Evaluation of a simple approach for crop evapotranspiration partitioning and analysis of the water budget distribution for several crop species

International audienceClimate variability and climate change induce important intra- and inter-annual variability of precipitation that significantly alters the hydrologic cycle. The surface water budgets and the plant or ecosystem water use efficiency (WUE) are in turn modified. Obtaining greater insight into how climatic variability and agricultural practices affect water budgets and regarding their components in croplands is, thus, important for adapting crop management and limiting water losses. Therefore, the principal objectives of this study are: (1) to assess the contribution of different components to the agro-ecosystem water budget and (2) to evaluate how agricultural practices and climate modify the components of the surface water budget. To achieve these goals, we tested a new method for partitioning evapotranspiration (ETR), measured by means of an eddy-covariance method, into soil evaporation (E) and plant transpiration (TR) based on marginal distribution sampling (MDS). The partitioning method proposed requires continuous flux recording and measurements of soil temperature and humidity close to the surface, global radiation above the canopy and assessment of leaf area index dynamics. This method is well suited for crops because it requires a dataset including long bare-soil periods alternating with vegetated periods for accurate partitioning estimation. We compared these estimations with calibrated simulations of the ICARE-SVAT double source mechanistic model. The results showed good agreement between the two partitioning methods, demonstrating that MDS is a convenient, simple and robust tool for estimating E with reasonable associated uncertainties. During the growing season, the proportion of E in ETR was approximately one-third and varied mainly with crop leaf area. When calculated on an annual time scale, the proportion of E in ETR reached more than 50%, depending on the crop leaf area and on the duration and distribution of bare soil within the year

Modelling airbone concentration and deposition rate of maize pollen

International audienc

Etude de la dispersion atmosphérique du pollen de maïs (contribution à la maîtrise des risques de pollinisation croisée)

PARIS-AgroParisTech Centre Paris (751052302) / SudocSudocFranceF

Modelling airborne concentration and deposition rate of maize pollen

International audienceThe introduction of genetically modified (GM) crops has reinforced the need to quantify gene flow from crop to crop. This requires predictive tools which take into account meteorological conditions, canopy structure as well as pollen aerodynamic characteristics. A Lagrangian Stochastic (LS) model, called SMOP-2D (Stochastic Mechanistic model for Pollen dispersion and deposition in 2 Dimensions), is presented. It simulates wind dispersion of pollen by calculating individual pollen trajectories from their emission to their deposition. SMOP-2D was validated using two field experiments where airborne concentration and deposition rate of pollen were measured within and downwind from different sized maize (Zea mays) plots together with micrometeorological measurements. SMOP-2D correctly simulated the shapes of the concentration profiles but generally underestimated the deposition rates in the first 10 m downwind from the source. Potential explanations of this discrepancy are discussed. Incorrect parameterisation of turbulence in the transition from the crop to the surroundings is probably the most likely reason. This demonstrates that LS models for particle transfer need to be coupled with air-flow models under complex terrain conditions

Variations in maize pollen emission and deposition in relation to microclimate

International audienc

Exchange of CO2 and water fluxes at two levels in a maritime pine forest

International audienc

Simultaneous measurements of carbon dioxide, water and energy exchange above four different ecosystems

International audienceOver the last decades many studies have been performed to determine mass and energy budgets of forests, croplands and grasslands. However, most measurements have been made in different geographical regions and at different periods of time. As the results depend on the meteorological conditions and vary in time it is difficult to intercompare them directly and evaluate the relative contribution of each ecosystem to global water and carbon exchanges. Therefore, there is a need to measure fluxes over different types of ecosystem during a given period of time, in a given region with similar meteorological conditions. In the present study we report flux data, as performed above four different canopies submitted to the same climate forcing. As a contribution to the Regional Experiment component of the CarboEurope-IP project, the carbon and energy budgets of four typical ecosystems of Les Landes region in South West of France, a forest clear-cut, a mature forest, a vineyard and an irrigated maize crop, were measured during an entire growing season, from 17 May to 12 October 2005. The energy balance closure is fairly good at all sites. CO 2 flux measurements show that the maize crop before irrigation and the clear-cut behave as sources of CO 2, whereas the vineyard and the mature forest act as sinks. However the maize crop becomes a substantial sink of CO 2 after the start of irrigation and canopy growth, with fluxes three times as large as for the 35- year old forest. Evapotranspiration is largest over the irrigated maize and lowest over the clear-cut, while the vineyard and the mature forest exhibit similar water fluxes. The data collected provides a good basis for a comparative study of the main ecosystems of the region, and for upscaling fluxes at the regional level, in conjunction with all other measurements performed during the 2005 CERES experiment

Simultaneous measurements of carbon dioxide, water and energy exchange above four different ecosystems

International audienceOver the last decades many studies have been performed to determine mass and energy budgets of forests, croplands and grasslands. However, most measurements have been made in different geographical regions and at different periods of time. As the results depend on the meteorological conditions and vary in time it is difficult to intercompare them directly and evaluate the relative contribution of each ecosystem to global water and carbon exchanges. Therefore, there is a need to measure fluxes over different types of ecosystem during a given period of time, in a given region with similar meteorological conditions. In the present study we report flux data, as performed above four different canopies submitted to the same climate forcing. As a contribution to the Regional Experiment component of the CarboEurope-IP project, the carbon and energy budgets of four typical ecosystems of Les Landes region in South West of France, a forest clear-cut, a mature forest, a vineyard and an irrigated maize crop, were measured during an entire growing season, from 17 May to 12 October 2005. The energy balance closure is fairly good at all sites. CO 2 flux measurements show that the maize crop before irrigation and the clear-cut behave as sources of CO 2, whereas the vineyard and the mature forest act as sinks. However the maize crop becomes a substantial sink of CO 2 after the start of irrigation and canopy growth, with fluxes three times as large as for the 35- year old forest. Evapotranspiration is largest over the irrigated maize and lowest over the clear-cut, while the vineyard and the mature forest exhibit similar water fluxes. The data collected provides a good basis for a comparative study of the main ecosystems of the region, and for upscaling fluxes at the regional level, in conjunction with all other measurements performed during the 2005 CERES experiment

Mesures simultanées des échanges de dioxyde de carbone, d’eau et d’énergie au-dessus de différents écosystèmes caractérisant la région des Landes

National audienc