Diversity Of Weed Communities Research Articles

Global Status of Herbicide Resistance Development: Challenges and Management Approaches

Chemicals are widely recommended for the suppression of weed in crop land. This paper attempts to a greater integration of ideas into the development of herbicide resistance. This may lead researchers to focus less on simply defining herbicide resistance and more towards comprehensive investigations of the resistance development. Weed expert in collaboration with plant biologists can work in synergy to come up with better approach and innovation aimed to curtain herbicides resistance challenges. Chemical herbicides exert undue pressure on weed fitness and the diversity of weed community’s changes over time in response to both herbicides and other strategies imposed on them. Repeatedly and intensively, the regular application of herbicides with similar effect may swiftly result in population shifts to tolerant, difficult to suppress and ultimately result to weed community that is herbicide resistant, particularly in absence of using herbicides with different modes of action. Weed expert and evolutionary biologists have to work in synergy toward an improve and broader knowledge of plant resistant development. This collaboration is likely to proffer innovative solutions to the herbicide resistance challenges.

Weed species structural and functional composition of okra fields and field periphery under different management intensities along the rural-urban gradient of two West African cities

In urban and peri-urban agricultural production systems of Sub-Saharan African cities, diverse and functional complex weed communities may help to maintain biodiversity and ecosystem services and therefore indirectly support crop performance. However, effects of agricultural intensification and urbanisation on important weed diversity in the West African region had received so far little attention, although in Burkina Faso and Ghana up to 90 per cent of the population depends on agriculture as a main source of income generation. Hence, our research focussed on the analysis of changes in weed assemblages’ structure and function of okra fields that were cultivated under different management intensities and were embedded into the rural, peri-urban and urban environment of two West African cities: Ouagadougou (Burkina Faso) and Tamale (Ghana). We found a strong relationship between gender and market orientation of okra cultivation. Market orientation of okra farmers was also a major driver in shaping weed species assemblages and led to the development of a distinct weed assemblage in urban areas that even showed higher diversity in weeds’ function. Morphological plant traits (life form, seed properties) were most affected by agricultural practises; distribution pattern of ecological traits (seed dispersal mode, pollination vector) seemed to be influenced additionally by environmental characteristics with less entomophilous but more ornithochorous weed species on okra fields within urban areas. Our results revealed that the management of okra was highly variable and that this variation was influenced by farmers’ socioeconomic background leading to changes in soil properties. These in turn may alter the functional diversity of beneficial weed communities beyond changes in species richness by potentially harming the provisioning of ecosystem services such as pest control and pollination.

Diversity and Spatial Heterogeneity of Weed Communities in a Sugarcane Cropping System in the Dry Tropics of Costa Rica

Weed diversity, structure, and distribution within and outside agricultural fields affect not only ecological processes but also weed management strategies. We studied how areas managed differently within and outside the field determine weed communities in a sugarcane cropping system in the dry tropics of Costa Rica. A total of 120 weed species were detected, which was similar to surveys conducted in subtropical and temperate conditions. Weed species richness was highest in undisturbed field borders and lowest in rows and furrows. The area where tractors turn within the field (turn area) had similar richness compared with the borders, despite being one of the most disturbed management areas studied. The most predominant weed species were divided between generalists and species that exhibited clear preferences for management area or soil texture. Soil texture was more important for determining weed community structure than management area when considering weed species affecting weed control decisions. The results indicated that disturbance in the management area and, especially, weed control practices are critical factors affecting weed diversity, but availability of resources for weed growth such as nutrients, soil moisture, and light can mitigate some of the limitations imposed by weed control on weed diversity, especially in the turn area. Differences in weed communities between management areas within fields indicated the existence of conditions that favor key weed species, and this information can be used to anticipate their population growth and help determine when and where more intensive control should be implemented.

Local and regional changes in taxonomic and functional diversity of arable weed communities in Burgundy (France) between the 1970s and the 2000s

Human activities lead to a process of homogenization of biotas in which specialist species are increasingly replaced by common and widespread species. Using a 30-year diachronic record of arable weed communities, we tested this hypothesis by quantifying changes in α- and β-diversity, using both taxonomic and functional diversity and by partitioning β-diversity into species replacement and richness differences. Arable weed communities were sampled in the same 158 fields of the Côte-d’Or region (northeastern France) between the 1970s and the 2000s. For each period, each field was characterized by crop types, soil characteristics and a High Nature Value (HNV) farmland index based on agricultural intensification at the landscape level. At the field scale, we observed a loss of 46% and 38% in α-taxonomic and functional diversity, respectively, which was in accordance with the decrease in the HNV farmland index over the same period. At the regional scale, there was an increase of 15% and 21% in β-taxonomic and functional diversity (across fields), respectively. Crop type and soil characteristics explained similar levels of variation in species replacement, and crop type explained much larger richness differences in the 2000s suggesting that crop and associated practices may exert a high filtering effect. Our results also highlighted a marked decline of common weeds; a process that is far from being counterbalanced by the few colonizing weeds. Rather than to biotic homogenization, this pattern of loss has led to a higher differentiation of arable weed communities. This could correspond to a fragmentation of suitable habitats for species that depend on weeds. This pattern was associated with a decrease of species richness per field; the loss of common species and their associated functions may be of greater significance for agroecosystem functioning.

Diversity of weed communities in soybean [Glycine max (L.)] crop growing under direct sowing depending on cover crops and different herbicide doses

Despite being harmful for agricultural production, weeds are an essential component of biodiversity in agricultural landscapes. A field study was conducted during the period 2007–2009 on grey-brown podzolic soil (sandy), designated as PWsp, with the granulometric composition of silt and classified Class 2 in agricultural land suitability. The study evaluated the structure of weed communities based on selected indicators of diversity of a soybean crop grown under no-tillage with mulch from winter rye, winter oilseed rape, and white mustard as well as using herbicide rates reduced by 25% and 50% in relation to the standard rate (2 L ha<sup>−1</sup>). The studied factors were as follows: (i) mulch plant species and mulch management method; (ii) rates of the foliar herbicide Basagran 600 SL (a.i. bentazon; 600 g L<sup>−1</sup>). The results of this study confirm that no-tillage with mulch significantly changes the diversity of weed flora in a soybean crop. Among the mulches used, the mowed rye and winter oilseed rape in particular increased the values of the general diversity (<em>H</em>'), species richness (<em>d</em>), and evenness (<em>J</em>') indices relative to the control treatment. On the other hand, the study found a strong decrease in the value of the dominance index (<em>c</em>). Reduced herbicide rates modified only the species richness index, in the case of which the 75% rate resulted in its significantly higher values compared to the full rate.

The effects of soil conditions and crop types on diversity of weed communities

The paper presents the diversity of weed communities growing in different crops (winter cereals, spring cereals, and tuber plants) and in diverse soil conditions. To determine weed diversity, phytosociological relevés were made. Simpson’s index of dominance and the Shannon index of biodiversity for weed communities in different crops growing in different soil conditions were calculated and compared. The highest values of the Shannon index and the lowest values of Simspon’s index of dominance were obtained for weed communities noted on compacted and semi-compacted soil with the following granulometric composition: silty loam with underlying sand at a depth of 100 cm, heavy silty sandy loam, silt with underlying sand at a depth of 50 cm, and silt with underlying sand at a depth of 100 cm. The highest index of dominance and low species diversity were determined for weed communities in light soils. The Shannon index of biodiversity was moderately positively correlated with soil pH and granulometric composition. Simpson’s index of dominance was moderately negatively correlated with granulometric composition and was weakly correlated with soil pH.

Weed Seed Banks Are More Dynamic in a Sod-Based, Than in a Conventional, Peanut–Cotton Rotation

Crop rotation promotes productivity, nutrient cycling, and effective pest management. However, in row-crop systems, rotation is frequently limited to two crops. Adding a third crop, especially a perennial crop, might increase crop-rotation benefits, but concerns about disruption of agricultural and ecological processes preclude grower adoption of a three-crop rotation. The objective of the present research was to determine whether weed seed banks differ between a sod-based rotation (bahiagrass–bahiagrass–peanut–cotton) and a conventional peanut–cotton rotation (peanut–cotton–cotton) and the importance of crop phase in weed seed-bank dynamics in a long-term experiment initiated in 1999 in Florida. Extractable (ESB) and germinable (GSB) seed banks were evaluated at the end of each crop phase in 2012 and 2013, and total weed seed or seedling number, Shannon-Weiner's diversity (H′), richness, and evenness were determined. ESB increased in H′ (36%), richness (29%), and total number of weed seeds (40%) for sod-based compared with conventional rotation, whereas GSB increased 32% in H′, 27% in richness, and 177% in total number of weed seedlings. Crop phase was a determinant factor in the differences between crop rotations. The first year of bahiagrass (B1) exhibited increases in weed seed and seedling number, H′, and richness and had the highest values observed in the sod-based rotation. These increases were transient, and in the second year of bahiagrass (B2), weed numbers and H′ decreased and reached levels equivalent to those in the conventional peanut–cotton rotation. The B1 phase increased the germinable fraction of the seed bank, compared with the other crop phases, but not the total number of weed seeds as determined by ESB. The increases in H′ and richness in bahiagrass phases were mainly due to grass weed species. However, these grass weed species were not associated with peanut and cotton phases of the sod-based rotation. The results of the present study demonstrated that including bahiagrass as a third crop in a peanut–cotton rotation could increase weed community diversity, mainly by favoring increases in richness and diversity, but the structure and characteristics of the rotation would prevent continuous increases in the weed seed bank that could affect the peanut and cotton phases.

Short communication. The role of rabbit density and the diversity of weeds in the development of cover crops in olive groves

Cover crops are an effective means to reduce soil erosion and to provide food and shelter for wildlife. However, in areas of intensive farming, which are characterised by the scarcity of weed communities, wild herbivores may focus their grazing on cover crops, which could make their implementation difficult. In this work, we test whether rabbit grazing can prevent the growth of herbaceous cover crops in olive groves in Southern Spain in addition to assessing the role of rabbit abundance and diversity of weeds in the development of cover crops. This question has been addressed by sowing Bromus rubens between the rows of five olive groves in Cordoba province (Spain). We then monitored the surface covered by B. rubens, along with both diversity of weed communities and rabbit abundance. Two rabbit exclusion areas were also placed in each olive grove in order to assess the impact of rabbits on the development of cover crops. Our results showed that the surface occupied by B. rubens was considerably higher in the rabbit exclusion areas (mean 56.8 ± 5.65 %) than in those areas in which they could feed (mean 35.6 ± 4.32 %). The coverage occupied by cover crops was higher in areas with lower rabbit density, although this relationship was modulated by the weed diversity index, since in areas with the same rabbit abundance the coverage was higher in those with a richer weed community. These findings suggest that high rabbit abundances can prevent the development of herbaceous cover crops in olive groves, particularly in areas in which alternative food resources (measured as weed diversity) are scarce.

Intensity of soil disturbance shapes response trait diversity of weed communities: The long-term effects of different tillage systems

Disturbances have a prominent role in structuring plant communities. However, in agroecosystems, the long-term effect of disturbances on determining trait distributions within weed communities remains little studied. We analyzed the effect of three tillage treatments, which differ in the intensity of soil disturbance, on the mean, the range and the distribution of four response traits within weed communities. We aim to test whether tillage acts as a filter restricting the range and the distribution of response traits within weed communities and leads to reduced response trait diversity or whether tilling may have a diversifying effect, creating opportunities for more phenotypes to coexist and increasing response trait diversity. To test this idea, we used data on weed abundance recorded over 24 years from an experiment in which conventional tillage (CT), minimum tillage (MT) and no-tillage (NT) systems were compared. We selected four response traits, maximum height, specific leaf area (SLA), seed weight and seed output, and computed the community weighted mean (CWM) of each trait, as well as four multi-trait metrics related to a different aspect of functional diversity. We found that soil disturbance increases available niche opportunities for weeds especially in terms of regenerative traits. CT, the greater soil disturbance, leads to a greater range and even distribution of the studied traits and that abundant weed species from CT plots hold more divergent trait values than those from MT and NT plots. Our results may be explained by the idiosyncrasy of our disturbance treatments that affect weed seed placement in the soil layers as well as the stratification and availability of soil nutrients. We also found that NT system selected for lower CWM of seed weight (and higher seed output) than MT and CT systems. NT places weed seeds mostly on the soil surface, where having a large seed output may be necessary to avoid the risk of decay or depredation. Conversely, MT and CT systems offer some advantage to other strategies such as larger seed sizes useful to germinate from depth. CWM of SLA was higher in NT and MT than in CT plots and this could be related to greater soil nutrient content in NT systems. In addition our results showed a general trend over experimental time for weed communities to increase in height (and slightly in SLA and seed production) while reducing in seed size. These features are generally associated with intensive farming systems.

Distribution patterns and traits of weed communities along an urban–rural gradient under rapid urbanization in Shanghai, China

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”.

Stochastic processes and crop types shape weed community assembly in arable fields

AbstractAimsIn agro‐ecosystems, crop types, i.e., the crop species and its associated agricultural practices, have been shown to influence the taxonomic as well as functional composition of weed communities. However, the processes underlying weed community assembly within a crop type are poorly understood, especially regarding the contributions of local factors and stochastic processes. In this study, we investigate the effects of the crop type in shaping local weed communities.LocationLTER Zone Atelier Plaine et Val de Sèvre, an intensive cereal system in western France.MethodsWe selected 105 fields of five crop types and investigated the functional structure of weed communities for those traits that define the Leaf–Height–Seed (L‐H‐S) strategy as well as phenological traits. We compared the observed trait distribution to trait distributions expected under random assembly. The trait distributions were described by the range, the community‐weighted mean and the dispersion of each trait, and simulated communities were generated with a null model approach that randomizes the ‘species × traits’ matrix to maintain equiprobable the occurrence of each trait combination. The relationship between trait values and species abundance within each community was investigated using Kendall rank correlation tests.ResultsOur results showed that, in ca. 90% of the fields, the functional diversity of weed communities did not differ from what would be expected under random assembly. Departures from random expectations essentially resulted from shifts in weighted mean values for phenological traits. Weed communities of sunflower, maize and spring pea had later onsets of emergence and flowering than randomly expected. Communities of winter wheat had smaller species and earlier onset of flowering, and communities from oilseed rape had a larger duration of the emergence period and earlier onset of flowering. In addition, we found a positive significant relationship between species abundance and trait values for phenology for spring pea, sunflower and maize, suggesting that species with a later onset of emergence and flowering period have higher performance in these weed communities.ConclusionsAt landscape scale, weed communities generally showed patterns of functional diversity in accordance with those expected under random community assembly, except for phenological traits in spring and summer crops, where patterns were rather consistent with environmental filtering.

Changes in Weed Communities of Spring Wheat Crops of Buenos Aires Province of Argentina

During 2004 to 2008, weed surveys were conducted in 373 wheat fields of two different cropped areas (southwest [SW] and southeast [SE]) of the southern region of Buenos Aires Province of Argentina where different weed communities were expected because of changes in cropping practices over time, including tillage, crop sequence, fertilizers, and herbicides applied. Weed communities differed between regions, with greater numbers of native species for the SW. Weed community diversity was also greater for the SW region, probably due to the more diverse land use that resulted in greater landscape heterogeneity. Rush skeletonweed, sand rocket, yellow starthistle and turnipseed occurred at higher constancy (proportion of fields in which a given species is present) in the SW region, whereas common chickweed, false bishop's weed, corn speedwell, and common lambsquarters were present more frequently in the SE region. Compared with the 1982 survey, constancy of weeds increased, but those species with high constancy in 1982 were also with high constancy in the recent surveys. Diversity (species richness) was greater in conventional than in a no-tillage system. The constancy of Italian ryegrass, sand rocket, and yellow starthistle was lower under no-till than conventional tillage. Surveys allow identification of changes in weed community related to different agricultural systems. Rotation of crops and livestock avoid the homogenization of the environment at the landscape level. Management strategies will be necessary to prevent the increase of weeds populations' size, preserving plant diversity and the properties of the agroecosystem.

Influence of Italian ryegrass (Lolium multiflorum Lam.) as intercrop with spring barley (Hordeum vulgare L.) on the diversity of weed communities

<p class="abstracttekst">The paper presents results of 3 years of studies (2009–2011) on the influence of Italian ryegrass on the development of weed communities in spring barley (without chemical weeds control) cultivated after potato, spring wheat and spring barley. The reaction of spring barley to the choice of the forecrop was compared with identical plots with pure stand of that cereal where herbicides were applied for weeds control. Evaluation of infestation with weeds was conducted during barley tillering and before harvest. That evaluation considered the number and composition of weed species. During harvest, the dry mass of weeds was also considered. The results were used for determination of Shannon-Wiener diversity index and species homogeneity coefficient, Simpson’s index of dominance as well as Sørensen similarity index.</p>Spring barley weeding was significantly higher in case of cultivating it in mixed stand with Italian ryegrass (without chemical control), than in pure stand (with control). In the plots with mixed crop, lower diversity and homogeneity of weeds’ communities were recorded than in pure stand. Barley in mixed crop sown after spring barley, during both times of evaluation (spring and before harvest), increased the value of the index of dominance according to the number of species the most. As concerns the composition of species, number and biomass, the communities of pure stand and mixed crop with Italian ryegrass on the plot after potato were the most similar.

长期不同施肥方式对麦田杂草群落的影响

以太湖地区农业科学研究所31a的长期肥料定位试验田为材料，分别于2011-2012年小麦苗期、拔节期和收获期进行了杂草群落调查，研究杂草类型与密度的分布、杂草多样性指数的变化，并对杂草种群分布与土壤养分因子进行冗余分析。结果表明：小飞蓬、看麦娘、大巢菜、稻槎菜、通泉草是本地区小麦生长期的主要杂草类型；随着小麦的生长以及氮肥、有机肥的施入，杂草密度呈下降趋势；施入有机肥降低了麦季杂草的群落多样性指数，在小麦生长的不同时期均衡施肥的CNPK处理以及不施肥的C0处理的群落各项多样性指数能维持在一个较高的水平。RDA分析显示土壤氮含量以及有机质含量与第一排序轴相关性大，是对杂草分布影响最大的两个土壤养分因子。太湖地区稻麦两熟制条件下，长期有机无机肥料单一或配合投入可显著影响麦田杂草的群落组成，其中氮肥和有机肥的施入能显著降低杂草密度；土壤养分的差异影响田面杂草密度和优势种群，均衡施肥能降低优势杂草种群的优势地位，抑制其发生危害程度，提高农田生态系统的生产力及稳定性。;Weeds are an essential biological component of farmland ecosystems. The maintenance of an appropriate amount of weeds plays a role in protecting the biological diversity of farmlands. Weeds affect crop yields by means of competition with crops for water, nutrients, light, and other natural resources and can also effectively change the farmland ecosystem structure and promote the cycling and energy flow of mineral elements and organic materials in the soil. The goal of weed management is to reduce the impact of weed growth on the crop yield and to inhibit hard-to-control weeds from becoming dominant, while simultaneously maintaining the diversity of the weed community which is controllable. At present, the comprehensive control of weeds through improving competitiveness of the crops has received growing attention; generally speaking, fertilizers and herbicides are the primary input for the farmland ecosystem. Fertilization can alter the natural succession process of the weed community in farmland by directly improving the yield and competitiveness of crops and changing the nutrient composition and the structure of soil. We studied the heterogeneity of the weed community diversity in wheat field in a rice-wheat rotation system after a 31-year long-term application of different organic or non-organic fertilizers, analyzed the effects of major nutrients on the characteristics of the weed, provided information on nutrient management for the coordination of weed control in wheat field, which contribute to the the protection of biodiversity and decrease of noxious weeds. Chemical fertilizer treatments were selected as follows: C0 (no fertilizer), CN (N fertilizer), CNP (N plus P fertilizer), CNK (N plus P fertilizer), CPK (P plus K fertilizer) and CNPK (N plus P and K fertilizers); manure treatments were selected as follows: M0 (manure), MN (manure plus N fertilizer), MNP (manure plus N and P fertilizer), MNK (manure plus N and K fertilizer), MPK(manure plus P and K fertilizer), MNPK(manure plus N, P and K fertilizer). We analyzed the Simpson, Shannon, Margalef, and Pielou indexes of these samples, at the same time, redundancy analysis (RDA) was executed to mining the relationship between fertilizer management and weeds. Among the weeds, <em>Conyza canadensis</em>, <em>Vicia sativa</em>, <em>Alopecurus aequalis</em>, <em>Mazus japonicus</em> and <em>Lapsana apogonoides</em> showed high density and were widely distributed in every trial area. These plants belong to the main dominant weed community that affects wheat yield in the Taihu area. The long-term application of nitrogen and organic fertilizers could significantly reduce the density of weeds; non-organic fertilizers and a combination of non-organic and organic fertilizers had a significant influence on the diversity of weeds, the application of organic fertilizers could reduce the diversity indices of weed community. In terms of the soil nutrient system itself, the soil organic materials and nitrogen content are the main environmental factors that affect the distribution of weeds. The result also indicates that the application of a balanced fertilizer allows all weed species available to shrive. Moreover, the balanced fertizer affects the appearance of dominant weeds, and improve the productivity and stability of farmland ecosystems.

Composition and diversity of weed community in transgenic CryIAb rice field

尽管基因工程技术可以增加作物产量, 但转基因作物是否对农田生态产生影响受到广泛关注。本研究通过田间定位试验, 应用群落生态学方法研究了转<i>CryIAb</i>基因抗虫水稻"Mfb"连续2年在传统栽培和半野生条件下对稻田杂草群落组成及多样性的影响。调查结果显示: 转CryIAb基因稻"Mfb"与非转基因稻"明恢86"田间杂草种类没有显著差异。稻田杂草的频度和密度与栽培方式有关, 半野生稻田杂草的频度和密度显著高于传统稻田, 但相同栽培条件下, 转基因稻"Mfb"与非转基因稻"明恢86"田间杂草频度和密度在整个生长期内均无显著差异。半野生稻田物种丰富度(Sr)指数明显大于传统稻田; 相同栽培条件下, 相同生长时期抗虫转基因水稻"Mfb"与其非转基因对照"明恢86"对稻田杂草群落丰富度的影响差异不显著。稻田杂草群落优势度(D)、均匀度(J)以及多样性(H)各处理、各生长时期内转基因稻与非转基因稻相比均没有显著差异。稻田杂草Shannon-Wiener多样性指数变化无明显规律, 相同栽培方式相同生长期的抗虫转基因水稻"Mfb"与其非转基因对照"明恢86"的Shannon-wiener指数差异不显著。综合上述分析, 转CryIAb基因抗虫稻对稻田杂草群落的组成及多样性没有显著影响。

Effect of fertilization patterns on the assemblage of weed communities in an upland winter wheat field

Aims Understanding the response of farmland weed community assembly to fertilization is important for designing better nutrient management strategies in integrated farmland ecological systems. Many studies have focused on weed characteristics, mainly crop-weed competition responses to fertilization or weed communities alone. However, weed community assembly in association with crop growth is poorly understood in the agroecosystems, but is important for the determination of integrated weed management. Biodiversity promotes ecosystem productivity in the grassland, but whether it applies to the agroecosystems is unclear. Based on an 11-year field experiment, the cumulative effects of different fertilization patterns on the floristic composition and species diversity of farmland weed communities along with wheat growth in a winter wheat-soybean rotation were investigated. Methods The field trial included five fertilization patterns with different combinations of N, P and K fertilizers. Species composition and diversity of weed communities, aboveground plant biomass and nutrient accumulation of weeds and winter wheat, light penetration to the ground surface and wheat yield were measured at each plot in 2009 and 2010. Multivariate analysis, regression and analysis of variance were used to analyze the responses of these parameters to the different fertilization treatments. Important Findings Four dominant weeds (Galium aparine L., Veronica persica Poir., Vicia sativa L. and Geranium carolinianum L.) accounted for similar to 90% of the total weed density in the 2 years of experimental duration. The residual weed community assembly was influenced primarily by topsoil available nutrients in the order P > N > K. Competition for nutrients and solar radiation between crops and weeds was the main indirect effect of fertilization on the changes in weed community composition and species diversity. The indices of species diversity (species richness, Shannon-Wiener, Pielou and Simpson indices) showed significant linear relationships with wheat yield. The balanced fertilization treatment was more efficient at inhibiting the potential growth of weeds because of solar radiation being intercepted by wheat. These results support the conclusion that wheat yield is favored by balanced fertilization, whereas the weed community is favored by PK fertilization in terms of density and diversity. However, the negative effects on wheat yield may be compromised by simultaneous positive effects of weed communities in the fertilization treatments, for instance, the NP and NK treatments, which are intermediate in terms of increasing wheat production and to a level maintaining a diverse community.

Effects of tillage, crop systems and fertilization on weed abundance and diversity in 4-year dry land winter wheat

The arable fields in central Spain have been dominated by cereal production, especially winter wheat. In this area, the defined action of weed management program requires a clear understanding of the factors and mechanisms conditioning weed community dynamics in agro systems. This study evaluated the effects of different agricultural management systems on the abundance and diversity of weed communities in winter wheat crops.Weed density and composition of weed species were sampled over four years; comparing monoculture wheat and rotational wheat in three agricultural management systems: (1) direct drilling (no-tillage, NT); (2) chisel ploughing (minimum tillage 15cm depth, MT) and (3) mouldboard ploughing (traditional tillage 20cm depth, CT). With the aim to be able to improve weed management in agro systems with semiarid environments; within each of the agricultural management systems, we examined the impact of mineral fertilization (traditional and balanced) as a tool for reducing the external inputs in arable cereals.Weed diversity was assessed using the three common diversity indices: Shannon's index, evenness index and species richness. The data collected showed total weed density was different per tillage system and each year of the study, but we did not find significant differences between crop systems over the study.The abundance, diversity and evenness of the weed community in the arable field, were significantly increased in NT systems. Within the direct drilling (NT) plots, rotational wheat showed the highest levels of weed infestation and diversity. Comparing traditional and balanced mineral fertilization of soil did not reveal a significant effect on weed abundance and diversity observed in field.

Urban sprawl and land abandonment affect the functional response traits of maize weed communities in a heterogeneous landscape

Landscape effects on arable weed communities have mainly been studied in areas dominated by intensive agricultural land use, while less attention has been paid to the same effects in cultivated fields close to the rural–urban interface. Our objective was to assess the effects of ongoing agricultural land abandonment and urban sprawl on arable weed communities since this is a widespread phenomena in Mediterranean landscapes.Weeds were sampled at three different distances (5, 10, 15m) from the field margin in 21 maize fields located within a 75km2 area in Liguria and Tuscany, Italy. Species were aggregated in functional response groups based on chorological categories, Raunkiær life forms and CSR plant strategies. Landscape surrounding each field was assessed in four circular buffers of radii ranging from 250 to 1500m. Attributes characterising fields and field margins were also considered.Community composition and diversity of weed communities were affected by field and landscape characteristics. Old and new abandonment increased species richness and weed diversity but had an opposite effect on the Raunkiær functional response groups. Urban sprawl was positively correlated with abundance of geophytes, competitive and cosmopolite species and negatively correlated with therophytes and competitive-ruderals. Most landscape parameters had stronger effect at the smallest scale. The effect of landscape parameters was clearer when weeds were classified by functional response trait than by taxonomy.

Species diversity of segetal communities in tuber crops and in winter and spring cereals

The work presents the results of studies on the diversity of weed communities in tuber crops as well as in winter and spring cereals under similar climatic and soil conditions. We examined overall species abundance in the groups analysed, the average species number per relevé, as well as weed cover of the study area. Additionally, species composition, number of individual species and their biomass were determined. Dominant species in each crop group were distinguished. Species diversity was determined based on the following ecological indices: the Shannon-Wiener index of biodiversity &lt;em&gt;H’&lt;/em&gt; and Simpson’s index of dominance &lt;em&gt;C&lt;/em&gt;. The indices were computed on the biomass and number-of-species basis. The objective of the work was to compare the structure and diversity of weed communities in the crops studied. The communities analysed differed in all the characteristics examined. Differences were found between biodiversity and dominance indices calculated for individual crop groups, but their significance depended on the method applied to calculate the indices.

Response of weed flora to conservation agriculture systems and weeding intensity in semi-arid Zimbabwe

A field study was conducted in the fifth (cowpea crop) and sixth (sorghum crop) seasons of a long-term conservation agriculture trial at Matopos Research Station to determine the effect of tillage, maize mulch rates and intensity of hoe weeding on weed density and community diversity. The experiment was a split-plot randomized complete block design with three replications. Tillage was the main plot factor; conventional tillage versus the minimum tillage (MT) systems of ripper tine and planting basins. Maize mulch rate (0, 4 and 8 t ha-1) was the sub-plot factor to which was super-imposed the intensity of hoe weeding treatment (low and high) as from the fifth season. Tillage system had no significant (P<0.05) effect on weed density and diversity. Whereas the maize mulch rate of 4 t ha-1 increased weed density in both crops, the mulch rate of 8 t ha-1decreased the density of Portulaca oleracea and Corchorus tridens in sorghum. Weed density was lower and community diversity higher in the high than the low weeding intensity treatment in sorghum. Although, frequent hoe weeding can be used to control weeds in MT systems, labour shortages may ultimately limit the area under MT in smallholder agriculture. Key words: Tillage, maize mulch, weed density, community diversity, cowpea (Vigna unguiculata (L.) Walp.), sorghum (Sorghum bicolor (L.) Moench).