*2.2. Soil Sampling and Analysis*

Comprehensive soil sampling was carried out to explore the spatial distribution of salinity and sodicity along and perpendicular to the drip-line, representing a total area of 2 m2 (Figure 4). Soil samples were collected from 41 locations along the drip-line between three nearby emitters that were perpendicular and diagonal to the central emitter. At each sampling location, disturbed soil samples (n = 246) were taken from six depths: 0–5, 5–10, 10–15, 15–30, 30–45, and 45–60 cm. In addition, representative intake soil samples were taken near the sampling locations mentioned above, from which the bulk density of each layer was calculated (Table 2). The gravimetric water content (WC) was measured shortly after the sampling event from the differences in weight before and after drying at 105 °C for 24 h. The rest of the soil samples were air-dried and thereafter passed through a 2-mm sieve.

**Figure 4.** Schematic view of soil sampling spots in an olive orchard under sub surface drip irrigation.


**Table 2.** Revivim olive orchard soil properties.

± Standard deviation, SSA\*—specific surface area (calculated according to [43]).

The concentration of the main cations (Na, K, Mg, and Ca) in the soil solution was obtained from the extraction of the soil to distilled water ratio of 1:1. Samples were shaken on an end-over shaker and then centrifuged at 4000 rpm for 10 min. The supernatant was analyzed for soluble cations, bicarbonate, and chloride concentration. The cation exchange capacity (CEC) was measured by the sodium acetate method [44] and the exchangeable cations concentrations (xNa, xK, xMg, and xCa) from the sodium acetate extraction [45]. The cations concentration was measured by atomic adsorption spectrophotometer (Analyst 400, ParkinElmer) and Chloride (Cl<sup>−</sup>1) concentration by Chloride Analyzer (926, Sherwood).

The sodium adsorption ratio (SAR) and the exchangeable sodium ratio (ESR) were calculated according to the Gapon equation.

$$\frac{\text{xNa}}{\text{xCa} + \text{xMg}} = K\_G \cdot \frac{\text{Na}}{\sqrt{0.5 \cdot (\text{Ca} + \text{Mg})}} \equiv ESR \quad = K\_G \cdot \text{SAR} \tag{1}$$

where, the concentrations of the soluble and exchangeable cation are in meq L−<sup>1</sup> and meq Kg−1, respectively. The *KG* is the Gapon selectivity coefficient.

Contours map of the spatial distribution of the WC, EC, Cl<sup>−</sup>1, SAR, and ESP in the soil profile were established with Surfer software (version 8, Golden Software, Colorado, USA) using the Kriging regression.
