Optimizing maize irrigation and fertilization management with APSIM Next Generation for current and future climate scenarios under semi-arid conditions in Morocco

Abstract

Rising food demand and intensifying climate stresses are putting growing pressure on African cereal systems. In Morocco, maize is a staple crop for smallholder farmers, yet it remains highly vulnerable to rainfall variability and water scarcity. To address these challenges, model-guided adaptation practices offer a promising pathway to enhance the resilience and sustainability of maize production under future climate conditions. The APSIM Next Generation model was calibrated and validated for irrigated maize in the Souss-Massa region in Morocco using data from three growing seasons (2022–2024), under varying levels of deficit irrigation and nitrogen supply. Adaptation strategies were then evaluated under different planting dates using multi-model climate projections. The model showed good accuracy in both calibration and validation for simulating maize phenology (R2 up to 0.91; RMSE = 0.5–1.1 days), leaf area index (R2 = 0.96/0.89; RMSE = 0.32/0.49), soil water content (R2 = 0.95/0.89; RMSE = 4.70/8.33 mm), and above-ground biomass (R2 = 0.97/0.95; RMSE = 1.25/1.01 t ha-1). Nitrogen dynamics were reasonably reproduced, showing moderate accuracy for soil nitrogen and high precision for nitrogen uptake. Under full irrigation and nitrogen supply, biomass declines by 2–6% by mid-century and 9–15% by late century, reaching 30% losses under severe resource limitation. Seasonal irrigation inputs increase by about 3–8% by mid-century and 9–25% by late century across scenarios, with peaks shifting later into hotter months. Early planting shifts irrigation demand into cooler periods and increases final biomass by 6%, with maximum gains observed under 75% ETc and nitrogen application. Variance decomposition reveals a shift from management-driven variance (sowing date and N-fertilizer 30% at baseline) to rainfall dominance by mid-century (SSP2-4.5) and temperature dominance by late century (SSP5-8.5 > 50%), with increasing higher‑order interactions. Biomass production‑risk analysis shows that full N with ≥75% ETc maintains high final above-ground biomass (75% probability at baseline; 50% under SSP2‑4.5 late‑century; 39% under SSP5‑8.5 late‑century), while early sowing provides a modest, diminishing buffer by late century as heat and drought intensify. (+2–20 percentage points). Adequate nitrogen supply, moderate irrigation, and earlier sowing are recommended to sustain final biomass in the near term, while heat-tolerant varieties are required for long-term silage maize production in the Souss-Massa region.