Improved water management through precise crop water requirement determination is needed to improve the efficiency of water use in agricultural production. As a result, appropriate irrigation scheduling which can lead to water saving, improvements in the yield and income can be designed. In this study, three non-weighing lysimeters having dimensions of 2 m×1 m×2 m were used to determine water requirement (ET c ) and crop coefficient (Kc) of onion (Bombay Red cultivar). Reference crop evapotranspiration (ET o ) was determined using weather data recorded at the site. The measured ET c values were 51.3 mm, 140.5 mm, 144.8 mm, and 53.9 mm during the initial, development, mid-season and late season growth stages respectively. Crop coefficient (K c ) values, calculated as ratio of ET c to ET o , were 0.47, 0.99, and 0.46 during the initial and mid-season stages and end of late season. Furthermore, third-order polynomials were fitted well to predict the crop coefficient values as functions of growing degree-days (GDD).

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In the background of improving Water Productivity, there is concern in deficit irrigation, which delivers a means of decreasing water depletion while reducing opposing effects on yield. A field experiment was conducted at Haramaya, Ethiopia during 2020 off-season. The objective was determining effects of irrigation levels and mulch types on yield and Water Productivity of Onion. The experimental design was a split plot in RCBD with three replications. The deficit irrigation levels 100%, 85%, 70% and 55% ETc used with the three mulch types no mulch, straw and white plastic mulch were used. The results revealed that the maximum yield of 38.43 ton ha-1 was recorded from 100% ETc with plastic mulch; whereas the minimum yield of 16.36 ton ha-1 was recorded from 55% ETc with no mulch. Higher Crop Water Productivity of about 9.04 kg ha-1mm-1 was obtained from 85% ETc with plastic mulch. With 85% ETc and plastic mulch the water saved, yield reduction and Crop Water Productivity were 113.13 mm, 9.57% and 9.04 kg ha-1 mm-1 respectively. In view of water saved and maximum yield, irrigation water application at 85% irrigation application levels and plastic mulch could be concerned. The current study recommends that, in water limited area, farming community can accept deficit irrigation level with 85% ETc under plastic mulch.

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Water is scarce resource in Central Rift Valley of Ethiopia and is major limiting factor for crop production. The field experiment was conducted in 2018 at Melkasa Agricultural Research Center during the off-season to identify irrigation method and irrigation application level that maximizes productivity of onion per unit of water consumed and enhanced onion crop production. The experiment was carried out using split plot design in RCBD having three replications. The experiment consisted of two irrigation methods viz., furrow and drip irrigation as main plot and three levels of manageable allowable depletion viz., 120%, 100% and 80% as sub-plot. The ANOVA revealed that their interaction had a significant (p<0.01) effect on bulb diameter, total bulb yield, marketable bulb yield and water productivity. The maximum total bulb yield (41.76 t/ha), marketable bulb yield (38.39 t/ha), bulb diameter (6.02 cm) and water productivity (13.05 kg/m 3 ) were observed from drip irrigation method at 80% management allowed depletion application, while significantly lower of 34.48 t/kg, 31.6 t/ha, 5.11 cm, and 6.84 kg/m 3 respectively were recorded from furrow irrigation method at 120% management allowed depletion application. Among all tested treatments drip irrigation method with 80% MAD was the best practice because of its high yield, water productivity.