Using HYDRUS-2D model to assess the optimal drip lateral depth for eggplant crop in a sandy loam soil of central Tunisia

The main objective of the work is to assess the optimal drip lateral depth for Eggplant crop (Solanum melongena L.) irrigated with a drip system in a sandy loam soil by means of field measurements and simulation models. Initially, the performance of Hydrus-2D was assessed based on the comparison between simulated soil water contents (SWC) and the corresponding measured in two plots, in which laterals with co-extruded emitters were laid on the soil surface (drip irrigation, DI-0) and at 20 cm depth (subsurface drip irrigation, SDI-20), respectively. In order to identify the optimal position of the lateral, the results of different scenarios, obtained by changing the installation depth of the lateral (5 cm, 15 cm and 45 cm) were compared in terms of water use efficiency (WUE), expresses as the ratio between actual transpiration and the total amount of water supplied during the entire growth season. Simulated SWCs resulted fairly close to the corresponding measured at different distances from the lateral and therefore the model was able to predict SWCs in the root zone with values of the Root Mean Square Error generally lower than 4%. According to the examined scenarios, soil evaporation decreases at increasing drip lateral depth, while the associated WUE tends to increase when the depth of the lateral rises from 0 to 20 cm. Depth installation greater than 20 cm involve a higher loss of water to deep percolation with consequent decrease of WUE.