Quand l'éleveur élève aussi...des arbres. Un esai de protection avec des manchons de jeunes arbres en milieu soudano-sahélien fortement pâturé

International audienceLes éleveurs sont parmi les principaux usagers de l'arbre. Ils s'en servent en particulier pour alimenter leur troupeau en période de soudure, à la fin de la saison sèche. Les pratiques d'exploitation de l'arbre des éleveurs sont parmi les plus élaborées de tous les usagers. Cependant, l'usage durable de cette ressource fourragère nécessite son renouvellement. Celui-ci est fortement lié à la protection dont bénéficie le plant lors de ses premières années. Cette protection est d'autant plus difficile que la pression du bétail est forte, ce qui est le cas notamment autour des campements d'éleveurs, où les systèmes de protections traditionnelles s'avèrent peu efficaces. Cette communication présente les résultats d'une expérimentation de manchons de protection en polypropylène en milieu de forte pression d'élevage, le campement Peul de Macina (200 km de Garoua). Le test a été réalisé sur deux essences, l'Afzelia, producteur de fourrage, et l'Eucalyptus, producteur de bois de service. Il a été doublé en station. L'efficacité du manchon dans les premiers mois de développement du plant, mais aussi l'intérêt des éleveurs pour ce système sont ici discutés. (Résumé d'auteur

Reconciling root plasticity and architectural ground rules in tree root growth models with voxel automata

Contacts: [email protected] models of tree root growth and function have to reconcile the architectural rules for coarse root topology with the dynamics of fine root growth (and decay) in order to predict the strategic plus opportunistic behaviour of a tree root system in a heterogeneous soil. We present an algorithm for a 3D model based on both local (soil voxel level) and global (tree level) controls of root growth, with development of structural roots as a consequence of fine root function, rather than as driver. The suggested allocation rules of carbon to fine root growth in each rooted voxel depend on the success in water uptake in this voxel during the previous day, relative to overall supply and demand at plant level. The allocated C in each voxel is then split into proliferation (within voxel growth) and extension into neighbouring voxels (colonisation), with scale-dependent thresholds and transfer coefficients. The fine root colonisation process defines a dynamic and spatially explicit demand for transport functions. C allocation to development of a coarse root infrastructure linking all rooted voxels depends on the apparent need for adjustment of root diameter to meet the topologically defined sap flow through this voxel during the previous day. The allometric properties of the coarse root system are maintained to be in line with fractal branching theory. The model can predict the dynamics of the shape and structure (fine root density, coarse root topology and biomass) of the root system either independently of soil conditions (purely genetically-driven) or including both the genetic and environmental effects of roots interacting with soil water supply and its external replenishment, linking in with existing water balance models. Sensitivity of the initial model to voxel dimensions was addressed through explicit scaling rules resulting in scale-independent parameters. The model was parameterised for two tree species: hybrid walnut (Juglans nigra x regia) and wild cherry (Prunus avium L.) using results of a pot experiment. The model satisfactorily predicted the root growth behaviour of the two species. The model is sparse in parameters and yet applicable to heterogeneous soils, and could easily be upgraded to include additional local influences on root growth (and decay) such as local success in nutrient uptake or dynamic soil physical propertie

Productivity and radiation use efficiency of lettuces grown in the partial shade of photovoltaic panels

Combining photovoltaic panels (PVPs) and crops on the same land unit were recently proposed as an alternative to the conversion of cropland into photovoltaic plants. This could alleviate the increasing competition for land between food and energy production. In such agrivoltaic systems, an upper layer of PVPs partially shades crops at ground level. The aim of this work was to (i) assess the effect on crop yield of two PVPs densities, resulting in two shade levels equal to 50% and 70% of the incoming radiation and (ii) identify morphological and physiological determinants of the plant response to shade. Experiments were conducted on four varieties of lettuces (two crisphead lettuces and two cutting lettuces), during two seasons. In all cases, the relative lettuce yield at harvest was equal or higher than the available relative radiation. Lettuce yield was maintained through an improved Radiation Interception Efficiency (RIE) in the shade, while Radiation Conversion Efficiency (RCE) did not change significantly. Enhanced RIE was explained by (i) an increase in the total leaf area per plant, despite a decrease in the number of leaves and (ii) a different distribution of leaf area among the pool of leaves, the maximal size of leaves increasing in the shade. Our result provides a framework for the selection of adapted varieties according to their morphological traits and physiological responses to PVP shade, in order to optimize agrivoltaic systems

Book of abstracts, 4th World Congress on Agroforestry

International audienc

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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Dealing with crop rotation in agroforestry: the impact of shade on winter wheat and sugar beet growth and yield under belgium conditions

peer reviewe

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

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