Effect of Moisture Depletion Rate and Irrigation Water Depth on the Productivity and Water Use Efficiency of Soybean Crop (Glycine max L.) Merr. under Drip Irrigation and Fixed Sprinkler Irrigation Systems

Background: Water management and its appropriate use are priorities in arid and semi-arid areas across the globe. Methods: A field experiment was carried out at Hisar in Al-Tunkopry district, Kirkuk Governorate, during 2023 summer season. Split-split plot design was adopted to implement the experiment, using randomized complete blocks design (RCBD). The main plots included irrigation method factor (sprinkler and drip) and the moisture depletion rate was placed in the sub plots (60 and 70% of the available water) while varing irrigation depth were placed in the sub-sub plots (50, 75 and 100)% of the net irrigation depth. Result: Results of the study revealed that the water requirement of the soybean crop under the sprinkler irrigation system reached 1275.9 and 1272.9 mm season-1 at 100% of net irrigation depth and at moisture depletion rates of 60 and 70%, respectively and in drip irrigation system it reached 1170.6 and 1201 mm season-1 for an irrigation level of 100% of the net irrigation depth and at a moisture depletion rate of 60 and 70%, respectively. The yield coefficient values (0.52, 0.90, 1.01, 0.90) and (0.44, 0.85, 0.96, 0.52) at a moisture depletion of 60% for the two methods (drip and sprinkler irrigation). The highest seed yield was 4.094 Mg ha-1 for the sprinkler irrigation treatment with a moisture depletion rate of 60% and an irrigation water level of 50% of the net irrigation depth, while the lowest yield was 2.41800 Mg ha-1 for the drip irrigation treatment with a moisture depletion rate of 60 and a level of 75% of the net depth. The drip irrigation achieved the highest water use efficiency 0.607072 kg m-3, in comparison to the sprinkler irrigation 0.362063 kg m-3.