Due to the adverse effect of global climate change on agricultural water management, maintaining soil moisture in the root zone is essential for optimal crop productivity. For effective irrigation, we used organic mulching to increase the yield and water productivity (WP) of Valencia orange in arid/desert climates. Here, the effect of rice straw mulching and irrigation rates [100, 85, and 70% of evapotranspiration reference (ETc)] on nutrient contents, quality, and yield of orange trees was evaluated. Under field conditions, the application of straw mulch significantly increased the concentration of some essential elements and photosynthetic pigments but reduced proline contents in orange leaves. Soil mulching significantly increased fruit and inflorescence retention, and resulted in a higher number and weight of fruit on branches, without compromising their taste or texture, compared to the treatment without mulching. Both irrigation and mulching also affected crop productivity and water use efficiency (WUE). This was evident when yield/fed increased by 22.7–23.8, 20.7–31.5, and 6.2–16.9% under mulching at 100, 85, and 70% ETc, respectively, compared to traditional conditions at 100% ETc without mulch. Although the maximum WUE under rice straw mulch was 5.72–5.84 kg/m3 at 70% ETc, it was 5.31–5.40, and 4.57–4.64 kg/m3 at 85, and 100% ETc, respectively. Organic mulching showed superior results with respect to increasing yields and WP, while saving 15.4% water and comparable benefit/cost with the traditional irrigation when orange trees were irrigated with 85% ETc. Together, this study could be a promising strategy for climate change adaptation and sustainable water management.