Towards Site-Specific Management: UAV- and Ground-Based Assessment of Intra-Field Variability in SHD Almond Orchards †

Through highly detailed data acquisition, a precision agriculture approach leads to the
optimization of inputs, improving, for instance, water and nutrient use efficiency. Highresolution vigor mapping in perennial orchards provides the spatial detail required to
achieve such targeted management. This exploratory case study characterizes the spatial
variability of vegetative vigor in a young SHD almond orchard in southern Sardinia by
integrating high-resolution unmanned aerial vehicle (UAV) imagery and Normalized
Difference Vegetation Index (NDVI) mapping with two consecutive seasons of ground
measurements; the NDVI raster was subsequently used to delineate three distinct vigor
zones. The NDVI was selected as a reference index because of its well-assessed
performance in field-variability studies. Field measurements, during the kernel-filling
period, included physiological assessments (stem water potential (Ψstem), SPAD,
photosynthetic rates), morphological evaluations, soil properties, yield, and quality
analyses. High vigor zones exhibited better physiological conditions (Ψstem = −1.60 MPa in
2023, SPAD = 38.77 in 2022), and greater photosynthetic rates (15.31 μmol CO2 m−2 s−1 in
2023), alongside more favorable soil conditions. Medium vigor zones showed
intermediate characteristics, and balanced soil textures, producing a higher number of
smaller almonds. Low vigor zones exhibited the poorest performance, including the most
negative water status (Ψstem of −1.94 MPa in 2023), lower SPAD values (30.67 in 2023), and
coarse-textured soils, leading to reduced yields. By combining UAV-based NDVI
mapping with ground measurements, these results highlight the value of precision
agriculture in intra-field variability identification, providing a basis for future studies that
will test site-specific management strategies in SHD orchards