SuMoToRI model simulations for optimizing sulphur fertilization in oilseed rape in the context of increased spring temperatures

For the last few decades, environmental policies have led to drastic reduction in sulphur (S)-containing industrial emissions leading to reduced S inputs into the soil. This is of concern for oilseed rape (Brassica napus L.), which like most Brassica species is a high S-demanding crop. In this context, monitoring S fertilization has become a central issue. Moreover, ongoing and projected climate change will affect crop yield and quality worldwide, thus justifying the prediction of climate effects via modelling approaches so that crop management and practices can be adjusted. In this modelling study, the growth and S status of winter oilseed rape (WOSR) were investigated from the end of winter until the onset of pod formation under contrasting S supplies in a range of climatic conditions acquired for seven major WOSR-producing northern countries and under the four Representative Concentration Pathway (RCP) scenarios (i.e. RCP2.6, RCP4.5, RCP6.0, and RCP8.5). Simulations were performed with the process-based model SuMoToRI (Sulphur Model Towards Rapeseed Improvement) for past datasets (1948-2005) and projections (2015-2099). Simulation results indicated decreased plant biomass (mainly leaves) as temperatures increased (as expected under the increasingly negative scenarios as the century progresses) and as daily incident radiation decreased in contrast to the mobile S of leaves (mainly sulphate), which tended to accumulate as a consequence of reduced S sink (i.e. leaves) size. These simulations highlighted the increased risks of S over-fertilization, which can lead to environmental issues that mainly comprise S leaching due to high mobile-S in leaves that senesce. Overall, this in silico study raises questions about the most suitable S fertilization strategies and associated farming practices for dealing with the expected adverse climatic conditions.