Abstract:
In arid and semiarid areas where agricultural development is severely constrained by water scarcity and its mismanagement, the need to use the available water efficiently is unquestionable. This research was conducted aiming at develop onion water - yield relation and optimum irrigation regime for the improvement of onion crop (Allium cepa L.) and irrigation water productivity contributing to the market oriented development scenario. A field experiment was conducted at Arba Minch area district, Southern Ethiopia during 2017 dry cropping season. The experimental treatments consisted four irrigation levels (100, 75, 50 and 25%ETc) and three irrigation intervals (3, 5 and 7days). The experiment was laid out according to randomized complete block design in factorial arrangement with three replications. Results of the analysis revealed that the interaction effects of irrigation levels and irrigation intervals showed highly significant (P<0.01) difference on number of leaves per plant and marketable bulb yield and significant (P<0.05) difference on plant height, neck diameter, bulb number, bulb diameter, bulb weight and total bulb yield but non significant difference on unmarketable bulb yield. The highest marketable bulb yield 27540 kgha-1 was obtained under control treatment which was statistically non significantly different with treatment combination of 100% ETc and 5 days interval. Maximum crop water productivity(4.66 kgm-3) was obtained under the treatment combination of 75% ETc and 3 days interval which consumed 25% less water as compared to control treatment, yield was reduced by 16% (4440 kgha-1). If the saved water is used to produce onion at the same irrigation scheduling, it will produce bulb yield 7132.47 kgha-1 this exceeds the loss of onion bulbs occurred due to deficit irrigation by 2692 kgha-1. This implies that it can bring 0.31 ha area of land in to production and increasing the irrigated area with the saved water would compensate for any yield loss. There were non significant different between treatment combination of 75% ETc with 3 days and 75% ETc with 5 days interval though; equal amount of water was saved. This implies that it can bring the same area of land in to production Therefore, 75% ET at 5 days interval can be an option in the study area when water was limiting factor. However, application of 100% ETc at 5 days interval was economically productive when adopted by onion farmers in the study area when water was non limiting factor.
