The deep percolation and actual evapotranspiration from flood irrigation in tropical floodplains ... more The deep percolation and actual evapotranspiration from flood irrigation in tropical floodplains were predicted using a numerical model, Hydrus-1D, and a bucket type water balance model. Field experiments were conducted on onion and maize crops grown from December 2015 to May 2016 in small irrigation schemes found in the Lake Tana floodplains of Ethiopia. Experimental fields were selected along a topographic transect to account for soil and groundwater variability. Irrigation volumes were measured using V-notches and irrigation depths (400-550 mm) were calculated, and daily groundwater levels were monitored manually from piezometers installed in the fields. The soil profiles were described at each field and physical properties (texture, FC, PWP, BD, and OM) were measured at each horizon which were used to derive model input parameters. Soil hydraulic properties (residual and saturated moisture content, saturated hydraulic conductivity, parameters related to: pore size distribution n, air entry α and pore connectivity l) were derived using KNN pedotransfer functions for tropical soils and fitted using Retention Curve Program for Unsaturated Soils, RETC. The seasonal actual evapotranspiration estimated by Hydrus and water balance models ranged from 320 to 360 mm for onion and from 400 to 470 mm for maize. The seasonal deep percolation estimated from both models was 12-41% of applied irrigation and with this flood irrigation management; the deep percolation is very high. Implementing precise irrigation and water saving practices that minimize deep percolation and unproductive excessive consumptive use are required to achieve the growing food demand with the available water. When less detailed information is available, the water balance model can be an alternative to predict deep percolation and actual evapotranspiration.
Soil Water Dynamics on Irrigated Garlic and Pepper Crops Using Hydrus–1D Model in the Lake Tana-Basin, Northwestern Ethiopia
Soil water is an important variable in regulating and predicting hydrological process for optimal... more Soil water is an important variable in regulating and predicting hydrological process for optimal irrigation. Hydrus-1D was used to simulate soil water dynamics under overhead irrigation in Dengeshita watershed at the plot level. Experiments were carried out from October-February 2017/2018 and from March – June 2018. The treatments were conservation agriculture (CA) and conventional tillage (CT). Irrigation depth, crop phenology, meteorological and soil parameters were determined. Soil parameters were estimated using a K-nearest neighbor approach (KNN) pedotransfer functions for tropical soils and fitted using retention curve optimization program. Sensitivity analysis result showed saturated soil water content (θs), saturated hydraulic conductivity (Ks), and pore size distribution (n) were the most important parameters for the model. The model performance using measured soil water content (SWC) was good with R2 of (0.64–0.77) and errors; RMSE of 0.021–0.063 and ME of 0.0013–0.040. B...
Irrigation efficiency and shallow groundwater in anisotropic floodplain soils near Lake Tana, Ethiopia
Irrigation and Drainage
Field experiments were conducted (December 2014 to May 2015) in a small irrigation scheme (60 ha)... more Field experiments were conducted (December 2014 to May 2015) in a small irrigation scheme (60 ha) to study the effect of flood irrigation on anisotropic soils with shallow groundwater in the Lake Tana floodplains of Ethiopia. Irrigation (470 ± 33 mm) 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 m) 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)%. RÉSUMÉ Des expériences sur le terrain ont été menées (de décembre 2014 à mai 2015) dans un petit périmètre d'irrigation (60 ha) afin d'étudier les effets de l'irrigation par crue sur les sols anisotropes des eaux souterraines peu profondes dans les plaines inondables du lac Tana en Éthiopie. L'irrigation (470 ± 33 mm) a été mesurée à l'aide d'encoches en V; la pluie n'a pas eu lieu et la nappe phréatique a été contrôlée quotidiennement à l'aide de piézomètres afin d'estimer la recharge à partir de champs d'oignons irrigués à l'aide de la méthode de fluctuation de la nappe phréatique. La recharge a été influencée par la quantité d'irrigation appliquée, la profondeur de la nappe phréatique, les variations saisonnières de la température, l'efficacité de l'application de l'irrigation et les stades de croissance des cultures. La diminution de la percolation profonde pendant les périodes les plus chaudes et les pics de croissance ont eu une incidence négative sur la réduction du déclin de la nappe souterraine provoquée par l'irrigation. L'anisotropie du sol a également joué un rôle majeur dans la quantité de recharge: malgré la prédominance de l'argile dans les sols supérieurs, la rapide élévation de la nappe phréatique (0.02 à 0.56 m) était due à la présence de structures granulaires et en blocs. La recharge était également influencée par l'efficacité de l'irrigation, indiquant une recharge plus élevée pendant les périodes de moindre efficacité. La recharge saisonnière représentait 34 à
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