In the rainfed agricultural systems of the sub-Saharan Africa, agricultural water scarcity is more related to the variability of rainfall and excessive non-productive losses via runoff and soil evaporation than the total annual precipitation in the growing season. Drylands in the Rift Valley of Ethiopia are characterized by poor sandy loam soils and unreliable, variable rainfall conditions. Between 18 and 30% of the rainfall is lost in the form of runoff under the traditional tillage system. With a Maresha-modified tied-ridger more rainwater can be conserved. However, simulations with FAO’s AquaCrop showed that the root zone soil water may become above the field capacity for consecutive days triggering water logging following heavy rain events in the shallow sandy loams. The question thus is: to tie or not to tie (-ridges) under the current rainfall conditions in the Rift Valley. Effect of tied-ridges with and without manure was studied during two years for maize at smallholder farms. The year 2009 was very dry (96% probability of exceedance) while 2010 had a normal growing season. Tied-ridges improved the amount of soil water in the root zone with 11% during a normal rainfall while their effect on a very dry year was negligible. Tied-ridges in combination with manure (4 Mg/ha) increased maize grain yield with 47% compared to the traditional tillage without manure. We used long-term rainfall data and AquaCrop to determine the water logging risk when untying the ridges is recommended. The long-term simulation revealed that combining tied-ridges and fertilizer enhance the utilization of above normal rainfall (>420 mm) during the maize growing season thus mitigating water logging effects. We conclude that tied-ridges can improve maize yield and rainwater use efficiency. The Maresha-modified tied-ridger can be eventually popularized among Ethiopian farmers owing to its simplicity and effectiveness.