*2.8. Measurements and Data Analysis*

The total nitrogen (TN) measurements were conducted by catalytic combustion at 720 ◦C using a Shimadzu TOC–VCSH analyzer, according to the manufacturer's instructions, with a 5.0% coefficient of variation. A total of six columns were prepared, and 82 samples were measured for TN. NH<sup>4</sup> <sup>−</sup> and NO<sup>2</sup> − were considered negligible in this study because of their weak concentrations in the R'mel groundwater [39]. The higher N-NO<sup>3</sup> − concentrations reported in the study area were mainly due to the shallow depth of the water table and the aerated conditions allowing the continued oxygenation of the soil and groundwater. According to Zarabi and Jalali [44], N-NO<sup>3</sup> − is the predominant form in N leachate solution due to its high solubility and lower affinity to be adsorbed by soil sites. The following conversion equation was used to express nitrate concentration in the leached solution.

$$\text{Nitrate} - \text{NO}\_3 \left(\frac{\text{mg}}{\text{L}}\right) = 4.4268 \times \text{Nitrate} - \text{N} \left(\frac{\text{mg}}{\text{L}}\right)^2$$
