Supplemental irrigation of cereals in semi-arid areas in Ethiopia - is it worth the effort?

Abstract: With a growing world population, estimated to 9.6 billion in 2050, the world food demand is estimated to increase with 45-50 %. One way to meet the demand is to increase the areal yield from the agricultural sector, where rain-fed agriculture has the highest potential. 95 % of the agriculture in Sub-Saharan Africa is rain-fed and the same region is predicted to holds the largest share of poor people in 2015. Since 40-70 % of the rural households highly depend of on-farm sources, investments to increase the agriculture productivity target both the poverty alleviation in the region as well as the world’s food security. By a tripartite methodology, this study analyzed the use of small-scale rain water harvesting (RWH) ponds for supplemental irrigation (SI) of cereals to reduce the inter-annual variability and to increase the areal yield in semi-arid areas in Ethiopia. A physically based simulation model (CoupModel) considering the plant-soil-atmosphere system was used to study how a C4-plant responded to different irrigation scenarios with 30 years climate data (1980-2009) from six regions in Ethiopia. Moreover, two years field data with maize yield from Triple Green project’s experimental fields in Ethiopia was used to analyze the correlation between SI and yield. Finally, ten farmers that used RWH ponds for SI of cereals within Triple Green project were interviewed to find out their perception of the RWH and SI. The model results showed that irrigation almost eliminated the inter-annual variability and increased the areal yield for all the climates. SI was most efficiently used in areas with more than 900 mm precipitation/year were the two annual rain periods could be bridged to create a prolonged growth season (>180 days). The mean annual irrigation water demand was estimated to 224 mm distributed over 7 irrigation events. The field results showed a moderate but significant 10 % increase of the areal yield with SI. None of the farmers wanted to use the RWH for SI of cereals, instead they wanted to use it to water their livestock, grow cash crop seedlings and fruit trees. If the future world food demand is to be targeted, the study suggests societal investments to build infrastructure to collect, store and distribute water for irrigation.