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Optimal water management in agriculture within the context of climate change using innovative technologies and numerical simulation – Field applications

Morianou Giasemi

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Summary

This dissertation investigates the optimization of irrigation and fertigation strategies in a drip-irrigated citrus orchard (grapefruit) under Mediterranean climate conditions. The main objective is to improve agricultural water use and reduce environmental impacts. The study combines field experiments, monitoring of key parameters, advanced laboratory techniques and numerical modeling with HYDRUS 2D/3D software to evaluate soil-water-plant interactions under different management scenarios.High-resolution measurements of soil hydraulic properties were carried out using specialized equipment (HYPROP, WP4C and KSAT). Both unimodal and bimodal van Genuchten functions were used to estimate the hydraulic parameters in order to accurately represent the water retention curve of the soil. The bimodal function showed better performance in the superficial soil layers (0–30 cm), which is probably due to the greater heterogeneity of the pore size distribution in these layers. This heterogeneity plays a crucial role in influencing water availability in the root zone.A comparative modeling study was then conducted to evaluate the simulation performance of both models using soil moisture data from field sensors. These data were used to calibrate and validate the model. Although the bimodal model achieved slightly better accuracy in simulating near-surface moisture content, the difference in overall performance according to the statistical evaluation criteria (MAE, RMSE, AIC, NSE) was found to be limited. Considering the lower computational effort and the reduced need for parameterization, the unimodal model was selected for further simulation scenarios. This choice represents a practical balance between model accuracy and operational efficiency.Subsequently, a series of irrigation and fertigation scenarios were simulated using the HYDRUS 2D/3D model. These scenarios explored the effects of different irrigation strategies (full and deficit irrigation), various configurations of drip tapes arranged in circular patterns around the trees, and alternative fertigation schedules. The results indicated that combining deficit irrigation with circular drip tape placements at greater distances from the tree trunk (100 and 120 cm), compared to the experimental setup at 60 cm, significantly reduced deep percolation and nitrate leaching. This, in turn, enhanced nitrogen uptake efficiency and mitigated the risk of groundwater contamination. The best performance was observed with the use of two circular drip tapes per tree, which overall outperformed all simulated single circular configurations.In parallel to the simulations, a combined field and laboratory study was conducted to assess the impact of deficit irrigation on fruit yield and quality. The results showed that reduced irrigation did not have a negative impact on overall fruit production. In some cases, it even improved quality characteristics, with an increase in total soluble solids (TSS), titratable acidity (TA) and antioxidant content being observed. Among the varieties studied, 'Ruby' showed remarkable tolerance to water stress while maintaining high fruit quality.This research highlights the value of a comprehensive and integrated approach combining a detailed hydraulic characterization of the soil, dynamic simulation models and the evaluation of different irrigation and fertigation strategies. The proposed framework provides a solid foundation for optimizing water and nutrient management in citrus orchards and offers practical, science-based solutions for sustainable resource use in perennial cropping systems, especially in regions facing water scarcity and increasing climate-related challenges.

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