Evaluation of Modern Irrigation Techniques with Brackish Water

University dissertation from Lund University

Abstract: Popular Abstract in English Improving irrigation practices and optimal exploitation of available water resources are vital issues facing water scarcity and similar problems in arid and semiarid countries (e.g., Egypt and Tunisia). In these countries, the use of saline and low quality irrigation water (i.e., brackish irrigation water) is often associated by soil salinization risk and soil degradation due to mismanagement and improper irrigation methods. In the present study, field, laboratory, and numerical experiments were conducted. Field experiments were carried out in Tunisia to investigate soil water and salinity distribution under different treatments of drip irrigation (i.e., surface drip irrigation without and with plastic mulch and subsurface drip irrigation surface) with two irrigation regimes (daily and bi-weekly) in a sandy loam soil. In addition, to explore the mobility of different tracers (i.e., dye and bromide) under surface drip irrigation in loamy sand soil as an indicator for the movement of fertilizers and organic pollutants through the field soil. Numerical simulations, on the other hand, were implemented to investigate the effect of geometric design aspects, irrigation regime and amount, and salinity of irrigation water on soil water and salinity distribution as well as irrigation efficiency for different soil types in the El-Salam Canal project region, Egypt under different drip irrigation techniques. These techniques were surface drip irrigation (DI), subsurface drip irrigation (SDI), alternate partial root-zone surface drip irrigation (APRDI), and alternate partial root-zone subsurface drip irrigation (APRSDI). Laboratory experiments were conducted for collected soil samples to provide required data for simulation implementation and analysis. Field results showed that mulching treatment with daily irrigation regime reduces groundwater contamination risk and improves soil water status within the soil domain in sandy loam soil over other drip irrigation treatments and regimes. In addition, the bromide flow faster as compared to dye. Therefore, fertilizers can move deeper than organic pollutants under surface drip irrigation. On the other hand, numerical simulations for El-Salam Canal cultivated land showed that under DI soil hydraulic properties should be considered during designing the drip system. Simulation results for SDI showed that shallow emitter depth is recommended in regions with shallow groundwater to reduce groundwater contamination risk and fertilizer leaching. In addition, it is preferable to control the wetted volume of any soil type by regulating the amount of irrigation water according to soil hydraulic properties. Simulation results also demonstrated that short inter-plant emitter distances (IPED) is appropriate to sustain a considerable amount of soil moisture in the zone of maximum root density under APRDI and APRSDI. Thereby, higher root water uptake rates were recorded with short IPED. Thus short IPED is preferable especially for root system with limited lateral extension. Salinity results showed that APRSDI is more suitable with non-saline irrigation water, especially for shallow rooted plants. However, short IPED and shallow emitter depth are recommended for reducing soil salinity below the plant trunk in case of using brackish irrigation water. Based on the above, HYDRUS-2D/3D can be used as a fast and cost effective assessment tool for water flow and salt movement under different treatments and techniques of drip irrigation.

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