Modeling and Biochar Soil Amendments to Optimize Water-Use Efficiency and Yield in Arid Valencia Orange Orchards

This study explores the sustainable optimization of Valencia orange production in Egypt's arid regions by analyzing the dual effects of deficit irrigation and biochar soil conditioning. Multi-season field experiments demonstrated that Partial Root-zone Drying (PRD) combined with 1200 kg ha⁻¹ of biochar significantly enhances the vegetative growth, physiological traits, and final yield components of Valencia orange trees in degraded sandy soils. Severe water restriction (50% Full Irrigation [FI]) constrained canopy development and chlorophyll formation. In contrast, the PRD strategy produced superior growth responses, achieving an increased canopy volume of 4.1–4.3%, an expanded leaf area of 27.0–28.3 cm², and total chlorophyll levels up to 3.0 mg g⁻¹ F.W. The application of biochar showed a significant, dose-dependent improvement in soil water-holding capacity and nutrient retention. Under the optimal interaction treatment (PRD combined with 1200 kg ha⁻¹ biochar), the trees achieved peak agronomic performance. This synergistic combination maximized canopy volume increase to 5.5–5.8%, expanded leaf area to 37.9–40.1 cm², and elevated chlorophyll content to 3.7–4.0 mg g⁻¹ F.W. Furthermore, this treatment upgraded fruit development and quality indices; fruit weight reached 231.4–240.6 g, total yield peaked at 48.5–50 ton ha⁻¹, TSS reached 13.7–14.2%, and Vitamin C maximized at 48.8–51.3 mg 100 mL⁻¹ juice, confirming that biochar effectively mitigates drought stress. Complementing these findings, the treatments were simulated using the SALTMED model software to evaluate its predictive fidelity under local Egyptian conditions. The software demonstrated exceptional accuracy, establishing a robust correlation between field-collected data and model-generated values. This alignment was statistically validated by an outstanding coefficient of determination (R² ranging from 96% to 98%). Consequently, the study strongly recommends utilizing SALTMED for managing fruit crops in Egypt to save time, labor, and costs, while providing reliable predictive data to optimize export and import operations for vital commodities like citrus.