Abstract
Simplified rotations often select weed flora consisting of one or several dominant species. In rotations consisting mainly of winter cereals, one of the most frequent weeds in Atlantic European countries is blackgrass (Alopecurus myosuroides Huds.). In order to reduce environmental impacts and avoid the selection of herbicide-resistant populations, alternative weed management strategies are necessary. The objective of the present study was to develop a methodology for using a weed dynamics model called ALOMYSYS for evaluating prospective diversified crop rotations based on expert opinion. These prospective rotations were developed for a particular region aiming at reducing herbicide use while keeping weed infestation similar to that in current cropping systems. The prospective systems were also evaluated economically by calculating costs and margins for the farmer. The simulations showed that the more diverse the rotation, the better blackgrass was controlled and the less herbicides (rates and frequencies) were necessary. Optimal herbicide spraying conditions and mouldboard ploughing were also less essential in diverse rotations. It was though essential to reason herbicide programs over the whole rotation and not simply as function of the preceding crop. The economic evaluation identified the interest of spring or winter pea either replacing or preceding oilseed rape (OSR) in OSR/wheat/barley rotations.
Highlights
One of the problems occurring in simplified rotations is the selection of a weed flora consisting of one or several dominant species that mimic the crop cycle, with seeds being least dormant when the crop is usually sown, and a post-emergent growth and development allowing reproduction before crop harvest (Fried et al, 2008; Fried et al, 2009)
– the cropping system during the whole simulated period, comprising the crop sequence including set-aside, temporary grassland and cover crops, the date of all operations and their characteristics, i.e. tool, working depth, tractor speed for tillage and mechanical weeding, active ingredient, rate and conditions for herbicides, seed density for sowing, nitrogen rates for fertilizer. These input variables influence the annual lifecycle of blackgrass, in interaction with weed stages, crop stages and environmental conditions
In the reference cropping systems, simulations showed blackgrass infestation to be usually stable when herbicides were applied in suboptimal conditions, with a medium-term infestation of approximately 30 weeds/m2 at crop harvest
Summary
One of the problems occurring in simplified rotations is the selection of a weed flora consisting of one or several dominant species that mimic the crop cycle, with seeds being least dormant when the crop is usually sown, and a post-emergent growth and development allowing reproduction before crop harvest (Fried et al, 2008; Fried et al, 2009). Doyle et al, 1986; Munier-Jolain et al, 2002), it presents the major advantage of using a mechanistic approach where the life-cycle is split into sub-processes depending on biological and physical effects of cropping systems, in interaction with the biological (e.g. weed stage) and physical conditions (e.g. soil structure). The objective of the present study was to develop a methodology for using the ALOMYSYS model for evaluating prospective diversified crop rotations based on expert opinion. These prospective rotations were developed for a particular region aiming at reducing herbicide use while keeping weed infestation similar to that in current farming systems. This study was part of a larger project evaluating diversified rotations (Schneider and Dumans, 2010, present journal number)
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