共查询到20条相似文献，搜索用时 62 毫秒
1.
2.
3.
The objective of this study is to offer a new framework for exploring and modelling the spatial variation in crop biomass – weed density relationships, adapting geographically weighted regression (GWR) to include a non‐linear regression model. The relationship between crop biomass and weed density is usually modelled by non‐linear regression models, in which the spatial heterogeneity of the relationship is ignored, although the effect of weeds on crop can differ in relation to topographic and edaphic variability. GWR attempts to capture spatial variability by calibrating a regression model to each location in space. We show the application of the method in different cereal cropping systems, with one or two weed species. The results indicate that GWR can significantly improve model fitting over non‐linear least squares (NLS) in some situations. Furthermore, the parameter estimates can be mapped to illustrate local spatial variations in the regression relationship under study and eventually to relate the spatial variability of the model to the environmental heterogeneity. We discuss the value of the GWR for analysing the observed spatial variability and for improving model development and our understanding of spatial processes. 相似文献
4.
A range of 111 rice cultivars was studied for weed-suppressing ability in field experiments with a sown infestation of Echinochloa crus-galli. Cultivars differed significantly in their ability to suppress the growth of E. crus-galli , and the differences were reasonably reproducible over three seasons. The same rice cultivars were tested in a laboratory screening for allelopathic potential, which showed significant differences in the ability to reduce root growth of E. crus-galli . Correlation between the laboratory screening and the field experiments showed that field performance could be described to some extent by E. crus-galli root length reduction in the laboratory. Plant height in the field experiment was correlated with weed biomass 8 weeks after seeding. Even among the most weed-suppressing rice cultivars, however, all heights were represented. None of the measured growth parameters from greenhouse studies could explain the distribution of weed-suppressing rice cultivars. This indicates that allelopathy in combination with competitive ability determines the weed interference outcome of a given rice cultivar. 相似文献
5.
6.
Assessment of the compensation point of Cirsium arvense and effects of competition,root weight and burial depth on below‐ground dry weight – leaf stage trajectories 
下载免费PDF全文
下载免费PDF全文 Farmers are recommended to employ mechanical control when Cirsium arvense is most sensitive to disturbance. Earlier studies suggest that this occurs at a stage of minimum below‐ground dry weight, coinciding with three to seven or seven to ten leaves per shoot, depending on the definition of below‐ground dry weight. However, some farmers notice better effects when mechanical control is performed at earlier leaf stages. To estimate the compensation point (CP), defined as the minimum weight of the entire below‐ground structure of C. arvense and to further understand links between initial root weight, planting depth and crop competition, three outdoor pot experiments were performed in Sweden in 2013‐2014. We hypothesised that (i) CP likely occurs before C. arvense has developed three leaves, (ii) relative depletion of the below‐ground system at CP is less at lower initial root weight compared with higher weight, and (iii) methodological variations in CP estimations have minor impact on the results. We found that the CP for C. arvense in all treatments occurred before shoots had developed three leaves and that treatment effects were minor (<0.5 leaf stages). Leaf and leaf stage definitions, choice of leaf range and model also had minor effects on CP estimates. Depletion of planted root fragments ceased around leaf stages 3‐4, and their partial replenishment also constitutes evidence for a CP at early leaf stages. For agronomy, our results imply that mechanical control of C. arvense should be performed earlier than previously recommended, probably before reaching an average of three to four leaves per shoot. 相似文献
7.
Distribution patterns and traits of weed communities along an urban–rural gradient under rapid urbanization in Shanghai,China 下载免费PDF全文
下载免费PDF全文 In order to better understand the effects of urbanization on weed communities, the distribution of weed communities in Shanghai, China, was systematically investigated. The diversity of weed communities and four environmental factors, including the relative light intensity, soil moisture, soil compaction and soil pH, were measured in 1375 plots along an urban–rural gradient. The species diversity indices in each area along the urban–rural gradient were compared by using a one‐way ANOVA. The weed communities were identified by using clustering methods that were based on relative dominance information. A canonical correspondence analysis was used to reveal the relationships between the species composition and the environmental factors at the community level and the Spearman's rank correlation test was used to test the relationship between the number of weed communities and each environmental factor. A total of 183 species, belonging to 41 families and 123 genera, was recorded. It was found that the species richness, Shannon–Wiener diversity index and Pielou evenness index followed a unimodal curve along the urban–rural gradient. The 1375 plots were divided into 133 weed community types. All four environmental factors significantly affected the species composition of the weed communities, but only soil compaction had significant effects on the number of weed communities. It was concluded that the diversification of habitat type and environmental change along the urban–rural gradient led to more weed communities in rural areas and fewer weed communities in urban areas. Based on the species' habitats and distribution patterns, the weeds were divided into “widespread”, “urban” and “rural”. 相似文献
8.
9.
10.
The parasitic weed Striga hermonthica poses a serious threat to cereal production in sub-Saharan Africa. Striga hermonthica seedbanks are long-lived; therefore, long-term effects of control strategies on the seedbank only emerge after several years. We developed a spatially explicit, stochastic model to study the effectiveness of control strategies in preventing invasion of S. hermonthica into previously uninfested fields and in reducing established infestations. Spatial expansion of S. hermonthica and decrease in millet yield in a field was slower, on average, when stochasticity of attachment of seedlings to the host was included and compared to the deterministic model. The spatial patterns of emerged S. hermonthica plants 4–7 years after point inoculation (e.g. seeds in a dung patch) in the spatial-stochastic model resembled the distribution typically observed in farmers' fields. Sensitivity analysis showed that only three out of eight life cycle parameters were of minor importance for seedbank dynamics and millet yield. Weeding and intercropping millet with sesame or cowpea reduced the seedbank in the long term, but rotations of millet with trap crops did not. High seedbank replenishment during years of millet monoculture was not sufficiently offset by seedbank depletion in years of trap crop cultivation. Insight from simulations can be employed in a participatory learning context with farmers to have an impact on S. hermonthica control in practice. 相似文献
11.
12.
13.
Co‐operative versus non‐co‐operative farmers' weed control decisions in an agricultural landscape 下载免费PDF全文
下载免费PDF全文 J L Gonzalez‐Andujar 《Weed Research》2018,58(5):327-330
This study presents a simple landscape model of the influence of seed dispersal on weed population dynamics between fields. In the model, three fields are interconnected through weed seed dispersal, where seed might move with field equipment, in irrigation water or may be wind‐dispersed. The model is intended to characterise the impact of field‐level weed management decisions on landscape‐level weed population dynamics. Two simple scenarios were studied. The first simulates farmers adopting common effective methods of control on each of the three fields. In the second scenario, farmers manage the weed population independently on each of the three fields. In the first scenario, weed populations were driven to extinction as might be expected with uniformly high levels of weed suppression in each of the three fields. In the second scenario, when the two nearest fields in the sequence experienced control, the weed population was driven to extinction in the second field but not in the first where weed populations were able to survive in spite of high levels of suppression. The results suggest that control measures within a field may not adequately reflect their impact on weed population dynamics when between field seed movement occurs. Another important result is the importance of proximity and spatial arrangement of fields and the resulting influence on weed population dynamics within a field. 相似文献
14.
15.
Field evaluation of allelopathic plant extracts alongside herbicides on weed management indices and weed–crop regression analysis in maize 下载免费PDF全文
下载免费PDF全文 Muhammad Zahid Ihsan Abdul Khaliq Azhar Mahmood Muhammad Naeem Fathy El‐Nakhlawy Fahad Alghabari 《Weed Biology and Management》2015,15(2):78-86
Synthetic herbicides are posing problems owing to the development of weed resistance and emerging debate on their associated health hazards and ecological threats. Allelopathic manipulations are evolving as applicable substitutes for weed management in agroecosystems. In order to assess the efficacy of potential allelopathic water extracts from different plant species, field experiments were conducted during 2010 and 2011. Sorghum bicolor L., Helianthus annuus L., Brassica napus L., Oryza sativa L., Zea mays L. and Morus alba L. aqueous extracts in different combinations alone or along with a reduced dose of herbicide were evaluated for weed suppression in a maize crop. A weedy check and two herbicidal treatments, S‐metolachlor + atrazine (pre‐emergence) and atrazine alone (early postemergence), were included for comparison. Sorghum, brassica or sunflower tank‐mixed with 25% of the recommended dose of atrazine significantly suppressed the total weed density and dry biomass, along with a concomitant decrease in the crop resistance indices and treatment efficacy indices over the control. The weed density and dry biomass that were recorded at 60 days after sowing showed a strong negative correlation, while the leaf area index, crop growth rate, dry matter accumulation and net assimilation rate predicted a strong positive correlation, with the stover and grain yield of maize. 相似文献
16.
Tomato leafminer Tuta absoluta was detected for the first time in Montenegro using pheromone traps in the middle of July 2010, in greenhouses in one location at the Montenegrin sea coast. In the period from the end of July to the first week of August, moths were captured in pheromone traps from other locations along the sea coast and surroundings of the city of Podgorica. According to the survey carried out by the authors from July to September 2010, T. absoluta was present in greenhouses in all tomato‐producing areas, while outdoors it was found only in the coastal area. Monitoring of T. absoluta continued in 2011. Pheromone traps were set up in five locations in the main tomato‐producing areas, both in greenhouses and outdoors, between 4 and 15 May. The first captured moths were detected after 7–15 days in all inspected locations, and captures continued until the end of September. According to the number of captured moths and the damage observed, it can be concluded that the population level in 2011 was lower in comparison with 2010, when up to 100% losses were detected in tomato crops in several locations. In 2011, tomato producers were already being informed about the pest and means of control, so most of them applied cultural and chemical control measures. 相似文献
17.
Relationships between soil properties and the occurrence of the most agronomically important weed species in the field margins of eastern Arkansas – implications for weed management in field margins 下载免费PDF全文
下载免费PDF全文 The work presented in this study adds to previous research on the occurrence, distribution and growth habitat of common weeds along roadsides in the Mississippi River Delta region of eastern Arkansas, USA. It addresses the relationships between soil properties (i.e. defined as a group of individual soil characteristics or attributes such as P, K, Ca, Mn and other nutrients) and the most agronomically important weeds of which the occurrence at field margins accounted for ≥ 10% of the total sampling sites. These were three broad‐leaved weeds (Amaranthus palmeri, Ipomoea spp. and Sida spinosa) and four grass weeds (Echinochloa crus‐galli, Urochloa platyphylla, Sorghum halepense and Digitaria sanguinalis). Soil properties were used as explanatory variables for weed occurrence (presence–absence) using partition analysis; the occurrences of the weeds under examination were partitioned by the application of a decision‐tree method. The most important soil properties explaining the occurrence of these weeds in field margins were extractable soil nutrients, specifically sodium, boron and copper content, as well as soil physical attributes, in order of importance, bulk density, silt content, field moisture capacity, hydraulic conductivity, wilting point, available water and clay content. Soil chemical properties proved least reliable in explaining weed occurrence at roadside field margins. Knowledge of the relationships between soil properties and weed occurrence can add to our understanding of weed biology and hence enhance the efficiency of weed management strategies. For example, the occurrence of A. palmeri, in soils with high bulk density (>1.4 g cm?3) and low organic matter content (<2.7%) and thus lower residual herbicide activity, will require integrated weed management of this species in field margins. This is of interest given the occurrence of herbicide resistance in roadside arable weeds, mainly A. palmeri, E. crus‐galli and S. halepense, in the Mississippi River Delta region of eastern Arkansas and other parts of the world. 相似文献
18.
19.
20.
Albert Berdjour Ibrahim Yakamba Dugje Israel Kwame Dzomeku Nurudeen Abdul Rahman 《Weed Biology and Management》2020,20(2):69-81
The cereal–legume cropping system is a common practice across the tropical world. However, there are limited quantitative data on the effect of cereal–legume intercropping on weed species diversity. A study was conducted in the Guinea savanna zone of Ghana to evaluate the effect of maize–soybean intercropping on yield productivity and weed species control. The treatments used include three maize maturity types (extra‐early: Abontem, early: Sammaz 27 and medium: Obatanpa) intercropped with soybean at three intraspacing (10, 20 and 30 cm), and their sole crop treatments were laid in a randomized complete block design with three replications. Results showed that the land equivalent ratio (LER) for the intercrops was above 1, indicating better intercrop productivity than the sole crops. An average of 40% land was saved for the intercrops compared with the sole crops. Intercropping Sammaz 27 maize with soybean significantly increased LER by 9% compared to the other types. Intercropping maize with soybean significantly reduced weed biomass at 6 and 9 weeks after planting (WAP) and at harvest relative to the sole maize. The weed biomass at 6 and 9 WAP and harvest increased (p < .05) with increasing soybean intraspacing. The grass and broadleaf weed species count at 6 WAP and harvest from the sole crops were significantly higher than that of the intercrops. The results suggest that intercropping early maize maturity type with soybean at 10 cm intraspacing could be used to increase grain yield, LER and control of grass and broadleaf weeds in a maize‐based cropping system in the Guinea savanna zones of West Africa. 相似文献