Nicolas Munier-Jolain

European Perspectives on the Adoption of Nonchemical Weed Management in Reduced-Tillage Systems for Arable Crops

Abstract Noninversion tillage with tine- or disc-based cultivations prior to crop establishment is the most common way of reducing tillage for arable cropping systems with small grain cereals, oilseed rape, and maize in Europe. However, new regulations on pesticide use might hinder further expansion of reduced-tillage systems. European agriculture is asked to become less dependent on pesticides and promote crop protection programs based on integrated pest management (IPM) principles. Conventional noninversion tillage systems rely entirely on the availability of glyphosate products, and herbicide consumption is mostly higher compared to plow-based cropping systems. Annual grass weeds and catchweed bedstraw often constitute the principal weed problems in noninversion tillage systems, and crop rotations concurrently have very high proportions of winter cereals. There is a need to redesign cropping systems to allow for more diversification of the crop rotations to combat these weed problems with less herbicide input. Cover crops, stubble management strategies, and tactics that strengthen crop growth relative to weed growth are also seen as important components in future IPM systems, but their impact in noninversion tillage systems needs validation. Direct mechanical weed control methods based on rotating weeding devices such as rotary hoes could become useful in reduced-tillage systems where more crop residues and less workable soils are more prevalent, but further development is needed for effective application. Owing to the frequent use of glyphosate in reduced-tillage systems, perennial weeds are not particularly problematic. However, results from organic cropping systems clearly reveal that desisting from glyphosate use inevitably leads to more problems with perennials, which need to be addressed in future research. Nomenclature: Catchweed bedstraw, Galium aparine L.; barley, Hordeum vulgare L.; maize, Zea mays L.; oilseed rape, Brassica napus L.; wheat, Triticum aestivum L. Resumen El cultivar sin inversión del suelo usando discos o picos, antes del establecimiento del cultivo, es la forma más común de reducir la labranza en sistemas de cultivos arables que incluyen cereales, colza y maíz en Europa. Sin embargo, nuevas regulaciones sobre el uso de plaguicidas podrían afectar la expansión de los sistemas de labranza reducida. La agricultura europea ha sido llamada a ser menos dependiente de los plaguicidas y a promover programas de protección de cultivos basados en los principios de manejo integrado de plagas (IPM). Los sistemas de labranza convencional sin inversión del suelo dependen totalmente de la disponibilidad de productos con glyphosate, y el consumo de herbicidas es mayoritariamente superior al compararse con sistemas de cultivo basados en el uso de arado. Malezas como zacates anuales y Galium aparine frecuentemente constituyen el principal problema de malezas en sistemas de labranza sin inversión del suelo y rotaciones de cultivos que además tienen proporciones muy altas de cereales de invierno. Existe la necesidad de rediseñar los sistemas de cultivos para permitir una mayor diversificación de las rotaciones de cultivos para así combatir estos problemas de malezas con un uso menor de herbicidas. Cultivos de cobertura, sistemas de manejo con residuos de cultivos, y tácticas que refuercen el crecimiento del cultivo en relación con el crecimiento de las malezas son también vistos como componentes importantes en los sistema IPM futuros, pero su impacto en los sistemas de labranza sin inversión del suelo necesita validación. Los métodos de control mecánico de malezas directo basados en implementos rotativos de deshierba, tales como azadones rotativos, han sido útiles en sistemas de labranza reducida donde la presencia de más residuos de cultivos y suelos menos trabajables son prevalentes, pero un mayor desarrollo de estos métodos es necesario para su aplicación efectiva. Debido al uso frecuente de glyphosate en sistemas de labranza reducida, las malezas perennes no son particularmente problemáticas. Sin embargo, resultados en sistemas de producción orgánicos han revelado claramente que el desistir del uso de glyphosate lleva inevitablemente a más problemas con malezas perennes, lo que necesita ser incluido en investigaciones futuras.

Weeds in agricultural landscapes. A review

There is currently an increasing societal and political shift towards more sustainable agricultural systems to provide both food production and ecological biodiversity levels. This shift has recently modified scientific questioning and brought up new research challenges for agro-ecological research. This is the case in particular for weed management, where issues have so far largely focused on the conflict between weeds and crop productivity. Here, we review recent findings that have led to a changing perception on weeds in agro-ecosystems and upcoming areas in terms of weed management options. Our main findings are that weeds have numerous interactions with other organisms and, in turn, some of these interactions can have direct, either negative or positive, effects on the functioning of the agro-ecosystem. Many interactions are species-specific, and therefore assessing the role of weed communities in the agro-ecosystem would benefit from further development in the functional grouping of weed species. In terms of weed management our review shows that alternative cropping systems can deliver both good levels of crop productivity and of weed management at the field level. Weeds respond to landscape attributes and there is a need to fully assess the scope for utilizing the spatio-temporal organization of cropping systems and uncultivated habitats as a tool for minimizing weed infestations. Weeds are also submitted to biological regulation through the predation of their seeds and further research is required to assess the effect of cropping systems and landscape on levels of weed natural enemies, and therefore on the potential contribution of biological regulation in the management of weeds.

Iterative Design and Evaluation of Rule-Based Cropping Systems: Methodology and Case Studies - A Review

The economic and regulatory context of crop production changes rapidly, but concerns about agricultural sustainability, including environmental impacts, are increasing steadily. To cope with complexity and uncertainty, innovative methodologies are required for designing, managing and evaluating prototype cropping systems. A generic approach combining iteratively design of cropping systems and evaluation of their performances is presented in this review article. It includes 5 main steps: (1) defining the set of goals and constraints for each cropping system, (2) identifying a suitable agronomic strategy, (3) formulating the consistent set of technical decision rules, (4) applying and evaluating the rule-based system, and (5) validating or refining the strategy and the rules. This methodology was applied to a range of environmental and production contexts, in a perspective of integrated crop production (ICP) prototyping. Three cropping system experiments conducted in France were brought together to demonstrate the potentialities of this system approach and discuss the methodological bottlenecks to address. The three case studies differed by the context of crop production and resource use: adaptation to limited irrigation water (Toulouse), introduction of innovative cropping systems (Versailles), and substitution of herbicides by non-chemical methods (Dijon). The consequences of the specific objectives in each case study on the experimental design and the evaluation process were discussed. Special attention was paid to the time step of the evaluation process, the duration of the improvement loops when prototyping cropping systems, the global evaluation of the systems and the evaluation of individual decision rules.

Reconciling Pesticide Reduction with Economic and Environmental Sustainability in Arable Farming

Reducing pesticide use is one of the high-priority targets in the quest for a sustainable agriculture. Until now, most studies dealing with pesticide use reduction have compared a limited number of experimental prototypes. Here we assessed the sustainability of 48 arable cropping systems from two major agricultural regions of France, including conventional, integrated and organic systems, with a wide range of pesticide use intensities and management (crop rotation, soil tillage, cultivars, fertilization, etc.). We assessed cropping system sustainability using a set of economic, environmental and social indicators. We failed to detect any positive correlation between pesticide use intensity and both productivity (when organic farms were excluded) and profitability. In addition, there was no relationship between pesticide use and workload. We found that crop rotation diversity was higher in cropping systems with low pesticide use, which would support the important role of crop rotation diversity in integrated and organic strategies. In comparison to conventional systems, integrated strategies showed a decrease in the use of both pesticides and nitrogen fertilizers, they consumed less energy and were frequently more energy efficient. Integrated systems therefore appeared as the best compromise in sustainability trade-offs. Our results could be used to re-design current cropping systems, by promoting diversified crop rotations and the combination of a wide range of available techniques contributing to pest management.

Effects of halving pesticide use on wheat production

Pesticides pose serious threats to both human health and the environment. In Europe, farmers are encouraged to reduce their use, and in France a recent environmental policy fixed a target of halving the pesticide use by 2018. Organic and integrated cropping systems have been proposed as possible solutions for reducing pesticide use, but the effect of reducing pesticide use on crop yield remains unclear. Here we use a set of cropping system experiments to quantify the yield losses resulting from a reduction of pesticide use for winter wheat in France. Our estimated yield losses resulting from a 50% reduction in pesticide use ranged from 5 to 13% of the yield obtained with the current pesticide use. At the scale of the whole country, these losses would decrease the French wheat production by about 2 to 3 millions of tons, which represent about 15% of the French wheat export.

Reducing pesticide use while preserving crop productivity and profitability on arable farms

Achieving sustainable crop production while feeding an increasing world population is one of the most ambitious challenges of this century1. Meeting this challenge will necessarily imply a drastic reduction of adverse environmental effects arising from agricultural activities2. The reduction of pesticide use is one of the critical drivers to preserve the environment and human health. Pesticide use could be reduced through the adoption of new production strategies3–5; however, whether substantial reductions of pesticide use are possible without impacting crop productivity and profitability is debatable6–17. Here, we demonstrated that low pesticide use rarely decreases productivity and profitability in arable farms. We analysed the potential conflicts between pesticide use and productivity or profitability with data from 946 non-organic arable commercial farms showing contrasting levels of pesticide use and covering a wide range of production situations in France. We failed to detect any conflict between low pesticide use and both high productivity and high profitability in 77% of the farms. We estimated that total pesticide use could be reduced by 42% without any negative effects on both productivity and profitability in 59% of farms from our national network. This corresponded to an average reduction of 37, 47 and 60% of herbicide, fungicide and insecticide use, respectively. The potential for reducing pesticide use appeared higher in farms with currently high pesticide use than in farms with low pesticide use. Our results demonstrate that pesticide reduction is already accessible to farmers in most production situations. This would imply profound changes in market organization and trade balance.

Ecological Intensification Through Pesticide Reduction: Weed Control, Weed Biodiversity and Sustainability in Arable Farming

Amongst the biodiversity components of agriculture, weeds are an interesting model for exploring management options relying on the principle of ecological intensification in arable farming. Weeds can cause severe crop yield losses, contribute to farmland functional biodiversity and are strongly associated with the generic issue of pesticide use. In this paper, we address the impacts of herbicide reduction following a causal framework starting with herbicide reduction and triggering changes in (i) the management options required to control weeds, (ii) the weed communities and functions they provide and (iii) the overall performance and sustainability of the implemented land management options. The three components of this framework were analysed in a multidisciplinary project that was conducted on 55 experimental and farmer’s fields that included conventional, integrated and organic cropping systems. Our results indicate that the reduction of herbicide use is not antagonistic with crop production, provided that alternative practices are put into place. Herbicide reduction and associated land management modified the composition of in-field weed communities and thus the functions of weeds related to biodiversity and production. Through a long-term simulation of weed communities based on alternative (?) cropping systems, some specific management pathways were identified that delivered high biodiversity gains and limited the negative impacts of weeds on crop production. Finally, the multi-criteria assessment of the environmental, economic and societal sustainability of the 55 systems suggests that integrated weed management systems fared better than their conventional and organic counterparts. These outcomes suggest that sustainable management could possibly be achieved through changes in weed management, along a pathway starting with herbicide reduction.

Contrasting weed species composition in perennial alfalfas and six annual crops: implications for integrated weed management

Weed communities are most strongly affected by the characteristics and management of the current crop. Crop rotation may thus be used to prevent the repeated selection of particular weed species. While weed communities are frequently compared among annual crops, little is known about the differences between annual and perennial crops that may be included in the rotations. Moreover, nearly all existing studies (17 articles reviewed) are based on local field experiments rather than commercial fields. We compared the weed composition in perennial alfalfas (Medicago sativa) and six annual crops: winter wheat (Triticum aestivum), oilseed rape (Brassica napus), pea (Pisum sativum), sunflower (Helianthus annuus), maize (Zea mays) and sorghum (Sorghum bicolor) using data from 632 commercial fields in western France. Weed species composition showed the strongest dissimilarities between perennial alfalfas and all annual crops, followed by the well-known differences between autumn- and spring/summer-sown annual crops. Indicator Species Analysis showed that most weed species either preferred perennial alfalfas (including Taraxacum officinale, Veronica persica, Crepis spp., Poa trivialis, Silene latifolia, Capsella bursapastoris and Picris spp.) or annual crops (including Mercurialis annua, Galium aparine, Fallopia convolvulus, Chenopodium album and Cirsium arvense). Perennial alfalfas thus suppressed many weeds that are widespread (and sometimes problematic) in annual crops while favouring other species. Shifted weed composition and reduced frequency of several noxious weeds suggest that perennial alfalfas may be used as a valuable part of integrated weed management, reducing the need for herbicides and sustaining plant and animal diversity in agricultural landscapes.

A plant nitrophily index based on plant leaf area response to soil nitrogen availability.

This article reports a new experimental method to measure plant nitrophily. Knowledge of the nitrophily of plant species has many potential applications such as studying the long-term evolution of flora and designing nitrogen management strategies in cropping systems. Plant nitrophily is commonly measured by the Ellenberg N score based on the natural occurrence of species along soil nitrogen gradients. The Ellenberg N score is known for species from restricted geographical areas representing a small proportion of total plant species diversity. In addition, measuring Ellenberg N score is not convenient. We propose a new definition of plant nitrophily referring to plant leaf area response to nitrogen availability. We compared habitat-based and response-based values of nitrophily to design a simple method to estimate a plant nitrophily index (NI). Eleven monocotyledonous and dicotyledonous plant species were grown in a greenhouse experiment at two levels of soil nitrogen. Nine species were weeds covering the range of the Ellenberg N score. Two crop species with unknown nitrophily, wheat and oilseed rape, were studied to illustrate our method. Plant leaf area was measured at one date for each species × nitrogen treatment combination. A NI was calculated as the ratio of leaf area at high nitrogen to leaf area at low nitrogen. Our results show for weeds a high interspecific diversity of the NI, ranging from 1.0 to 4.2. The NI was strongly and positively correlated to Ellenberg N score, with R2 of 0.73. The more nitrophilic a species according to habitat preferences, the more leaf area responded to increasing nitrogen supply. This is the first time that a quantitative relationship is found between Ellenberg N score and a growth variable measured non-destructively for both monocotyledonous and dicotyledonous species. Therefore, calculating the response of leaf area to nitrogen supply provides a new simple and non-destructive method that can be used for the assessment of a NI of any species. As an illustration of the method, a NI was estimated for new species. It was at 2.1 and 4.5 for wheat and oilseed rape, respectively, indicating that they were respectively moderately and highly nitrophilic. This method will help to assess the relative nitrophily of weeds vs. crops. Such knowledge could be used to design nitrogen management strategies promoting crop growth but not weed growth, thus reducing the use of herbicides.

Uncertainty analysis and evaluation of a complex, multi-specific weed dynamics model with diverse and incomplete data sets

Weed dynamics models are needed to test prospective cropping systems but are rarely evaluated with independent data (validated). Here, we evaluated the FlorSys model which quantifies the effects of cropping systems and pedoclimate on multispecific weed dynamics with a daily time step. We adapted existing validation methodologies and uncertainty analyses to account for multi-specific, multi-annual and diverse outputs, focusing on missing input data, incomplete and imprecise weed time series. Field data ranged from entirely monitored cropping system trials to annual snapshots recorded on farm fields by the French Biovigilance-Flore network. FlorSys satisfactorily predicted weed seed bank, plant densities and crop yields, at daily and multi-annual scales, at well monitored sites. It overestimated plant biomass and underestimated total flora density. Missing processes (photoperiod dependency in flowering, crop:weed competition for nitrogen) and inadequately predicted scenarios (weed dynamics in untilled fields, floras with summer-emerging species) were identified. Guidelines for model use were proposed. Weed dynamics models must be validated before using them for cropping system design.Methods were developed to evaluate a mechanistic model with incomplete data sets.Data sets comprise cropping system trials and a farm field survey network.FlorSyss domain of validity and guidelines for simulations were determined.Missing processes necessary for predicting weed dynamics in fields were identified.