The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Jonathan Storkey - One of the best experts on this subject based on the ideXlab platform.
-
modelling seedling growth rates of 18 temperate arable weed species as a function of the environment and plant traits
Annals of Botany, 2004Co-Authors: Jonathan StorkeyAbstract:d Background and Aims The early growth rate of seedlings in the exponential phase is an important ecophysiological trait in crop/weed Competition models based on assessments of relative weed green area. An understanding of the role of various plant traits in determining early growth rate may also be useful for identifying contrasting weed strategies for establishment before canopy closure. d Methods The response of seedling relative growth rate (RGR) to the environment was measured in outdoor sand beds in the autumn and the spring for 18 temperate annual weed species and two crops. Seedling growth was modelled using thermal time and effective day-degrees (combining the effect of temperature and radiation). The contribution of various plant traits in determining variability in RGR was investigated using regression analysis. d Key Results The effective day-degree model was more effective for describing early weed growth than thermal time. Variability in RGR measured in the autumn was largely determined by differences between the species in net assimilation rate (NAR), whereas in the spring leaf area ratio (LAR) played a larger part. There were differences between the broadleaf and grass species in the relative contribution of NAR and LAR to RGR in both seasons. RGR in the spring was negatively correlated with initial seedling size. d Conclusions The parameters derived in this study can be used to calibrate empirical models of crop yield loss based on relative weed green area to different growing seasons and assessment dates. The grass weeds, which tended to have large seeds, had a higher investment in roots in the seedling stage, potentially making them more competitive later in the season when resources become limiting. a 2004 Annals of Botany Company
-
the combination of a simulation and an empirical model of crop weed Competition to estimate yield loss from alopecurus myosuroides in winter wheat
Field Crops Research, 2003Co-Authors: Jonathan Storkey, J Cussans, P J W Lutman, A M BlairAbstract:Abstract An empirical model of yield loss from assessments of relative weed green area (weed green area/weed+crop green area) was fitted to data from a series of Competition trials of winter wheat and black-grass ( Alopecurus myosuroides Huds.). Because of the different growth rates of the crop and the weed, relative weed green area increased with time. Consequently, the parameter that describes the competitiveness of the weed (the relative damage coefficient) was highly dependent on the time the weed population was assessed. The ability of two simulation models of crop and weed growth to predict the change in this parameter was investigated. The first was a simple thermal time model, which took no account of Competition for resources. This model always underestimated the relative damage coefficient at later assessment dates. Its potential for incorporation into a weed management system was, therefore, limited. The second model included a more comprehensive description of Competition for light in the period when shading limits plant growth. This model was more successful at predicting the change in the relative damage coefficient. It could potentially be used in future weed management systems to calibrate a generic value of the relative damage coefficient for a specific weed species to a range of assessment dates.
Clarence J Swanton - One of the best experts on this subject based on the ideXlab platform.
-
timing effect and recovery from intraspecific Competition in maize
Agronomy Journal, 2010Co-Authors: Eric R Page, M Tollenaar, Lewis Lukens, Clarence J SwantonAbstract:In production agriculture, it is not uncommon for a crop to experience both intra- and interspecific Competition during the normal course of development. Although the Competition between crop plants (i.e., intraspecifc) is often considered independently of Crop-Weed Competition (i.e., interspecific), the mechanisms through which yields are reduced may be common to both. The objective of this study was to use the experimental structure of a critical time for weed removal study to examine the timing and effect of intraspecific Competition on maize (Zea mays L.) biomass accumulation and phenological development. A field trial was conducted in which maize stands were thinned from a higher to a lower density at six stages of development. Results indicated that intraspecific Competition at densities of 8 and 16 plants m -2 did not affect maize biomass accumulation until the 14th and 12th leaf tip stages, respectively. Before these stages, maize seedling growth at 8 or 16 plants m -2 was not resource limited. Increases in leaf area index and specific leaf area at the onset of intraspecific Competition, and the recovery of plants following the removal of competitors, suggest that reductions in the rate of crop growth and development may have been linked to Competition for light quantity.
-
the importance of light quality in crop weed Competition
Weed Research, 2009Co-Authors: J G Liu, Kris J Mahoney, Peter H Sikkema, Clarence J SwantonAbstract:Plant Competition is thought to be driven by limiting resources. We propose that plant Competition is triggered initially by the red to far-red light ratio (R:FR) originating from neighbouring plants, followed by a series of complex physiological processes, which exclude direct resource Competition. Field experiments were conducted in 2005 and 2006 in which maize (Zea mays) was grown hydroponically. The effect of R:FR signal being reflected from the leaf surface of Amaranthus retroflexus was isolated by avoiding direct Competition for light, water and nutrients. Results showed that the low R:FR reflected from the leaf surface of A. retroflexus did alter the carbon allocation pattern of maize when compared with maize growing free of weeds. Prior to silking, maize grown under low R:FR experienced temporal changes in plant height, persistent changes throughout the sampling period in root and shoot dry weights and rate of leaf appearance, but no changes in leaf area. At silking, low R:FR reduced ear and total plant dry weight. These results support the hypothesis that changes in R:FR acts as an early signal of pending Competition by initiating a shade avoidance response. Data from this experiment suggest that once a plant is physiologically triggered into a shade avoidance response, these plants do so at a physiological cost, which may constrain plant development and possibly reduce reproductive fitness.
-
comparison of empirical models depicting density of amaranthus retroflexus l and relative leaf area as predictors of yield loss in maize zea mays l
Weed Research, 2006Co-Authors: Stevan Z Knezevic, Stephan F Weise, Clarence J SwantonAbstract:Summary The outcome of Crop-Weed Competition should be predicted as early as possible in order to allow time for weed control measures. Maize grain yield losses caused by interference from Amaranthus retroflexus L. (redroot pigweed) were determined in 1991 and 1992. The performance of three empirical models of Crop-Weed Competition were evaluated. Damage functions were calculated based on the weed density or relative leaf area of the weed. In the yield loss-weed density model, values of I (percentage yield loss at low weed density) were relatively stable for similar emergence dates of A. retroflexus across years and locations. Estimated maximum yield loss (A) was more variable between locations and may reflect environmental variation and its effect on Crop-Weed Competition, at least in 1991. The two-parameter yield loss-relative leaf area model, based on m (maximum yield loss caused by weeds) and q (the relative damage coefficient) gave a better fit than the single-parameter version of the model (which includes only q). In both relative leaf area models, the values of q varied between years and locations. Attempts to stabilize the value of q by using the relative growth rate of the leaves of the crop and weed were successful; however, the practical application of such relative leaf area models may still be limited owing to the lack of a method to estimate leaf area index quickly and accurately.
-
The Critical Period of Weed Control in Grain Corn (Zea mays)
Weed Science, 1992Co-Authors: Michael R. Hall, Clarence J Swanton, Glenn W. AndersonAbstract:Field studies were conducted in southern On- tario to determine the critical period of weed control in grain corn and the influence of weed interference on corn leaf area. The Gompertz and logistic equations were fitted to data representing increasing durations of weed control and weed interference, respectively. The beginning of the critical period varied from the 3- to 14-leaf stages of corn development. However, the end of the critical period was less variable and ended on average at the 14-leaf stage. Weed interference reduced corn leaf area by reducing the expanded leaf area of each individual leaf and accelerat- ing senescence of lower leaves. In addition, weed interference up to the 14-leaf stage of corn development impeded leaf expansion and emergence in 1989. Nomen- clature: Corn, Zea mays (L.). Additional index words. Weed interference, density, bi- omass, crop yield loss, corn leaf area, Gompertz, logistic. Information regarding the critical period of weed control in corn may lead to less reliance on the use of residual herbicides and to more reliance on well-timed postemergence herbicides (23). Reductions in quantities of herbicide applied will reduce potential environmental contamination and will reduce selection pressure for herbicide-resistant weeds. In addition, timing of cover crop seeding and cultivations could be improved based upon critical period information. Finally, it has been suggested that the value of critical period studies rests with the eventual uncovering of the physiological basis for Crop-Weed Competition and its eventual use for weed control (22). Limited research has been reported on the critical period of weed control in grain corn. In Mexico a weed-free penod of 50 d from seeding was required to prevent corn grain yield loss (10). In the United States a weed-free requirement of 4 wk was required to prevent corn yield losses resulting from johnsongrass (Sorghum halepense (L.) Pers.) interference (15). In Canada, preliminary studies determined weed-free requirements that varied from 28 to 56 d after planting3. Weed interference can adversely affect corn leaf area (4, 26). Zanin et al. (26) determined that leaf area index and leaf area duration were correlated with yield loss and accurately indicated the onset of weed interference. However, more information on the influence of weed interference upon corn leaf area development is needed. This information could be used in the development of a crop monitoring system which could accurately detect the beginning of the critical period for corn yield loss resulting from weed interference. Such a monitoring system would improve timing of weed control measures. Therefore, the objectives of this study were to determine the critical period of weed control in grain corn at selected locations in Ontario and the influence of weed interference on corn leaf area.
Nicolas Munierjolain - One of the best experts on this subject based on the ideXlab platform.
-
assessing innovative sowing patterns for integrated weed management with a 3d crop weed Competition model
European Journal of Agronomy, 2014Co-Authors: Nathalie Colbach, Alban Collard, Sebastien H M Guyot, Delphine Meziere, Nicolas MunierjolainAbstract:Weed dynamics models are needed to design innovative weed management strategies. Here, we developed a 3D individual-based model called FlorSys predicting growth and development of annual weeds and crops as a function of daily weather and cropping practices: (1) crop emergence is driven by temperature, and emerged plants are placed onto the 3D field map, depending on sowing pattern, density, and emergence rate; plants are described as cylinders with their leaf area distributed according to height; (2) weed emergence is predicted by an existing submodel, emerged weed seedlings are placed randomly; (3) plant phenology depends on temperature; (4) a previously developed submodel predicts available light in each voxel of the canopy; after emergence, plant growth is driven by temperature; when shaded, biomass accumulation results from the difference between photosynthesis and respiration; shading causes etiolation; (5) frost reduces biomass and destroys plants, (6) at plant maturity, the newly produced seeds are added to the soil seed bank. The model was used to test different sowing scenarios in an oilseed rape/winter wheat/winter barley rotation with sixteen weed annuals, showing that (1) crop yield loss was negatively correlated to weed biomass averaged over the cropping season; (2) weed biomass was decreased by scenarios allowing early and homogenous crop canopy closure (e.g. reduced interrows, increased sowing density, associated or undersown crops), increased summer fatal weed seed germination (e.g. delayed sowing) or, to a lesser degree, cleaner fields at cash crop sowing (e.g. sowing a temporary cover crop for “catching” nitrogen); (3) the scenario effect depended on weed species (e.g. climbing species were little affected by increased crop Competition), and the result thus varied with the initial weed community (e.g. communities dominated by small weed species were hindered by the faster emergence of broadcast-sown crops whereas taller species profited by the more frequent gap canopies); (4) the effect on weed biomass of sowing scenarios applied to one year was still visible up to ten years later, and the beneficial effect during the test year could be followed by detrimental effects later (e.g. the changed tillage dates accompanying catch crops reduced weed emergence in the immediately following cash crop but increased seed survival and thus infestation of the subsequent crops). This simulation showed FlorSys to predict realistic potential crop yields, and the simulated impact of crop scenarios was consistent with literature reports.
A M Blair - One of the best experts on this subject based on the ideXlab platform.
-
the combination of a simulation and an empirical model of crop weed Competition to estimate yield loss from alopecurus myosuroides in winter wheat
Field Crops Research, 2003Co-Authors: Jonathan Storkey, J Cussans, P J W Lutman, A M BlairAbstract:Abstract An empirical model of yield loss from assessments of relative weed green area (weed green area/weed+crop green area) was fitted to data from a series of Competition trials of winter wheat and black-grass ( Alopecurus myosuroides Huds.). Because of the different growth rates of the crop and the weed, relative weed green area increased with time. Consequently, the parameter that describes the competitiveness of the weed (the relative damage coefficient) was highly dependent on the time the weed population was assessed. The ability of two simulation models of crop and weed growth to predict the change in this parameter was investigated. The first was a simple thermal time model, which took no account of Competition for resources. This model always underestimated the relative damage coefficient at later assessment dates. Its potential for incorporation into a weed management system was, therefore, limited. The second model included a more comprehensive description of Competition for light in the period when shading limits plant growth. This model was more successful at predicting the change in the relative damage coefficient. It could potentially be used in future weed management systems to calibrate a generic value of the relative damage coefficient for a specific weed species to a range of assessment dates.
Jannie Olsen - One of the best experts on this subject based on the ideXlab platform.
-
evolutionary agroecology the potential for cooperative high density weed suppressing cereals
Evolutionary Applications, 2010Co-Authors: Jacob Weiner, Hans W Griepentrog, Sven Bode Andersen, Wibke Wille, Jannie OlsenAbstract:Evolutionary theory can be applied to improve agricultural yields and/or sustainability, an approach we call Evolutionary Agroecology. The basic idea is that plant breeding is unlikely to improve attributes already favored by millions of years of natural selection, whereas there may be unutilized potential in selecting for attributes that increase total crop yield but reduce plants’ individual fitness. In other words, plant breeding should be based on group selection. We explore this approach in relation to Crop-Weed Competition, and argue that it should be possible to develop high density cereals that can utilize their initial size advantage over weeds to suppress them much better than under current practices, thus reducing or eliminating the need for chemical or mechanical weed control. We emphasize the role of density in applying group selection to crops: it is Competition among individuals that generates the ‘Tragedy of the Commons’, providing opportunities to improve plant production by selecting for attributes that natural selection would not favor. When there is Competition for light, natural selection of individuals favors a defensive strategy of ‘shade avoidance’, but a collective, offensive ‘shading’ strategy could increase weed suppression and yield in the high density, high uniformity cropping systems we envision.