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1.
Surveys of weed vegetation of the western Balkan peninsula (1939–2006) were used to study changes in species composition. A large data set of arable weed vegetation was compiled and analysed with direct and indirect ordination, regression and beta (β) diversity analysis. Five environmental variables (altitude, season, year, crop, phytogeographical region) were used to determine broad-scale changes in weed species composition. The most important parameter was phytogeography and the second was crop. Altitude and season were found to be less important, although significant, which contrasts with results from Central and Northern Europe. β-diversity was higher in cereals and in summer, while decline along the altitudinal gradient previously demonstrated in Central Europe, was not observed. In southern parts of the studied area, thermophilous species have shifted to higher altitudes. The results and ranking of importance of environmental and spatial variables are discussed in relation to similar studies in Northern and Central Europe.  相似文献   

2.
In order to better understand the effects of urbanization on weed communities, the distribution of weed communities in Shanghai, China, was systematically investigated. The diversity of weed communities and four environmental factors, including the relative light intensity, soil moisture, soil compaction and soil pH, were measured in 1375 plots along an urban–rural gradient. The species diversity indices in each area along the urban–rural gradient were compared by using a one‐way ANOVA. The weed communities were identified by using clustering methods that were based on relative dominance information. A canonical correspondence analysis was used to reveal the relationships between the species composition and the environmental factors at the community level and the Spearman's rank correlation test was used to test the relationship between the number of weed communities and each environmental factor. A total of 183 species, belonging to 41 families and 123 genera, was recorded. It was found that the species richness, Shannon–Wiener diversity index and Pielou evenness index followed a unimodal curve along the urban–rural gradient. The 1375 plots were divided into 133 weed community types. All four environmental factors significantly affected the species composition of the weed communities, but only soil compaction had significant effects on the number of weed communities. It was concluded that the diversification of habitat type and environmental change along the urban–rural gradient led to more weed communities in rural areas and fewer weed communities in urban areas. Based on the species' habitats and distribution patterns, the weeds were divided into “widespread”, “urban” and “rural”.  相似文献   

3.
Over‐winter mortality, that is, winterkill, reduces cereal crop competitive ability and yield. While management and environmental variables are known to affect winterkill, the extent to which weeds contribute to increased winterkill is largely unknown. Winter annual weeds may increase winterkill through resource competition and by increasing incidence of and damage from plant pathogens that cause winterkill. We evaluated the impact of summer annual (Avena fatua) and winter annual (Bromus tectorum) weeds on the over‐winter survival rate of winter wheat over three winters, during which plots were covered with snow. Pink snow mould (Microdochium nivale), a winterkill pathogen known to infect B. tectorum and winter wheat, was common in wheat stands. In weed‐free treatments, mortality rates were initially near zero, but increased by nearly 45% in each subsequent winter, presumably due to an increase in snow mould disease in continuously cropped winter wheat. Whereas A. fatua infestation had no impact on crop survival rates, winter wheat survival in B. tectorum‐infested plots was 50% less than the weed‐free control in the second and third years of this study. Among B. tectorum‐infested plots, winter wheat over‐winter survival declined with increasing weed seed produced in the previous summer. Overall, this study demonstrated that winter annual weed infestations can reduce crop stand densities below replanting thresholds by reducing fall‐sown cereal winter survival. The effects of winter annual weeds on winter wheat may be meditated by increased proliferation of snow mould disease.  相似文献   

4.
Weed species loss due to intensive agricultural land use has raised the need to understand how traditional cropland management has sustained a diverse weed flora. We evaluated to what extent cultivation practices and environmental conditions affect the weed species composition of a small‐scale farmland mosaic in Central Transylvania (Romania). We recorded the abundance of weed species and 28 environmental, management and site context variables in 299 fields of maize, cereal and stubble. Using redundancy analysis, we revealed 22 variables with significant net effects, which explained 19.2% of the total variation in species composition. Cropland type had the most pronounced effect on weed composition with a clear distinction between cereal crops, cereal stubble and maize crops. Beyond these differences, the environmental context of croplands was a major driver of weed composition, with significant effects of geographic position, altitude, soil parameters (soil pH, texture, salt and humus content, CaCO3, P2O5, K2O, Na and Mg), as well as plot location (edge vs. core position) and surrounding habitat types (arable field, road margin, meadow, fallow, ditch). Performing a variation partitioning for the cropland types one by one, the environmental variables explained most of the variance compared with crop management. In contrast, when all sites were combined across different cropland types, the crop‐specific factors were more important in explaining variance in weed community composition.  相似文献   

5.
R H LI  †  & S QIANG 《Weed Research》2009,49(4):417-427
The diversity and composition of floating weed seed communities were surveyed in 27 sites across the main rice-growing regions in China with the aim of better understanding weed seed dispersal via irrigation water. Seed of 74 species, belonging to 20 families, were identified from floating matter on the water surface in lowland rice fields. Thirty-five species from three families: Poaceae (15), Asteraceae (11), and Polygonaceae (9), accounted for 47% of all species identified. Species with seed maturing in the summer accounted for 64% of the weed seed and their mean relative abundance was 0.74. Species richness, Shannon–Wiener index and Pielou evenness index were significantly different among the floating weed seed communities. The diversity of weed seed communities in the Yangtze river valley was higher than that in other sites, and some sites were dominated by only a few weed species, such as Beckmannia syzigachne , Alopecurus aequalis , A. japonicus , and Polypogon fugax. At all sites, the dominant weed seeds reflected the dominant weed species in the previous crop. The 27 sample sites of weed seed communities can be clustered into two groups on the basis of previous crop, either lowland rice or sites with previous crops of winter fallow, winter wheat or oilseed rape. Canonical correspondence analysis (CCA) revealed that irrigation frequency, previous crop, and latitude, but not soil type or longitude, significantly affected species composition. The numbers of floating weed seed species were high in lowland rice fields; composition was affected by previous crops and irrigation frequency. Filtering irrigation water and collecting and removing floating weed seeds from the water surface could be integrated into weed management practices to control weeds in lowland rice fields.  相似文献   

6.
The goal of this study was to identify factors determining weed species composition in soyabean crops in Hungary, where its expanding production faces difficult weed problems. The abundance of weed flora was measured in 262 fields across the country, along with 38 background variables. Using a minimal adequate model containing 24 terms with significant net effects, 21.6% of the total variation in weed species data could be explained. Plot location (edge vs core position, the single site variable in our analysis) was found to be the most important explanatory variable that was followed by a set of environmental (temperature, precipitation, altitude, soil texture, pH, Ca, K, Na and humus content), cultural (cultivar maturity, organic manure, fertiliser P and N, row spacing) and weed management (flumioxazin, pendimethalin, dimethenamid, propaquizafop, bentazone, quizalofop‐p‐ethyl, quizalofop‐p‐tefuril, linuron, thifensulfuron) factors. Variation partitioning revealed that environmental variables accounted for about four times more variance than cultural and about two and half times more than weed management variables. Chenopodium album, Ambrosia artemisiifolia, Hibiscus trionum, Echinochloa crus‐galli and Convolvulus arvensis were the most dominant and frequent weeds, but their abundance was influenced by different factors. The responses of weed species to the studied variables provide new information about their ecological behaviour, and our findings also can be used to develop better weed management strategies.  相似文献   

7.
This study assessed the cultural and weed management factors influencing the weed communities of Hungarian rice fields. Hungary is situated at the northern limit of rice production with a history of about 300 years of rice culture. We surveyed the weed flora and 25 background variables in 100 active rice fields. Using a minimal adequate model containing 11 terms, 48.5% of the total variation in weed species data could be explained. The net effects of nine variables on species composition were significant. Crop cover was found to be the most important explanatory variable, which was followed by the herbicides penoxsulam and azimsulfuron, tillage depth, phosphorous and potassium fertilisers, years after last rotation, water depth in May, sowing type, pendimethalin and water conductivity. Filamentous algae, as the most abundant group of weeds, were positively associated with deep tillage, deep water and surface sowing. Echinochloa crus‐galli, one of the most troublesome grass weeds, was associated with low rice cover, shallow water and later years after crop rotation, while weedy rice favoured high crop cover, deep water and soil sowing. These findings can be used to design improved weed management strategies. The occurrence of red list species and charophytes in diverse micro‐mosaic patterns deserves attention from a conservation perspective, as well. The maintenance of these unique charophyte communities can be facilitated by shallow tillage without soil inversion.  相似文献   

8.
During the last decade, maize has become the crop with the second largest acreage in Germany. Therefore, agricultural advisors and the plant protection sector are interested in an overview of the weed species composition in maize fields, their determining factors and trends. From 2001 to 2009, a weed survey was conducted in 1460 maize fields throughout Germany. Data on crop management and soil characteristics were collected via farmer questionnaires. Principal component analysis and redundancy analysis were used to analyse patterns in weed species composition. The late spring and summer germinating species Chenopodium spp., Echinochloa crus‐galli and Solanum nigrum occurred with high densities and frequencies, but their occurrence was determined by different factors. Other frequent weed species were those that typically accompany autumn‐sown crops. The variation in species composition was significantly related to environmental factors (9.1% explained variance), particularly geographical latitude and precipitation, and management factors (4.7% explained variance), particularly crop sequence. The relative importance of these factors seems universal, when compared with surveys in other crops and regions. The factor ‘year’ was of minor importance (0.9% explained variance). Over the 9‐year period, no changes in weed species composition could be determined. The results suggest that despite the limited impact of crop management on weed species composition, farmers can use crop sequence to suppress individual species. The survey furthermore sets a baseline against which future changes can be measured in a landscape of rapidly changing agricultural land use.  相似文献   

9.
Variation partitioning by canonical correspondence analysis (CCA) was applied to analyse spatial variation in the species composition of a weed community for an area of farmland in southern Finland. The farmland, covering 450 ha, was sampled with a 60 m × 60 m grid. Data on weed species were collected along with the following groups of explanatory variables: spatial variables (the terms of second-order polynomial trend surface regression equation generated on the x and y co-ordinates of sample quadrats: x, y, x2, xy, y2, x2y and xy2), farmer variables (nine farms), soil variables (four soil types and pH value), crop variables (barley, oats, sugarbeet, potato and turnip rape) and physical variables (area of field, altitude, slope and aspect in four directions). The main variation in species composition along the first and second CCA axes was caused by interplay between farmer and crop variables. Farmer and crop variables explained more of the variation than did soil or physical variables. All the variables were to some extent spatially structured. The spatial variables contributed 54.5% of the total variation, of which pure spatial variation accounted for 12.2%. The highest covariation with spatial variables was detected with farmer (33.7%) and crop variables (25.7%). Variation partitioning by CCA is recommended for studying the relationship between the spatial variation in weed communities and explanatory variables.  相似文献   

10.
There is a need for management strategies to control dominant perennial weeds and restore seminatural communities. We compared the effects of five weed control treatments on dense Pteridium aquilinum relative to an untreated experimental control over an 8‐year period with the aim of restoring acid grassland. The weed control treatments tested were as follows: cutting and bruising, both twice and thrice annually, and herbicide treatment (asulam in year 1 followed by annual spot retreatment of all emergent fronds). Pteridium aquilinum performance and plant species composition were monitored. Data were analysed using Bayesian mixed‐effect models and multivariate techniques. Cutting twice and thrice yearly and the asulam treatment all reduced frond density to zero; both bruising treatments were ineffective. The plant communities in the cut and asulam‐treated plots showed differences from the untreated and bruised plots; the asulam‐treated plots contained more ruderal species and the cut plots were more typical of acid grassland. Acid grassland recovery was fastest in the asulam‐treated plots, but the cut plots caught up after approximately 5 years. There were two important conclusions. First, an intractable weed like P. aquilinum can be eradicated and a vegetation more suited for grazing can be achieved by the continuous application of some treatments over many years. Here, success was achieved by cutting twice/thrice annually, or by a single asulam application followed by annual spot spraying of all emergent fronds for 8 years. Second, bruising, a treatment favoured by some conservation organisations, did not work and cannot be recommended. The use of long‐term, continuously applied treatments might be considered for all perennial weeds with large underground root/rhizome systems.  相似文献   

11.
A long-term study of weed flora shifts in different tillage systems   总被引：1，自引：0，他引：1  
Knowledge of the long-term effects of tillage on weed flora will provide useful information to improve weed management in agroecosystems. Field studies were conducted from 1991 to 1997 to evaluate the effects of tillage systems on weed density and species composition before control methods in rotations including wheat ( Triticum aestivum L.), soyabean [ Glycine max (L.) Merr.] and maize ( Zea mays L.). In wheat, annual broad-leaved species showed higher populations in conventional tillage in 4 out of 6 years, and grassy annuals and perennial species showed an erratic response with tillage systems. In summer crops, broad-leaved populations were higher under conventional tillage than non-tillage for the last 5 years in the wheat/soyabean rotation and for the last 4 years in the maize/soyabean rotation. The weed spectrum changed rapidly in non-tillage plots. With time, in the absence of tillage, grassy annual populations increased in the maize/soyabean rotation, and wind-dispersed weed populations increased in the wheat/soyabean rotation. Perennial weeds showed an inconsistent behaviour in relation to tillage systems in the maize/soyabean rotation.  相似文献   

12.
How weed communities assemble represents one the key issues of weed science. For a decade, functional approaches have been applied to investigate the processes that govern weed community assembly. In most previous studies, trait values have been generally averaged over multiple populations and habitats. Consequently, conspecifics display similar trait values while neglecting the considerable influence of intraspecific variability to detect changes in functional diversity in response to environmental drivers. However, this influence has been shown to be critical, especially, at local scales. Here, we studied changes in weed functional diversity at the field scale in four crop sequences. We focused on intra‐ and interspecific variability of four key functional traits involved in response to resource acquisition processes, the latter being modified by climate, management and competition. The relative influence of intra‐ and interspecific variability among the crop sequence types was highlighted using a diversity partitioning approach. It provides evidence for substantial amount of intraspecific variability in the weed community and underlines its essential role in response to fine‐scale environmental drivers. In addition, we investigated the response of the three most abundant species to competition with the crop, the growing season and the crop sequence type. We highlighted that these species showed a wide range of combinations of trait values, suggesting the co‐existence of several successful strategies. Based on these results, we emphasise that neglecting intraspecific variability can lead to substantial underestimations of the functional weed response to management and crop‐weed competition at the field scale.  相似文献   

13.
A LUNDKVIST 《Weed Research》2009,49(4):409-416
To assess the effects of timing and frequency of weed harrowing on weed abundance and crop yield, different pre- and post-emergence weed harrowing sequences were applied to spring cereals and peas in field experiments performed during 2003 and 2004 in Sweden. Post-emergence harrowing was performed at crop growth stages 2–3 and 5–6 true leaves respectively. The best weed control was obtained by a combination of pre- and post-emergence harrowing, but these treatments also caused yield losses of 12–14% in spring cereals, while no yield losses were observed in peas. Pre-emergence weed harrowing treatments alone or combined with weed harrowing shortly after crop emergence proved to be most effective against the early emerging annual weed species Sinapis arvensis and Galeopsis spp. Post-emergence harrowing alone in peas had no effect on S. arvensis . The late emerging annual weed species Chenopodium album and Polygonum lapathifolium were most effectively controlled when pre-emergence weed harrowing was combined with one or two weed harrowing treatments after crop emergence.  相似文献   

14.
This article documents the impact of site conditions and farming practices on the occurrence of rare and endangered weeds on arable land in the Czech Republic. A survey was conducted between 2006 and 2008 in winter cereals, spring cereals and wide‐row crops. The relationship between the occurrence of plants and explanatory factors was analysed using a multivariate analysis to calculate species frequencies in different types of farming, crops and altitudes. In total, 290 relevés were recorded, with a total number of 172 weed species. Nineteen weeds, classified as rare and endangered species according to the national Czech list, were identified in 106 relevés. The highest effect on the occurrence of rare and endangered weed species was observed for altitude. Almost half of the recorded endangered and rare species belonged to the thermophilous weed vegetation typical for cereals on basic soils. A higher occurrence of endangered species has been confirmed for organic farming, where the sum of frequencies was 4.5 times higher than in conventional farming. Field size was not included in our analyses, but could be a factor affecting weed assemblages. The highest frequency of rare species was recorded in spring cereals, followed by winter cereals and wide‐row crops. Higher numbers were identified within fields with higher weed coverage. Lower farming intensity and diversified farming systems at higher altitudes provided better conditions for the occurrence of rare species than intensively farmed lowlands.  相似文献   

15.
An exploratory weed survey was carried out on 240 crop fields in eastern Ethiopia to assess the influence of some environmental and crop management factors on weed species composition and distribution, and to investigate the association of the recently introduced Parthenium hysterophorus L. with other components of the weed flora. A total of 102 weed taxa belonging to 36 plant families were recorded. Asteraceae, Poaceae and Fabaceae were the most abundant families based on the number of species recorded. Digitaria abyssinica (Hochst. Ex A. Rich) Stapf was the most frequent species (63%) and Parthenium hysterophorus the second most frequent (54%). The latter species was ranked as the most important weed by 90% of the farmers in the lowlands while 86% of the farmers in the highlands ranked the former species as the worst weed. According to a partial canonical correspondence analysis (pCCA), altitude, rainfall, month of planting, number of weedings and soil type were the major environmental/crop management factors influencing the species distribution in the study area. The first pCCA axis clearly structured highland and lowland weed species while the second axis distinguished those species that grow on sandy soils. Parthenium hysterophorus has, in a very short time period, emerged as one of the most troublesome weed species in eastern Ethiopia.  相似文献   

16.
Weed communities of winter wheat as influenced by input level and rotation   总被引：5，自引：0，他引：5  
The influence of cropping systems constituted by the combination of three input levels (low, intermediate and high) and four 2-year rotations between a spring summer crop and winter wheat ( Triticum aestivum L.) on the density and composition of the winter wheat weed flora was evaluated from 1989 to 1992. Spring summer crops were maize ( Zea mays L.). soyabean ( Glycine max (L.) Merr.). sugar beet ( Beta vulgaris L.) and sunflower ( Helianthus and L.) Total weed density at the end of the wheat tillering stage ranged from 2.5 to 128.7 plants m-2 and generally decreased with cropping intensity, although to a differing extent, depending upon rotation. Differences among weed communities of the 12 cropping systems were mostly dependent upon input level. The effect of the preceding crop on the weed flora composition of winter wheat was evident only with reduced herbicide use (low-input systems). Weed species could be ascribed to four categories: (a) species sporadically associated with cropping systems (most of the weeds); (b) species associated with a specific input level (e.g. Papaver rhoeas L. to low and intermediate input levels and Veronica persica Poiret to the high input ievel): (c) species associated with a specific rotation (e.g. Anm majus L. to sugar beet winter wheat): and (d) species associated with specitie plots that become important every other year (e.g. Convolvulus arvensis L. and Stellaria media (L.) Vill.).  相似文献   

17.
The relative abundance of the weed functional types in dryland and irrigated rice in the Kharif (summer) crop field and dryland lentil and wheat in the irrigated Rabi (winter) crop field was studied at the agricultural farm of Banaras Hindu University, Varanasi, India. A total of 22 species, belonging to 17 families, was recorded in the dryland and irrigated rice ecosystems and 18 species, belonging to eight families, were recorded in the dryland lentil and irrigated wheat ecosystems. The Importance Value Index (IVI) of the hemicryptophytes showed an increasing trend with the crop growth period in the case of the dryland rice, whereas in the irrigated rice plots, a reduction in the IVI of the hemicryptophytes, with a related increase in the importance of the therophytes, was observed as the crop attained maturity. Also, the trend of a decreased IVI was observed for the geophytes in the fertilized dryland rice plots. The principal components analysis (PCA) ordination showed the uniqueness of the crop plot in terms of weed species composition. The PCA analysis of the functional types on the basis of the crop plots indicated that the hemicryptophyte and therophyte weed species composition was heavily altered at the initial and final sampling, although the weed flora was dominated by the therophytes and geophytes. These results suggest the prioritization of hierarchical temporal management options for the functional weed types in different crop plots and that this approach warrants further investigation.  相似文献   

18.
Agricultural intensification, besides increasing land productivity, also affects weed communities. We studied weed shifts in cropping sequences differing in the identity and number of crops grown. We also evaluated whether dissimilar weed communities in different cropping systems converge towards more similar communities, when the same sequence is cropped during 2 years. In three locations in the Rolling Pampa, Argentina, field experiments were conducted including five cropping systems in the first year (winter cereal/soyabean, field pea/soyabean, and field pea/maize double crops, and maize and soyabean as single crops), while the same sequence was grown in the following 2 years (wheat/soyabean double crop and maize). Changes in weed community composition and structure were analysed through multivariate analyses and frequency–species ranking plots. Weed communities differed first among sites, while weed shifts within each site were mainly associated with growing season and crop type. Differences among crop sequences were higher in the first year, mostly related to specific crop grown, rather than to the number of crops in the sequences. Differences were reduced when the same sequence was grown during two consecutive seasons. Frequency of highly common weeds was negatively associated with the number of days with high crop cover. Our findings contribute to understand weed shifts in consecutive growing seasons, which may help readapting crop sequences to reduce the occurrence of abundant weed species.  相似文献   

19.
Studies of the dynamics of a weed community: III. Long-term influence of cultivation techniques on the species composition of the seedbank The species composition of the seedbank was followed for eight years on four experimental plots differing in cultivation treatment (deep or shallow) and either treated or untreated with herbicides. The results show that the species composition was not affected by herbicides but there were quantitative changes: some species, such as Euphorbia exigua and Anagallis arvensis became more dominant without increasing in number. Conversely, in unweeded plots there were qualitative and quantitative changes in the species composition with the arrival of ‘opportunistic’ species such as Thlaspi arvense and Sinapis arvensis, which considerably increased in number although they were practically absent at the start. The type of cultivation modified these changes a little by mixing, in the cultivated layer, the annual additions of new seeds with the existing seedbank.  相似文献   

20.
Predicting the risk of weed infestation in winter oilseed rape crops   总被引：1，自引：0，他引：1  
Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.  相似文献   

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