-The evolution of natural ecosystems is controled by a high level of biodiversity, In sharp contrast, intensive agricultural systems involve monocultures associated with high input of chemical fertilisers and pesticides. Intensive agricultural systems have clearly negative impacts on soil and water quality and on biodiversity conservation. Alternatively, cropping systems based on carefully designed species mixtures reveal many potential advantages under various conditions, both in temperate and tropical agriculture. This article reviews those potential advantages by addressing the reasons for mixing plant species; the concepts and tools required for understanding and designing cropping systems with mixed species; and the ways of simulating multispecies cropping systems with models. Multispecies systems are diverse and may include annual and perennial crops on a gradient of complexity from 2 to n species. A literature survey shows potential advantages such as (1) higher overall productivity, (2) better control of pests and diseases, (3) enhanced ecological services and (4) greater economic profitability. Agronomic and ecological conceptual frameworks are examined for a clearer understanding of cropping systems, including the concepts of competition and facilitation, above-and belowground interactions and the types of biological interactions between species that enable better pest management in the system. After a review of existing models, future directions in modelling plant mixtures are proposed. We conclude on the need to enhance agricultural research on these multispecies systems, combining both agronomic and ecological concepts and tools. species mixture / plant mixture / cropping system / agroforestry system / agrobiodiversity / resource sharing / crop model / competition / facilitation

-The evolution of natural ecosystems is controled by a high level of biodiversity, In sharp contrast, intensive agricultural systems involve monocultures associated with high input of chemical fertilisers and pesticides. Intensive agricultural systems have clearly negative impacts on soil and water quality and on biodiversity conservation. Alternatively, cropping systems based on carefully designed species mixtures reveal many potential advantages under various conditions, both in temperate and tropical agriculture. This article reviews those potential advantages by addressing the reasons for mixing plant species; the concepts and tools required for understanding and designing cropping systems with mixed species; and the ways of simulating multispecies cropping systems with models. Multispecies systems are diverse and may include annual and perennial crops on a gradient of complexity from 2 to n species. A literature survey shows potential advantages such as (1) higher overall productivity, (2) better control of pests and diseases, (3) enhanced ecological services and (4) greater economic profitability. Agronomic and ecological conceptual frameworks are examined for a clearer understanding of cropping systems, including the concepts of competition and facilitation, above-and belowground interactions and the types of biological interactions between species that enable better pest management in the system. After a review of existing models, future directions in modelling plant mixtures are proposed. We conclude on the need to enhance agricultural research on these multispecies systems, combining both agronomic and ecological concepts and tools. species mixture / plant mixture / cropping system / agroforestry system / agrobiodiversity / resource sharing / crop model / competition / facilitation

Nowadays, in a context of climate change, economical uncertainties and social pressure to mitigate agriculture externalities, farmers have to adopt new cropping systems to achieve a sustainable and cost-effective grain production. Conservation agriculture consists of a range of cropping systems based on a combination of three main principles: (1) soil tillage reduction, (2) soil protection by organic residues and (3) diversification in crop rotation. Conservation agriculture has been promoted as a way to reduce production costs, soil erosion and soil fertility degradation under both tropical and temperate conditions. Conservation agriculture-based cropping systems have diffused widely under Brazilian large-scale farms' conditions and more recently in Europe in the context of medium-size mechanized farms. Their diffusion, however, is still limited under small-scale non-mechanized farms' conditions of tropical countries. To assess the advantages and limits of such new cropping systems, this article compares experiences with conservation agriculture from the tropical Cerrado region of Brazil and from temperate conditions of Europe. It focusses on agronomic performances, environmental impacts and economical results. Conservation agriculture systems appear to be interesting options to achieve sustainable and intensive crop production under different agroecological environments because they use efficiently available resources and maintain soil fertility. However, this mostly results from the permanent presence of an organic mulch on the soil surface and the incorporation of cover crops in the rotations. Such modifications require a significant reorganization of the production process at farm level, and when facing technical or socioeconomic constraints, most farmers usually opt for applying only partially the three main principles of conservation agriculture. Investigating more fully the consequences of such partial implementation of conservation agriculture principles on its actual efficiency and assessing the most efficient participatory approaches needed to adapt conservation agriculture principles to local conditions and farming systems are top priorities for future research. (Résumé d'auteur

Increasing the use of synthetic fertilisers and pesticides in agroecosystems has led to higher crop yields, accompanied by a decline in biodiversity at the levels of field, cropping system and farm. Biodiversity decline has been favoured by changes at landscape level such as regional farm specialisation, increases in field size, and the removal of hedgerows and woodlots. The loss of biodiversity in agroecosystems has increased the need for external inputs because beneficial functions are no longer provided by beneficial species as natural enemies of crop pests and ecosystem engineers. This trend has led to a strong reliance on petrochemicals in agroecosystems. However, many scientists have been arguing for more than two decades that this reliance on petrochemicals could be considerably reduced by a better use of biotic interactions. This article reviews options to increase beneficial biotic interactions in agroecosystems and to improve pest management and crop nutrition whilst decreasing petrochemical use. Four agronomic options are presented. First, it has been shown that the choice of cultivar, the sowing date and nitrogen fertilisation practices can be manipulated to prevent interactions between pests and crop, in either time or space. Nevertheless, the efficacy of these manipulations may be limited by pest adaptation. Second, beneficial biotic interactions may result from appropriate changes to the habitats of natural enemies and ecosystem engineers, mediated by soil and weed management. Here, knowledge is scarce, and indirect and complex effects are poorly understood. Third, changes achieved by crop diversification and, fourth, by landscape adaptation are promising. However, these practices also present drawbacks that may not necessarily be outweighed by beneficial effects. Overall, these four management approaches provide a powerful framework to develop sustainable agronomic practices. (Résumé d'auteur