Diversity and assembly of weed communities: contrasting responses across cropping systems

Diversity and weed community composition of mid-season plant stands and autumn seedbanks were examined in spring barley–red clover cropping systems that varied according to crop rotation, tillage and weed management. Weed plant and seed density data collected over 4 years were used in the calculation of species richness (number of species), evenness (Shannon's E) and diversity (Shannon's H′), and in multivariate analysis (canonical discriminant analysis) of weed communities. Weed diversity indices were low (H′ < 2.0) but sensitive to management practices. Evenness had intermediate values (E = 0.4–0.8), suggesting little evidence of truly dominant species, particularly in the seedbanks. The difference in the number of species between treatments was never large (approximately two to four species). Overall, diversity indices were highest in the low disturbance treatments, particularly those with minimum weed management. Factors affecting ordination were somewhat different from those affecting diversity. Tillage had little effect on weed diversity indices but had a more major role in determining weed community composition. Seedbanks in no-till and monoculture-chisel plough treatments appeared to have more distinctive species composition compared with other treatments. Weed species assembly in seedbanks showed little discrimination across treatments and over time, confirming the ability of seedbanks to buffer disturbances across a variety of cropping systems. The use of diversity indices revealed part of the complexity of weed communities associated with disturbance in cropping systems, whereas ordination singled out species–cropping systems associations, which may be more meaningful to weed management.     

Weeds and weed management in rice production in Japan

The area of paddy rice fields in Japan was 1.79 million ha in 1998 almost all of which was planted with young seedlings from nursery boxes by a mechanical rice transplanter. Japanese farmers controlled paddy weeds mainly by chemical herbicides, which were applied around 1.8 times in one growing season of rice by sequential treatment. The cost of herbicides was 35 320 ¥/ha on average, the main of which was ‘one‐shot’ herbicides, while weeding labor for the paddy field, including herbicide application, was 19.0 h/ha, or 29 976 ¥/ha in labor cost, in 1998. Under the Integrated Weed Management (IWM) for sustainable paddy rice production, other technologies for weed management are also recommended to paddy farmers, such as ecological or cultural, mechanical, biological methods and so on.     

Tillage and nitrogen management effects with sequential and ready-mix herbicides on weed diversity and wheat productivity

In this experiment, weed management was studied in zero tillage (ZT) and conventional tillage (CT) wheat with and without crop residue and nitrogen (N). The treatment ZT with crop residue retention (R) and 75% of required N plus GreenSeeker? (GS)-aided N management (ZTRNGS) resulted in a reduction of density and dry weight of weeds compared to CT and ZT without residue. Sequential application of pendimethalin and sulfosulfuron (PMT-SSF) reduced the weed density and dry weight compared to the weedy check (WC). Importantly, the richness and diversity indices were high in ZTRNGS and in WC treatments. Greater wheat grain (5.11 t/ha) and biomass yield (13.31 t/ha) were observed in ZTRNGS than CT without residue and blanket split application of N (CTN). The treatment ZTRNGS recorded 14.1% and 16.9% higher gross and net returns, respectively, over CTN. This study demonstrates that surface retention of crop residue in ZT is more useful than residue incorporation under CT for effective weed control, improving crop yield and profitability.     

河南省小麦田杂草组成及群落特征

为明确河南省小麦田杂草的种类组成和群落特征,采用倒置"W"9点取样法对河南省36个区县的小麦田杂草进行了调查。结果表明,小麦田杂草有77种,隶属于20科65属,其中以禾本科、菊科、十字花科为主;优势杂草有10种,分别为播娘蒿、野燕麦、荠菜、猪殃殃、婆婆纳、麦家公、麦瓶草、节节麦、雀麦、硬草;常见杂草有28种,一般性杂草有39种。从杂草区域分布来看,伏牛山区小麦田杂草群落的物种丰富度、多样性最高,杂草有49种,Shannon-Wiener指数最高,为2.94;豫南平原区Pielou指数最小,为0.75,Simpson指数最高,为0.098,优势杂草突出。聚类分析结果表明,河南省小麦田的杂草群落可以划分为3组,第1组为豫北平原区、豫南平原区和伏牛山区的杂草群落,第2组为南阳盆地区和桐柏大别山区的杂草群落,第3组为太行山区的杂草群落。     

Benchmark study on glyphosate-resistant cropping systems in the United States. Part 4: Weed management practices and effects on weed populations and soil seedbanks

BACKGROUND: Weed management in glyphosate‐resistant (GR) maize, cotton and soybean in the United States relies almost exclusively on glyphosate, which raises criticism for facilitating shifts in weed populations. In 2006, the benchmark study, a field‐scale investigation, was initiated in three different GR cropping systems to characterize academic recommendations for weed management and to determine the level to which these recommendations would reduce weed population shifts. RESULTS: A majority of growers used glyphosate as the only herbicide for weed management, as opposed to 98% of the academic recommendations implementing at least two herbicide active ingredients and modes of action. The additional herbicides were applied with glyphosate and as soil residual treatments. The greater herbicide diversity with academic recommendations reduced weed population densities before and after post‐emergence herbicide applications in 2006 and 2007, particularly in continuous GR crops. CONCLUSION: Diversifying herbicides reduces weed population densities and lowers the risk of weed population shifts and the associated potential for the evolution of glyphosate‐resistant weeds in continuous GR crops. Altered weed management practices (e.g. herbicides or tillage) enabled by rotating crops, whether GR or non‐GR, improves weed management and thus minimizes the effectiveness of only using chemical tactics to mitigate weed population shifts. Copyright © 2011 Society of Chemical Industry     

Development of chemical weed control and integrated weed management in China

More than 200 species of weeds are infesting main crop fields in China, among which approximately 30 species are major weeds causing great crop yield losses. About 35.8 million hectares of crop fields are heavily infested by weeds and the annual reduction of crop yields is 12.3–16.5% (weighted average). Along with rural economic development, approximately 50% of the main crop fields undergo herbicide application. Chemical weed control has changed cultural practices to save weeding labor in rice, wheat, maize, soybeans and cotton. At the same time, continuous use of the same herbicides has caused weed shift problems and weed resistance to herbicides. Consequently, integrated weed management in main crops is being developed.     

青海省春小麦田杂草群落组成及其多样性分析

为明确青海省春小麦田杂草发生种类及其群落特征,采用倒置“W”九点取样法对青海省东部农业区和柴达木盆地农业区春小麦田杂草种类、生活型、科属组成、群落结构及杂草多样性进行调查。统计分析发现：小麦田有85种杂草,隶属24科64属。其中,菊科和禾本科是数量最多的科别,杂草分别为16种和14种。从杂草的综合优势度来看,藜(Chenopodium album L.)、野燕麦(Avena fatua L.)、萹蓄(Polygonum aviculare L.)、苦苣菜(Sonchus oleraceus L.)、苣荬菜(Herba Sonchi Brachyoti)5种杂草为优势杂草,芦苇(Phragmites australis(Cav.)Trin.)、赖草(Leymus secalinus(Georgi) Tzvel.)、狗尾草(Setaria viridis(Linn.) Beauv.)、藏蓟(Cirsium eriophoroides)、荞麦蔓(Fagopyrum esculentum Moench.)、节裂角茴香(Hypecoum leptocarpum Hook.f.et Thoms.)...     

Ecological weed management by cover cropping: effects on weed growth in autumn and weed establishment in spring

Cover crops grown in the period between two main crops have potential as an important component of a system‐oriented ecological weed management strategy. In late summer and autumn, the cover crop can suppress growth and seed production of weeds, whereas the incorporation of cover crop residues in spring may reduce or retard weed emergence. Based on these two criteria, six cover crop species were evaluated for their weed suppressive potential in 2 years of experimentation in the Netherlands. Fodder radish, winter oilseed rape and winter rye had the strongest competitive ability in autumn; the competitive strength of Italian ryegrass was intermediate and white lupin and lucerne were poor competitors. Competitiveness was strongly correlated to early light interception. Surprisingly, doubling the recommended sowing density did not increase weed suppressive ability. Although a poor competitor in the fall, after incorporation in spring, lucerne had the strongest inhibitory effect on seedling establishment, followed by winter oilseed rape and white lupin. Winter rye and fodder radish did not affect seedling establishment, whereas Italian ryegrass was not evaluated because of re‐growth after incorporation. Competition in autumn and subsequent residue‐mediated suppression of weed establishment in spring varied among the cover crop species, with winter oilseed rape offering relatively strong effects during both periods.     

Cover crops and mulches influence weed management and weed flora composition in strip‐tilled tomato (Solanum lycopersicum)

This study was conducted in the Mediterranean environment of Central Italy from 2011 to 2013 with the aim of evaluating the effects of winter cover crops and their residues on weed composition in a cover crop‐tomato sequence. Treatments consisted of five soil managements (three cover crop species ‐ hairy vetch, phacelia, white mustard, winter fallow mulched with barley straw before tomato transplanting and conventionally tilled soil), two nitrogen fertilisation levels (0 and 100 kg N ha^?1) and two weed management levels (weed free and weedy) on tomato. Cover crop residues were arranged in strips on the soil surface and then used as beds for transplanting the tomato seedlings in paired rows. Rotary hoeing was performed in the bare strips between paired tomato rows. At tomato harvesting, the weed aboveground biomass and density was higher in nitrogen‐fertilised tomato than unfertilised tomato, except in hairy vetch and barley straw that showed similar values. Hairy vetch used as a cover crop and dead mulch was the most suppressive species with the highest production of residues, while phacelia and mustard were not suitable for controlling weeds. The tomato yield was high in nitrogen fertilised and weed‐free treatments, except in barley straw mulch, which showed similar values among the weed management treatments. The mulch strips caused variations in weed species composition that was mainly composed of perennial ruderal weeds, while in tilled soil, the weed flora was dominated by annual photoblastic weeds.     

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。     

Management practices influence the competitive potential of weed communities and their value to biodiversity in South African vineyards

Weeds have negative impacts on crop production but also play a role in sustaining biodiversity in agricultural landscapes. This trade‐off raises the question of whether it is possible to promote weed communities with low competitive potential but high value to biodiversity. Here, we explored how weed communities respond to different vineyard management practices in South Africa's Western Cape, aiming to identify whether any specific practices are associated with more beneficial weed communities. Eight weed community characteristics representative of abundance, diversity and functional composition were used as indicators of competitive potential and biodiversity value. We explored how these responded to farm management strategy (organic, low input or conventional) and weed management practices (herbicides, tillage, mowing or combinations of these) using ordination and mixed models. Mown sites were associated with weed communities of high biodiversity value, with higher weed cover in both winter and summer, higher diversity and more native weeds. Mowing also promoted shorter weeds than either tillage or herbicides, considered to be less competitive with grapevines. However, high summer weed cover may be problematic where competition for water is critical, in which case tillage offers a method to limit summer weed cover that did not adversely affect diversity or native weeds. In contrast, herbicide‐treated sites had characteristics indicative of a lower biodiversity value and higher potential for competitiveness with few native weeds, lower diversity and relatively tall, small‐seeded weeds. Mowing in winter combined with tillage in spring may thus optimise the biodiversity benefits and production costs of Western Cape vineyard weeds.     

黄河三角洲地区棉田杂草组成及其群落特征

采用倒置"W"九点取样法对黄河三角洲棉田杂草种类及其群落结构进行了调查,并进行物种多样性分析。结果表明:黄河三角洲棉田杂草有61种,隶属于19科、47属,其中菊科杂草最多,有13种;其次是禾本科,有9种。优势杂草有马唐、芦苇、马齿苋、牛筋草、鳢肠、打碗花、藜、稗、铁苋菜和白茅10种,区域性优势杂草有6种,常见杂草3种,一般杂草42种。从区域分布来看,垦利、广饶、河口等地杂草丰富度指数、香农指数、辛普森指数、均匀度指数普遍较高。从聚类分析结果来看,该地区棉田杂草群落变化与空间距离、地理环境、种植模式等因素有密切关系。东营和利津两区县聚类分析的欧氏距离最小,为10.5;黄河南岸的高青和黄河三角洲其他县区之间欧氏距离最大,为23.4。     

Response of weed flora to combinations of reduced tillage, biocide application and fertilization practices in a 3-year crop rotation

Weed flora in a crop rotation of soybean, sugar beet, and spring wheat were studied under combinations of conventional and reduced tillage, biocide application, and chemical fertilization to investigate whether any combination of conservational practices offers the potential to increase weed community diversity while maintaining weed biomass at an acceptable level. Weed density increased under reduced biocide application. Weed density and size increased under manure compost application (with reduced chemical fertilization) because of weed seed introduction. Weed emergence from seeds dispersed in the previous year was greater under reduced tillage. Two-year individuals increased under a combination of reduced tillage, reduced biocide application and manure compost application. These increases in weed population density and size under conservational practices were yet not consistent; rather, they showed an annually fluctuating trend. In terms of weed diversity, species richness and Shannon's diversity index were higher under manure application because of the introduction of new species and probably as a result of suppression of weed growth and reproduction, which can reduce the chance of dominance by certain species. When combined with manure application, reduced tillage may offer the potential for increasing diversity by reducing the competitiveness of dominant species and facilitating establishment of new or minor species.     

The effect of tillage system and use of a paraplow on weed flora in a semiarid soil from central Spain

Field experiments were conducted to study weed population shifts in long‐term conservation tillage systems. The objectives of this study were to determine weed community abundance, diversity and composition on conventional tillage (CT), minimum tillage (MT), no‐tillage with paraplow (ZT) and no‐tillage (NT) systems, and to identify species that are associated with specific tillage systems. The paraplow is a subsoiling technique that results in a deep loosening of the soil, in order to alleviate compaction in certain soils where NT is practiced. The results showed significant differences in both the composition and the abundance of weeds, depending on the tillage systems. Weed diversity, species richness and Shannon's diversity and evenness indices were higher under the conservation tillage systems than in the CT system. In addition, various weed species were associated with reduced tillage systems. For instance, Anthemis arvensis, Hirschfeldia incana and Lolium rigidum became more prevalent in the NT system, whereas Chenopodium album and Filago pyramidata dominated in the ZT system. Therefore, the application of a paraplow treatment changed the weed community in the NT system. Other weed species, such as Capsella bursa‐pastoris and Torilis nodosa, dominated in all three conservation tillage systems, whereas soil disturbance by mouldboard ploughing favoured species such as Polygonum aviculare and Phalaris paradoxa.     

Effects of weed harrowing and undersown clover on weed growth and spring cereal yield

Weed competition and nutrient scarcity often restrict organic cereal production, especially where the availability of livestock manure is limited. While harrowing of annual weeds and legume cover crops can be used, these methods are both executed in early spring and may hinder each other. Two cycles of a 2‐year crop rotation were carried out in south‐east Norway (60°42′N, 10°51′E, altitude 250 m) with weed harrowing and undersown cover crops (WHCC) at two fertiliser rates (40 and 100 kg nitrogen ha^?1). The effect of the WHCC treatments was measured by weed density and species, weed biomass, changes in weed seedbank and grain yield. The weed density depended on the interaction between WHCC, fertiliser and year. On average, pre‐emergence weed harrowing reduced weed density by 32% and weed biomass by 49%, while pre‐ and post‐emergence weed harrowing reduced weed density by 59% and weed biomass by 67% compared with the untreated control. Spergula arvensis became more abundant at low rather than at high fertiliser rates. On average, white clover cover crop sown after pre‐emergence weed harrowing resulted in the highest yields for both oat (+12.1%) and wheat (+16.4%) compared with the untreated control. Despite differences in weed population density and biomass among WHCC treatments within years, the weed biomass, weed density and seedbank increased for all WHCC treatments over the 4‐year period. More research is required into improving the efficacy of mechanical and cultural weed suppression methods that organic systems rely on.     

耕作措施与秸秆还田对小麦-玉米轮作体系土壤质量的影响

通过在陕西关中平原地区连续7年的田间定位试验,运用多元方差分析及因子分析法比较评价了冬小麦-夏玉米轮作体系下4种耕作措施(深松、旋耕、免耕、传统耕作)及2种秸秆管理措施(玉米秸秆还田、不还田)对土壤质量的影响。结果表明:玉米收获后0~20 cm土壤容重免耕处理最大,旋耕、翻耕处理次之,深松处理最小;秸秆还田0~10 cm土壤容重较不还田处理降低2.33%,达显著水平。小麦、玉米收获后0~20 cm土壤养分组、有机质环境组及酶活性组指标变量受不同耕作措施的影响均大于受秸秆管理措施的影响。传统耕作两季土壤质量均最差。深松、旋耕有一定后效,且有机质养分因子得分较高,免耕则相反。综合土壤质量、作物产量及经济效益,玉米秸秆还田/深松/旋耕/播种小麦-小麦秸秆高留茬/免耕/播种玉米模式适宜在该区推广。     

Impact of cropping systems on the weed seed banks in the northern Great Plains, USA

Very little research has been done on weed seedbank communities in the northern Great Plains region of the USA. The objectives of this study were to evaluate the effects of management systems on the weed seed banks and to assess the relationship between the weed seed banks and the above-ground weed communities. The seed banks were sampled along a range of areas of above-ground weed diversity in organic and conventional spring wheat production fields near Big Sandy, Montana, over 2 years. Eight 1 m × 0.33 m areas were selected in each field to encompass a wide range of above-ground weed diversity and soil cores were taken in each area to a depth of 20 cm and split in half at 10 cm. The number of seeds recovered from the top 10 cm of soil and the 10–20 cm depth were significantly affected by the sampling year and an interaction between the cropping system and the sampling year. The year was the only significant predictor affecting the weed seedbank diversity at both depths. A significant interaction between the management system and the year observed at the 10–20 cm sampling depth reflected the higher rate of decrease in diversity occurring between 2005 and 2006 in the conventionally managed fields compared with the organic fields. A multivariate ordination indicated that, although the year played a significant role in determining the weed seedbank communities, the management system had a role only during 2006. We failed to detect strong correlations between the above-ground and underground weed communities. The results of this study suggest that, in the studied region, yearly fluctuations in environmental factors have significant impacts on the weed seed banks.