Recommendations
The current model framework is freely available and can therefore in principle be used by anyone for new policy questions or impact studies. However, it is still necessary to have basic knowledge of programming in order to easily use the tools available on Github. Some knowledge of soil-plant interactions and crop modeling is also needed to correctly assess the current shortcomings. In order to give governments or farmers the opportunity to work with this tool themselves, a translation is still needed to the needs and background of these end users. Before this translation can take place, it is advisable to work on a number of shortcomings in the model itself and its input in the short term.
The model framework with SWAP-WOFOST and open data layers for Flanders demonstrated to be good enough to simulate crop yield even with limited input data and model simplifications. However, there is certainly room for improvement, especially with regard to sugar beet simulations.
The yield database contains valuable but limited data, mostly from variety trials located in West- and East-Flanders. Usually no data is available on groundwater levels. It is necessary to include existing yield data from trials throughout Flanders in the database, preferably through structured collaboration with all trial centers. In addition, targeted field experiments under different known hydrological conditions would be welcome. Measurements of soil and crop growth would have to take place there, with special attention to drought and oxygen stress for the most important crops in Flanders. In this way, the crop parameters can be updated to recent varieties under Flemish conditions, and site-specific management data and environmental factors can be used for model validation, where significant improvements in the simulations can be expected.
Models are only a representation of reality, and input data and parameters also inherently have uncertainty. Only old soil properties derived from the Aardewerk database and the Belgian soil map were available at regional scale. The maximum rooting depth allowed by the soil was approximated based on clay content and calculated bulk density. In reality, soil compaction might affect rooting depth in agricultural fields. It would be appropiate to revise the rooting depth for each soil type and include soil compaction when available. A project is currently being financed by the Environment Department of the Flemish government, namely “Inschatting van de vochtretentiecapaciteit van bodems op basis van bodem- en landgebruikskenmerken”, which was awarded to Antea Belgium, Ghent University and the Soil Service of Belgium, which will be ready in February 2025. The aim of this project is to determine current pedotransfer functions for soil moisture characteristics for Flanders through easily measurable soil parameters. This information will be very valuable to improve the current soil parameters in the model.
The characterization of the seasonal groundwater level fluctuations was based on a simple sinus function and maps of the average highest groundwater level (GHG) and average lowest groundwater level (GLG). These fluctuations can be also estimated from the drainage classes presented on the Belgian soil map, but they are already outdated and therefore less reliable. A project is currently underway, financed by the Environment Department of the Flemish government and carried out by, among others, Antea group, namely “Update drainageklassen van de bodemkaart”. This project should provide an updated map of groundwater tables and drainage classes that can also be used as input for the model in this project. In addition, there is a need for a regional groundwater model that describes phreatic groundwater dynamics, which is crucial to predict its impact on the growth of arable crops. The ongoing research project TURQUOISE, financed by FWO SBO, may be able to take its first steps here.
Increasing the resilience to the effects of climate change through restoration/remediation of drained wetlands to promote infiltration and water storage is a major goal in Flanders. Farmers and policy-makers would need to adapt to the impacts of excessive soil water in agricultural areas close to restored wetlands, so nature reserves and (adapted) agriculture can coexist. The case study at De Zegge-Mosselgoren is a good example of how these two land uses influence each other and how conflicts can arise. The developed model instruments can now be used with local data and by including all relevant factors (agricultural practices, specific water management, …). Future research in these types of areas can then estimate the consequences of specific rewetting scenarios for agricultural plots. However, it would also be good to conduct a number of pilot studies in which the impact is also monitored in reality, so that the model can be further validated and systematically improved.