麦田硬草的空间分布型及抽样技术研究

硬草的空间分布为聚集分布,分布的基本成分是个体群,聚集强度随着杂草密度的增加而增强。这种分布在杂草密度较低时由环境因素造成,在杂草密度较高时由杂草自身特性或与环境的共同作用造成。取样方法以棋盘式取样误差率显著低于其他取样方法。利用空间分布的有关参数,在允许误差范围内给出了不同杂草密度下的理论抽样数。     

稻茬油菜田稻槎菜的空间分布型及抽样技术

应用种群空间分布型聚集度指标对稻槎菜的空间分布型进行了测定。结果表明,泾县稻茬油菜田稻槎菜的空间分布型均符合聚集分布。分布的基本成分是个体群,聚集强度随着杂草密度的增大而增强。这种分布在杂草密度较低时由环境因素造成,在杂草密度较高时由杂草自身特性或与环境的共同作用造成。对其抽样技术进行研究,6种取样方法中Z字形和双对角线式取样误差率较低,以Z字形抽样最佳。同时,利用空间分布的有关参数,在允许误差的范围内给出了不同杂草密度下的理论抽样数。     

内蒙古草地生产力时空变化及驱动因素分析

基于草地资源普查资料和GIS技术,以生物量与可食牧草比例作为影响草地生产力的主要因子,以县域为单位,对内蒙古草地生产力的时空变化特征及其分布的地域差异性进行了分析.结果表明:2000-2003年与1981-1985年相比,大部分地区生物单产及可食牧草产量均明显减少,可食牧草比例也明显降低;生物单产、可食牧草产量以及可食牧草比例高值区与次高值区均明显减少;大部分地区草量变化与草质变化具有时空一致性.最后从气候变化、草畜矛盾、现有草原管理制度及建设状况方面,对内蒙古草地生产力变化成因进行了分析.     

四川口岸外来杂草的调查与监测

通过实地调查、监测和文献调研,对四川口岸外来入侵杂草的种类组成、分布、生活型、原产地、入侵途径以及危害程度进行了分析。结果表明:四川口岸常见杂草种类共48科、138属、196种,其中外来杂草14科31属39种,尚未见检疫性入侵杂草分布。外来杂草中,菊科植物种类最多,生活型以一年生草本为主;原产地以美洲为主,引入途径以人为无意引入为主;有11种入侵杂草给当地生态环境带来严重危害;在和我国其他省市分布的入侵植物种类资料对比后,提出了对口岸防控外来入侵植物的建议。     

新疆棉田牧草盲蝽的空间分布规律

为明确新疆棉田牧草盲蝽Lygus pratensis(Linnaeus)的空间分布型,于2012-2014年对新疆喀什地区棉田牧草盲蝽种群数量进行了系统调查,应用5种聚集度指数、Iwao m*-m回归方程和Taylor幂法则分析判定牧草盲蝽成虫、若虫及整个种群(成虫和若虫)在棉田的空间分布型,并利用种群聚集均数分析聚集原因。结果表明,牧草盲蝽成虫、若虫及整个种群的久野指数C_A0、负二项分布参数k0、丛生指数I0、聚块指数m*/~-1,表明三者在新疆棉田均呈聚集分布。且牧草盲蝽成虫和若虫的Blackith聚集均数λ2,说明二者在棉田的聚集是由环境因素引起的。Iwao m*-m回归分析结果表明,牧草盲蝽成虫、若虫和整个种群个体间相互吸引,分布的基本成分为个体群(α0、β1);Taylor幂法则分析结果表明,牧草盲蝽成虫、若虫和整个种群在棉田更趋向于聚集分布,聚集度依赖于密度。     

甘肃河西地区口岸外来杂草的调查与监测

通过实地杂草疫情监测,对甘肃河西地区口岸入侵杂草的种类、原产地、生活型、引入途径、入侵性等方面进行了调查分析。调查发现口岸地区常见杂草29科107种,菊科、豆科、禾本科、藜科杂草为4个优势科;其中88种为外来入侵杂草,主要集中在菊科和禾本科,原产地亚洲和欧洲为主,主要的入侵方式为无意引入。尚未发现检疫性入侵杂草分布。另外针对加强检疫监管及进境粮谷及矿砂携带杂草撒漏扩散提出几点建议。     

二点委夜蛾种群空间分布型及抽样技术研究

对田间二点委夜蛾调查资料,通过Cassie扩散系数C、Kuno指标CA、平均拥挤度m*等指标判断二点委夜蛾幼虫为聚集分布,进一步采用核心(Neyman,奈曼)分布和负二项(Mosaic)分布的理论频次分布公式,经卡方X2检验,确定二点委夜蛾幼虫的空间分布型为负二项分布。聚集分布的原因是由二点委夜蛾的聚集习性和环境因素所形成的。在此基础上明确了抽样方式和序贯抽样模型。     

外来入侵植物长芒苋在中国不同地区的表型变异与环境适应性

长芒苋(Amaranthus palmeri)是近年来入侵我国的超级杂草,已在我国从南到北的多个点定殖,一旦大面积扩散势必会对农业生产和生物多样性保护等构成极大威胁。长芒苋在我国入侵点的纬度跨度大于其原产地北美洲的分布,探明其在我国不同纬度的地理种群的环境适应机制,对评估扩散潜能、建立早期监测预警等防控措施具有重要意义。本研究在同质种植园实验条件下,通过测定长芒苋不同纬度地理种群的生活史、形态及生物量等11个性状指标来分析其在我国的表型变异与环境适应性。结果表明,在同质园条件下,长芒苋不同地理种群间株高等7个表型性状指标差异不显著,而开花和发芽时间、花序长以及比叶鲜重4个指标具有显著差异(p<0.01),且它们的表型变异随年平均温度(纬度)线性增加或降低。开花时间随纬度的升高而缩短,发芽时间、花序长和比叶鲜重随纬度的升高而增加。基于长芒苋不同纬度地理种群间表型性状的异同,我们推断表型可塑性促进了其在我国不同地理环境中的定殖,表型变异(如高纬度种群开花时间提前)可促进其环境适应性进化,拓展其在我国的适生性分布区,增强其向原产地适应环境梯度之外地区入侵和扩散蔓延的潜力。     

马铃薯甲虫空间分布型及抽样技术研究

马铃薯甲虫Leptinotarsa decemlineata (Say)是我国马铃薯恶性入侵害虫。本研究利用聚集度指标检验、Taylor幂法则和Iwao回归法对马铃薯甲虫成虫、幼虫和卵在田间的空间分布型进行了研究。聚集度指标检测各虫态均为聚集分布,且种群聚集主要是由马铃薯甲虫各虫态本身的聚集行为,或由其本身的聚集行为与环境异质性共同作用所致。建立了马铃薯甲虫成虫、幼虫和卵在田间调查的理论抽样数学模型。田间抽样方法,成虫应采用大五点、对角线法;幼虫最适应采用Z字型法;卵最适应采用对角线法。     

不同轮作制度对定西地区农田杂草群落的影响

为探讨不同轮作制度对定西地区农田杂草群落的影响,采用倒置"W"九点取样法,调查了定西地区7种不同轮作制度下田间杂草的种类、数量、地上生物量等。在试验田发现11个科共15种杂草;从杂草发生密度、地上生物量上看,苦苣菜、藜是农田优势杂草,防除的目的杂草;不同轮作田的杂草群落由优势杂草组成;从不同轮作田杂草群落的物种多样性来看,马铃薯胡麻轮作马铃薯小麦轮作胡麻小麦轮作胡麻连作小麦胡麻轮作小麦马铃薯轮作胡麻马铃薯轮作;对不同轮作田杂草群落进行聚类,可分为四类。通过对不同轮作田中杂草的密度、地上生物量和综合优势度比的综合分析,可以看出胡麻连作、小麦胡麻轮作、马铃薯胡麻轮作、小麦马铃薯轮作中杂草的危害性较大。马铃薯小麦轮作、胡麻小麦轮作和胡麻马铃薯轮作对杂草有一定的控制作用。     

小麦田不同杂草群落及防除时间对小麦产量的影响

为明确小麦田不同杂草群落及防除时间对小麦产量的影响,于2013—2015连续两年在山东省聊城市高唐县小麦田中设无草对照区、禾本科杂草区、阔叶杂草区以及混合杂草自然发生区4种不同杂草群落以及不同的杂草防除时间,测定在不同条件下小麦产量及各项产量构成指标的情况。结果表明,阔叶杂草对小麦产量的影响大于禾本科杂草,冬小麦田杂草的最佳防除时间为4月1日之前,在此期间除草对小麦产量影响均不大,但之后防除或不除草会造成小麦严重减产甚至绝产,2014年4月15日除草可造成在阔叶杂草区和杂草混合生长区的小麦减产30.5%和32.6%,不除草可造成在禾本科杂草区、阔叶杂草区和杂草混生区的小麦减产8.6%、91.4%和94.3%,2015年趋势和2014年一致。从构成小麦产量的3个指标来看,杂草危害主要影响小麦的总穗数,其次为穗粒数,对千粒重影响最小。     

Can an integrated management approach provide a basis for long-term prevention of weed dominance in Australian pasture systems?

Broad-leaved weeds in pasture, such as Carduus nutans, Onopordum spp. and Echium plantagineum are a major problem for graziers in southern Australia. Previous attempts to combat these weeds with a single technique have only resulted in short-term success. An approach to long-term control, combining biological control with different grazing and herbicide strategies, was evaluated in an integrated weed management (IWM) programme, in south-eastern Australia. This IWM study was one of the few that has focused on biological control agents. During the field trials, the impacts of grazing and herbicide treatments on the weed and biological control agents, as well as on pasture composition, were monitored. This paper concentrates on the part of the study that focuses on the role and importance of pasture composition as part of weed management. The main pasture components were monitored using botanal , a sampling technique for estimating species composition and pasture yield in the field. IWM is a long-term ecological approach and after 3 years, major trends were just becoming apparent. This study shows that pasture composition can be manipulated to increase productivity and sustainability. It demonstrates that broad-leaved weeds can be reduced when high level pasture background management and chemical control are combined.     

United States Department of Agriculture-Agricultural Research Service research on pest biology: weeds

Over 125 permanent full-time scientists conduct research within the USDA Agricultural Research Service (ARS) on issues related to weeds. The research emphasis of most of these scientists involves ecology and management or biological control of weeds. Many scientists perform research on weed biology as components of their primary projects on weed control and integrated crop and soil management. Describing all ARS projects involved with weed biology is impossible, and consequently only research that falls within the following arbitrarily chosen topics is highlighted in this article: dormancy mechanisms; cell division; diversity of rangeland weeds; soil resources and rangeland weeds; poisonous rangeland plants; horticultural weeds; weed traits limiting chemical control; aquatic and semi-aquatic weeds; weed/transgenic wheat hybrids; seedbanks, seedling emergence and seedling populations; and weed seed production. Within these topics, and others not highlighted, the desire of ARS is that good information on weed biology currently translates or eventually will translate into practical advice for those who must manage weeds.     

Influence of sowing density and spatial pattern of spring wheat (Triticum aestivum) on the suppression of different weed species

To better understand the potential for improving weed management in cereal crops with increased crop density and spatial uniformity, we conducted field experiments over two years with spring wheat ( Triticum aestivum ) and four weed species: lambsquarters ( Chenopodium album ) , Italian ryegrass ( Lolium multiflorum ), white mustard ( Sinapis alba ), and chickweed ( Stellaria media ). The crops were sown at three densities (204, 449, and 721 seeds m⁻²) and in two spatial patterns (normal rows and a highly uniform pattern), and the weeds were sown in a random pattern at a high density. In most cases, the sown weeds dominated the weed community but, in other cases, naturally occurring weeds were also important. There were strong and significant effects regarding the weed species sown, the crop density, and the spatial distribution on the weed biomass in both years. The weed biomass decreased with increased crop density in 29 out of 30 cases. On average, the weed biomass was lower and the grain yield was higher in the uniform compared to the row pattern in both 2001 and 2002. Despite the differences in weed biomass, the responses of L. multiflorum , S. media , and C. album populations to crop density and spatial uniformity were very similar, as were their effects on the grain yield. Sinapis alba was by far the strongest competitor and it responded somewhat differently. Our results suggest that a combination of increased crop density and a more uniform spatial pattern can contribute to a reduction in weed biomass and yield loss, but the effects are smaller if the weeds are taller than the crop when crop–weed competition becomes intense.     

Alteration of plant species mixtures by virus infection: Managed pastures the forgotten dimension

What occurs when virus infection is spreading within a mixed plant species population? This question is important not only for economically significant, mixed species managed systems but also for environmentally significant mixed wild species populations. It received attention in recently published ecological studies on wild plant species, but these, and recent general pasture research publications, rarely mention earlier virus studies involving mixed species managed pasture. This review seeks to rectify that situation. It describes 10 diverse examples of past research on mixed species managed pasture done over two decades on three continents that demonstrated plant species balance changes arising from virus infection. These examples showed that plants belonging to susceptible pasture cultivars sensitive to systemic virus infection are sufficiently weakened that their ability to withstand competition from nonhost plants of other pasture species, or weed species, was diminished sufficiently to alter the plant species balance. Also, a similar alteration occurred when they were competing with virus-resistant or virus-tolerant host plants of the same or other pasture species, or a virus-resistant weed species. Such competition also diminished seed production, which decreased their ability to regenerate. Notably, as reported subsequently with wild plant species populations, when two different pasture species infected by the same virus compete with each other, growth of the more sensitive species is suppressed. Because managed mixed species pastures constitute an important component of regenerative agriculture, retaining an optimal balance of pasture species and delaying pasture decline from weed invasion both require effective management of virus diseases.     

Appropriateness of inexpensive, hand-held global positioning system units for creating weed maps in a pasture

This paper describes the practical use of a global positioning system receiver (hand-held GPS) as a means of measuring and describing pasture areas invaded by weeds. The accuracy of two GPS units, a hand-held GPS with an external antenna (GPS with an antenna) and the differential global positioning system receiver (DGPS), were examined in Morioka, northern Japan. In addition, an area of weed patches and a pasture, determined using the GPS with an antenna, were compared to the measurements made with a conventional tape and a weed map was created based on the coordinate data of latitude and longitude measurements. The accuracy of the GPS with an antenna was poor (8.3 m); however, the precision of the unit was reasonable in measuring area. An area estimation error by the GPS with an antenna was 7% when practically measuring weed patches of 141 m² and 1% in a paddock of 12 566 m². From these results, it appears that the GPS with an antenna might have an acceptable error in measuring areas for weed control in a pasture. A weed map produced from the coordinate data surveyed using the GPS with an antenna enables the state of weed growth and its domination in an area of pasture to be visually understood. Therefore, GPS technologies easily can be applied to quickly obtain information on weed infestation.     

Designing a sampling scheme to reveal correlations between weeds and soil properties at multiple spatial scales

Weeds tend to aggregate in patches within fields, and there is evidence that this is partly owing to variation in soil properties. Because the processes driving soil heterogeneity operate at various scales, the strength of the relations between soil properties and weed density would also be expected to be scale‐dependent. Quantifying these effects of scale on weed patch dynamics is essential to guide the design of discrete sampling protocols for mapping weed distribution. We developed a general method that uses novel within‐field nested sampling and residual maximum‐likelihood (reml ) estimation to explore scale‐dependent relations between weeds and soil properties. We validated the method using a case study of Alopecurus myosuroides in winter wheat. Using reml , we partitioned the variance and covariance into scale‐specific components and estimated the correlations between the weed counts and soil properties at each scale. We used variograms to quantify the spatial structure in the data and to map variables by kriging. Our methodology successfully captured the effect of scale on a number of edaphic drivers of weed patchiness. The overall Pearson correlations between A. myosuroides and soil organic matter and clay content were weak and masked the stronger correlations at >50 m. Knowing how the variance was partitioned across the spatial scales, we optimised the sampling design to focus sampling effort at those scales that contributed most to the total variance. The methods have the potential to guide patch spraying of weeds by identifying areas of the field that are vulnerable to weed establishment.     

Improvement of carpet grass (Axonopus affinis Chase) pasture by fertilization and oversowing with the aid of selective herbicides

An experiment was done to determine the effect of spring and autumn application of asulam and dalapon, nitrogen fertilizer and oversown white clover (Trifolium repens L.) on the productivity of subtropical pasture dominated by carpet grass (Axonopus affinis Chase). Assessments were made of pasture yield, botanical composition, weed invasion and recolonization by pasture species during the 12-month period following herbicide application. Both herbicides decreased the yield of carpet grass and increased that of the more productive paspalum (Paspalum dilatatum Poir.) except after autumn application when the yield of paspalum was greatly reduced by dalapon. White clover became established only on plots treated with herbicide and only after autumn application. Clover yields were greatest on plots treated with dalapon. Asulam was considered to be the most suitable herbicide for altering the balance between carpet grass and paspalum because dalapon initially reduced paspalum yield after autumn application and delayed recovery of total pasture. In addition, dalapon permitted greater invasion by broadleaf weeds. This work showed that herbicides have a potential role for speeding up botanical changes in unproductive carpet grass pasture and further refinement of the technique might provide a useful tool for increasing pasture productivity.     

Effects of the relative time of emergence and the density of common lambsquarters (Chenopodium album) on corn (Zea mays) yield

Common lambsquarters (Chenopodium album) is one of the world's worst weeds. In order to study the competitive potential of single‐cross 704 corn (Zea mays) in competition with common lambsquarters at different relative times of emergence and density levels of the weed, an experiment was conducted in 2006 at the farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran. This experiment was designed as a split plot based on a randomized complete block design with three replications. The emergence time of the weed was considered at three levels (7 days and 14 days earlier than corn and simultaneously with corn) as the main plot, while the density of the weed was considered at six levels (0, 4, 8, 12, 16, and 20 plants per m²) as the subplot. The results showed a decrease in the grain yield and biomass of corn, as the emergence time of corn was delayed in comparison with the weed in a way that the maximum reduction was observed at the earlier emergence of the weed, compared to corn, and also at a high density of the weed. As the weed emerged earlier than corn, the rate of yield loss resulting from the first flush of weeds was not that high. However, with every few days that the weed emerged earlier than corn, the rate of yield loss became higher as the density of the weed increased to its maximum. The maximum reduction in the yield components was observed at 14 days earlier emergence of the weed, compared to corn, and at high densities, as the corn plants were overshadowed by the weed canopy and no ear was produced.     

Barley seed vigour and mechanical weed control

Two field experiments investigated the influences of crop seed vigour on the effect of weed harrowing and crop:weed interactions in spring barley. Artificially reduced seed vigour, which was similar to the variation within commercial seed lots, caused a reduction in germination rate, delayed time of emergence and, consequently, caused reduced competitive ability against weeds. During both years, the reduced seed vigour increased the average weed biomass by 169% and 210%, and reduced the average crop yield by 16% and 21%. Without the influence of weeds, the yield reduction was estimated to be 8% and 10%. A three‐times harrowing strategy reduced the weed biomass by 75% and 72% on average. However, it also caused damage to the crop and reduced yield. There was no clear interaction between barley seed vigour and weed harrowing in the experiments but, in one year, reduced seed vigour tended to decrease the effect of weed harrowing and also increased crop damage. Results in both years, however, indicate potential possibilities for successful integrated weed control by adding the use of high seed quality to a weed harrowing strategy.