Nitrogen forms affect root structure and water uptake in the hybrid poplar

The study analyses the effects of two different forms of nitrogen fertilisation (nitrate and ammonium) on root structure and water uptake of two hybrid poplar (Populus maximowiczii x P. balsamifera) clones in a field experiment. Water uptake was studied using sap flow gauges on individual proximal roots and coarse root structure was examined by excavating 18 whole-root systems. Finer roots were scanned and analyzed for architecture. Nitrogen forms did not affect coarse-root system development, but had a significant effect on fine-root development. Nitrate-treated trees presented higher fine:coarse root ratios and higher specific root lengths than control or ammonium treated trees. These allocation differences affected the water uptake capacity of the plants as reflected by the higher sapflow rate in the nitrate treatment. The diameter of proximal roots at the tree base predicted well the total root biomass and length. The diameter of smaller lateral roots also predicted the lateral root mass, length, surface area and the number of tips. The effect of nitrogen fertilisation on the fine root structure translated into an effect on the functioning of the fine roots forming a link between form (architecture) and function (water uptake)

Light and tree size influence belowground development in yellow birch and sugar maple

The effects of light and tree size on the root architecture and mycorrhiza of yellow birch (Betula alleghaniensis Britton) and sugar maple (Acer saccharum Marsh) growing in the understory of deciduous forests in southern Qu

Soil layer condensation peak as a response to soil water properties under Sudanese climatic conditions

International audienceThe soil apparent density is strongly dependent on their physico-chemical properties. It can be negatively impacted by human activities such as soil work or animal pasture or natural salinity influenced by irrigation.. In contrast it can be improved for different depths by agricultural practices. A " condensation peak " defined as an increase in the apparent density was found for the heterogeneous soils of Niger for several profiles of 5 soil classes and for a very shallow depth (10 cm maximum) with a very variable extreme depth (from 35 to 150 cm) associated with extreme density values (from 1.45 to 2). The depth of this peak, for soils neither saline nor vertic, varies inversely with the proportion of soil fine elements (silts+clays). However it corresponds to an average value of useful water (AWC) of 100mm (CV=24.4%). In sodic and alkaline soils this peak can be observed at shallow depths (from 53 to 61cm with a CV from 15 to 40%), thus for much lower AWC values (from 74 to 87cm with a CV from 26 to 47%). It can be found either below or above an impermeable horizon of a maximal density of 2.. This peak is likely to be associated with a multi-annual alternance of humectation-dessication at this depth. Its occurrence is based on an interplay of intrinsic physical and hydric soil properties but also on extrisnic parameters sch as the pluviometry, the location at the scale of the watershed and the micromodelling

Fonctionnement écophysiologique des arbres en association

The authors first present the state of the current knowledge on the sharing of resources in agrolignicolous covers. After a brief reminder of the roles played by each resource, existing methodologies and current research axes are presented, as well as research perspectives in the field of modelling of plant reactions to variations of their environmental conditions. / Les auteurs présentent d'abord l'état des connaissances sur le partage des ressources dans les couverts agrolignicoles. Après un bref rappel des rôles joués par chacune de ces ressources, les méthodologies existantes et voies actuelles de recherche sont présentées, puis les perspectives de recherche dans le domaine de la modélisation de la réponse des plantes aux variations des conditions de leur environnement

How earthworm activities affect banana plant response to nematodes parasitism

The burrowing nematode Radopholus similis and the lesion nematodes Pratylenchus spp. are considered as major constraints to banana cultivation worldwide. As an alternative to the use of chemical pesticides in commercial banana plantations, the possible role of the earthworm Pontoscolex corethrurus was studied regarding the reducing harmfulness of the main plant-feeding nematodes of banana. The interactions among banana plants, plant-feeding nematodes and earthworms have been tested in a controlled experiment combining treatments including or not earthworms and nematodes, over a complete vegetative banana development cycle. The aim of the work was to evaluate how earthworm activity can affect the pathogenicity of the three main plant-feeding nematodes associated with dessert banana (Musa spp. AAA group, cv. Cavendish) in Guadeloupe (French West Indies), R. similis, Pratylenchus coffeae and Helicotylenchus multicinctus. Results showed that damages caused by plant-feeding nematodes were lowered in the presence of the earthworm P. corethrurus; the population of plant-feeding nematodes did not decrease whereas root damage induced by nematodes was significantly reduced (50% reduction of root necrosis in the presence of earthworms). Moreover, in the presence of P. corethrurus, we observed a change of soil porosity. On the one hand, the burrowing activity of earthworms destroyed most of the initial structural porosity (mesobiotic pores, 3-300 mu m) and on the other hand, they increased the volume of the finest structural pores diameter class (microbiotic pores, 0.3-3 mu m). P. corethrurus also stimulated phosphorus mineralization. Soil bioturbation carried out by P. corethrurus could have enhanced the efficiency of microbial community that is involved in phosphorus bioavailability. This observation was corroborated by a higher phosphorus availability in earthworm casts (1386 +/- 38 mg 13 kg(-1) of dry matter in cast versus 778 +/- 61 mg P kg(-1) of dry matter in the soil compartment not influenced by earthworm activity), and a better plant phosphorus nutrition in the presence of earthworms. Phosphorus uptake resulted in a better plant nutrition and a better tolerance to plant-feeding nematodes. Besides, the reduction of the mesobiotic porosity by bioturbation could also have disturbed the nematodes activities during their soil phase and contributed to the reduction of their damage

Agroecological transition : a viability model to assess soil restoration

Since the 1950s, intensive and specialized agricultural systems using a few select species and relying heavily on agrochemical inputs have enabled a huge increase in food production. However, in parallel, drawbacks appeared including biodiversity loss, greenhouse gas emission, erosion, and water pollution. Today shifting farming systems to mitigate soil degradation trends is indispensable. Using viability theory, we propose a dynamic model of the sequence of agricultural productions and practices that can be implemented in the long term to restore soil quality while respecting a set of agronomic and economic constraints. The paths to soil restoration vary depending on agronomic and economic constraints, the time available for restoration, the initial soil conditions, and investment capacities. Economic valuation of the minimum cost of restoration shows that the agroecological transition may be costly and that farmers can have difficulty meeting the costs, thus raising the question of how the cost of agroecological transition is to be shared. Recommendations for Resource Managers The mathematical viability theory is used to design a new model of farm management to assess possibilities and cost of the agroecological transition more precisely the successive choices of crops and agricultural practices intended to restore topsoil quality. This discrete dynamical model has an irregular time step corresponding to agricultural cycles and to dates of parcel release retrieved by using an inverse approach. The agronomic and economic constraints are mixed depending both on states and controls. The economic constraints are imposed on a monthly time step while states and controls variables evolve with the agricultural cycles what best fit the economic situation farmers must face. The trajectory selection criteria is the minimum cost of restoration. Optimal viable strategies depend on initial soil quality and available capital, time of exercise, constraints, and of crops and practices diversification. Computations were made with a software specially developed for this study using data sets collected in the French West Indies

Mixing plant species in cropping systems: concepts, tools and models. A review

Correspondance: [email protected] audienceThe 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

Innovations agro-écologiques et organisationnelles pour une gestion durable de la qualité de l'eau dans des régions de monoculture à forts niveaux d'intrants phytosanitaires. Rapport final du Projet n°ANR-05-PADD-010

La question de la qualité des eaux est devenue aiguë dans certains bassins versants occupés en majorité par des systèmes de culture basés sur un recours fréquent aux pesticides. C'est le cas des bassins bananiers aux Antilles et viticoles en Languedoc pour lesquels il faut concevoir des alternatives plus favorables au développement durable des régions concernées. Plusieurs changements de pratiques agricoles sont envisageables. Les modalités de leur mise en oeuvre dans l'espace d'un bassin versant et par des exploitations agricoles diverses, et de la prise en charge collective du changement par des interventions publiques ou privées restent à définir. L'objectif du projet GeDuQuE était d'identifier et d'assembler des innovations techniques et organisationnelles, et de réaliser une évaluation intégrée par simulation de leur contribution au développement durable

Innovations agro-écologiques et organisationnelles pour une gestion durable de la qualité de l'eau dans des régions de monoculture à forts niveaux d'intrants phytosanitaires. Rapport final du Projet n°ANR-05-PADD-010

La question de la qualité des eaux est devenue aiguë dans certains bassins versants occupés en majorité par des systèmes de culture basés sur un recours fréquent aux pesticides. C'est le cas des bassins bananiers aux Antilles et viticoles en Languedoc pour lesquels il faut concevoir des alternatives plus favorables au développement durable des régions concernées. Plusieurs changements de pratiques agricoles sont envisageables. Les modalités de leur mise en oeuvre dans l'espace d'un bassin versant et par des exploitations agricoles diverses, et de la prise en charge collective du changement par des interventions publiques ou privées restent à définir. L'objectif du projet GeDuQuE était d'identifier et d'assembler des innovations techniques et organisationnelles, et de réaliser une évaluation intégrée par simulation de leur contribution au développement durable