Optimizing irrigation practices for sustainable olive production in semi-arid areas: A comparative analysis of the efficiency of Subsurface and Surface drip irrigation systems

Abstract : Irrigated olive trees constitute the main arboricultural component of orchards in semi-arid regions, and the optimization of irrigation practices is crucial to sustain the production, increase agricultural water productivity and reallocate water savings to other higher-value uses. Numerous technical strategies have been implemented in the last two decades, to promote water conservation in irrigated agriculture, namely the adoption of subsurface drip irrigation system. This study delves into a comprehensive comparative analysis between subsurface (SDI) and surface (DI) drip irrigation systems over an olive orchard, with an emphasis on the evolution of evaporative fraction (EF) and the ratio of transpiration (T) to evapotranspiration (ET), soil moisture distribution patterns, as well as water use efficiency and water productivity. The experiment was carried out over two irrigated olive plots located in the Tensift basin (Morocco), from May to October 2022. Each plot is subjected to a specific irrigation pattern, and equipped with an Eddy-Covariance system to quantify the energy balance components, along with Time-Domain-Reflectometry (TDR) sensors installed at various depths, to monitor the soil water content. Besides, the partitioning of ET into T and evaporation (E) over the two irrigation systems was performed using the Conditional Eddy-Covariance (CEC) scheme and validated using sap flow measurements collected over SDI plot during April 2023. The ET of the DI system was higher than that of the SDI one, with diurnal ET values ranging between 0.58-3.02 (mm/day) and 0.48-2.74 (mm/day) for DI and SDI systems, respectively. Our findings suggest that although a smaller irrigation water amount was applied in SDI (194 mm) compared to DI (320 mm), crop yield revealed no significant differences. This thorough assessment intends to add substantial knowledge to the lasting debate about sustainable irrigation practices over olive orchards and assist policymakers in making informed decisions to enhance water use efficiency while sustaining overall agricultural production. Keywords: subsurface and surface drip irrigation; evapotranspiration; water productivity; water use efficiency; olive trees; semi-arid areas.