Differentiation was carried out by comparison of the amplified DNA fragments in gel electrophoresis after PASA‐PCR. In A. rudis, differentiation was possible with one PCR and genomic DNA as probe. A ‘nested’ PCR was necessary for the differentiation of sensitive and resistant A. retroflexus. PASA is useful for the identification of resistant weed biotypes and also as a monitoring tool to map resistance occurrence and distribution. Advantages include the fast and clear separation of those plants with and without mutations at an early stage of development, its easy and consistent performance and quick results compared with existing resistance detection tests. These advantages, when combined with management strategies, enable further activities to reduce herbicide resistance.     

农业景观与害虫种群控制

20世纪以来,我国农村城镇化和农业设施化的快速发展,造成农业景观的急剧变化以及农田生境的破碎化。国内外十分重视这种景观变化对农业生态系统功能和生物多样性以及害虫种群控制的影响。本文针对国内外有关农业景观变化和生境破碎化对昆虫与天敌群落组成、多样性及种群序列变化的影响研究进行系统论述,着重介绍农业景观变化对害虫种群控制的原理和作用机理,分析景观结构与农田生物多样性,及寄主—寄生物、猎物—捕食者、植物—害虫—天敌的相互关系,以及影响这种关系的景观因子作用力的模拟,旨在揭示农业景观变化对害虫种群动态的潜在影响,提示了今后害虫治理研究的热点问题。     

Detection and recovery of Rhizoctonia solani in naturally infested glasshouse soils using a combined baiting, double monoclonal antibody ELISA

A combined baiting, double monoclonal antibody immunoassay was developed that allows specific and sensitive detection of the economically important soil-borne plant pathogen Rhizoctonia solani in naturally infested soils. The assay is quick, taking only three days to complete from receipt of soil samples and the immunoassay format allows recovery of Rhizoctonia isolates from colonized baits for determination of anastomosis group (AG) affiliation and pathogenicity. The assay was tested on naturally infested soils from commercial glasshouses used to grow lettuce. Using the immunoassay, conventional anastomosis tests against known AG isolates, and pathogenicity tests, it was shown that R. solani isolates recovered from soil samples were pathogenic towards lettuce and belonged to AG4. Furthermore, those isolates that exhibited strong pathogenicity towards lettuce were recovered from sites that had experienced severe Rhizoctonia damage in previous lettuce crops. The possibility of developing a preplanting test to predict damage to specific crop plants due to the presence of particular AGs in the soil is discussed.