Introduction:  Caraway is a plant from the umbelliferae, whose cultivation in arid and semi-arid regions has a high economic justification compared to other crops. The importance of using medicinal plants is the presence of effective substances in them, and the quality of medicinal plants is more important than agricultural plants. Iran is located in an arid and semi-arid region, and salinity is one of the environmental stresses that cause temporary or permanent damage. Salinity stress can change the amount of element absorption by the plant by changing the potential difference and affecting the absorption power of water and solutes by the roots. Nutrients necessary for the growth of agricultural plants are divided into two categories: high-consumption and low-consumption nutrients. By supplementing the consumption of low consumption nutrients, it is possible to improve the condition of plant growth in stressful conditions. Based on the studies conducted on agricultural plants, it has been determined that the use of micronutrient fertilizers in stressful situations can lead to an increase in the growth and yield of these plants, but this has not been well established in the case of medicinal plants, including caraway. . In this regard, this experiment was conducted to investigate the effect of salinity stress and the low consumption elements of manganese and iron on the morphological characteristics, yield, yield components and the amount of caraway essential oil.
Materials and Methods: This experiment was carried out in the split plots basis of randomized complete blocks in Zahedan region of Iran. The experimental factors include salinity stress as the main factor in three levels (Irrigation with normal or control water (1.2 deciSiemens/m), irrigation with relatively salty water (3 deciSiemens/m) and irrigation with salty water (5 deciSiemens/m)) and low consumption elements as secondary factors in four levels (no fertilizer consumption, consumption of manganese, iron, manganese + iron) were. Plant height, number of sub-branches, number of umbrella per plant, number of seeds per umbrella, number of seeds per plant, weight of 1000 seeds, seed yield, biomass, harvest index, essential oil percentage and essential oil yield were measured and weighed. At the end, after ensuring the normality of the data, their analysis was done using SAS statistical software, comparison of averages was done by Duncan's multi-range test and at the probability level of 5%. Graphs and figures were also drawn by Excel software.
Results and Discussion: The results showed that salinity had a significant effect at the probability level of one percent on plant height, number of umbrella per plant, number of seeds per umbrella, seed yield and biomass, and had a significant effect at the probability level of five percent on the number of branches per plant, number seeds per plant, weight of 1000 seeds and essential oil yield, but it had no effect on harvest index and essential oil percentage. According to the results, irrigation with relatively salty and salty water led to a decrease of 29.9 and 18.4 percent of grain yield, respectively, compared to irrigation with normal water. Nevertheless, the application of manganese and iron micronutrient fertilizers in the conditions of salinity stress to some extent led to the mitigation of the effects of salinity stress, so that the increase in grain yield due to the use of iron fertilizer in irrigation treatment with saline water was about 25.5% compared to the absence of fertilizer use. The highest yield of essential oil was achieved with 7.49 liters per hectare under favorable conditions. In this study, manganese and iron micronutrient fertilizers had a significant effect at the one percent probability level on plant height, number of umerellaper plant, seed yield and biomass, and a significant effect at the five percent probability level on the essential oil yield of caraway. Iron consumption with an average of 345.70 kg per hectare had more grain yield. Despite the lack of significant effect of micronutrient fertilizers on grain yield components, the application of these fertilizers increased them. Considering the increase in seed yield and the yield of caraway essential oil under conditions of application of manganese and iron, the use of these fertilizers in caraway cultivation is recommended.
Conclusion: In this experiment, salinity stress had a significant effect on all the morphological traits, yield components, seed yield and essential oil yield of caraway, except for the traits of harvest index and percentage of essential oil, and led to their reduction. The negative effect of salinity stress on the weight of 1000 seeds, number of umbrella per plant, number of seeds per umbrella and number of seeds per plant can be considered the most important factor in reducing seed yield under these conditions. Based on the results, it can be concluded that manganese and iron and their combined use causes an increase in the morphological traits, seed yield and yield components and the yield of the essential oil in this medicinal plant. In general, considering the increase in seed yield and the yield of caraway essential oil under the conditions of application of manganese and iron, the use of these fertilizers in the cultivation of caraway can be justified.