Process-based assessment of wheat yield gap in Mediterranean rainfed conditions: Cultivar, nutrient, and sowing optimization

Wheat production in Morocco remains constrained by persistent yield gaps arising from climatic variability, soil fertility decline, and suboptimal farm management. This study aimed to quantify attainable and actual yields of bread wheat ( Triticum aestivum L. ) and to identify management pathways for reducing these gaps under rainfed conditions in Morocco. The Environmental Policy Integrated Climate (EPIC) model was calibrated and validated for five representative cultivars across major rainfed agroecological zones using multi-season field observations. Model evaluation showed high predictive accuracy for grain yield (R² = 0.87, RMSE = 0.25 t/ha, NRMSE = 12.5 %), above-ground biomass (R² = 0.93, RMSE = 1.2 t/ha, NRMSE = 8.7 %), and leaf area index (R² = 0.81, RMSE = 0.73, NRMSE = 15.2 %). Simulated potential yield ( Y p ) averaged 5.4 t/ha, of which 66 % was attainable under water-limited rainfed conditions ( Y w = 3.6 t/ha) and 48 % was realized as observed farmer yield ( Y a = 2.6 t/ha), resulting in an exploitable yield gap of approximately 52 % (2.8 t/ha). Scenario analysis indicated yield gains of 25–35 % from improved nitrogen use and 30–40 % from supplemental irrigation, while integrated management closed 40–65 % of the exploitable gap and raised mean yields to 3.8–4.2 t/ha. Across management strategies, intermediate-input scenarios delivered strong economic performance, achieving marginal rate of return values of 257–433 % with modest additional costs (266–1389 MAD/ha). These findings demonstrate that targeted integration of water and nutrient management can substantially enhance wheat productivity and resilience, offering a practical framework for advancing sustainable intensification and national food self-sufficiency. • EPIC was calibrated and validated for five Moroccan bread-wheat cultivars. • Farmers achieve only 48 % of potential wheat yield under current practices. • Early sowing proved a low-cost strategy to raise yields and reduce variability. • Moderate irrigation and balanced fertilization maximized economic returns.