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Pradel M.,UR TSCF | Pacaud T.,UR TSCF | Cariolle M.,Institute Technique Of La Betterave
Waste and Biomass Valorization | Year: 2013

Organic waste land application generates nitrogenous emissions that have impacts on acidification, eutrophication and global warming. To assess these impacts with Life Cycle Assessment, emission factors are commonly used without taking into account neither the type and performance of land application techniques nor the type of organic waste applied. This paper proposes a methodological framework to assess the nitrogenous emissions by coupling technological performances of spreader and biophysical models, focusing on sewage sludge spreading in different weather and soil conditions. The first step consists of creating several spreading scenarios by combining a cropping system and a "spreader/sewage sludge" couple. The second step consists of testing the technological spreader performances regarding spatial distribution, application rate and soil compaction with a spreading simulator and the COMPSOIL model. Nitrogenous emissions are then simulated with STICS and DEAC models for different application rates and soil bulk densities. Finally, the simulated nitrogen losses from the models are linked with the real amounts of sewage sludge applied and the compacted soil due to spreader performances. Our approach shows that ammonia emissions during sewage sludge spreading can be directly linked to the spreader performances whereas nitrate leaching depends more on the soil and on the weather conditions. Nitrous oxide emissions mostly depend on the spreader weight and to the soil and the weather conditions. This method paves the way to new approaches: integrating technological performances of machines into biophysical and agricultural models in order to assess environmental impacts of agricultural practices. © Springer Science+Business Media B.V. 2012.


Baey C.,École Centrale Paris | Didier A.,Institute Technique Of La Betterave | Lemaire S.,Institute Technique Of La Betterave | Maupas F.,Institute Technique Of La Betterave | Cournede P.-H.,École Centrale Paris
Ecological Modelling | Year: 2013

A wide range of models have been proposed and developed for modelling sugar beet growth, each of them with different degrees of complexity and modelling assumptions. Many of them are used to predict crop production or yield, even when they were not originally designed for this purpose, and even though their predictive capacity has never been properly evaluated. In this study, we propose the evaluation and comparison of five plant growth models that rely on a similar energetic concept for the production of biomass, but with different levels of description (individual-based or per square meter) and different ways to describe biomass repartition (empirical or via allocation): Greenlab, LNAS, CERES, PILOTE and STICS. The models were all programmed on the same modelling platform, calibrated on a first set of data, and then their predictive capacities were assessed on an independent data set. First, a sensitivity analysis was carried out on each model to identify a subset of parameters to be estimated, to reduce the variability of the models. We were able to reduce the number of parameters from 10 to 4 for Greenlab, and from 16 to 1 for STICS. Three criteria were then used to compare the predictive capacities of the models: the root mean squared error of prediction and the modelling efficiency for the total dry matter production and the dry matter of root, and the yield prediction error. All the models provided good overall predictions, with high values of the modelling efficiency. The use of sensitivity analysis allowed us to reduce the variability of the models and to enhance their predictive capacities. Models based on an empirical harvest index gave good yield predictions, and similar results compared to allocation models for the total dry matter, but the harvest index might not be very robust. The crucial role of initiation was also pointed out, as well as the need for an accurate estimation and modelling of this early phase of growth. © 2013 Elsevier B.V. All rights reserved.


Baey C.,École Centrale Paris | Didier A.,Institute Technique Of La Betterave | Lemaire S.,Institute Technique Of La Betterave | Maupas F.,Institute Technique Of La Betterave | Cournede P.-H.,École Centrale Paris
Ecological Modelling | Year: 2013

Modelling the interindividual variability in plant populations is a key issue to enhance the predictive capacity of plant growth models at the field scale. In the case of sugar beet, this variability is well illustrated by rate of leaf appearance, or by its inverse the phyllochron. Indeed, if the mean phyllochron remains stable among seasons, there is a strong variability between individuals, which is not taken into account when using models based only on mean population values. In this paper, we proposed a nonlinear mixed model to assess the variability of the dynamics of leaf appearance in sugar beet crops. As two linear phases can be observed in the development of new leaves, we used a piecewise-linear mixed model. Four parameters were considered: thermal time of initiation, rate of leaf appearance in the first phase, rupture thermal time, and difference in leaf appearance rates between the two phases. The mean population values as well as the interindividual variabilities (IIV) of the parameters were estimated by the model for a standard population of sugar beet, and we showed that the IIV of the four parameters were significant. Also, the rupture thermal time was found to be non significantly correlated to the other three parameters. We compared our piecewise-linear formulation with other formulations such as sigmoïd or Gompertz models, but they provided higher AIC and BIC.A method to assess the effects of environmental factors on model parameters was also studied and applied to the comparison of three levels of Nitrogen (control, standard and high dose). Taking into account the IIV, our model showed that plants receiving Nitrogen tended to have a later time of initiation, a higher rate of leaf appearance, and an earlier rupture time, but these differences were not dose-dependent (no differences between standard and high dose of Nitrogen). No differences were found on the leaf appearance rate of the second phase between the three treatments. © 2013 Elsevier B.V.

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