Diversity Of Weed Communities Research Articles

Ecology and Diversity of Weed Communities in the Northern Andes under Different Anthropogenic Pressures

Weeds can have both positive and negative effects on agricultural environments. However, despite the growing interest in the ecology of weed communities in agricultural areas, a few studies have been carried out in the northern region of the Andes of Colombia, where urban and agricultural expansion have generated highly disturbed scenarios. The aim of this study was to analyze the diversity of vegetation and weed seed banks in three agricultural production systems and a forest ecosystem in the northern Andes of Colombia. Hill numbers were used to compare diversity, Beta diversity to assess changes in composition, and range—abundance–dominance curves at different sites. Likewise, indicator species were analyzed to find species associations to each system. The results revealed differences in the composition of weeds between the forest ecosystem and the agricultural production systems, with higher equitability in the forest ecosystem and higher dominance in agricultural systems. Significant differentiation was observed among the dominant species within each agricultural system, particularly highlighting those species considered pests due to their unique life history traits. These traits confer them with a greater advantage in the face of various anthropogenic selection pressures. These findings highlight the impact of anthropogenic disturbances on the ecological dynamics of weed communities in different ecosystems, which should be considered when planning integrated weed management techniques.

Convergent Adaptation of Multiple Herbicide Resistance to Auxin Mimics and ALS- and EPSPS-Inhibitors in Brassica rapa from North and South America.

Herbicide-resistant weeds have been identified and recorded on every continent where croplands are available. Despite the diversity of weed communities, it is of interest how selection has led to the same consequences in distant regions. Brassica rapa is a widespread naturalized weed that is found throughout temperate North and South America, and it is a frequent weed among winter cereal crops in Argentina and in Mexico. Broadleaf weed control is based on glyphosate that is used prior to sowing and sulfonylureas or mimic auxin herbicides that are used once the weeds have already emerged. This study was aimed at determining whether a convergent phenotypic adaptation to multiple herbicides had occurred in B. rapa populations from Mexico and Argentina by comparing the herbicide sensitivity to inhibitors of the acetolactate synthase (ALS), 5-enolpyruvylshikimate-3-phosphate (EPSPS), and auxin mimics. Five B. rapa populations were analyzed from seeds collected in wheat fields in Argentina (Ar1 and Ar2) and barley fields in Mexico (Mx1, Mx2 and MxS). Mx1, Mx2, and Ar1 populations presented multiple resistance to ALS- and EPSPS-inhibitors and to auxin mimics (2,4-D, MCPA, and fluroxypyr), while the Ar2 population showed resistance only to ALS-inhibitors and glyphosate. Resistance factors ranged from 947 to 4069 for tribenuron-methyl, from 1.5 to 9.4 for 2,4-D, and from 2.7 to 42 for glyphosate. These were consistent with ALS activity, ethylene production, and shikimate accumulation analyses in response to tribenuron-methyl, 2,4-D, and glyphosate, respectively. These results fully support the evolution of the multiple- and cross-herbicide resistance to glyphosate, ALS-inhibitors, and auxinic herbicides in B. rapa populations from Mexico and Argentina.

Diversity of Summer Weed Communities in Response to Different Plum Orchard Floor Management in-Row

The effect of five methods of in-row weed management on the species composition and diversity of summer weed communities in a plum orchard was evaluated. Different methods of orchard floor management (OFM) were implemented for seven consecutive years from 2009 to 2015. Festuca rubra L. ssp. rubra–rhizomatous perennial grass was sown as a cover crop in the alleys of the orchard, in the tree planting year. In the seventh year of OFM implementation, the treatments were ranked according to the decreasing value of the Shannon–Wiener floristic diversity index as follows: tillage, post-emergence herbicides spraying, mowing, mulch, and weedy control. The highest value of Simpson dominance index was found in the control treatment. In plots with such treatments as control, mowing, tillage, and mulch, the dominant species was F. rubra. This meant that the rhizomatous cover crop from the alleys penetrated and affected the in-row flora. Vegetation of mulched plots was characterized by low value of density and soil cover. The obtained results indicated that the flora developing in the control, sprayed with post-emergence herbicides, tilled and mowed plots had greater potential to provide ecosystem services, than the flora of mulched plots.

Weed community dynamics under repeated fertilization with different nutrient sources over 5 years

Soil fertility management through the application of synthetic fertilizer or livestock manures is crucial to maintaining the productivity and profitability of cropping systems. Little, however, is known about the response of weed communities to different livestock manure nutrient sources. As weed communities with increased diversity are considered part of more sustainable agroecosystems, it is necessary to find management practices that result in diverse weed communities of acceptable densities without negative impacts on crop productivity. Here, we monitored the effect of five nutrient sources, with similar goals for nitrogen (N) management, including synthetic fertilizer, liquid pig manure, two types of solid pig manure, and solid dairy manure on the weed community in a five-year (2008-2012) study. The abundance, species richness, Simpson’s diversity, Simpson’s evenness, and species turnover in weed communities were assessed over time. Crop biomass, mid-season plant-accessible soil nitrate-N, and pre-season soil phosphorus were determined. The application of liquid pig manure or synthetic fertilizer enhanced crop biomass likely through increased crop accessibility to N. The continued use of these sources of nutrients over time, contributed to low density, low species richness, and low diversity weed communities, particularly through the decline of broadleaf weed species. Liquid pig manure and synthetic fertilizer treatments were lower in weed density and diversity than solid manures. Solid manure treatments were associated with increased weed densities and reduced crop biomass; however, these nutrient source treatments resulted in more diverse weed communities. Regardless of the nutrient treatments, we observed drastic declines in weed community abundance, species richness, and diversity in drier years. Our study suggests that a management practice that increases the accessibility of N to the crop, possibly through a mixture of solid manures and synthetic fertilizers or liquid pig manure, may be ideal for promoting a profitable cropping system with decreased densities and improved diversity in weed communities. Technological advances that provide more precise placement of solid manures to increase the accessibility of N to the crop, may further contribute to achieving such profitable and multifunctional agroecosystems.

Conservation agriculture practices lead to diverse weed communities and higher maize grain yield in Southern Africa

Weed development is one of the major constraints to cereal cropping systems in Southern Africa with potential severe crop losses. Understanding weed community responses to different conservation agriculture (CA) components ( i.e ., no-tillage, NT; crop rotation, R; and mulching, M) and/or their combinations is crucial in Southern Africa where farmers apply different combinations depending on local context. Here, for the first time, we assessed how weed density, community diversity and structure respond to different combinations of CA components [conventional tillage (CT), CT+M, CT+R, CT+M+R, NT, NT+M, NT+R, NT+M+R]. The study was carried out over three seasons at two locations with contrasting soil textures i.e ., clayish, and sandy. At the sandy location, across seasons, weed density (number of individuals per unit area) and community diversity (distribution of individuals within the species) were significantly and positively affected by precipitation and not by cropping system. Weed richness (number of species) was affected by the interaction of season and cropping system, with the highest number of weed species being recorded in the NT+M+R system in the seasons with medium to high precipitation. At the clayish location, an opposite pattern was observed, and weed density was lower in seasons with medium-high precipitation than under low precipitation. Weed community diversity was 50 % higher under NT+M than under CT+R, whereas weed species richness decreased with the increase of precipitation. At both locations, the implementation of rotation and mulching either in NT or CT systems resulted in the modification of the structure of weed community with respect to CT and NT alone, and these CA combinations were associated with highest maize grain yield. Overall, eight weed species common to both locations were responsible for most of the community structure differences among cropping systems. Structural equation modelling showed that at the sandy location precipitation did not affect grain yield, but positively affected weed density, diversity, evenness, and richness. By contrast, at the clay location, precipitation positively affected grain yield, but did not modify weed density and evenness, and reduced weed community diversity and richness. At this location, weed density negatively affected grain yield. The differential weed-crop relationship supports the need to find a site-specific equilibrium between the control of weeds and the maintenance of their diversity. • Rotation & mulch in no-tillage-NT & conventional tillage-CT modified weed community. • In sandy soil rainfall positively affected weed density & diversity and not yield. • In sandy soil weed diversity positively affected grain yield. • In clay soil rainfall positively affected yield & reduced weed diversity & richness. • In clay soil, weed density negatively affected grain yield.

Winter cover crops and dynamics of weeds in agricultural systems of the Argentine Rolling Pampas

The aim of this study was to determine if different mixtures and monocultures of cover crops (CC) reduce aerial dry matter, number and diversity of autumn-winter weeds. Two experiments with different CC species were implanted in the INTA Pergamino Agricultural Experimental Station (Pergamino, Buenos Aires, Argentina, 33° 51´ S, 60° 34´W) in 2018 and 2019. The species used were: Avena sativa, Triticosecale and Vicia villosa. Mixtures and monocultures of CC were used, in different proportions and densities, and were compared with a chemical fallow. Two cuts of CC were made aboveground at tillering and milk grain stages (Z 2.5 and 7.3, respectively) to obtain aerial dry matter of CC (ADMcc, g.m−2), ADM of weeds (ADMw, g.m−2) and number of weeds (weeds.m−2). Moreover, weed species were identified and Shannon diversity and evenness indices and effective specific richness were calculated. In 2018, the highest ADMcc was recorded in Avena sativa at Z 2.5 as well as the highest weed density. At Z 7.3, the highest ADMcc was recorded in Avena sativa, Triticosecale and their mixture. At that stage, the highest ADMw was recorded in the chemical fallow. In 2019, the 3:1 Avena sativa/Vicia villosa mixture showed the highest ADMcc and diversity of weed community showed non-significant differences from the chemical fallow at Z 2.5. There were non-significant differences in ADM among CC and diversity of weed community in the CC was practically null at Z 7.3. At both stages, the highest number of weeds and ADMw was observed at chemical fallow, whereas in CC, non-significant differences were detected. The results obtained indicate that CC reduce the number, ADMw and diversity of the weed community, regardless of the mixtures used.

Composition and environmental interpretation of the weed communities in the main planting base of jujube (Ziziphus jujuba Mill. cv. 'LingwuChangzao'), Ningxia province of China.

BackgroundZiziphus jujuba Mill. cv. ‘LingwuChangzao’ is a traditional jujube cultivar in northwest China. It is of great significance to explore the weed community composition and environmental characterization for the ecological control and comprehensive management of weeds in jujube orchards. In this article, a total of 37 species were recorded in 40 sample plots (1 m × 1 m). Moreover, fourteen environmental indicators to characterize the spatial locations, climate and soil nutrient characteristics of the plant communities were adopted.MethodologyThrough the two-way indicator species analysis (TWINSPAN) quantity classification and canonical correspondence analysis (CCA) ranking methods, the types of weed communities in the main planting base of jujube ‘LingwuChangzao’ and the main environmental factors affecting the change and distribution of weed types were analyzed.ResultsThe weed communities within the study area were divided into 15 types by the TWINSPAN classification. There were significant differences in soil factors to the species diversity indices of the weed communities, the diversity of weed communities was negatively correlated with available potassium, whereas positively correlated with soil water content. The CCA results showed that community structure and spatial distribution of weed communities were affected by soil water content, total potassium, soil organic carbon, total phosphorus, total nitrogen. Our results can be used as a reference for orchard weed management and provide a theoretical basis for weed invasion control and creating a higher biodiversity in arable land under the background of environmental change.

Modeling weed community diversity based on species population density dynamics and herbicide use intensity

Herbicide programs change weed population density as well as weed community composition. The repeated use of a given program can result in a weed community that progressively becomes more difficult to manage or could lose its ability to provide ecosystem services. Simulation of those changes using stochastic models considering population dynamics of multiple species makes it possible to identify a priori potential community changes that might result from the use of a given herbicide program. The objectives of this work were to model the population dynamics of weed species under different herbicide programs and how those dynamics change weed community diversity over time. Weed population dynamics were stochastically modeled along ten years using population growth rate (lambda) for each species under different herbicide programs. Lambda values were obtained from an eight-year long, field experiment, and these were used to parameterize the stochastic ranges for the model for each weed species. Population trajectories were modeled for each individual species over ten years and the results were used to estimate richness, diversity, and evenness for each herbicide use scenario. The repeated use of glyphosate alone had a minimal effect on richness, but it caused a strong reduction in weed diversity and evenness. Programs with more mechanisms of action and the use of both preemergence and postemergence herbicides were slightly more likely to suffer the loss of weed species than programs with single or just a few herbicides. Conversely, the former had a higher probability of maintaining weed diversity and evenness than the latter. According to simulations, losses in weed community diversity are reversible, especially when highly competitive species were eradicated allowing other species with lower lambda to increase their populations. However, the eradication of species with low reproductive rates reduced diversity and evenness. The effects of herbicide programs on the weed community lasted for several years even after those programs were modified indicating that seed banks play a major buffering role in the rate of change of weed community composition. Thus, frequent changes in management interrupting the repeated use of specific weed control programs, even under high herbicide intensity use (i.e., number of applications and mechanisms of action), can help maintain weed diversity in agroecosystems.

Weed communities in the irrigated rice paddies of northern Iran

Dedicated insights into the diversity, spatial and temporal distribution of rice weed communities, as well as underlying ecological factors, are critical for developing effective ecological weed management strategies in these agroecosystems, leading to the preservation of biodiversity and ecosystem services in a sustainable agriculture framework. To fulfill this aim, 108 vegetation relevés were conducted at 23 sites of rice paddies throughout 9 counties in the north of Iran at various altitudes, during three different phenological stages of rice. Data from vegetation relevés was analyzed using TWINSPAN, resulting in the identification of four main plant community types related to the different stages of rice growth: Echinochloa crus-galli–Paspalum distichum, Spirodela polyrrhiza–Lemna minor, Monochoria vaginalis s.l.–Marsilea quadrifolia, and Cyperus difformis–Ammannia baccifera. Complementary direct (canonical correspondence analysis) and indirect gradient analyses (detrended correspondence analysis) confirmed these communities’ separation and indicated that the most significant environmental factors affecting plant community distribution were soil water content and soil pH. Moreover, out of 72 segetal species of investigated rice paddies, 12 species were alien to Iran, indicating that this agroecosystem provides an important source for the introduction, distribution, and possible spread of alien species into other adjacent ecosystems. Our findings contribute to the knowledge of detecting patterns of weed composition and distribution in rice paddy ecosystems, as well as their interpretation in relation to environmental gradients. They can support the establishment of ecological weed management practices in northern Iran's paddy fields.

The Yield and Weed Infestation of Winter Oilseed Rape (Brassica napus L. ssp. oleifera Metzg) in Two Tillage Systems

Results from a four-year field experiment were used to evaluate the effect of conventional tillage (CT) and no-tillage (NT) systems on the yield, selected yield and crop structure elements, weed infestation, and contents of fat and glucosinolates in the seeds of winter oilseed rape (Brassica napus L. ssp. oleifera Metzg). The study proved the beneficial effect of the NT system on the winter rape seed yield only during the precipitation shortage in the growing season. In the years with a sufficient sum of precipitation, a higher seed yield was produced in the CT than in the NT system. Considering the average values from the four-year study period, the seed yield and straw yield, plant density after emergence and before harvest, number of branches and main shoot length, and finally the 1000 seed weight were significantly higher in the CT compared with the NT system. In contrast, the NT system proved more beneficial regarding seed weight per silique and fat content of the seeds. The statistical analysis of the study results showed no effect of the tillage systems on the glucosinolate content of the seeds. In turn, a significantly higher number and air-dry weight of weeds as well as an increased density of Viola arvensis weeds were demonstrated in the NT plot compared with the CT plot of winter oilseed rape. Sonchus asper and Sonchus arvensis were identified in the NT plot but not in the CT plot. A significantly higher density of Chenopodium album and Euphorbia helioscopia weeds was detected in the CT system compared with the NT system. The statistical analysis of study results regarding weed community diversity showed similar values to the Shannon-Weinner diversity index (H’) in both tillage systems and a significantly higher value of the Simpson dominance index (SI) in the NT system compared with the CT system.

Weed Community Composition in Simple and More Diverse Cropping Systems

Weed communities in three cropping systems suitable for the Midwestern USA were studied from 2017 to 2020 to examine how crop diversification and the intensity of herbicide use affected weed community diversity, stand density, and aboveground mass. A baseline 2-year cropping system with corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) grown in alternate years was diversified with cool-season crops, namely oat (Avena sativa L.), red clover (Trifolium pratense L.), and alfalfa (Medicago sativa L.) in 3-and 4-year systems. Herbicide was not applied in the cool-season crops. Changing weed management regime from broadcast to banded application and interrow cultivation in corn and omitting herbicide in cool-season crops of the 3- and 4-year rotations resulted in an overall reduction of herbicide a.i mass. The reduction in the mass of herbicide active ingredients was associated with increases in weed stand density, aboveground mass, and community diversity. Increased weed abundance under herbicide mass reduction was not associated with crop yield loss. In the cool-season crops phases of the 3- and 4-year rotations, weed emergence was increased but weed growth was not, as compared with the warm-season crop environments. The dominance of aggressive weed species such as common waterhemp (Amaranthus tuberculatus (Moq ex DC) J.D. Sauer) and common lambsquarter (Chenopodium album L.) tended to be greater in corn and soybean phases of the rotations than in oat, red clover, and alfalfa.

Impact of new management practices on arable and field margin plant communities in sunflower, with an emphasis on the abundance of Ambrosia artemisiifolia (Asteraceae)

AbstractSome troublesome weeds such as Ambrosia artemisiifolia have led farmers to adopt herbicide‐tolerant varieties (HTVs) in cultivated sunflower fields. Agricultural practices associated with the use of HTVs have raised concerns among public authorities, prompting the recommendation to monitor the potential effects of HTVs on biodiversity. In this context, we surveyed the vegetation of 239 sunflower fields and their margins in three French regions between 2017 and 2019, with a specific focus on A. artemisiifolia. We collected information on 21 explanatory variables covering agricultural practices, landscape factors, and spatiotemporal data. Herbicide‐tolerant varieties fields were associated with lower weed diversity but similar field margin community diversity. This lower weed diversity can be attributed to the greater use of herbicides and shorter crop rotations, whereas landscape factors may be more important for the diversity in field margins. Conventional fields with traditional varieties showed lower abundance of A. artemisiifolia compared with organic fields and HTV fields. A. artemisiifolia abundance was higher in the most infested region, in fields with a high proportion of sunflower crops in the crop rotation, late sowing dates, high numbers of hoeing operations, and high numbers of post‐emergence treatments. We interpreted the association of hoeing and HTV use with a high abundance of A. artemisiifolia as a response to weed infestation rather than its cause. In conclusion, no unintended effects of HTVs were found in field margins, but practices associated with HTVs lead to lower weed community diversity and HTV fields had still high A. artemisiifolia abundance after weed control.

К синтаксономии сегетальной растительности Северо-Запада Российской Федерации

The tendency to gradual reduction of crop is observed now in the North-West of the Russian Federation. From 2010 for 2021 the total area under crops in four regions (Leningrad, Novgorod, Pskov, Vologda) has decreased from 1150.7 to 907.5 thousand hectares. Studies of specific structure of weed communities of the North-West of the Russian Federation started in the first decade of the XX century with inspections of crops by A. I. Maltsev in the St. Petersburg region (Maltsev, 1908, 1909). Since the beginning of the XXI the study of weed plants were focused at the All-Russian Institute of Plant Protectionwhere monitoring of crops of the North-West of the Russian Federation (Mysnik, 2012; Luneva, Mysnik, 2016, 2017, Luneva et al., 2009) has became the priority direction. In spite of previous wide floristic researches, the diversity of weed communities of this region is still not established. The first results of the floristic classification of weed vegetation in the North-East of the Russian Federation are presented. The dataset is based on 278 relevés made by N. N. Luneva, I. N. Nadtochiy, E. V. Filippova, T. D. Sokolova, Yu. V. Eroshina for field seasons in 1999–2916. The research area covered Leningrad, Novgorod, Pskov and Vologda regions. Data processing was carried out according floristic classification approach (Westhoff, Maarel, 1978), using TWINSPAN algoritm in JUICE software packages (Tichy, 2002). The new syntaxa are named in accordance with the rules of the International Code of Phytosociological Nomenclature (Theurillat et al., 2021). DCA-ordination using the CANOCO 4.5 software package (Ter Braak, Smilauer, 2002) was produced to identify patterns of environmental differentiation. The habitat moisture and soil richness-salinity scales status of communities (Ramenskiy et al., 1956) was calculated and basic agroclimatic parameters were identified to characterize the ecological variability of habitats. The communities were classified within the order of Aperetalia spica-venti J. Tx. et Tx. in Malato-Beliz et al. 1960 of the class Papaveretea rhoeadis S. Brulo et al. 2001 and were assigned to the alliance Scleranthion annui (Kruseman et Vlieger 1939) Sissingh in Westhoff et al. 1946), which unites the most mesophytic weed communities distributed mainly on gray forest, sod-podzolic, podzolic and other types of soils of the forest zone. The alliance diagnostic species are Stellaria media, Tripleurospermum inodorum, Capsella bursa-pastoris, Lepidotheca suaveolens, Thlaspi arvense, Centaurea cyanus. Three species from the diagnostic groups of ruderal vegetation classes are also active in their cenoflora — Elytrigia repens, Viola arvensis, Taraxacum officinale. From the diagnostic group of the Papaveretea rhoeadis class and the order Aperetalia spica-venti with high constancy, species are found Cirsium setosum, Chenopodium album, Sonchus arvensis, less often are Fallopia convolvulus. The group of species of the alliance Scleranthion annui includes Stellaria media, Tripleurospermum inodorum, Capsella bursa-pastoris, Lepidotheca suaveolens, Thlaspi arvense, Centaurea cyanus. Unlike the weed communities of other regions of the Russian Federation (Khasanova et al., 2021 Yamalov et al., 2021a, b), apophytes are not significantly presented in cenophlora, but such ruderal species as Elytrigia repens, Viola arvensis, Taraxacum officinale are active. The identified associations and communities are different geographically, in terms of crop affinity and the system of agricultural machinery, the type of soils and heat conditions. The most widespread are the communities of the ass. Tussilagi farfarae–Centauretum cyani, which occur in the Leningrad, Novgorod, Pskov and Vologda regions. The associations Galeopsetum bifidae (Novgorod, Pskov and Vologda regions) and Lamio purpurei–Persicarietum lapathifolii (Leningrad, Novgorod and Pskov regions) are of slightly smaller range. Syntaxa are differentiated according to the level of habitat heat conditions from the higher (ass. Echinochloo crusgalli–Galietum aparinis, ass. Lamio purpurei–Persicarietum lapathifolii) to the lower (community Fumaria officinalis) ones. Communities of the associations Echinochloo crusgalli–Galietum aparinis and Lamio purpurei-Persicarietum lapathifolii are formed on swamp, peat and podzolic-swamp soils. The community Polygonum aviculare and the ass. Mentho arvensi–Sonchetum arvensis are formed on weakly and medium-podzolic, as well as sod-podzolic soils. The other syntaxa are confined to sod-carbonate soils. According to the spectrum of crop, syntaxa were distributed as follows: associations Echinochloo crusgalli–Galietum aparinis, Mentho arvensis–Sonchetum arvensis, Lamio purpurei–Persicarietum lapathifolii and the community Polygonum aviculare occur mainly on fields with vegetable crops (potatoes, carrots, cabbage, beets, etc.); Tussilagi farfarae–Centauretum cyani, Galeopsetum bifidae, the communities of Fumaria officinalis and Achillea millefolium — on grain crops (barley, oats, rye, triticale and wheat). The main factors of differentiation of the studied communities are the type of soil, cultivated crop and humidification.

Effects of band steaming on weed control, weed community diversity and composition and yield in organic carrot at three Mediterranean sites

AbstractBand steaming is a non‐chemical weed control method of increasing interest for highly remunerative, low competitive crops. This study aimed to test the field application of a new prototype of band‐steaming machine in three organic fields under contrasting Mediterranean environmental conditions. Trials were conducted in carrot under real‐field conditions to investigate the effects of three steaming doses and one control (no steaming) on weed vegetation and crop yield. Soil temperature at steaming application, weed density at species level during carrot crop growth, and weed and carrot biomass at harvest were sampled at each site. Band steaming significantly affected total weed density: when comparing the untreated control with the highest steam dose, weed density reduction ranged from 62% (−492 plants m−2) at site II to 94% (−146 plants m−2) at site III. Generally, diversity of weed communities decreased with increasing steaming dose, indicating a progressive species filtering effect: Fumaria officinalis L. and Sonchus oleraceus L. were filtered by steaming application at site I, while Polygonum lapathifolium L. and Portulaca oleracea L. were filtered at sites II and III. Weed community composition was affected by steaming dose at two sites out of three. Small seeded species (seed mass <1.5 mg) were less tolerant of steaming than species with large seeds. Through reduction in weed density, steam application gave carrot a competitive advantage, increasing fresh yield from 47% at site III (+3,646 g m‐2) to 92% at site II (+1,866 g m‐2), compared with yields at non‐steamed plots.

Weed shift and community diversity in conservation and conventional agriculture systems in pigeonpea- castor systems under rainfed semi-arid tropics

Conservation agriculture (CA) is an alternative sustainable production system to conventional tillage system for resource conservation in rainfed agriculture. Weeds are the major constraints for adoption of CA in rainfed regions. A seven years study was done at ICAR- Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, India, to study the effects of different tillage practices and residue levels on weed shift, diversity and crop yields. It was observed that annual weed species were dominant in conventional tillage (CT) and reduced tillage (RT), whereas a shift towards perennials was observed in zero tillage (ZT). The CT recorded significantly lower weed density and weed biomass (12.89 m−2 and 35.60 g m−2) over RT (17.33 m−2 and 38.37 g m−2) and ZT (36.67 m−2 and 69.58 g m−2) after seven years, respectively. A shift in weed species, higher weed density and weed biomass in dicots (Tridax procumbens L and Euphorbia hirta L. and a marginal decrease in monocots (Bulbostylis barbata, Digitaria sanguinalis L) was observed in ZT. The marginal decrease in monocots was due to higher precipitation immediately after herbicide application which reduced the control of weeds due to leaching. The anchored residues 10 and 30 cm recorded lower monocots and total weed count over No residue. The study suggests that integrated weed management (combination of herbicide and removal of chance weeds) and in RT are efficient strategies to minimise the weed infestation in CA and these methods not only reduce the over reliance on herbicides but also improve the productivity of pigeon pea (Cajanus cajan L.), castor (Ricinus communis) and the environmental performance of CA. ZT and RT recorded the highest Shannon index, Pieloús evenness index and species richness over CT which indicates a higher weed species diversity in ZT as compared to CT. This study helps to improve the understanding of crop–weed communities and in the development of cost effective environmentally sound weed management strategies.

Weed community diversity in conservation agriculture: Post-adoption changes

Conservation agriculture has been identified as one of the farming systems likely to deliver sustainable agriculture but its effects over time on the diversity and composition of weed communities are poorly documented. Using a network of 100 winter wheat fields selected to encompass a gradient of years in conservation agriculture from 1 to 20 years in the Bourgogne-Franche-Comté region (France), we analyzed the changes that occurred in the diversity of weed communities over several years, both in α- and β-diversity using a taxonomic (species level) and functional (10 response traits) approach. Based on three weed surveys (before the last herbicide use, before harvest, before sowing the following crop), we identified weeds able to maintain and/or to produce propagules. All the observed weed communities were rich (average species richness of 23.9 species), diverse (average Shannon diversity of 2.15) and equitably composed of low-density species. The results showed an increase in species richness, total weed abundance and α-functional diversity but no change in species diversity and species evenness over time. Heterogeneity and average values of β-taxonomic and β-functional diversity between communities were high in the early years following the adoption of conservation agriculture. Heterogeneity and average β-taxonomic and β-functional diversity decreased over time, leading to a homogenization of weed community assemblages. Despite major changes in cultural practices related to conservation agriculture, homogenization of weed community was not immediate and did not concern all the traits studied.

Fitosociología de malezas en plantaciones bananeras en el departamento del Magdalena, Colombia

Las malezas constituyen un factor limitante en la producción de banano en Colombia. Para contribuir a la fundamentación de su manejo, se propuso evaluar la estructura y diversidad de las comunidades de malezas en cuatro zonas productoras de banano (Alta, Media, Baja y Norte) en el departamento del Magdalena. Se realizaron levantamientos durante 2016 y 2017 mediante muestreo sistemático utilizando cuadrados de 1m2 en fincas seleccionadas en cada zona con método de control químico, cobertura y mecánico, y se calculó la frecuencia, densidad y dominancia de las malezas para estimar el índice de valor de importancia (IVI), la diversidad alfa y el índice de similitud de Bray-Curtis. Se identificaron 122 especies incluidas en 93 géneros y 39 familias. Poaceae y Cyperaceae presentaron mayor riqueza específica y Commelinaceae mayor IVI. Commelina erecta, Axonopus compressus y Melothria pendula fueron las especies de mayor importancia ecológica en las plantaciones. Los parámetros fitosociológicos difieren entre zonas y métodos de control. Las zonas con mayor y menor diversidad fueron Norte y Baja, respectivamente. Hubo mayor similitud entre las zonas Media y Baja, así como entre Media y Alta, en tanto, la Norte fue la más disímil. Pocas especies fueron muy abundantes y frecuentes, señalando la tendencia a baja diversidad. Los resultados más importantes permiten concluir que las condiciones agroecológicas de cada zona y el método de control empleado influyen en los parámetros fitosociológicos y diversidad de especies, determinando la composición y estructura de las comunidades de malezas asociadas al cultivo en el departamento del Magdalena.

Multi-year weed community dynamics and rice yields as influenced by tillage, crop establishment, and weed control: Implications for rice-maize rotations in the eastern Gangetic plains

In South Asia's rice-based cropping systems, most farmers flood and repetitively till their fields before transplanting. This establishment method, commonly termed puddled transplanted rice (TPR), is costly. In addition, it is labor and energy intensive. To increase labor and energy efficiency in rice production, reduced or zero-tilled direct seeded rice (ZT-DSR) is commonly proposed as an alternative tillage and crop establishment (TCE) option. Effective management of weeds in ZT-DSR however remains a major challenge. We conducted a four-year experiment under a rice-maize rotation in Northwestern Bangladesh in the eastern Gangetic Plains to examine the performance of two TCE methods and three weed management regimes (WMR) on the diversity and competitiveness of weed communities in the rice phase of the rotation. The Shannon-Weiner Diversity Index, a measure of species diversity, was significantly greater under ZT-DSR than puddled TPR. It was also greater under no weed control (Weedy) and two manual weeding (MW) treatments compared to chemical herbicide with manual weeding (C + MW). In DSR Weedy plots, weed communities began shifting from grasses to sedges from the rotation's second year, while in the ZT-DSR and C + MW treatments, sedges were consistently predominant. In both puddled TPR Weedy and TPR C + MW treatments, broadleaves and grasses were dominant in the initial year, while sedges dominated in the final year. There were significant main effects of year (Y) and weed management regime (WMR), but not of TCE. Significant Y × TCE and TCE × WMR interaction effects on rice yield were also observed. Grain yields under ZT-DSR were similar to puddled TPR. ZT-DSR with one application of pre-emergence herbicide followed by one hand weeding at 28 days after establishment however resulted in significantly higher grain yield (5.34 t ha−1) compared the other weed management regimes. Future research should address methods to effectively manage weed community composition shifts in both ZT-DSR and TPR under rice-maize rotations utilizing integrated and low-cost strategies that can be readily applied by farmers in the eastern Gangetic Plains.

Agriculture intensification reduces plant taxonomic and functional diversity across European arable systems

Abstract Agricultural intensification is one of the main drivers of species loss worldwide, but there is still a lack of information about its effect on functional diversity of arable weed communities. Using a large‐scale pan European study including 786 fields within 261 farms from eight countries, we analysed differences in the taxonomic and functional diversity of arable weeds assemblages across different levels of agricultural intensification. We estimated weed species frequency in each field, and collected species' traits (vegetative height, SLA and seed mass) from the TRY plant trait database. With this information, we estimated taxonomic (species richness), functional composition (community weighted means) and functional diversity (functional richness, evenness, divergence and redundancy). We used indicators of agricultural management intensity at the individual field scale (e.g. yield, inputs of nitrogen fertilizer and herbicides, frequency of mechanical weed control practices) and at the landscape scale surrounding the field (i.e. number of crop types, mean field size and proportion of arable land cover within a radius of 500 m from the sampling points). The effects of agricultural intensification on species and functional richness at the field scale were stronger than those of intensification at the landscape scale, and we did not observe evidence of interacting effects between the two scales. Overall, assemblages in more intensified areas had fewer species, a higher prevalence of species with ruderal strategies (low stature, high leaf area, light seeds), and lower functional redundancy. Maintaining the diversity of Europe's arable weed communities requires some simple management interventions, for example, reducing the high intensity of field‐level agricultural management across Europe, which could be complemented by interventions that increase landscape complexity. A free Plain Language Summary can be found within the Supporting Information of this article.

Species composition, richness, and diversity of weed communities of winter arable land in relation to geo-environmental factors: a gradient analysis in mainland Italy

The interest in knowledge of the weed communities of arable land is growing worldwide. Italy is one of the countries in Europe that is the most biodiverse, geographically and environmentally heterogeneous, and rich in arable weed species. Thus, in this study, the geo-environmental factors influencing the floristic composition, the species richness, and the Shannon diversity of weed communities of Italian winter arable crops were investigated along a gradient across mainland Italy. Original data were collected in the spring of 2018 in 106 winter cereal and legume arable fields from one fixed area plot per field. Environmental and geographic data were retrieved for each plot, including latitude, longitude, elevation, soil texture, soil pH, continentality, temperature, and precipitation. The effect of crop type was also tested. Latitude was the main driver of floristic differentiation between the studied plant communities, followed by precipitation, temperature, continentality, elevation, and longitude. Soil features and crop type had no significant effects. Higher values of species richness and Shannon diversity were found in southern areas and at higher elevations. Significant explanatory variables accounted for 11.55% of the total variation in species composition of the surveyed communities. The results are discussed and compared with those of similar studies in other Eurasian countries.