Effect of salinity and foliar application of Zn and Fe on yield and morphological and quality traits of Carum copticum

Introduction Today salinity stress and salinization of soil is one of the most important environmental stress. As the amount of salt increases the plant growth rate decreases. Salinity cause imbalance in soil nutrient content. At this condition we have to use suitable nutrients to achieve appropriate yield. This experiment was conducted to evaluate the effect of salinity and zinc and iron application on yield and some morphological traits and quality of ajowan.   Material and methods A split plots based on randomized complete block design with three replications was used in Khezri, South Khorasan in 2010. Salinity levels of irrigation water (970, 3500 and 7700 µs.cm-1) andfoliar application of micronutrients (control, Fe, Zn and Fe + Zn) were as main plot and sub plot, respectively. Each plot consisted six rows. The length of rows was 4 m. Distance between rows and plants on the rows was 40 and 20 cm, respectively. Data analysis was conducted by MSTATC and SPSS software and means were compared by Duncan’s multiple range tests at 5 % probability level.   Result and Discussion Seed yield significantly affected by salt stress and its interaction with foliar application treatment. The highest (258.11 g.m-2) and the lowest (171.56 g.m-2) seed yield respectively was related to treatments low salinity+ iron and high salinity+ (iron+zinc). In high salinity conditions, which showed a significant reduction in seed yield than low and common salinity, there was no significant difference between the levels of foliar application with control. In fact, iron foliar application in low salinity (control) significantly increased seed yield, but iron + zinc spray application did not significantly change seed yield in comparison with control (without foliar application). On the other hand, in common salinity stress, foliar application treatments did not increase the yield, but in high salinity, the treatments increased seed yield. In low salt stress conditions foliar application of iron increased significantly seed yield, however foliar application of iron+zinc could not affect seed yield. On the other hand, in the common salt stress conditions, foliar application treatments could not increase seed yield, but under severe salt stress these treatments enhanced the yield. In general, under low, common and high salinity stress, the highest seed yield respectively was related to foliar application treatments iron, control and zinc. Seed yield reduction under salinity stress is related to its impact on shoot growth. In this experiment seed yield reduction was related to the decline of umbel number per plant. Correlation coefficient between seed yield and umbel number per plant also was positively significant. Like seed yield, salinity stress reduced different growth parameters such as plant height and branch number per plant. Effect of foliar application on seed essential oil percent and yield was not significant. However, in sever salinity stress, like seed yield, essential oil yield also declined. Although in high and common salt stress, foliar application had not any significant effect on essential oil yield, but under low salt stress, iron foliar application significantly increased essential oil yield. The results of this experiment show that the response of plant height and branch number per plant to irrigation treatments are opposite to each other. Considering that in all foliar application treatments, plant height increased, it can be concluded that the stimulus effect of these treatments on stem longitudinal growth causes the competition of the main stem with lateral branches. Therefore the number of branch per plant in iron and zinc foliar application treatments has declined. It has been reported that zinc deficiency can reduce plant height and yield due to adverse effects on biosynthesis of auxin.       Conclusion Totally, the results of this experiment showed that, due to the significant interaction between salinity and foliar application, microelements should be used with care and after further studies in this plant. Possibly, some plant responses to foliar application and salinity interactions can be related to the presence of different compounds in water used in salinity treatments. Also, the lack of response of some growth parameters such as yield and plant height to the foliar application can be due to complicated plant nutrition relationships with soil conditions such as pH and other soil nutrient concentrations.