Regulated deficit irrigation scheduling of onion in a semiarid region of Ethiopia

A regulated deficit irrigation experiment was conducted at one of the experimental sites of Sekota Agricultural Research Center, Woleh (Ethiopia) on one of the major irrigable crops in the area, onion. The irrigation method was a gravity drip. There were eight treatments with three replications: one period stresses at first, second, third and fourth growth stages and continuous partial stresses of 50%ETc and 75%ETc with two controls of 25%ETc and 100%ETc of the irrigation requirements. The experiment was conducted during the dry season with almost no rainfall. The average onion yield was 19.34 Mg/ha. The minimum yield (5.5 Mg/ha) occurred in the fully-stressed treatment. The maximum yield (25 Mg/ha) was obtained in the full-irrigation treatment. It was observed that water deficit at first and fourth growth stages, gave non-significantly different yields from the optimum application. However, in no case the yields were higher than that in the optimum (full) irrigation. If the water deficit is in the second and third growth stages, or during all stages as 25%ETc, 50%ETc, and 75%ETc water deficit, the yields were significantly different from optimal irrigation. All deficit irrigations increased the water use efficiency of onion from a minimum of 6% by stressing the crop during the first growth stage to a maximum of 13% by partially stressing the crop at 75%ETc of the optimum application throughout the growing season.