1 AGRICULTURAL PRODUCTIVITY OPTIMIZATION IN WATER SCARCE SEMI-ARID REGION OF ETHIOPIA Yenesew Yihun 1 , Bart Schultz 2 , Abraham Mehari Haile 3 , Teklu Erkossa 4 1 PhD student at UNESCO-IHE Institute of Water Education, E-mail: y.yihun@unesco-ihe.org ; 2 Professor of Land and Water development, UNESCO-IHE, Delft, the Netherlands; 3 Senior Lectures, UNESCO-IHE, Delft, the Netherlands; 4 Irrigation Engineer, IWMI, Addis Ababa, Ethiopia. Abstract Water scarcity is one of the major constraints for development of agriculture in arid and semiarid areas of Ethiopia. Ethiopia has a high population density (85 million) growing at a fast rate of 3.2%. Even under the best rainfed season, there will be a cereal deficit of up to 6.5 million tons per year. Hence, it is imperative to identify and implement technologically feasible, socially, economically and environmentally acceptable irrigation water and crop management practices for optimum agricultural production and productivity under drought and deficit water supply conditions. To this end, a PhD research focusing on enhancing Tef production was initiated in 2009 and field and experimental investigations are on-going. The implications on yield of land preparation, seeding rate (25, 10 and 5 Kg per ha) are being studied in conjunction with water deficit irrigation (75%, 50% and 25% of optimum water requirement). FAO AquaCrop model is being employed to simulate yield response to water and to explore alternative water management strategies in Tef production. Tef (Eragrostis Tef) is overwhelmingly important and critical for the national food security - it is a major stable food crop. Preliminary results have indicated that properly preparing the land thereby impounding the limited water supply and reducing the washing of fertilizers could increase the yield from the current 0.9 ton/ha to 2.5 ton/ha even when only 75% of the water demand of Tef is supplied. Furthermore, reducing the seeding rate from 25 to 10 kg/ha could minimize lodging problems and potential raise the yield to 5 tons/ha. Key words: Irrigation water management; Tef; Ethiopia; Food security; Water Deficit