Nicolas Beaudoin

Simulation of Biomass and Nitrogen Dynamics in Perennial Organs and Shoots of Miscanthus × Giganteus Using the STICS Model

Biomass production by perennial plants promises to increase land use efficiency and reduce greenhouse gas emissions from cropping systems dedicated to bioenergy production. The modelling of both biomass production and the environmental impacts of these systems over the long term is needed in order to evaluate their sustainability. New equations have been added to the STICS soil-crop-atmosphere model to provide a better description of perennial organs and their relationship with non-perennial ones, corresponding to the rhizomes and shoots, respectively in the Miscanthus × giganteus case study. Their description is intended to be generic for perennial plants, supported by the functional approach of STICS. The new version of STICS 8 was calibrated using published data and then validated against independent data. It was able to simulate the biomass and nitrogen content of the shoots (with a model efficiency of 0.95 and 0.70, respectively) and reproduce the dynamic of biomass and nitrogen in perennial organs (with a model efficiency of 0.41 and 0.63, respectively). Some of the model’s improvements are discussed. Modifications to the model allowed simulations of the effect of cultural practices, such as nitrogen fertilisation or harvest date, on the biomass and nitrogen content of rhizomes and shoots.

Conversion of a Conventional to an Organic Mixed Dairy Farming System: Consequences in Terms of N Fluxes

Organic farming practices are a possible way to reconcile agricultural production and water quality, but the comparative merits of conventional and organic farming practices regarding the nitrogen (N) issue are complex and still being debated. This study was designed to investigate the choices governing conversion to organic farming of an experimental mixed dairy farm in Lorraine (eastern France) and to highlight the associated changes in N fluxes. The study was conducted over a suitably long period of time at a farm scale integrating the diversity of practices in one conventional and then two autonomous organic systems (a grazing livestock system and a mixed dairy system). Two indicators were used to draw up the main features. First, the farm-gate N budgets show that the organic farm has a balance twice as low as the conventional system. Second, the soil surface balance exhibited substantial differences between functional zones. Finally, this study shows that an accurate estimation of soil surface balance requires taking into account the spatial distribution within the farm area based on practices and their rationale.

Main Lessons Drawn from the Simulation Study

The study of the literature relative to the impact of cover crops on nitrate leaching, and hence their primary role as “nitrate-trapping” catch crops in annual cropping systems, reveals a lack of data relating to certain regions in France. The same is true concerning their impact on other variables, such as the water balance or the yield of the next crop. However, since the planting of cover crops has become compulsory in all vulnerable zones since 2012, it is of the utmost importance to assess how effective they are in terms of reducing the nitrate concentration of drainage water, as a function of the soil and climate context in a broad range of French conditions. By doing so, it will be possible to optimize the associated management technique and identify situations in which their use may have negative consequences on the next crop and, potentially, on groundwater recharge.

Main Lessons Drawn from the Analysis of the Literature

Planting and destruction are the two main phases in cover crop management techniques. Their dates and implementation conditions play a key role in terms of the various functions targeted for these crops (nitrate-trapping, erosion prevention, weed control, effect on next crop, etc.). The analysis of the literature therefore focused on cover crop planting and destruction techniques. The aim was to identify the different methods and, if possible, their effectiveness with respect to the success of sowing and destruction. The issue of the implementation of these techniques by farmers was then examined by analysing the constraints in terms of organization of labour and implementation costs.