Rain-fall shortage constrains production in small-holder agriculture in developing countries and with ongoing climate change these shortages may increase. Rain-water harvesting are interesting technologies that decrease this risk. Therefore, one would expect an increasing use of these technologies in drought-prone areas. However, data collected in Ethiopia shows that the share of irrigated land in total landholding declines with farm size. This study investigates why the share declines with farm size using panel data collected in 2005 and in 2010. A random-effect tobit model is estimated for the share of irrigated land as a function of variables affecting returns, market prices, source of finance and expectation formation. The findings show farm-specific factors such as credit per hectare, distance to market, ease of selling output, landholding, regional differences, aridity and distance of plots from natural water sources significantly affect the share. Thus, encouraging investment has to consider farm-size, and also geographical, environmental and regional diversity.