不同牧草种植模式对退化农田土壤养分的影响

为了筛选出牧草最优种植模式,为退化农田地力提升和土地可持续利用提供理论和技术支撑,以敖汉苜蓿和老芒麦为材料,设置3种不同种植模式：单播敖汉苜蓿(Ms)、单播老芒麦(Es)和混播牧草（敖汉苜蓿+老芒麦,In）,以休闲处理为对照(CK)。结果表明：随种植年限增加,土壤速效磷含量先降后升;有机质、速效钾、全氮、全钾含量上升。与CK比较,第1年,各种植模式均提高了土壤有机质、速效钾、碱解氮和全氮含量;Ms和In提高了土壤全磷、全钾含量。第2年,Ms、Es和In土壤碱解氮含量在10~20 cm土层显著降低20.91%~40.05%,速效磷含量在20~40 cm土层显著降低32.19%~39.65%;土壤有机质、全钾含量总体呈升高趋势,速效磷、速效钾含量呈下降趋势,全磷含量在20~40 cm土层显著降低。     

施肥对农田土壤碳氮磷化学计量特征及相关酶活变化的影响

归纳不同施肥条件下土壤养分和微生物量碳氮磷(CNP)化学计量特征及与之相关的酶活性变化,从施肥制度与土壤中养分平衡的关系着手制定出更加合理的施肥措施.通过数据整合分析,收集已公开发表施肥土壤中CNP化学计量比和酶活性变化的相关中、英文文献,提取有效数据,然后进行数据分析,通过绘制森林图明确土壤和微生物量CNP化学计量特...     

猪繁殖与呼吸综合症诊断技术的研究进展

猪繁殖与呼吸综合征是目前养猪业中一种严重的病毒性传染病,分布广泛且对养猪业造成巨大损失。就该病的临床症状,病理变化,血清学,分子生物学等诊断与检测方法的研究进展进行综述。     

岩溶山区石漠化生境灌木层植物功能群划分

植物功能群是研究复杂生态系统结构和功能的有效途径。植物功能群组成的变化情况是生态系统功能的重要表现形式,同时也是生态系统对环境因子变化响应的主要指标之一。因此,研究不同石漠化程度下,植物功能群组成的变化,对于揭示岩溶山区生态系统植被自我更新规律具有重要意义。以岩溶山区石漠化生境灌木层为研究对象,利用地理环境特征与植物适应功能关系来划分植物功能群,将岩溶地区石漠化生态系统灌木层划分为7 个植物功能群。有助于了解岩溶石漠化生态系统功能群结构及功能,同时对石漠化生态系统的恢复与重建提供理论基础。     

花生品种退化原因及防止对策

在花生生产过程中，因引种、繁种、利用的不合理，常常会造成花生品种种性退化。花生种性退化后，不良植株比率增多，导致经济性状变劣、抗逆性下降、适应性减弱，尤其是病害加重，在生产上造成产量和品质均有不同程度的降低。要保持生产中花生品种的优良特性，就必须了解花生品种退化的原因，有针对性地采取预防措施，使花生品种在推广使用过程中始终保持固有的优良特性，以实现花生的高产与稳产。     

优良品种退化原因及防止对策

<正>生产上推广的品种在使用过程中常易发生混杂退化,出现农艺性状和经济性状变劣的现象,造成生活力降低、抗性减退、产量下降、品质变劣等情况。现将其产生的原因与防止对策介绍如下。     

硫包衣尿素在夏玉米上的应用效果研究

为了了解硫包衣尿素在夏玉米上的应用效果,充分的发挥肥料作用,通过田间试验,研究了硫包衣尿素和普通尿素不同用量、不同施肥方法（普通尿素为基肥＋1次追肥;硫包衣尿素为一次性基施）对夏玉米出生长、产量、氮肥表观利用效率等的影响。结果表明：硫包衣尿素以等氮量或减量30%采取一次性施肥的方式,夏玉米的生长和产量与普通尿素当地习惯施肥无显著差异,其产量分别达到了10789.17 kg/hm2、10595.11 kg/hm2;在夏玉米上应用硫包衣尿素可显著提高肥料的利用效率和农学效率,其中硫包衣尿素减量30%处理氮肥表观利用率和生产率分别达到了42.59%和20.74kg/kg。硫包衣尿素以一次性基施的施肥方式替代普通尿素基肥加追肥是可行的,能达到省工、节肥、增效的目的。     

猪繁殖与呼吸障碍综合征检测技术的研究进展

猪繁殖与呼吸障碍综合征(PRRS)是以母猪繁殖障碍和仔猪严重的呼吸道症状及高死亡率为特征的猪病毒性传染病。其发生与流行给养猪业造成巨大的经济损失,现已成为危害养猪业较严重的病毒性疾病之一。及时、准确地检测出该病以便采取相应的措施, 是成功防制该病的关键。本文就从血清学、病原学、分子生物学等方面阐明了猪繁殖与呼吸障碍综合征的检测技术,从而为兽医临床诊断与治疗提供参考。     

猪超量使用矿物质添加剂的危害与防控

矿物质添加剂已在养猪生产中广泛应用,其生物和经济作用明显,促进了养猪业的发展和养殖效益的提高。不过,乱用、滥用矿物质添加剂养猪的现象并不鲜见,不仅对猪自身及其产品和环境带来危害,也威胁到消费者的健康安全,应引起整个行业的重视。一、主要矿物质过量使用的危害与防控     

浅谈棉花品种退化的原因及对策

棉花是常异花授粉作物，品种群体的遗传基础复杂，棉花的经济性状受环境因素的影响较大，在大田连年种植易发生混杂退化，造成产量下降，纤维品质变劣。     

基于网络的鸡病防治与诊断专家系统的设计

目前中国鸡病防治中存在一些暂时无法解决的难题,如基层中鸡病诊断专家缺乏、鸡病防控不及时等。基于现状,利用计算机网络技术和人工智能技术,将SQL数据库和ASP.NET技术相结合,设计并开发了基于网络的鸡病防治与诊断专家系统。该系统将鸡病诊断和鸡病防治知识进行集成,采用基于规则的模糊化的混合推理策略,实现了鸡病诊断和防治的数字化和智能化,用户可通过网络实现鸡病诊断、鸡病防治、鸡群管理、知识查询和统计分析等功能。经验证性试验和专家评测,该系统结构合理,功能完善,可以满足广大基层用户的需求,具有一定的推广应用前景。     

Selection for yield in wheat breeding

Summary If selection based on F₃ yield tests is to be effective, the yield tests must be successful in discriminating among yield genotypes. The available literature indicates that simple tests with limited or no replication are not very effective, although more extensive, replicated tests may be.Data from an experiment comparing F₃ yield tests with a single seed descent procedure showed that F₃ selection based on a two-replicate test with single seed descent procedure did not justify the extra work involved.     

The Setting of Acoustic Emission Detecting Parameters in Concrete Structure

In order to solve the problem that the choice of acoustic emission (AE) parameters in concrete detection are determined only by experience, several tests were conducted. Through lead-breaking and stimulant loading tests, the reasonable value of threshold at which noise can be efficiently insulated was obtained. Through lead-breaking tests, time parameters (PDT, HDT, HLT) which fit concrete samples were obtained. The velocity and attenuation of AE signals in concrete also were measured through lead-breaking tests. This method of ascertaining detection parameters by testing is practical for AE detection in concrete structures.     

Tests with Controlled Net Mean Stress Equaling Constant of an Remolded Unsaturated Loess

The disruption, yield and water content change of a remolded unsaturated loess is studied during the course of shear tests with controlled net mean stress equaling constant. Two types of density's triaxial drained shear tests with controlled net mean stress and suction equaling constants are conducted. The test results show that the disruption stress increases with suction. A new method to identify the field stress under triaxial drained shear tests with controlled net mean stress equaling constants is suggested, and the shape of loading-collapse yield curve are similar in q-s plane and in p-s plane. The soil-water characteristic curve is dependent on deviatoric stress, and the soil-water characteristic curve including water content, suction, net mean stress and deviatoric stress is proposed.     

糯玉米新品种“银糯一号”的选育

“银糯一号”是北京农学院生物技术系于2000年是以XN-5自交系为母本，BN51自交系为父本杂交而成的糯玉米杂交种。该品种经2000~2001年的测交试验，2002~2003年的产比试验，2004-2005年的北京市区域试验，皆比对照“中糯一号”增产30.8%（鲜穗）和20.7%（鲜粒）以上，大面积生产鲜穗产量达10800kg/公顷以上。在2006年3月北京市农作物品种审定委员会审定通过(京审玉2006008)。     

State and Prospects of Diesel Engine Fault Diagnosis Technique

As a kind of complex power machinery, diesel engine is being paid more and more attention to its condition monitoring and fault diagnosis technology. In the fault diagnosis field of diesel engine, the technique of signal process, character abstraction and identification method have formed a system, but there is a certain distance away from practical. This paper analyzes the common faults and influencing factor of diesel engine. The principle, characteristic and disadvantage of modern fault diagnosis technology, such as various time-frequency methods based on vibration signal, speed fluctuation method, iron content and spectrometry, grey system theoretical diagnosis method, artificial neural network and expert system fault diagnosis method, were reviewed. The difficulties and the development direction of diesel engine fault diagnosis were put forward in the end.     

Analysis of Load-bearing Characteristics of Concrete Pile Composite Foundation

Some conclusions were drawn from two groups of in-site tests on concrete pile composite foundations. In the tests, it was found that the pressure under the rigid loading slab is different, in which the pressure under the center of the slab is the less and under the edge of the slab is the biggest. The pile-soil stress ratio is not a constant; it increases with the adding of the load. Most of the pile-soil ratio vary from 9 to 13 in these tests and the load that the piles share can be more than seventy percent of the whole load. It was proved that the bearing capacity of the concrete pile composite foundation is high with a little settlement, so it will be used more and more in the future.     

Step-by-step Method of Structural Damage Diagnosis

Base on the existing step-by-step structural damage diagnosis method, a three-step structural damage diagnosis method is developed. According to the analysis of the characteristic of genetic algorithm, a new idea of excluding the undamaged element by means of step-by-step evaluation is developed to deal with the damage diagnosis problem. In this method, sensitivity genetic algorithm is used to exclude the undamaged element step by step and residual force method is used to fix the damage district. According to the simulation research of a 2D framed structure, it is shown that the step-by-step structural damage diagnosis method can gain the ideal results when it's difficult for a single damage diagnosis method to get the good results. It is also indicated that sensitivity genetic algorithm is a good way to exclude the undamaged element step by step.     

Bearing capacity of solid waste ground reinforced by stone column

Based on presented tests of improvement of solid waste ground by stone column, the failure mode of lateral expansion of column body can be found. It is assumed that solid waste surrounding column is in Rankin's positive limit situation caused by lateral expansion of column body, self weight solid waste and column is neglected, the calculation theory of limit bearing capacity of stone column can be extended on equilibrium of solid waste and column. The limit bear capacity of stone column can be calculated on parameters by complete tests and reference data. The heavy dynamic penetration tests were finished in stone column and the characteristic value of bearing capacity can be recommended on blow count. It is shown that bearing capacities of calculation and field test are close.     

作物氮素诊断技术的研究综述

氮素是作物生长发育和产量品质形成所必需的营养元素。本文在简述研究背景和作物氮素营养监测与诊断技术需求的基础上,介绍了作物氮素营养监测技术的发展历程及发展趋势,综述了作物氮素营养诊断技术的国内外研究进展,指出快速、无损、准确地监测作物氮素状况,对于农业生产可持续发展和生态环境保护具有重要意义。