Irrigation efficiency and shallow groundwater in anisotropic floodplain soils near Lake Tana, Ethiopia

Abstract

Field experiments were conducted (December 2014 to May 2015) in a small irrigation scheme (60\xa0ha) to study the effect of flood irrigation on anisotropic soils with shallow groundwater in the Lake Tana floodplains of Ethiopia. Irrigation (470\xa0±\xa033\xa0mm) was measured using V‐notches; rainfall did not occur, and the groundwater table was monitored daily using piezometers to estimate recharge from irrigated onion fields using the groundwater table fluctuation method. Recharge was influenced by applied irrigation amount, groundwater table depth, seasonal temperature variations, irrigation application efficiency and crop growth stages. The decreased deep percolation during the hottest periods and peak growth stages negatively influenced the reduction in groundwater decline caused by irrigation. The soil anisotropy also played a major role in the recharge amount: despite clay dominance in the topsoils, rapid groundwater table rises (0.02–0.56\xa0m) were due to the presence of granular and blocky structures. Recharge was also influenced by irrigation efficiency, indicating higher recharge during periods of lower efficiency. The seasonal recharge was 34–46% of applied irrigation and there is much room for improving irrigation efficiency which is only 46 (±12) to 51 (±17)%. © 2019 John Wiley & Sons, Ltd.