The role of nitrogen, calcium and potassium foliar application on reduction of salinity advers effect in cumin (Cuminum cyminum L.) under hydroponic condition

Introduction Salinity stress is one of the limiting factors in crop production especially in agricultural lands of arid and semi-arid regions. Under salinity stress, the availability of nutrients is reduced due to poor soil conditions. In contrast, the use of these elements by foliar spray is an appropriate method to increase the efficiency of nutrients absorption. Application of some elements by foliar spray reduces the negative effects of salinity. According to the reports regarding the positive effects of nitrogen, calcium and potassium as inducers of salt tolerance, this study was designed to investigate the response of cumin plant in hydroponic conditions to salinity stress and foliar spray of the above mentioned elements. Material and methods This research was conducted in 1395 in a research greenhouse in Fasa, Iran. A factorial experiment was conducted in a completely randomized design with three replications. The first factor was salinity stress in three levels including control (semi Hoagland solution), semi Hoagland solution + 75 mM sodium chloride and semi Hoagland solution + 150 mM sodium chloride. The second factor was foliar spray treatments consisted of control (distilled water), calcium nitrate, potassium nitrate, ammonium nitrate and calcium nitrate + potassium nitrate which were prepared with concentrations of 5/857, 7.214 and 2.857 kg per 1000 liters of water, respectively. These concentrations were selected in such a way that the nitrogen concentration used in all of them was equal. Salinity treatments were applied to Hoagland solution. Spraying of the desired compounds was carried out every two weeks until the end of the flowering stage. Results and discussion The results showed that increasing in salinity stress reduced plant dry weight and leaves chlorophyll content in cumin. Foliar spray of calcium nitrate + potassium nitrate and calcium nitrate alone could somehow prevent the adverse effects of salinity on cumin. Compared to control, salinity level of 75 mM did not reduce the leaf relative water content in cumin. But increasing the salt stress to 150 mM reduced the relative water content of the leaves. While increase in salinity stress increased ion leakage, compared to control foliar spray of calcium nitrate, potassium nitrate, ammonium nitrate and calcium nitrate + potassium nitrate could reduce ion leakage in cumin. At salinity level of 75 mM sodium chloride, foliar spray of calcium, potassium and ammonium and at 150 mM sodium chloride, calcium spray could somewhat neutralize the adverse effects of salinity stress on chlorophyll a. The results showed that salt stress increased the sodium content of the cumin shoot. In fact, salinity stress disturbs the cationic balance of cumin and prevents the absorption nutrient elements and provides the possibility of more sodium absorption by cumin. In all salinity treatments, compared to control, foliar spray of the utilized compounds increased the number of umbel per plant. Calcium and potassium sprays with a competitive effect reduced the sodium absorption and to some extent could play a role in improving the yield components of cumin. Conclusions Overall, the results of this study showed that increase in salt stress caused disturbance in leaf relative water content, ion leakage and chlorophyll content of cumin. However, foliar spray of calcium nitrate and potassium nitrate increased leaf relative water content and reduced ion leakage in cumin. Also, increase in salt stress caused a disturbance in cationic balance and prevented other cations such as calcium, potassium and magnesium to be absorbed while allowed cumin to absorb more sodium. Finally, the use of various spray combinations could improve the number of umbrellas per plant, the number of seeds per umbrella and the weight of 1,000 seeds of cumin in 75 mM salt stress conditions.