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Irrigated agriculture is the world’s largest water consumer, while at the same time water resources are under increasing pressure from rapidly growing demands and climate change. In Greece, about 45% of the total cultivated area is being irrigated and groundwater is the main source of irrigated water supply. Due to the scarcity of fresh water, the islands of Greece face serious problems by saltwater intrusion in coastal aquifers. In these areas, it is a common practice to utilize saline groundwater in irrigated olive orchards. Thus, estimation of all water fluxes temporally and spatially within and out of the crop root zone, and evaluation of issues like salinity are necessary to fully assess the efficiency of irrigation systems and methods. Simulation models can be used to investigate these issues over several seasons and scenarios. In this study, HYDRUS 2D/3D was used to evaluate data measured during one season (2022) in an olive (Olea europaea) orchard in Crete, Greece. The model efficiency was assessed by comparing model simulations against the observations of θ and EC obtained by an IoT-based monitoring system installed in the frame of HORIZON 2020-Agricapture project in irrigated fields of the Merabello area (Eastern Crete). The system includes the monitoring of soil moisture and atmospheric sensors, providing information on irrigation scheduling to farmers. Three IoT-devices were established in the study field, connected with an advanced soil moisture, temperature, and electrical conductivity sensor Teros12 (METER group, Inc. USA) installed at 0.3 m depth. Meteorological data collection was possible through a weather station (Davis Vantage Pro2™) installed in the area. Comparison of simulated against observed θ and EC showed a good precision of HYDRUS 2D/3D model for olive trees irrigation, with the Nash-Sutcliffe and the Root Mean Square Error (RMSE) being within the acceptable ranges. Model results can be used to improve the decision-making IoT system and advise farmers on various aspects of irrigation under saline environment, as, for example, in scheduling irrigation events for leaching salts, to avoid crop damage.The authors acknowledge contribution of the AgriCapture CO2 - Horizon 2020 project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004282.

In the Mediterranean area, Greece is considered as one of the most important olive producing countries. Specifically, olive (Olea europaea) is the main crop covering more than 75% of the total tree cultivation area, while about 45% of the total cultivated area is being irrigated. Groundwater is the main source of irrigated water in Greece, but the growing demand and the climate change are putting this resource in risk. The design of an optimal irrigation plan, based on detailed measurements and modeling tools, can effectively contribute towards water saving with no loss on crop yield, in the area. In this study, an IoT-based decision-making system for the management of irrigation water resources of olive orchards in a small sub-basin of Lasithi, Crete, Greece is presented. The system integrates monitoring of soil moisture and atmospheric parameters in four fields within the study area and modeling approaches, using the modules of MIKE-SHE model, to simulate water flow in the unsaturated zone at the sub-basin level. Additionally, 45 soil samples (from 3 different soil depths) have been collected and analyzed from the study area for soil texture, bulk density, rock percentage, pH, organic matter, and mineral nutrients. After the successful calibration of the model (comparison of simulated against observed soil moisture values) the spatio-temporal representation of soil moisture is used as guidance for developing optimal irrigation scheduling, considering olive tree water requirements, for the entire study area (sub-basin), even for olive orchards with lack of monitoring equipment installation.ACKNOWLEDGEMENTSThe authors acknowledge contribution of the AgriCapture CO2 - Horizon 2020 project. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 101004282

The aim of this paper is the creation of an integrated and free-access web platform for parcel irrigation water management on a large spatial scale (Water District of Crete, in Greece) in order to: a) accurately determine the irrigation needs of the main crops for Crete such as olives, citrus, avocados and vineyards, b) design strategies, for optimal adaptation of the agricultural sector in the context of climate change, and c) incorporate the dynamic integration of the above information through the creation of a digital platform. In the proposed decision-making system, essential factors are taken into account, such as real-time meteorological data, information about the type and spatial distribution of the agricultural parcels in Crete, algorithms for calculation crop evapotranspiration per development stage and age of the crops, satellite remote sensing techniques in combination with field surveys to depict accurate soil texture map for the whole island of Crete as well as sustainable cultivation practices for saving water per crop and parcel geomorphology. Based on the proposed decision-making system, users will have the opportunity in any specific location/farm in Crete to know the irrigation needs of the crops in real-time and obtain information about proper climate-water adaptation practices. The main novelty points of the proposed platform include the derivation of parcel-level soil texture data from Sentinel-2 satellite imagery and field samples, the comprehensiveness of the irrigation management information, the relatively low data requirements and the application interface simplicity provided to the end-user.

Orchards with tree crops are of critical importance to the global economy and to the environment due to their ability to be productive for many years without the need for replanting. They are also better adapted to extreme climatic conditions compared to other crops. However, new challenges are emerging as climate change threatens both tree production and water supply. Drip irrigation (surface and subsurface) is an irrigation method that has the potential to save water and nutrients by placing water directly into the root zone and minimizing evaporation. Many irrigation designs and strategies have been tested to best perform drip irrigation for any given soil, crop and/or climate conditions. The researchers’ need to find the optimal combination of irrigation management and design in the most economical and effortless way led to the use of comprehensive numerical models such as HYDRUS 2D/3D. HYDRUS 2D/3D is a widely used mathematical model for studying vadose zone flow and transport processes. A review of HYDRUS 2D/3D applications for simulations of water dynamics, root uptake and solute transport under drip irrigation in the four most common categories of tree crops (citrus, olive, avocado and deciduous fruit/nuts) is presented in this study. The review promotes a better understanding of the effect of different drip irrigation designs and treatments, as well as the reliability provided by HYDRUS 2D/3D in the evaluation of the above. This manuscript also indicates gaps and future challenges regarding the use of the model in simulations of drip irrigation in tree crops.

Despite the fact that the olive tree is one of the best-adapted species in Mediterranean hydroclimate conditions, climate extremes impose negative effects on olive fruit set and development and subsequently on crop yield. Considering that the frequency of climate extremes is increasing in the last years due to climate change, Good Agricultural Practices (GAPs) have to be applied in order to mitigate their impact on olive trees. In this context, 18 experimental olive groves (irrigated and rainfed) were established, located on the island of Crete (south Greece). A set of 13 GAPs were applied in different combinations, mainly targeting to reduce water losses and erosion, alleviate heat stress and increase water use efficiency. Each experimental orchard was divided into two parts, the control (business-as-usual) and experimental (GAPs implementation). Four indicators were used for the assessment of GAPs performance, namely, Water Productivity (WP), Economic Water Productivity (EWP), Runoff (RF), and Yield (Y). WP and EWP were found to be up to 2.02 and 2.20 times higher, respectively, in the demonstration part of the orchards compared to the control, while Y was found to be up to 119% higher. RF was higher up to 190% in the control compared to the demonstration part of the experimental orchards. The above results clearly demonstrate that the implementation of the proposed GAPs can significantly support the adaptation of olive crops to extreme conditions.