Using Low-Cost Proximal Sensing Sensors for Detecting the Water Status of Deficit-Irrigated Orange Orchards in Mediterranean Climatic Conditions

Water scarcity in the Mediterranean significantly affects the sustainability of citrus cultivation in eastern Sicily, a key production area in Italy. Innovative monitoring approaches are crucial for assessing citrus water status and applying precise irrigation strategies. This study evaluates the potential of low-cost proximal sensors based on thermal infrared (TIR) (e.g., canopy temperature, Tc; ΔT; crop water stress index, CWSI) and visible near-infrared (VNIR) (e.g., normalized difference vegetation index, NDVI) data, combined with stem water potential (SWP), for determining citrus water status proxies across four fields under different water regimes (full irrigation, FI, and deficit irrigation, DI) and cultivar/rootstock combinations. Temporal and spatial differences were detected for most variables during the irrigation season. A 6% decrease in NDVI corresponded to higher Tc values in July (up to 37.6 °C). CWSI highlighted cumulative water deficits, reaching 0.65 ± 0.15 in September. More negative SWP values (−1.91 ± 0.38 MPa) were found under DI compared to FI (−1.70 ± 0.17 MPa) conditions. Microclimatic differences influenced ΔT, with lower values in fields 3–4, despite site-specific SWP, NDVI, and Tc variations. The use of VNIR and TIR tools provided valuable insights for describing the spatial and temporal variability of citrus water status indicators under Mediterranean conditions, supporting their sustainable irrigation management.