# Remote and Proximal Sensing Techniques for Site-Specific Irrigation Management in the Olive Orchard
## 3 Results  
### Proximal Soil Sensing and Profile Description  
The soil apparent electrical conductivity ranged between 21.6 and 48.0 mS m\({}^{-1}\) in the 0-0.75 m soil profile (\(\text{ECa}_{1}\)) and between 33.5 and 55.2 mS m\({}^{-1}\) considering a deeper soil volume (\(\text{ECa}_{2}\), about 0-1.50 m) (Figure 3). The mean values of \(\text{ECa}_{1}\) and \(\text{ECa}_{2}\) for the entire field were 32.7 and 41.6 mS m\({}^{-1}\), respectively. Higher values of \(\text{ECa}\) were measured on the South and East side of the field. Low variation of gamma total counts (\(\text{TC}_{\text{gamma}}\)) was measured by gamma-ray spectroscopy. The values ranged between 376 and 442 Bq kg\({}^{-1}\) and indicated a homogeneous mineralogy of the soil parent material. These \(\text{TC}_{\text{gamma}}\) values were similar to those measured in other soils developed in mixed fluvial deposits of Central Italy [22]. The same study measured values around 250-300 Bq kg\({}^{-1}\) in soils developed on calcareous rocks and 550-600 Bq kg\({}^{-1}\) in soils on feldspathic sandstones [22]. The maps of radionuclides contribution (40 K, 232 Th, 238 U) showed low variability of the values and a patchworked pattern, which made them unsuitable for further statistical analysis. For this reason, the radionuclide maps were not used for the next step of data analysis. Although the variability of the absolute \(\text{TC}_{\text{gamma}}\) values was low, the map (Figure 3) showed an evident area with lower values (about 380 Bq kg\({}^{-1}\)) in the northern part of the field due to surficial stoniness, characterized by about 10-15% of medium and coarse gravel (1-6 cm size). Surficial stoniness was virtually absent in the rest of the orchard. Two of the six soil profiles were described in this gravelly area (P1 and P2), and they showed the presence of coarse fragments (from 2 to 12%) up to a depth of 0.90 m, whereas the other profiles showed coarse fragments \(\leq\)2% only in the Ap horizons. Table 1 shows the two extremes of the soil spatial variability, characterized by the profiles P1 (gravelly area, lower \(\text{TC}_{\text{gamma}}\), lower \(\text{ECa}\)) and P4 (not gravelly area, higher \(\text{TC}_{\text{gamma}}\), higher  
Figure 2: Flow chart of the experiment. Legend: NDVI, normalized difference vegetation index; \(\text{ECa}_{1}\) and \(\text{ECa}_{2}\), apparent electrical conductivity at 0–0.75 and 0.75–1.50 m soil depth; \(\text{TC}_{\text{gamma}}\), total count gamma ray; FI, full irrigation; DI, deficit irrigation; RF, rainfed conditions. ECa). As a result, the field was characterized by deep (1.5 m) and loamy soils, with a slight increase in clay for illuviation in deep horizons (+6%). Thus, it was classified as Calcaric Luvisol (Loamic, Profondic) according to the international WRB classification [61]. The profiles were similar for other characteristics: loamy texture (tending to loamy-clay in deep Bt horizons), low calcium carbonate content (from 2 to 2.5%), sub-alkaline pH (8-8.3) and absence of salinity. The organic carbon (TOC) of the topsoil (Ap1 horizons) varied from 9 to 37 g kg\({}^{-1}\). The TOC of the subsoil horizons varied between 6.5 (deeper Bt horizons) and approximately 10 g kg\({}^{-1}\), and the differences between profiles were minimal. Total nitrogen showed the same pattern of TOC, the C/N ratio was relatively stable (approximately 10). Although the soil texture and chemical parameters of the described profiles were quite homogeneous, the different content of the coarse fragments influenced the modelling of the soil available water capacity (AWC). According to the pedotransfer function of Saxton and Rawls [63], coarse fragments have a negative coefficient, and therefore tend to decrease AWC. For this reason, soil profiles with 10-15% of gravels showed lower AWC (115 mm m\({}^{-1}\), for both the profiles) than the other profiles with gravels \(\leq\)2% (AWC from 130 to 141 mm m\({}^{-1}\)).