Supplementary potassium and calcium improves salt tolerance in olive plants

•Potassium and calcium treatments were applied to evaluate the possible alleviation of salt stress.•The treatments improved the nutritional balance in olive tree under salinity stress.•The K treatment at 40 mM KNO3 enhanced salt adaptive ability of olive grown under 100 and 200 mM NaCl.•The fertilization based on K and Ca for olive trees are recommended under high saline conditions. Soil salinization increase, aggravated by the foreseen low precipitation related to climate change, is a worldwide problem causing crop yield reductions, affecting population and environmental issues due to the salt-containing low-quality water. Enhancing the salt tolerance of plants, especially crops, is an interesting and effective solution to minimize salt-related crop problems. Toward this goal, we evaluated in this study the effect of potassium (K) and calcium (Ca) application on plant growth, nutrient uptake, water status and electrolyte and potassium leakage of two-year-old potted olive plants grown under saline conditions (100 and 200 mM NaCl). Results showed that all measured parameters were affected by salinity. However, the application of K and Ca enhanced the growth parameters, improved the water status and reduced the electrolyte and K leakage, the latter reflecting a positive effect in membrane integrity. The nutritional balance was moderately improved in salt-stressed plants treated with K and Ca. The significant reduction in sodium (Na) concentration in both leaves and roots, and the enhancement of K and Ca concentration in the different plant tissues indicated that the K and Ca supply raised the Na exclusion mechanism. The largest positive effect of K was observed with 40 mM KNO3 dose at both salinity levels. Furthermore, the beneficial effect of Ca was achieved with 40 and 10 mM CaCl2 in plants grown at 100 and 200 mM NaCl, respectively. Thus, for this relatively salt-tolerant and economically important crop, K and Ca are recommended to supply in order to mitigate the harmful effects of salinity and to develop saline agriculture in, for instance, coastal saline land.