Evaluation and design of multispecies cropping systems with perennials: are current methods applicable?

The existing methods are applicable to multispecies cropping systems with perennials. However, the particular features of these cropping systems highlight the drawbacks of each of them. Therefore, combining these approaches, where and when it is possible, should be preferred. Whatever the method, evaluation of the new systems requires new indicators development, to account for the multiple productions with very different timescales and serving varying objectives. Development of simple and effective sets of indicators adapted to these systems is a powerful tool to boost the design realm, for practitioners and researchers alike

Evaluation and design of multispecies cropping systems with perennials: are current methods applicable?

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Fruit-trees in agroforestry systems - review and prospects for the temperate and Mediterranean zones. Abstract number 33

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Compromis biodiversité-nuisibilité des communautés adventices dans les systèmes de culture : développement d'une méthode de diagnostic combinant simulations et indicateurs

The ambivalent nature of arable weeds, both bioagressors and support for biodiversity, must be taken into account to design more sustainable cropping systems. The aim of this study was to develop a tool and a method allowing the assessment of cropping system performances (i) to reduce weed harmfulness against crops (ii) while promoting the role of weeds to maintain biodiversity in agroecosystems. To do so we developed a set of 10 indicators reflecting the characteristics of weed communities in terms of harmfulness and contribution for biodiversity. The indicators were calculated from outputs of the FLORSYS model, a mechanistic model that predicts multi-specific weed dynamics as a function of cropping systems in interaction with pedoclimate. Following an agronomic diagnosis method, farm surveys were carried out in order to identify contrasted cropping systems in two French agricultural regions. With the new tool resulting from the linking of FLORSYS with the newly developed indicators, the 26 identified cropping systems were simulated and assessed over 30 years with a multi-specific flora and repeated with 10 different weather scenarios. Our results showed an antagonism in most of the studied systems between weed-induced yield loss and maintaining weed-based trophic resources for seed-predating birds and insects as well as for pollinators. However, biodiversity and production goals could be conciliated in certain systems. The analysis of the results with a classification and regression tree method enabled to identify combinations of crop management techniques that optimized one or several indicators. The methodology newly developed in this work has laid the foundations to make possible the design of new weed management strategies.Le caractère ambivalent des adventices des parcelles cultivées, à la fois bioagresseurs des cultures mais aussi piliers de la biodiversité de l’agroécosystème, doit être pris en compte pour concevoir de nouveaux systèmes de culture plus durables. L’objectif de ce travail de thèse était de développer et tester un outil et une méthode permettant d’évaluer les performances des systèmes de culture pour (i) réduire la nuisibilité des adventices vis-à-vis de la culture et (ii) promouvoir le rôle des adventices pour le maintien de la biodiversité dans l’agroécosystème. Pour cela nous avons mis au point un jeu de 10 indicateurs traduisant les caractéristiques des communautés adventices en termes de dommages et de bénéfices pour l’agroécosystème, calculés à partir des sorties du modèle FLORSYS, un modèle mécaniste de prédiction des communautés adventices sous l’effet des systèmes de culture en interaction avec les états du milieu. Suivant une méthode de diagnostic agronomique, des enquêtes ont été réalisées chez des agriculteurs de manière à identifier des systèmes de culture contrastés dans deux régions agricoles. A l’aide du nouvel outil d’évaluation issu du couplage FLORSYS-indicateurs, les 26 systèmes de culture identifiés ont été simulés et évalués sur une période de 30 ans avec une flore initiale composée de 16 espèces adventices annuelles, sous 10 scénarios climatiques différents. Nos résultats mettent en évidence un antagonisme entre la réduction des pertes de rendements dues aux adventices et le maintien de ressources pour les oiseaux et insectes granivores et les pollinisateurs dans la majorité des systèmes étudiés. Toutefois, des compromis entre objectifs de biodiversité et de réduction de la nuisibilité sont observés dans certains systèmes. L’analyse des résultats avec une méthode d’arbres de classification et de régression a permis d’identifier les combinaisons de techniques du système de culture permettant d’optimiser un ou plusieurs indicateurs. La méthodologie développée dans ce travail de thèse, ainsi que les premiers résultats de diagnostic posent les bases nécessaires pour engager un travail de conception de nouvelles stratégies de gestion des adventices efficaces et respectueuses de la biodiversité

Using a sensitivity analysis of a weed dynamics model to develop sustainable cropping systems. I. Annual interactions between crop management techniques and biophysical field state variables

International audienceEnvironmental problems mean that herbicide applications must be drastically reduced and optimized. Models that quantify the effects of crop management techniques on weed dynamics are valuable tools for designing weed management strategies. Indeed, the techniques to be optimized are numerous and diverse, and their effects vary considerably with environmental conditions and the state of the weed flora. In the present study, a mechanistic weed dynamics model, ALOMYSYS, was used to carry out in silico experiments in order to: (1) rank crop management components according to the resulting decrease in weed infestation, and (2) study the sensitivity of the major component effects to biophysical field state variables in order to identify indicators and thresholds that could serve for future decision-rules for farmers. The various results were compiled into rules for optimizing timing and other options (tillage tools, herbicide types) for the different crop management techniques. The rules were based on a series of biophysical field state variables, i.e. cumulated rainfall, thermal time, soil moisture and weed densities prior to the operation, in the previous and pre-previous crops. For instance, the first tillage should be delayed until the cumulated rainfall since harvest exceeds 50 mm and be carried out in moist conditions. Mouldboard ploughing is advised if the infestation of the previous crop exceeds 20 weeds/m(2) and particularly if this exceeds 0.3 times that of the pre-previous crop. Ploughing should occur when the cumulated rainfall since harvest reaches 100-200 mm. The effects of crop succession and long-term effects of management techniques have been studied in a companion paper (Colbach et al. 2012)

How does reduced herbicide use affect biodiversity and crop production?

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Changing agricultural practices modifies the species and trait composition of the weed flora. A simulation study using a cropping system model

International audienceCropping systems change over time to adapt to socio-economical and environmental constraints and to profit from technological innovations. These changes can result in unexpected side-effects which are difficult to determine in fields. The objective of the present study was to use a cropping system model to evaluate the impacts of modified agricultural practices ex ante on weeds. The FLORSYS model quantifies the effect of crop succession, management techniques and climate on multi-specific weed dynamics over the years; it was parameterized with functional relationships predicting model parameters (e.g. pre-emergent seedling mortality) from species traits (e.g. seed mass). Cropping systems typical of three French regions were determined from farm surveys and the Biovigilance data base. These control scenarios as well as various management modifications were simulated in each region, using a weed flora consisting of sixteen major weed species. Each scenario was simulated over 27 years and repeated 10 times, by randomly choosing each year annual climate series measured in the tested region. The control and prospective scenarios were analysed for their total weed density and their species compositions, showing for instance that the weed flora was more diverse in the longer Burgundy (oilseed rape / winter wheat / winter barley, with mouldboard ploughing every three years) and Poitou-Charentes rotations (OSR / winter wheat / sunflower / winter wheat, with ploughing three years out of four) than in the Aquitaine maize monoculture. Modifying management practices modified both weed density and composition. For instance, simplifying or abandoning tillage greatly increased weed infestation. If it was moreover accompanied by earlier sowing, infestations increased even more, but only when autumnal weed species dominated. Introducing temporary crops before spring crops (as required by recent French regulations) reduced densities, particularly in autumnal weeds. Simplifying the three-year Burgundy rotation to a two-year oilseed rape/wheat increased weed densities, particularly when mouldboard ploughing was also abandoned. Conversely, diversifying rotations decreased densities in Burgundy (addition of a spring pea) and, particularly, in Aquitaine (maize monoculture changed to a four-year rotation). Abandoning ploughing though still increased densities. Some cultural changes (e.g. no-till) greatly changed weed flora composition. To understand these changes, the relationships between management practices and weed species traits were studied with RLQ and fourth-corner analyses. Longer rotations were thus shown to select weed species with elongated/flattened seeds (which present little dormancy) and long emergence periods. These species are able to emergence in crops irrespective of their sowing date. Conversely, rotations with late-sown crops (i.e. spring crops or late-sown autumn crops) favoured species with round seeds which are more dormant, thus reducing germination prior to crop sowing. Frequent mouldboard ploughing selected species with thick-coated seeds which are also those least prone to mortality. Ploughing also favoured species with low-lipidic seeds which germinate later and more slowly. Both consequences, low mortality and reduced germination, improve seed survival after burial by ploughing until a further ploughing moves seeds again closer to soil surface where emergence is possible. More generally, frequent tillage favoured monocotyledonous species and species with a late and short emergence period, thus limiting fatal germination triggered by early tillage. Glyphosate before sowing in direct-drilled fields selected seeds with low area/mass ratios which germinate later and can thus avoid the glyphosate application

Does Integrated Weed Management affect the risk of crop diseases? A simulation case study with blackgrass weed and take-all disease

Integrated Weed Management (IWM) is necessary to reduce environmental damages by herbicides. The modifications required for IWM in cropping systems can result in unexpected side-effects, e.g. an increased risk of bioagressors other than weeds, either because the new cropping systems favour these bioagressors or because they favour weeds that are potential bioagressor hosts, thus increasing the contagion risk for crops. To evaluate these risks, the present case study worked with two model pests, a grass-weed species (blackgrass, Alopecurus myosuroides Huds.) and a soil-borne cereal pathogen (Gaeummanomyces graminis (Sacc.) von Arx et Olivier var. tritici Walker, responsible for take-all disease) which strongly interact and depend on cropping systems. For each pest, a model quantifying the effects of cropping systems in interaction with pedoclimatic conditions on pest dynamics was chosen from literature (AlomySys for weed dynamics, TakeAllSys for disease incidence) and linked with a new interaction model predicting the effect of one bioagressor on the other. A simulation study was then carried out, testing a herbicide-intensive reference system identified in farm surveys and a series of IWM systems combining several modifications (e.g. mouldboard ploughing, mechanical weeding, delayed sowing) to compensate for herbicide reductions. Each scenario was simulated over 27 years and repeated 20 times, with randomly chosen weather series from two different pedoclimates. The best IWM systems were more efficient than the herbicide-intensive reference system to control the grass weed. In the case of weed-free simulations, none of the IWM systems increased disease incidence, and the best systems even slightly reduced it. Integrating the reduction in weed seed production due to the disease in the simulations did not significantly change the simulation outcome, irrespective of the tested cropping system. Conversely, when the role of weed in disease transmission was taken into account, disease incidence in cereals crops considerably increased, particularly when past non-host crops in the rotation were infested by the weed. Nevertheless, the best IWM systems presented negligible weed-induced disease increase. The present results can be extrapolated to similar pest types (e.g. with propagules surviving in soil and negligible dispersal between fields). The modelling and simulation approach were easily feasible thanks to the availability of consistent models of cropping system effects on the two pests and experimental data on their interactio