Weed Communities In Fields Research Articles

Functional shifts in weed community composition following adoption of conservation agriculture

AbstractTo better understand the changes in weed communities following the adoption of conservation agriculture (CA), we investigated the functional composition of weed communities in fields implementing CA continuously from 1 to 21 years. Weed surveys were conducted in 100 winter wheat fields of 53 farmers in the Bourgogne‐Franche‐Comté region, Eastern France. Ten response traits were selected to highlight changes in the functional composition of weed communities, using weighted mean value for quantitative traits and an approach based on composition analysis for qualitative traits. Out of the 10 traits, four were impacted by the time following the adoption of CA significantly, whereas two only showed trends. Specific leaf area, leaf dry matter content, seed dispersal mode and soil seedbank longevity did not change over time following adoption of CA, whereas changes were observed for plant type, Raunkiær's life forms, Ellenberg's indicator value for light and, germination and flowering periods. Phanerophyte and geophyte life forms, summer‐germinating species and spring‐ and summer‐flowering species increased with time following adoption of CA. Shade‐tolerant species, not present in fields recently converted to CA, established later. Community‐weighted mean of seed mass and the percentage of graminoids tended to increase with time following adoption of CA. Some functional shifts in weed communities occurred quicker than others (i.e., summer‐germinating species increased after at least 10 years of continuous application of CA principles). These results can be used to inform farmers moving towards CA about expected changes.

Weed communities and their negative impact on rice yield in no-input paddy fields in the northern part of Japan

Although weeds cause serious yield losses in agriculture, relatively few studies have been conducted on the relationship between weeds and yield loss in no-input rice production systems, where no herbicides are used. This study investigated weed communities in rice paddy fields and their influence on rice yield, by comparing 16 no-input paddy fields in northern Japan. The weed seed community in the paddy field soils, before transplanting, were analyzed using a spontaneous germination test, and the established weed communities in the fields were examined at the full heading growth stage of the rice. The weed community structures showed a marked difference between the seeds in the soil and the established weed communities. Although eight weed species germinated from the soil, only four weed species were observed in the fields at the full heading stage of the rice. The two dominant weed species, Monochoria vaginalis and Cyperaceae, accounted for 84% of the total weed biomass in the field. The multiple linear regression analysis revealed that during the period of no-input cultivation, soil NO3 concentrations, air temperature, and sunlight hours had significant effects on the biomass of M. vaginalis, but not on Cyperaceae. Furthermore, the two dominant weed species had different impact on rice yield; Cyperaceae had a large negative effect on rice yield, whereas M. vaginalis did not. These results indicated that weed management in no-input paddies should be directed towards the control of specific weed species such as Cyperaceae sp., rather than the entire weed community.

Spring weed communities of rice agrocoenoses in central Nepal

AbstractRice field weed communities occurring in central Nepal are presented in this study. The research was focussed on the classification of segetal plant communities occurring in paddy fields, which had been poorly investigated from a geobotanical standpoint. In all, 108 phytosociological relevés were sampled, using the Braun-Blanquet method. The analyses classified the vegetation into 9 communities, including 7 associations and one subassociation. Four new plant associations and one new subassociation were proposed: Elatinetum triandro-ambiguae, Mazo pumili-Lindernietum ciliatae, Mazo pumili-Lindernietum ciliatae caesulietosum axillaris, Rotaletum rotundifoliae and Ammanietum pygmeae. Due to species composition and habitat preferences all phytocoenoses were included into the Oryzetea sativae class and the Ludwigion hyssopifolio- octovalvis alliance. As in other rice field phytocoenoses, the main discrimination factors for the plots are depth of water, soil trophy and species richness. The altitudinal distribution also has a significant influence and separates the Rotaletum rotundifoliae and Elatinetum triandro-ambiguae associations. The study shows that anthropogenic rice fields can harbour relatively rich rush and water vegetation. More than 80 species were noted in the vegetation plots. Several of them are considered to be extremely rare and have been recorded on the world Red List.

Weed communities in Italian maize fields as affected by pedo-climatic traits and sowing time

Abstract This study examined relationships between weed communities and some pedo-climatic traits in Italian maize cultivation areas. A weed dataset was amassed from studies conducted independently by research groups during 1998–2013. Included were herbicide efficacy field trials and weed surveys from about 600 sites representing 175 northern and central Italy maize fields. The dataset was honed to results from untreated plots in which weed data were collected at least once (June/July) each season. For sites observed more often, only the survey with the highest weed species count was used. Of the approximate 120 species found, just five were present on more than 50% of sites: Chenopodium album, Echinochloa crus-galli, Amaranthus retroflexus, Solanum nigrum, and Persicaria maculosa. Indices were calculated to describe weed community structure: total weed species count, monocotyledonous and dicotyledonous species counts, and total weed density. Additional soil and climate site data were collected or obtained from regional databases: pH reaction, texture, organic matter content, total nitrogen, Mg/K ratio, assimilable phosphorus, cation exchange capacity (CEC), and C/N ratio, annual total precipitation, annual mean temperature, and Thornthwaite climate classification. Pedo-climatic traits and weed indices relationships were investigated using linear correlation analysis (CA), discriminant analysis (DA), and principal component analysis (PCA). CA and PCA highlighted a weak bias (higher count and density) by monocotyledonous species for sand and alkaline soils, while clay and alkaline soils favored dicotyledonous species. DA classified the sites well based on weed indices using soil parameters as predictor variables, in particular for a Piemonte region (northwest Italy) data subset. Soil texture, CEC, pH, and some nutrient contents significantly predicted some weed indices. This study pointed out that Italian maize field weed communities are influenced by some pedoclimatic traits; the weak relationships observed might be mitigated by the overall influence of crop practices on weed dynamics.

Weed communities of transgenic glyphosate‐tolerant soyabean crops in ex‐pasture land in the southern Mesopotamic Pampas of Argentina

Mas MT, Verdú AMC, Kruk BC, De Abelleyra D, Guglielmini AC & Satorre EH (2010). Weed communities of transgenic glyphosate‐tolerant soyabean crops in ex‐pasture land in the southern Mesopotamic Pampas of Argentina. Weed Research50, 320–330.SummaryWeed surveys were performed in commercial no‐till glyphosate‐tolerant soyabean crops in southern Entre Ríos province (Mesopotamic Pampas of Argentina) in 2005 and 2007, during the soyabean grain filling to maturity growth stages. The objectives were to describe the weed communities in fields recently introduced to crop production and to analyse the effect of the new cropping patterns on assemblages. The fields surveyed varied in the length of the no‐till period (1–11 years), the previous crop and the soil productivity rating. Weed communities were described in terms of composition, constancy, life forms, morphotypes and (only during 2007) frequency. Tragia geraniifolia, Bidens subalternans, Sida spinosa, and Eryngium horridum were species associated with fields with more than 5 years of no‐till glyphosate‐tolerant crops. These fields had a significantly higher relative abundance of perennials (52% versus 32%) and of dicotyledons (66% versus 39%) than fields with less than 5 years of no‐till. Previous crop and soil productivity affected weed community structure. Six species, five of them annuals, were associated with fields that had high yields and maize as the previous crop. In contrast, perennials and dicotyledons had the highest relative abundance when wheat–soyabean double cropping was the previous crop. The results show that changes in cropping systems acted as filters on functional traits, modifying the previous weed community assemblage. The information may be used to develop integrated crop–weed management strategies, leading to a reduction in the assemblage of highly competitive weed communities.

Effects of genetically modified herbicide-tolerant (GMHT) rice on biodiversity of weed in paddy fields

To detect potential changes in properties of weed communities in fields of GMHT rice Bar68-1, trials were carried out from 2007-2008 at Changsha, China with conventional indica rice D68 served as control. The average richness of weed community measured by species accumulation curve tended to be identical in the fields of Bar68-1 and D68 as the number of sampling points increased. There were no significant differences (p > 0.05) in diversity indices which included numbers of species(S), Shannon- Wiener (H’), Pielou evenness (J’), Simpson diversity (D) and evenness (E) indices. Species composition for these two weed communities was roughly comparable. The top four weed species, sorted by individual abundance, were Monochoria vaginalis (Burm. f.) Presl ex Kunth, Lindernia procumbens (Krock.) Philcox, Cyperus diformis L. and Juncellus serotinus (Rottb.) .B. Clarke in the fields of Bar68-1 and D68. ABC curves showed that the weed communities were “unpolluted”. The data above confirm the hypothesis that the difference between the effect of GMHT rice Bar68-1 on biodiversity of weed in paddy fields and that of non-GM rice D68 was not significant.

Differentiation of arable field weed communities in the northern part of the Silesian Upland (S Poland)

Differentiation of arable field weed communities in the northern part of the Silesian Upland (S Poland)The purpose of this paper is to present the role of the selected species (i.e. associations character species, endangered as well as the most expansive weeds) in arable field communities in the area of the Tarnowskie Góry Ridge and the Chełm, two mesoregions of the Silesian Upland (southern Poland). On the basis of 750 phytosociological relevés taken using the method of Braun-Blanquet (Braun-Blanquet 1964) between 1995 and 2009, eight weed associations as well as numerous rump communities were distinguished. Phytocoenoses without a significant contribution of the association character species comprised about 68% of the patches analysed in the cereal crop and about 12% of the communities established in the root plant crop. Very often the character species of cereal weed associations occurred sporadically or in small numbers. Some expansive weeds (e.g.Apera spica-venti(L.) P. Beauv.,Avena fatuaL.,A. xvilisWallr.,Chenopodium albumL.,Echinochloa crus-galli(L.) P. Beauv.,Elymus repensL.,Galinsoga ciliata(Raf.) S. F. Blake,G. parvifloraCav.) played an important role in the communities analysed. The vanishing of some weed species and the spread of others has resulted in the transformation of the composition and structure of the segetal communities, a vast majority of rare and endangered weed species in the studied area are considered to be very sensitive to modern agriculture methods, e.g. chemicalization, introduction of new crop cultivars, effective cleaning of seed materials, drainage etc. (Siciński 1998; Warcholińska 1998).

Weed communities and eco-niches in wheat fields of the Yellow River irrigation zone of Lanzhou

The composition and eco-niches of weeds in wheat fields of the Yellow River irrigation zone of Lanzhou were field investigated based on eco-niche theory and method.The results show that Calystegia hederacea,Chenopodium album,Cephalanoplos segetum,Portulaca oleracea,Amaranthus retroflexus,Setaria viridis,Sonchus brachyotus and Polygonum aviculare form the main eco-damage population.Based on calculations of time,horizontal and vertical stretches of weed eco-niches,C.album is the dominant species and C.hederacea is the main weed.C.album and C.hederacea niches extensively overlap.The result illustrates that potential factors of wheat field weeds will induce field weed communities change as field environment varying.

Mapping the potential annual total nitrogen load in the river basins of Japan with remotely sensed imagery

The increase of nutrient loads such as nitrogen and phosphorus to a river due to land cover changes in surrounding areas has been one of the major sources of water pollution or eutrophication. Monitoring the influent nutrient load from river basins to rivers is now crucial in the management of river basin environments. The monitoring is not easy, however, because it requires spatial and temporal measurement tools for land cover changes in the river basin and water qualities, and also it requires models relating them. In this study, we first analyzed the relation between the land cover types estimated from monthly maximum Normalized Difference Vegetation Index (NDVI) imagery calculated from NOAA Advanced Very High Resolution Radiometer (AVHRR) imagery and the annual total nitrogen load discharged from river basins. We found that the runoff load factor from urban areas is higher than those of forested areas. We also found that the impacts of land cover such as plantation and field weed communities on the total nitrogen load of each river are higher than the impacts of other land cover types such as Beech and Camellia japonica community type. Finally, we produced two advanced maps of the potential annual total nitrogen load (PTNL) index and the potential annual total nitrogen load for each river basin area (PTNL/area) index by considering the relationship between the land cover types and the annual total nitrogen load discharged from river basins in Japan. The PTNL map will be useful for the risk assessment of total nitrogen load impact on lakes and the sea through rivers from each basin. The PTNL/area index, which considers the effects of river basin areas, will allow evaluation of the state of river basins.

Variation in metabolism of BOA among species in various field communities – biochemical evidence for co-evolutionary processes in plant communities?

The capacity of benzoxazolinone metabolization of dicotyledonous species characteristic for the former vegetation classes Secalietea (grain field weed communities) and Chenopodietea (hoed vegetable communities) was estimated by the production of BOA-6-OH, BOA-6-β-O-glucoside, and BOA-N-glucoside. Except for Urtica urens, Galinsoga ciliata, and Polygonum aviculare (Chenopodietea), all species tested were able to synthesize BOA-6-OH, its glucoside, and BOA-N-glucoside, but effectiveness of BOA metabolism differed highly depending on species and plant organ. There was no correlation between bacterial phenoxazinone production and appearance of metabolites in the plants. Bioassays demonstrated that N-glucosylation is more efficient in BOA detoxification than O-glucosylation. The intermediate BOA-6-OH, however, is more harmful than BOA itself. It is therefore assumed that the ability to synthesize BOA-N-glucoside reduces the sensitivity to BOA strikingly. Since the detoxification capacity did not correlate with the taxonomic position, the affiliation of the species tested with the corresponding plant communities was taken into consideration. Evidently, the ecobiochemical potential of species to detoxify benzoxazolinone, regarded as an essential secondary compound in rye and wheat fields, reflects their occurrence in those plant associations. The ability to cope with the compound could be the result of co-evolutionary processes and presents a hidden aspect of allelopathic interaction.

Native maize field weed communities in south‐central Mexico

Maize (Zea mays L.) field weeds of an important agricultural region of south‐central Mexico were analysed for their phytogeographical composition, using data from a floristic list (317 species) and the cover values of 378 Braun–Blanquet relevés. Exotic species played a small role (16% of species, 13% of weed vegetation cover). The fields were dominated by species distributed between Mexico and Central America (14/47%) and those New World species with a wide distribution on the American continent, including temperate areas (10/20%). Other area types (Mexican endemics, species of warmer America, species with northern affiliations and species of Old World origin) may contribute numerous species, but these are not as competitive. The data show that native anthropogenic weed communities have evolved in Mesoamerica.