Irrigation Strategies for Carob Tree: Evaluating the Impact of Water Stress and Supplemental Irrigation under Mediterranean Climate

Climate change and increasing drought in the Mediterranean regions provoke serious challenges to agriculture, especially for rainfed crops. Carob tree (Ceratonia siliqua L.) is a resilient tree that is cultivated in dry and poor soils, but the absence of precise data on its irrigation needs limits the possibility of improving its production. In our research, we evaluate the irrigation needs and physiological response of carob trees by applying different irrigation strategies and using precision irrigation technologies.

The experiment was conducted from 2022/2024 at an 8-ha commercial carob tree orchard in the region of Murcia, Spain, with subsurface drip irrigation (SDI) installation. Three irrigation strategies were applied: full irrigation (FI), deficit irrigation (DI), and no irrigation (rainfed). Precision irrigation tools were used for supplemental irrigation during the critical growth periods. It is proven that supplemental irrigation, in addition to rainfall, can increase the yield. Soil probes and dendrometers were used to record moisture content and indicate the water stress. Additionally, stomatal conductance (gs) and stem water potential was measured.

The SDI system played a key role, as it allows for a more precise distribution of water directly in the root zone, improving the tree's access to water and reducing losses due to evaporation. From the physiological point of view, the stomatal conductance was the best indicator, responding faster to water supply. In terms of sensors, the combination of soil moisture sensors (at 30 and 60cms) to understand the correct soil water distribution, and dendometers which at each phenological stage (Bud-break, summer stop and post-summer growth) allow to determine whether the trees were growing, in standby, or water stress. The results showed increased fruit production and more consistent yields with full irrigation treatment, suggesting it supports uniform growth. However, variability due to factors like root damage through SDI installation, own variety variability, soil and alternate bearing was noted. The integration for the new seasons of new tools as remote sensing and machine learning will help reduce deviations.

This experiment has demonstrated the value of carob cultivation as an alternative, profitable and sustainable production, since this crop survives with low irrigation water quality and very low irrigation supplies, from 100 to 200 mm/year, applying complementary and deficit irrigation strategies.