Paris, France
Septemer 30, 2009
INRA researchers in Dijon are trying to develop tools and methods that will enable farmers to reduce their use of herbicides in the future. They are basing this work on their knowledge of the effects of cropping systems on the dynamics of weeds. Moreover, weed management is not solely intended to control harmful species but also maintain a degree of biodiversity in the environment.
The effects of cropping systems (crop successions and cultivation techniques) on weeds are complex. They influence different processes in the life cycle of species (emergence, competition, seed production, etc.). Moreover, weed species respond differently, depending on their characteristics. Cultivation techniques can interact with each other and with climatic conditions; for example, tillage will only bury seeds when carried out on dry soil, whereas under moist conditions it will also stimulate germination. In addition, the effects also accumulate over several years. For instance, the seeds of many species can survive for several years; they may be moved back to the soil surface by ploughing several years after they were produced and buried, thus leading to sudden and abundant weed emergence in a field.
In this context, modelling becomes essential to synthesise and quantify these effects in a broad range of situations, to analyse their interactions and to assess the long-term cumulative effects of cropping systems on weeds. The design of such models and their practical application will then make a considerable contribution to the development of integrated weed management strategies
The first of these models was developed for a common and pernicious species, black-grass (Alopecurus myosuroides Huds.). This model was based on representing the annual life-cycle of black-grass as a succession of stages (e.g. germinated seeds, pre-emergent growth, seedling emergence, etc.), linked by demographic functions dependent upon the effects of cropping systems. The input variables of the model are the initial seed bank, cropping system components (crop, tillage, sowing, herbicide treatments, fertilisation, mowing, harvest) and the pedoclimatic environment (temperature, rainfall, soil characteristics, etc.). At output, the model calculates, on a daily basis, the density of black-grass individuals at each life-stage and the viable seed bank remaining in the soil.
This model designed by the Dijon researchers is called AlomySys. It has been evaluated over several years, an essential step in development before it can be used to promulgate advice to farmers. This evaluation has shown that the model satisfactorily ranks cropping systems according to their infestation by black-grass and correctly predicts the extent of infestations. Thanks to its daily time-step and its integration of interactions with the environment, this type of model can assist technical institutes and researchers to evaluate and design cropping systems and then advise farmers regarding optimisation of their crop management strategies.
In practice, these models are integrated in software systems that are made available to researchers and technical institutes. Having demonstrated the efficiency of this approach with respect to black-grass, the scientists have now applied a comparable method to a multi-specific weed flora in order to reflect field conditions as closely as possible and how they are managed by farmers.
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