The prospects for the future are clear. Agriculture will have to respond to changing patterns of demand for food and combat food insecurity and poverty amongst marginalized communities. In so doing, agriculture will have to compete for scarce water with other users and reduce pressure on the water environment. Moreover, water managers have to unlock the potential of agricultural water management practices to raise productivity of water, spread equitable access to water, and conserve the natural productivity of the water resource base. This PhD thesis presents field tests combined with modelling work on the cultivation of irrigated Teff (Eragrostic Tef) in the Awash Rift Valley of Ethiopia. The field experiments were conducted during the dry season for two years. The results of these studies revealed that dealing with improvement of water productivity is closely related to the irrigation practice of regulated deficit irrigation and has a direct effect on yield, as the amount of water applied decreases intentionally the crop yield drops. Overall, this research has demonstrated the potential and the limitations of combining experimental fieldwork with modelling to optimize agricultural water productivity for Teff cultivation. Focusing on only experimental fieldwork is a single approach, and is hardly ever sufficient for achieving the best solutions to current water management problems. New guidelines on using the combined effort of experimental work in the field to produce field experimental data and using models are clearly needed. It is to these needs as well as to the required increase of Teff production under water scarce conditions that this research provides its main contribution.