# Hydrochemical Characteristics and Suitability Assessment of Groundwater Quality for Irrigation
## 2 Materials and Methods
### Classifications for Irrigation Water Quality  
In this study, three classifications were applied: Nejgebauer's, US USSL, and FAO. The domestic classification is [PERSON]'s classification, which is adapted to the natural conditions of the Vojvodina province [20]. This classification considers dry residue and the ratio of Ca\({}^{2+}\) and Mg\({}^{2+}\) to Na\({}^{+}\) (Table 3).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Determination Method** & **Level of Quantification** \\ \hline TDS (mg/L) & US EPA 160.1 & 5 \\ EC (\(\mu\)S/cm) & US EPA 120.1 & 5 \\ pH & SRPS H.Z1.111: 1987 & - \\ Ca\({}^{2+}\) (mg/L) & ISO 6058 & 4 \\ Mg\({}^{2+}\) (mg/L) & ISO 6059 & 4 \\ Na\({}^{+}\) (mg/L) & APHA AWWA WEF 3111 B & 0.2 \\ K\({}^{+}\) (mg/L) & APHA AWWA WEF 3111 B & 0.1 \\ HCO\({}^{-}\) (mg/L) & SRPS EN ISO 9963-1 & 6 \\ Cl\({}^{-}\) (mg/L) & SRPS ISO 9297 & 5 \\ SO\({}_{4}^{2-}\) (mg/L) & ASTM D516-90 & 4 \\ NO\({}_{3}\)\({}^{-}\) & UP 1.98/PC 12 & 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Analyzed parameters, determination methods, and levels of quantification (SEPA) [18].  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Criteria** & **Formulas** \\ \hline \multirow{4}{*}{(1)} & **Sodium hazards** & \\  & Sodium percentage & \multirow{2}{*}{\(\text{SSP}=\frac{\text{Na}^{\pm}+\text{K}^{\pm}}{\text{Ca}^{2+}+\text{Mg}^{ \pm}+\text{Na}^{\pm}+\text{K}^{\mp}}\times 100\)} \\  & (SSP) & \\ \hline \multirow{2}{*}{(2)} & Sodium absorption ratio & \multirow{2}{*}{\(\text{SAR}=\frac{\text{Na}^{\pm}}{\sqrt{\frac{\text{Ca}^{2+}+\text{Mg}^{ \pm}}{2}}}\)} \\  & (SAR) & \\ \hline \multirow{2}{*}{(3)} & Residual sodium carbonate (RSC) & \multirow{2}{*}{\(\text{RSC}=\left(\text{HCO}_{3}^{-}+\text{CO}_{3}^{2-}\right)-\left(\text{Ca}^{2+}+ \text{Mg}^{2+}\right)\)} \\  & Permeability index & \\  & (PI) & \\ \hline \multirow{2}{*}{(5)} & Kelly’s ratio & \multirow{2}{*}{\(\text{KR}=\frac{\text{Na}^{\pm}}{\text{Ca}^{\pm}+\text{Mg}^{\pm}}\)} \\  & (KR) & \\ \hline \multirow{4}{*}{(6)} & **Magnesium hazards** & \multirow{2}{*}{\(\text{MAR}=\frac{\text{Mg}^{\pm}}{\text{Ca}^{\pm}+\text{Mg}^{\pm}}\)} \\  & Magnesium adsorption ratio & \\ \cline{1-1}  & (MAR) & \\ \hline \multirow{2}{*}{(7)} & **Total hardness** & \multirow{2}{*}{\(\text{TH}=2.5\times\text{Ca}^{2+}+4.1\times\text{Mg}^{2+}\)} \\ \cline{1-1} \cline{3-3 The other two classifications that were carried out in this study, which are widely accepted, are the US Salinity Laboratory classification (USSL) and the FAO classification.  
The USSL classification delves into the relationship between salinity and alkalinity, while the FAO provides detailed analyses, considering salinity, infiltration, and toxicity of specific ions. The classifications aid in categorizing water for irrigation based on potential salinization and alkalization risks [21]. Table 4 explains how classes are defined for the assessment of usability.  
The basis of these classifications is the analysis of potential problems of salinization and alkalization, i.e., analysis of the concentration of total salt in water and of sodium, or its relation to divalent cations (Ca2+ and Mg2+).The FAO classification provides more detailed analyses. The FAO classification looks at salinity that affects crop water availability, infiltration that affects the infiltration rate of water into the soil, and the toxicity of certain ions such as Na+ and Cl-. This classification has an additional advantage because it also includes a list of plants that are sensitive, semi-sensitive, or tolerant to the presence of the mentioned specific ions. In the study area, some of the cultivated plants are: beans and corn as sensitive plants; tomato, carrot, wheat, and rye as semi-sensitive; sugar beet and barley as tolerant plants [22].