Deficit Irrigation During Different Growing Stages Affects Growth Characteristics, Yield and Water Use Efficiency of Onion

The main subject of deficit irrigation is to increase the water use efficiency of plants by omitting a partial amount of irrigation water with no significant influence on crop yield. An experiment was contacted to evaluate the effects of deficit irrigation during different growth stages, on vegetative characteristics; yield and water relations of onion cv. Azarshahr, based on randomized complete block design with 8 treatments and 4 replicates. Treatments were consist of: I (1, 1, and 0.8), I2 (0.75, 1 and 0.8) I3 (0.75, 0.75 and 0.8) I4 (0.6, 1 and 0.8) I5 (0.6, 0.75 and 0.8) I6 (0.6, 0.6 and 0.8) I7 (1, 1, and 0.6) I8 (0.75, 0.75 and 0.6), numbers indicate the soil water content based on field capacity at vegetative growth, bulb formation and bulb maturity stages in onion plants, respectively. At the establishment stage, plants have been received the full irrigation. The results showed that vegetative traits including leaf number, plant height, bulbing ratio, bulb dry weight and bulb yield were significantly affected by the deficit irrigation, so by increasing the irrigation water supply, the number of leaves, plant height, yield and dry weight were increased. By increasing of irrigation water supply ET and RWC were increased as well as. Water use efficiency was improved by increasing the irrigation water supply but, there was no significant difference between the full and medium irrigation treatments. Yield response factor (Ky) of I8 treatment which had received the least amount of water was the highest (2.32). These results suggest that the bulb formation stage in onion crop is very sensitive to water stress whereas; during the vegetative growth and maturity stage the sensitivity is reasonably low.