Estimation of Actual Water Requirements and Water Productivity of Date Palm (Phoenix dactylifera L.) cv. Barhi under the Conditions of Southern Iraq

Date palms (Phoenix dactylifera L.) struggle in arid places due to water scarcity and rising demand. Therefore, water consumption needs to be optimized economically to support sustainable practices. The bubbler irrigation method was applied in the southern part of Basrah Governorate (Abu Al-Khasib District) to assess water productivity and estimate the irrigation water requirements of Barhi date palms. Four irrigation levels were applied in this study, defined as follows: T1 (45% of the total crop water requirement), T2 (65%), T3 (85%), and TC (full irrigation, serving as the control). The corresponding water were 99, 143, 188, and 221 m³ palm⁻¹ during the 2023–2024 growing seasons covering the entire year. Reference evapotranspiration (ET_O) was calculated using the U.S. Class A Pan method. The crop coefficient (Kc) was then adjusted using FAO calculations to account for local climatic parameters, including wind speed, relative humidity, and plant height. Each treatment was replicated nine times to ensure statistical robustness produced 36 experimental units using a randomized complete block design (RCBD). Daily ETo readings ranged from 2.86 to 13.33 mm/day, averaging 7.8 mm/day annually. Adjusted crop evapotranspiration (ETc adj) was 2955 mm/year, while Kc ranged from 0.77 to 1.15. Summer and winter watering frequency disturbances occurred at 5-day and 32-day intervals. Analysis of variance among irrigation settings revealed significant differences in water productivity and agricultural output. Treatment 1 had the highest water productivity (0.77 kg m^-³), followed by T3, T2, and TC (0.59, 0.54, and 0.50 kg m^-³). T3 and TC yielded the most at 110 and 111 kg palm⁻¹, respectively, with no statistically significant difference between them. Most importantly, the T3 treatment achieved a 15.1% savings in irrigation water compared to the TC treatment without a significant decrease in yield. According to research, increasing irrigation water did not increase productivity correspondingly but did diminish water efficiency. Although irrigation at 45% of the total water requirement (T1) resulted in reduced yield, this treatment may still be considered a feasible option under severe water-scarcity conditions due to its substantially higher crop water productivity.