The salinity level and SAR indicate different water classes according to their appropriateness for agricultural purposes (Table 3). SAR values are influenced by calcium and magnesium contents. According to FAO, calciumis not toxic, however, scale formation such as calciumcarbonate and calciumsulfate can create problems in the irrigation system together with a reduced acceptance by the market when the salts precipitate on fresh fruits and vegetables [9]. Magnesium is essential for field
crops, whichwhen its composition is too low, should be added to the irrigation water (even though, in reality, this is not done because of the high cost). Nevertheless, magnesium can also have the same negative impact as sodium when applied in extensive amounts, in particular if the magnesium to calcium ratio is higher than 1 [10]. In fact, Severino et al. [11] found that high concentrations ofmagnesium and calciumreduce
the SAR ratio but, at the same time, increase electrical conductivity thus giving origin to awaterwith quality not completely appropriate for irrigation. Specific guidelines for calcium and magnesium have to be stipulated with respect to the amount already present in the soil and irrigation water. However, FAO provides values usually in the range of 0–400 mg/l and 0–61 mg/l for calcium and magnesium, respectively [9]. SAR, salinity, trace elements, etc. are the parameters usually used to identify whether water from a source can be utilized or not for irrigation. However, these parameters do not take into account all the components that have to be present (such as nutrients, etc.) in order to
maximize crop yields by using less water resources [13]. Therefore