Modelling Faba bean production in northern Europe: Model calibration and evaluation

Crop models are widely used to evaluate how management practices influence biomass production, yield, grain quality (e.g., protein and nitrogen concentration), and environmental outcomes such as soil nitrogen balance. Grain legumes such as faba bean are of increasing interest in European cropping systems due to their high protein value and ability to fix atmospheric nitrogen, yet the yields and environmental effects remain uncertain under northern European conditions. APSIM Next Generation is widely used globally but lacks a dedicated model for faba bean. This study aimed to fill this gap by adapting APSIM's soybean model to simulate faba bean growth, phenology, grain and biomass yield, enabling its application in faba bean management and impact assessments. The Soybean model within APSIM Next Generation was adapted by adjusting crop-specific parameters. Phenology calibration used field data from three sites in Denmark (2016–2018), while model evaluation employed long-term trials from northern Germany (2012−2022). Nitrogen and grain yield calibrations incorporated additional data from Denmark and Germany (2006–2008, 2015–2018). The adapted model accurately predicted phenological stages, with R 2 values of 0.84 for maturity and 0.97 for flowering dates. Simulated grain yields in northern Germany (2017–2022) fell within expected ranges but were slightly overestimated, with an RMSE of 1.7 t ha −1 . However, the correlation between simulated and observed yields was low (R 2 = 0.1), reflecting faba bean's sensitivity to unfavorable weather during flowering. Predictions for aboveground biomass and grain nitrogen were less accurate (R 2 < 0.07), indicating areas requiring further calibration. The adapted APSIM model shows promising performance in simulating faba bean phenology and yield levels, though refinement is necessary, particularly for biomass and grain nitrogen predictions. Despite current limitations, the adapted APSIM model offers a promising tool for exploring management strategies to enhance faba bean productivity and reduce environmental impacts under diverse growing conditions. • Growing degree days were used to calibrate faba bean phenology. • APSIM Next Generation simulated phenology and grain yield. • Model evaluation used field data from northern Europe conditions. • Phenological progression was accurately simulated. • Grain yield was systematically overestimated across locations.