Effects of saline irrigation on the physiology and ornamental quality of Euphorbia Ascot Rainbow and its relationship with salinity indexes based on the bulk electrical conductivity

•Moderate salinity (5 dS m−1) produced plants unsuitable for commercial purposes.•Measuring the bulk EC just after irrigating was an accurate substrate salinity index.•Leaching when this index exceeded 1.9 dS m−1 controlled salt stress effectively. Water scarcity and the global demand for better water management policies are leading to a more intensive use of brackish water in plant production. Irrigating with saline water, farmers seek a certain leaching fraction to prevent salt‐induced damage which will depend on the plant tolerance to salts. In this sense, soil electrical conductivity (EC) and moisture sensors are essential for optimizing the leaching fraction in irrigation systems by automatically monitoring the water content and the bulk EC (ECb). However, since the ECb depends on both salt and moisture content, indexes are needed to account for this interaction to estimate the actual salinity conditions in the soil solution. This experiment was carried out in a polycarbonate greenhouse in which plants of Euphorbia Ascot Rainbow (Euphorbia) were irrigated at three salinity levels [1.8 (control), 3.3 (EC3), and 4.9 (EC5) dS m−1)]. The effects of the irrigation treatments on the physiology and morphology of Euphorbia and the reliability of three salinity indexes derived from the ECb were evaluated. The results showed that EC3 plants reduced their growth without being affected in terms of physiological and photochemical performance. The salinity index based on the ECb measured immediately after irrigation (ECbai) showed the greatest sensitivity to salinity changes. A threshold of 1.9 dS m−1 for this index should not be exceeded when producing Euphorbia plants.