摘要:

SummaryLa connaissance de la longévité des semences enfouies dans les sols cultivés est un élément indispensable à l'estimation des risques d'infestation des parcelles agricoles. Le dispositif expérimental est constitué de parcelles artificiellement infestées par semis de 17 mauvaises herbes annuelles, et cultivées en monoculture de blé d'hiver ou d'orge de printemps. L'évolution annuelle du stock semencier est étudiée sur une période de 5 ans, en l'absence de toute réinfestation par de nouvelles semences. La viabilité des semences est aussi estimée et des analyses de flore permettent d'observer les pertes dues aux levées de plantules. Les résultats montrent que l'evolution du potentiel semencier est plus ou moins rapide selon les espèces; deux groupes ont été constitués: (i) espèces àévolution rapide, à taux annuel de deéroissance voisin de 80%, pour l'ensemble desquelles les levées au champ représentent en moyenne 15% du stock annuel (Alopecurus myosuroides, Avena fatua, Centaurea cyanus, Galium aparine, Lapsana communisetMatricaria perforata); (ii) espèces àévolution lente, à taux annuel de décroissance voisin de 40%; la viabilité des semences de certaines espèces augmente au cours de la conservation; les levées ne représentent en moyenne que 8% du potentiel semencier (Aethusa cynupium, Amaranthus ratro‐flexus, Capsella bursa pastoris, Chenopodium album, Euphorbia exigua, Fallopia convolvulus, Kickxia spuria, Papaver rhoeas, Polygonum persicaria, Sinapis arvensisetViola arversis). Ces résutats montrent la relativement faible persistance des semences dans les sols cultives; ils sont discutés par rapport à d'autres méthodologies dont les plus criticables au plan agronomique concernent les ex

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00821.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryA simple initial classification of types of models is given and the essential role of models in science, especially in agricultural science, is reviewed. Empirical models are contrasted with mechanistic models, and these are related to the levels of aggregation considered, and crucially, to the difference between description and understanding. Examples of mechanistic models to simulate aggregated biochemical systems and to interpret experimental data, with reference to nutrition and metabolism in animals, are presented. Requirements for successful modelling in an agricultural context are discussed, followed by consideration of the problems and promise of linking the modelling viewpoint into a biological research programme. Finally, the ranges of possible objectives and potential contributions of mathematical modelling in agricultural science are explored.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00822.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryWeed species in arable ecosystems are adapted to the conditions produced by agricultural management. In order to give preventive and curative guidelines to weed management one needs to predict the composition of the weed vegetation after certain (soil) cultivation measures. Dormancy mechanisms of seeds in the seedbank and the environmental conditions in the furrow before and after cultivation are usually such that the vegetation composition is heterogeneous. Multivariate analyses enable us to describe and classify weed vegetation and to analyse its relationship to environmental factors.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00823.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryThe implications of recent studies on the inappropriatness of replacement series and additive methods in competition studies, and some possible alternatives, are discussed in the context of weed research, Replacement series are usually inadequate to assess competitive interactions and can be misleading. In particular they may be biased in favour of the larger species. Many of the criticisms of replacement series also apply to additive experiments. Response models relating yield per individual to the densities of the species in the mixture provide methodology for answering many questions about mixtures. This paper proposes a framework for using these models to: (i) measure the effect of weed species on yield per individual and yield per unit area for the crop and weed species; (ii) develop methods of biological control of weeds both within a seaons and over seasons, based on the interference between crop and weed species and the population biology of the weed species; (iii) establish a cost‐benefit analysis of certain of the biological weed‐control programmes. The inclusion of the effect of relative emergence time and management practices in response models is considered as well as experimental design for crop‐weed experi

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00824.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryUntil recently the modelling of crop‐weed interactions has largely ignored the complexities resulting from the patchy distribution of weeds and the multi‐species nature of weed communities. Some progress has now been made in dealing with these two sources of variation. A population dynamical approach has proven to be quite helpful in this respect. In this approach the whole life‐cycle of the species is considered, divided in a step by step fashion into separate stages, thereby offering a top‐down modelling approach. Such models can easily be extended over a period of years, helping in developing long‐term control strategies: complexity can be added as the need arises. Spatial heterogeneity can be taken into account by explicitly defining a spatial scale and the dispersal process. The multi‐species nature of competition can be dealt with by using neighbourhood models of plant interference. A few recent contributions from the literature, using weeds as an example, are reviewed here against a more general background of weed

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00825.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryStudies of weed population dynamics may be conducted at various levels of complexity. The simplest level involves monitoring a single component of the population throughout several seasons, determining population trends and rates of change. This approach is highly descriptive and, therefore, has a low predictive value. However, it may be useful to evaluate the long‐term effects of various control techniques. In demographic studies, the life‐cycle of the species is divided into various functional stages and the number of individuals present in each stage is monitored throughout the season. From these data, various demographic parameters can be calculated. Population changes through time can be predicted by simulation techniques. This approach offers a practical compromise between the simplicity of long‐term studies and the high analytical and predictive power of more complex analyses. In mechanistic analysis, the population is broken down into a large number of components connected by various physiological und ecological processes. Detailed studies are conducted on each of these individual processes, determining their relationships with environmental factors. The data obtained are integrated into computer models in order to predict the dynamics of the population under various situations. Often the inquirer is confronted by the problem of choice of level of complexity at which it is necessary to study the populations concerned. This choice may depend on the goal of the study, the resources and experience of the people etc. Making the right choice is not always easy, but is essential for the success of any research prog

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00826.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryChanges in dormancy ofSpergula arvensisseeds were studied during pre‐incubation at constant temperatures and under a temperature regime that condensed the annual temperature cycle into 73 days. Each day in the regime represented the mean day and night temperatures and day lengths of 5 successive days of an average year in The Netherlands. Incubation occurred in water or loamy sand, in darkness. Germination of the seeds was tested in water or KNO3over a range of temperature. Seeds were irradiated with saturating doses of red light. In half of the treatments, pre‐incubated seeds were dehydrated at the transfer to the conditions of the germination test. Breaking of dormancy occurred under conditions of 'spring'. It did not depend on exposure to low‘winter’temperatures, but was induced by rising 'spring’temperatures. Seeds developed secondary dormancy in late‘autumn'. The expression of the changes in dormancy that were induced during pre‐incubation depended on the conditions of the germination test. Light, nitrate and dehydration stimulated germination. The experiments predicted that field emergence from nitrate‐poor soils that have not been dehydrated will be restricted to a short period in autumn, whereas disturbance of nitrate‐rich soils followed by a dry spell will stimulate germination ofS. arvensisseeds from early spring to late autumn. The data presented good explanations for the cosmopolitan character and the serious weediness of this species. Its classification as a summer or winter an

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00827.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryAt UCPE we are exploring high‐level, ecologically based models of growth and resource allocation in herbaceous plants, including weed species. In them, allocation is driven by variables from Plant Strategy Theory, such as below‐and above‐ground‘environmental stress'. A‘hyperbolic’model is described in which the allocation of resources into above‐and below‐ground plant parts is jointly controlled by (i) the absolute amounts of below‐and above‐ground stress that the plant‘perceives'; (ii) the ratio of below‐ground to above‐ground stress; and (iii) by the maximum growth potential of the plant itself. The inputs to the model are the fraction of its maximum potential that the plant attains and its root‐shoot allometric growth coefficient. The outputs from the model are indices of the above‐and below‐ground stresses‘perceived’by the plant. The latter arc otherwise particularly difficult to estimate when growth and allocation are being controlled simultaneously by several suboptimal environmental variables, a

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00828.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryIn most quantitative studies on interplant competition, static regression models are used to describe experimental data. However, the generality of these models is limited. More mechanistic models for interplant competition, which simulate growth and production of species in mixtures on the basis of the underlying physiological processes, have been developed in the past decade. Recently, simulation models for competition between species for light and water were improved and a detailed version was developed for sugarbeet and fat hen (Chenopodium albumL.). The model was validated with data sets of five field experiments, in which the effect of fat hen on sugarbeet production was analysed. About 98% of the variation in yield loss between the experiments (which ranged from –6 to 96%) could be explained with the model. Further analysis with the model showed that the period between crop and weed emergence was the main factor causing differences in yield loss between the experiments. Sensitivity analysis showed a strong interaction between the effect of the variables weed density and the period between crop and weed emergence on yield reduction. Different quantitative approaches to crop‐weed competition are discussed in view of their practical applicability. Simulations of experiments, where both the weed density and the period between crop and weed emergence were varied over a wide range, showed a close relation between relative leaf cover of the weeds shortly after crop emergence and yield loss. This relation indicates that relative leaf cover of the weeds accounts for both the effect of weed density and the period between crop and weed emergence. This relation has the potential to be developed into a powerful tool for weed‐control advisory sy

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00829.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SummaryThe performance of a herbicide is influenced by a number of factors, such as temperature, humidity, weed species and stage of development of the weed. Trials in glasshouses and climatic chambers have shown that the shape of the dose‐response curve of a herbicide is dependent only on the mode of action of the herbicide. Therefore, the performance of a herbicide under different climatic conditions can be described as a parallel displacement of the dose‐response curve. The same seems to be the case regarding the performance of a herbicide against different weed species or against one weed species at different growth stages. The trial programme is in an introductory phase, but the intention is, on the basis of trials where the influence of the above mentioned factors are quantified, to build up a simulation model that adjusts the dose to the conditions prevailing at the time of spraying. In this paper, the results from trials in climatic chambers to test the effect of a herbicide under different climatic conditions, and glasshouse trials with three weed species at three stages of development, are summari

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1988.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY