*3.3. Sodicity Spatial Distribution*

The outcome of the long-term sodification is described by the calculated values of the SAR as a measure for the sodicity of the liquid phase and by the sodium adsorption percentage (ESP = 100 xNa/CEC) as a measure the sodicity of the solid phase. The spatial SAR distribution is shown for the transect along (Figure 9a) and perpendicular (Figure 9b) to the drip line. The spatial ESP distribution is shown in Figure 9c,d for transects along and perpendicular to the drip line, respectively. In general terms, the spatial distribution patterns obtained for the SAR and ESP resemble the one obtained for the salinity (Figure 7), demonstrating that a higher salinity in the soil solution resulted in higher SAR and consequently higher ESP. The SAR values obtained between nearby emitters, above a below the dripline, exhibited values >15% and reached values even higher than 30% at the top soil layers (Figure 10). Therefore, sodicity hazardous of soil structure degradation which can negatively affects soil hydraulic properties should be considered. Nevertheless, since high sodicity levels were accompanied by high salinity levels, the latter, may offset the negative sodicity effect on the stability of soil structure. The fact that sodicity levels increased with salinity implied a chemical equilibrium between the soil-solution and solid phase. In support of this argument is the linear correlation obtained from all samples between the ESR and SAR (Figure 11) with a slope of 0.0134, which is close to the commonly accepted value of the Gapon constant, KG = 0.015, e.g., [50]. In addition, a positive linear correlation was obtained (data is not shown) between ESP and SAR (ESP = 0.77SAR + 3.34, R2 = 0.73). It is well established [51] that if cation exchange reactions have reached equilibrium, the ESP values are similar to the SAR at the range of 0 to 40.

**Figure 9.** SAR (meq L<sup>−</sup>1) 0.5 distribution (**a**) along the drip line, (**b**) perpendicular to the drip line and, ESP (%) distribution, (**c**) along the drip line, and (d) perpendicular to the drip line. The black and white stars indicate the location of the drippers.

**Figure 10.** An overall distribution of the SAR (meq L<sup>−</sup>1) 0.5 at all six depths, 0–5, 5–10, 10–15, 15–30, 30–45, and 45–60 cm. The black and white stars indicate the location of the drippers.

**Figure 11.** Exchangeable sodium ratio (ESR) as a function of sodium adsorption ratio (SAR).
