基于农田养分管理的杂草生态防控策略

农田杂草是农田生态系统的一个组成部分,揭示杂草种群对养分管理模式的响应及其机制是进一步通过科学的养分管理来实现防控农田杂草的关键。为此,作者总结了农田养分管理与杂草的关系的研究进展、指出了存在的问题,并从农田杂草的重点防控对象、农田优势杂草种群和竞争临界期的确定以及杂草的生态化学计量学特征等方面对杂草生态防控策略进行了分析。在此基础上,作者提出了土壤营养调控假设,期望为制定农田杂草综合管理策略以及保护农田生态环境提供新的思路。     

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。     

不同施肥模式对南方红壤稻田冬春杂草群落特征的影响

为掌握不同施肥模式下南方稻田冬春杂草群落特征,丰富稻田生物多样性保护理论,为稻田冬春作物结构调整提供杂草综合防除技术途径,本研究借助稻田长期定位试验,分别于2007年1月（冬季）和4月（春季）对杂草群落进行监测。结果表明,日本看麦娘是南方红壤水稻冬闲田优势杂草种群,春季相对密度达到65％以上,其优势度随季节和施肥模式而有所变化。长期不施磷的冬闲稻田杂草的总密度和生物量显著降低。有机和无机肥配合施用较单施无机肥能明显提高田间杂草的生物多样性,而在此基础上种植豆科绿肥能够显著降低田间杂草的生物量,其冬季田间杂草生物量仅为62g／m^2,低于整个试验区的平均值（67g／m^2）,而其生物多样指数却较其他施肥模式高。因此,通过稻田施肥与冬季利用模式的结合,可以对冬闲田杂草群落进行有效控制。     

我国农田杂草综合治理的现状及进展

农作物受杂草危害所造成的减产损失很大.据统计,世界危害性较大的农田杂草有90多种,每年受草害减产为9.7%;我国农田危害性较大的杂草有50多种,危害面积达6亿多亩,由于草害每年约减产粮食1700多万吨,棉花25万吨,用于除草耗费劳力达50—60亿劳动工日.分布面广、危害性大,防除又较难的杂草有10多种,其中以稻田稗草、扁秆藨草、麦田看麦娘、野燕麦、旱地作物农田的马唐、牛筋革、藜、蓼、苋等对稻、麦、棉、大豆等作物生产的危害损失最大.     

农田杂草抗药性的发生为害、原因与治理

抗药性是杂草防除最大难题之一。杂草抗药性演化速度由抗药性突变起始频度、除草剂选择压、杂草适合度及杂草种子库寿命四个因素控制。治理抗药性杂草必须进行综合治理：在农业防治基础上根据除草剂发生抗药性的风险大小，采取合理轮用、混用等措施可延缓、预防抗药性；抗性杂草发生后及早发现，控制抗性中心以防止其蔓延。     

贵州省农田杂草群落及危害

贵州省农田发生杂草种类有８７科３０６属５８０种；其中农田主要杂草１５８种，重要杂草１６种，危害较重的杂草１７种，区域性主要杂草２３种，常见主要杂草１０２种；杂草群落因作物、海拔而变化；全省２级以上杂草危害面积１５４．２～２０９．９万ｈｍ２，占种植面积的４０．４％～６０．５％，产量损失率１１．７％，年粮食损失１．４５～２．５５亿ｋｇ，受害程度小麦＞玉米＞烤烟＞油菜＞水稻。     

重庆市农田杂草发生现状及治理对策

通过对重庆市农田杂草发生现状的调查,阐述农田杂草的危害,结合目前农村化学除草剂的应用情况,提出农田杂草的控制技术和综合治理思路.     

青海保护性耕作农田杂草群落组成及生物多样性

采用倒置“W”9点取样法对青海保护性耕作农田杂草种类进行了调查,以明确田间杂草的种类组成及群落结构.结果表明,青海省保护性耕作农田杂草有67种,隶属于25科,其中优势杂草有密花香薷(Elsholtzia densa Benth)、猪殃殃(Galium maborasense Masamune)、野燕麦(Avena fatua Linn.)、藜(Chenopodium album L.)、苣荬菜(Sonhus arvensis Linn.)、大刺儿菜(Cephalanoplos setosum(Willd.) Kitam.)6种,是构成青海各地区保护性耕作农田杂草群落的主要优势种,区域性优势杂草有5种,常见杂草有17种,一般杂草有39种.湟中地区主要形成猪殃殃+密花香薷+藜+野燕麦+大刺儿菜+芦苇+尼泊尔蓼为主的杂草群落;民和地区为狗尾草+藜+扁蓄+野燕麦+田旋花+荞麦蔓+大刺儿菜,平安地区为野燕麦+猪殃殃+苣荬菜+大刺儿菜+赖草+荞麦蔓+密花香薷+扁蓄+泽漆,化隆地区为薄蒴草+猪殃殃+野燕麦+荞麦蔓+苣荬菜+密花香薷,大通地区为野燕麦+猪殃殃+藜+大刺儿菜+问荆+密花香薷,刚察地区为密花香薷+西伯利亚蓼+薄蒴草+藜+微孔草+旱雀麦+苣荬菜+野胡萝卜.湟中和大通地区保护性耕作农田杂草群落的物种丰富度、多样性及均匀度较其它地区高,而优势度较低.从群落相似性来看,湟中和大通群落结构最为相似.地理环境、气候条件及控草措施的不同,可能是导致保护性耕作农田杂草发生及群落组成产生差异的原因.     

玉米与不同植物间作对田间杂草群落动态变化的影响

2008年和2009年对玉米苗期-拔节期、喇叭口期-授粉期、成熟期田间杂草群落的密度、生物量和多样性进行监测。结果显示,玉米与向日葵、苜蓿、甘薯、花生间作系统中,玉米-向日葵间作模式能明显降低田间杂草总密度和生物量,但抑制效果随着玉米的生长,越到后期效果越不明显,第二年的抑制效果也明显弱于第一年。2008年,玉米-向日葵间作处理杂草总密度在苗期-拔节期、喇叭口期-授粉期、成熟期分别是对照的44.46%、43.64%和76.23%,总干重分别是对照的12.65%、20.77%和58.14%;2009年,总密度在各时期分别是对照的78.33%、81.19%和88.26%,总干重分别是对照的52.99%、88.28%和83.55%。此外,玉米-向日葵间作还能提高成熟期田间杂草的生物多样性,2008年多样性指数是对照的1.15倍,2009年是对照的1.13倍。玉米与苜蓿、甘薯、花生间作模式与对照相比不能降低甚至还增加了田间杂草的发生与危害,但均比对照提高了杂草的生物多样性。初步表明,玉米与向日葵间作,既能增加农田生态系统的多样性,又有一定的控制杂草效果。     

农田生态系统生物多样性与害虫综合治理

本文评述了农田生态系统中生物多样性的概念及其与害虫发生的关系;探讨了农田生态系统中生物多样性影响害虫发生的生态机制,农田生态系统中生物多样性在害虫综合治理中的作用;提出了利用生物多样性进行害虫综合治理的策略和措施。     

Weed flora and soil seedbanks in fields dominated by Imperata cylindrica in the moist savannah of West Africa

Imperata cylindrica (L.) Raeuschel is a dominant and infamous grass weed in the savannah of West Africa. Research to reduce the weed to non-damaging levels is a priority activity at many agricultural institutions. The successful development and implementation of long-term I. cylindrica management strategies depend on the ability to predict changes in weed composition after I. cylindrica has been controlled effectively. The weed flora and soil seedbank were assessed from 329 fields dominated by this species in the fringes of the humid forest (HFF), coastal/derived savannah (CDS) and in the southern Guinea savannah (SGS) in 1996 and 1997. The objectives of the study were to correlate species composition of the weed flora with that of the soil seedbank and to determine the effect of management factors and soil properties on the composition of the weed flora. Species richness in the weed flora and in the weed seedbank was higher in the SGS than in the CDS and HFF. Mean weed density per field was generally higher in the HFF (156 ± 25.0 weeds m^–2) than in the CDS (108 ± 8.1 weeds m^–2) and in the SGS (92 ± 6.3 weeds m^–2). Weed composition varied with agroecological zone as well as with management factors and soil properties. Sørenson's index of similarity was low (mean=0.20) in all zones, indicating poor similarity between the weed flora above-ground and the soil seedbank.     

Weed dynamics in the Mediterranean urban ecosystem: ecology, biodiversity and management

This paper presents a review of weed dynamics in the Mediterranean urban ecosystem, seen both in an ecological and biological perspective and also in relation to the interaction between human activity and the survival strategies of the various phytocoenoses. Although generalizations on urban weeds cannot easily be drawn on account of the wide range of microenvironments, anemochoric dissemination mechanisms (Asteraceae), resilience (grasses) and perennation are of particular importance. The reasons underlying the undesirability of weeds in the urban environment are investigated. Not only are weeds considered unsightly, but they may also give rise to ‘functional’ obstacles, damaging sidewalks or clogging storm drains. Furthermore, they may adversely affect human health by releasing allergenic pollen into the atmosphere. Management of urban weeds is based almost exclusively on mechanical control, as chemical measures may involve a toxicity risk for man. Paradoxically, certain weeds species may however have a positive effect if they are linked to fauna (butterflies, birds, etc.) considered to give a favourable impression in the cityscape. Finally, the possibility of favouring the biodiversity of the urban ecosystem by introducing some wildflowers typically associated with the degree of biodiversity of the surrounding environment is discussed.     

Weed suppression by soil steaming in combination with activating compounds

The aim of this study was to determine the weed suppression potential of soil steaming plus activating compounds (KOH or CaO) to boost soil temperature. Different combinations between the compounds and rates were tested in experiments carried out in the field and in a controlled environment. Treatment effects were assessed on field weed vegetation and on seedbank and seedling emergence of three winter ( Alopecurus myosuroides , Matricaria chamomilla and Raphanus raphanistrum ) and four spring annuals ( Amaranthus retroflexus , Echinochloa crus-galli , Fallopia convolvulus and Setaria viridis ), were assessed on field weed vegetation. Neither maximum soil temperature (from 72 to 85°C) nor duration of high temperature in the 3 h following application consistently affected weed suppression. In the field, no significant effects on total weed density were recorded, but there were some significant effects on individual species. The weed seedbank was clearly suppressed by activated steaming: total seedling emergence was inversely related to increasing KOH rates both in the 0–10 and 10–20 cm soil layers, while for CaO the relationship was significant only in the 0–10 cm layer. Winter annuals were more sensitive to KOH than CaO and spring annuals had a more pronounced species-specific response to treatments. There was a strong negative relationship between compound rate and seedling emergence for all species. Alopecurus myosuroides was the most sensitive to the steam-alone treatment (77% reduction), whereas M. chamomilla and E. crus-galli were the least sensitive. Results from this study indicate that the type and rates of activating compounds for soil steaming must be adjusted to the weed community composition.     

Weed vegetation and its conservation value in three management systems of Hungarian winter cereals on base-rich soils

Floristic composition and conservation value of the weed vegetation of winter cereal fields on base-rich soils in western Hungary was compared among three management systems: (i) small, extensively managed fields; (ii) small, intensively managed fields and (iii) large, intensively managed fields. Data were analysed by principal components analysis (PCA) and redundancy analysis (RDA). Most variation in species composition was explained by the differences between the three field types, particularly by the difference between the extensively managed fields and the two types of intensively managed fields and by crop cover. There were several species positively associated with small extensively managed fields, but no species associated with either of the two types of intensively managed fields. Logistic regression was made of the occurrence of species groups important for nature conservation on the first RDA axis, representing the distinction between the extensively and intensively managed fields. This showed that Red List and insect-pollinated plant species occurred more frequently in small extensively managed fields, but there was no difference between fields in the frequency of bird seed-food species.     

Weed flora and weed management in established olive groves in Albania

Weed flora were surveyed during 2000 and 2001 in 10 established olive groves that were located in the area of Vlora, in south‐western Albania. The effectiveness of six weed management treatments (soil tillage, straw mulch, cover cropping [a mixture of rye with peas], and grazing, as well as glyphosate and diuron application) on the weed flora, olive yield, and fruit quality also were investigated in two locations during 2000, 2001, and 2002. More than 80 weed species were recorded, representing a total of 14 families, in which the families Poaceae, Fabaceae, Asteraceae, Ranunculaceae, and Rosaceae predominated. The glyphosate application provided the highest and most consistent level of weed control, whereas diuron achieved sufficient weed control. The straw mulch provided acceptable weed control but the cover crop and the grazing did not sufficiently control the weeds. The highest fruit and oil yields were produced by the trees treated with the straw mulch as a result of the highest mean fruit weight in each year, followed by the soil tillage treatment. However, the olive trees in the plots treated with glyphosate or grazing provided lower or equal, respectively, fruit and oil yields than did those in the untreated plots (control). The results indicated that certain non‐chemical weed control methods, such as straw mulch, can be implemented successfully in established olive groves, providing satisfactory control of weeds and promoting the highest fruit and oil yields.     

Effects of three management strategies on the seedbank, emergence and the need for hand weeding in an organic arable cropping system

The effects of three different weed management strategies on the required input of hand weeding in an arable organic farming system, the weed seedbank in the soil and the emerging weed seedling emergence were studied from 1996 to 2003. Strategies were based on population dynamic models and aimed for (1) control of weeds as carried out in standard organic farming practice, (2) control of all residual weeds that grow above the crop and (3) prevention of all weed seed return to the soil. Under all strategies, the size of the seedbank increased during the conversion from conventional to organic farming systems. The increase under strategy 3 was significantly smaller than the increase under the other strategies. From 1999 onwards, the weed densities in plots treated with strategy 3 became significantly lower than the weed densities in plots treated with the other strategies. The time needed for hand‐weeding required to prevent weed seed return, in addition to the time needed in standard organic farming practices, reduced during the course of the study. A management strategy aimed at the prevention of seed return (strategy 3) can reduce the size of the increase of the seedbank, which is usually observed after transition from conventional to organic farming. This study provides unique real‐world data that are essential for evaluating population dynamic models. The results may contribute to the development of weed management systems based on ‘no seed’ threshold strategies and to a further decrease in the dependence on herbicides.     

Weed flora and seed yield in quinoa crop (Chenopodium quinoa Willd.) as affected by tillage systems and fertilization practices

The effects of tillage system and fertilization regimes on weed flora in quinoa (Chenopodium quinoa Willd.) were evaluated by means of two field experiments in 2011 and 2012. The experiments were laid out in a split-plot design with two main plots (conventional and minimum tillage) and four sub-plots (fertilization regimes). The results indicated that weed biomass and density in quinoa were influenced by the different fertilization and tillage treatments. Moreover, seed yield in conventional was 5%–13% higher than that of minimum tillage, probably due to the lower weed density and biomass. Concerning fertilization treatments, total weed density and biomass increased under manure application and inorganic fertilization. Tillage effects on weeds were species specific. The density of perennial weeds such as purple nutsedge (Cyperus rotundus L.) and the density of small-seeded weeds such as redroot pigweed (Amaranthus retroflexus L.) and common purslane (Portulaca oleracea L.) were significantly lower under the conventional tillage than under the minimum tillage system.     

Weed management in organic agriculture: are we addressing the right issues?

Summary Despite the serious threat which weeds offer to organic crop production, relatively little attention has so far been paid to research on weed management in organic agriculture, an issue that is often approached from a reductionist perspective. This paper aims to outline why and how this problem should instead be tackled from a system perspective. Compared with conventional agriculture, in organic agriculture the effects of cultural practices (e.g. fertilization and direct weed control) on crop:weed interactions usually manifest themselves more slowly. It follows that weed management should be tackled in an extended time domain and needs deep integration with the other cultural practices, aiming to optimize the whole cropping system rather than weed control per se . In this respect, cover crop management is an important issue because of its implications for soil, nutrient, pest and weed management. It is stressed that direct (physical) weed control can only be successful where preventive and cultural weed management is applied to reduce weed emergence (e.g. through appropriate choice of crop sequence, tillage, smother/cover crops) and improve crop competitive ability (e.g. through appropriate choice of crop genotype, sowing/planting pattern and fertilization strategy). Two examples of system-oriented weed management systems designed for organic agriculture are illustrated as well as future perspectives and problems.     

Weed problems and their management in rice fields of Malaysia: An overview

The available literature on weed problems and weed control in rice fields in Malaysia is reviewed and suggestions for future research are included. The problem of weed competition with rice is of great economic importance in the country because it causes a 10–35% reduction in grain yield. About US$4.10 million is spent annually on herbicides for rice alone, and this amounts to approximately 7% of the total expenditure on herbicides. The shift in methods of rice culture from transplanting to direct seeding has magnified the weed problem. The problem of weedy rice is particularly acute in the direct-seeding rice areas. Although a number of sulfonylurea herbicides (e.g. cinosulfuron, metsulfuron, bensulfuron and pyrazosulfuron) have been found to be suitable alternatives to the old herbicide 2,4-D, an integrated weed management program must be developed in order to reduce the problem of herbicide resistance in weeds. Weed control methods that are more friendly to the environment and affordable to farmers must be sought. Weed-competitive and allelopathic rice varieties must be produced. The problem of weeds in rice calls for systematic studies on biotechnological methods of control of weedy rice. Detailed studies on the biology and ecology of notorious rice weeds, particularly Oryza sativa L. (weedy rice), Echinochloa spp., Leptochloa chinensis (L.) Nees, Fimbristylis miliacea (L.) Vahl. and Limnocharis flava (L.) Buch. need to be done in order to formulate successful weed control measures.