Nitrogen fertilization strategy for Swiss winter wheat under climate-induced rainfall reduction: A model-based assessment

Reduced rainfall and nitrogen (N) use in warm-summer humid continental climates may lower wheat yields. Our study employs the DSSAT-Nwheat process-based crop simulation model to quantify the effects of N input and rainfall on various phenological stages of the Swiss wheat genotype CH Nara, calibrated and evaluated using field data from 2018 to 2022. Simulations over 42 years (1981–2022) across five different Cambisols used historical daily weather data to test rainfall reductions from 20 % to 100 % during three critical periods (30 days before anthesis, 30 days after anthesis, and ±30 days around anthesis) as well as throughout the entire season. Nitrogen fertilizer treatments ranged from zero to 140 kg N ha⁻¹. The model accurately simulated yields with an RMSE of 895.5 kg ha⁻¹ during calibration and 1091.4 kg ha⁻¹ during validation. Results showed that yields were not adversely affected by rainfall reductions up to 40 %, regardless of N levels or timing. However, yields significantly declined when reductions exceeded 60 %, especially with N applications above 100 kg ha⁻¹. Optimal yields were noted at 140 kg N ha⁻¹, but benefits decreased under scenarios of reduced rainfall, indicating that N recommendations may need to be lowered in response to projected rainfall reductions. This study provides quantitative guidance for adapting wheat fertilization strategies to maintain productivity while accounting for future rainfall variability.