RESPONSE OF ONION (Allium cepa L.) TO DEFICIT IRRIGATION UNDER SURFACE AND DRIP IRRIGATION METHOD IN CENTRAL RIFT VALLEY OF ETHIOPIA

Abstract

Onion (Allium cepa L.) is the most important and widely cultivated vegetable crop in the Central Rift Valley of Ethiopia. However, available water resources are the most limiting factor for crop production in the area. A field experiment was conducted on loam soil at the experimental farm of Melkass agricultural research center, Ethiopian Institute of agriculture research with the objective of evaluating the effects of irrigation method and deficit irrigation on yield and water use efficiency of onion. The experiment consisted of two irrigation methods (Drip and furrow) and four deficit irrigation levels (85%ETc, 70%ETc, 60%ETc, and 50%ETc) and control irrigation of 100%ETc and laid out using split plot design in RCBD with three replication. Irrigation methods were used as the main plot and the five irrigation levels as sub-plot. Irrigation water was applied at allowable soil moisture depletion (p=0.25) of the total available soil moisture throughout the crop growth stage. The study has shown a highly significant (P ≤ 0.01) difference on yield, yield parameters and water productivity of onion. The highest total onion bulb yield (52.1t/ha) was obtained from applying 100%ETc under drip irrigation method and had no significant difference with drip irrigation at 85%ETc irrigation application. Onion bulb yield decreased with an increase in levels of water deficit. Both water productivity and irrigation water productivity increased with increase in water deficit level. The highest water productivity and irrigation water productivity were obtained under furrow and drip irrigation, respectively. Deficit irrigation application of 85%ETc, 70%ETc and 60%ETc under drip method apparently gave a non-significant difference for most yield attributes. Among furrow irrigation techniques, the highest onion yield (43.4t/ha) was obtained from convention furrow irrigation with 100% ETc irrigation application and the highest water productivity and irrigation water productivity were observed in alternate furrow irrigation at 70%ETc irrigation application. Hence, under Melkassa climatic condition, onion could be irrigated under drip and alternate furrow irrigation method at 70%ETc deficit irrigation applications considering the availability of water resources and crop water productivity