Introduction Wheat (Triticum aestivum L.) serves as Iran's most strategic crop for food security, yet its production in arid regions faces severe constraints from limited water resources and erratic rainfall patterns. Dryland farming systems in khuzestan province experience significant yield gaps due to moisture stress during critical growth stages. While supplemental irrigation offers potential relief, its effectiveness depends fundamentally on concurrent nutrient management. This study investigated the integrated effects of supplemental irrigation and soil test-based optimal nutrition on yield, water use efficiency, and economic viability of dryland wheat in Baghmalek County, Khuzestan province.
Materials and Methods A field experiment was conducted during the 2023-2024 growing season in Baghmalek County, Khuzestan (Coordinates: 32°49' N, 49°50' E, 827 m altitude). The soil at the experimental site had a pH of 7.79, EC of 1.57 dS m⁻¹, 0.84% organic carbon, 7.54 mg kg⁻¹ available P, and 138 mg kg⁻¹ available K. The experiment followed a randomized complete block design with three treatments and three replications, using plots of 50 m² (10m × 5m). The wheat cultivar 'Dehdasht' was sown at a rate of 200 kg ha⁻¹ with 13 cm row spacing. Treatments included: 1) Farmer's conventional practice (rainfed, control); 2) Farmer's conventional practice + combined package of supplemental irrigation and improved nitrogen management; and 3) Soil test-based optimal nutrition + supplemental irrigation. In treatments with supplemental irrigation (T2 and T3), nitrogen fertilizer was split-applied to enhance use efficiency, as top-dressing without adequate moisture is ineffective under rainfed conditions. This approach aligns with the recommendations of the Dryland Agricultural Research Institute of Iran. The optimal nutrition treatment involved: basal application of 100 kg ha⁻¹ ammonium phosphate and 100 kg ha⁻¹ potassium sulfate based on soil test, seed priming with humic acid and zinc (1.5 L per 100 kg seed), 120 kg ha⁻¹ urea at first irrigation, foliar application of amino acids and seaweed extract at tillering, foliar application of potassium silicate at stem elongation, and 80 kg ha⁻¹ urea at second irrigation. Supplemental irrigation consisted of two events: 50 mm (2,500 L per plot) at planting and 30 mm (1,500 L per plot) at the booting stage. All other agronomic practices were uniform. At maturity, yield components (spikes m⁻², grains per spike, thousand kernel weight), biological yield, and grain yield were measured. Water use efficiency (WUE) was calculated using both total seasonal rainfall and effective rainfall (estimated using a reliable rainfall method). Economic analysis was performed using partial budgeting with wheat priced at 20,500 Tomans kg⁻¹. Data were analyzed using SPSS software with Duncan's test at p≤0.05.
Results and Discussion The results revealed that the integrated treatment (optimal nutrition + supplemental irrigation) significantly outperformed the others. It achieved the highest grain yield at 4368 kg ha⁻¹, representing a 47% increase over the control (2962 kg ha⁻¹). This treatment also recorded the highest thousand kernel weight (44.65 g), a 21% increase over the control. Notably, while the combined package of supplemental irrigation and improved nitrogen management (T2) significantly increased the number of spikes per unit area (231 spikes m⁻² compared to 165 in the control), it failed to significantly boost grain yield (3660 kg ha⁻¹) or thousand kernel weight. It should be noted that the observed yield increase in T2 is attributable not solely to supplemental irrigation, but also to the split application of nitrogen—a component inherently enabled by water availability in this treatment. This demonstrates that the conjunctive use of water and nitrogen, without balanced nutrition, cannot effectively translate vegetative growth into grain yield. The synergy between water and all essential nutrients was crucial. WUE calculations based on effective rainfall plus irrigation showed the integrated treatment reached 1.54 kg m⁻³, the highest among all treatments. Economic analysis using the partial budgeting method demonstrated a superior benefit-to-cost ratio of 1.36 for the integrated management, confirming it as the most profitable option for farmers. The study confirms that while the combined use of water and nitrogen primarily influences yield component establishment (spike number) a soil test-based comprehensive optimal nutrition program is essential for grain filling and final yield realization.
Conclusion This study conclusively demonstrates that a targeted, integrated approach combining supplemental irrigation with a balanced, soil test-based nutrition program is essential for unlocking the yield potential of dryland wheat in arid regions. The synergy between water and nutrients not only achieves substantial yield gains (47% increase) but also enhances the efficiency of water use and provides strong economic justification (benefit-to-cost ratio of 1.36). This integrated crop management strategy offers a viable pathway toward sustainable intensification, ensuring greater productivity and resilience in rainfed farming systems of Khuzestan and similar agro-ecologies.