Strategies for present and future bubbler irrigation system management in a Saharan date palm oasis under climate change

Abstract

Date palm oases in North Africa have historically supported agriculture through indigenous irrigation techniques such as foggaras and tabias, made possible by a relatively stable water supply. However, the sustainability of these systems is increasingly threatened by irrational water use, climate change and environmental resources degradation. In response to these challenges, we introduced and evaluated a modern irrigation system “the bubbler” in the Saharan oasis of Jemna (southern Tunisia) cultivated with adult palm tree. Field experiments were performed during two crop growing seasons (2018–2019). Decagon 5TE sensors were installed for real-time soil monitoring at six different soil depths in the root zone and directly below the bubbler emitter. The numerical model Hydrus-1D was calibrated and validated against the collected soil water content (θ) and pore water electrical conductivity (ECp) data. The model was then used to study the effect of different farmer irrigation amounts (T_1 F (66 % crop evapotranspiration (ETc); T_2 F (135 % ETc)) on root water uptake, yield production and soil salinity. In addition different irrigation optimization scenarios were investigated under current climate condition (T₁ (100 % ETc- schedule based on Cropwat), T_1LR (120 % ETc- Cropwat schedule with leaching requirement fraction (LR), T₃ (100 % ETc- schedule based on observed crop growth stages and LR) and future climate change (T_4cc (100 % ETc- same schedule as T₃); T_5cc (80 %ETc- same schedule as T₃)). The results demonstrated that following an irrigation schedule (T₃) designed to meet 100 % of crop water requirements, with irrigation water salinity (ECw) equal to 3.2 dSm⁻¹ and five irrigation events including LR (120 mm) during date palm fruit stage, succeeded to leach the root zone to soil water electrical conductivity values (ECsw) lower than 7 dSm⁻¹ and to increase the root water uptake, achieving approximately 81 % of the potential crop yield under current situation. However the use of schedule implemented based on current situation (T₃), for the future period, using different condition of irrigation water salinity and crop water need (T_5cc) result in a significant crop yield decrease from an average of 81 % in 2020 to about 55 % in 2090 associated with an increase of ECsw to 20 dSm⁻¹ which represent a threat to agriculture land sustainability. Indeed, to meet the double challenge of water scarcity and salinity, it is strongly recommended to optimize irrigation scheduling according to crop water requirements during observed crop growth stages and salinity levels. Further studies of various irrigation schedules with bubbler system under arid climate and brackish water need to focus on its impact on oasis sustainability especially when used for traditional oases.