امیر کاظمی آرپناهی

90% of Iran's land area is in arid and semi-arid areas. It is expected that by 2025, about two-thirds of the world's agricultural lands will face a water deficit. The yield also decreases by 50 to 90% under drought stress conditions compared to non-stressed conditions. Among the different types of stress, drought stress at the end of the season is the most important stress in Mediterranean areas such as many areas of Iran. Therefore, the yield of small grains cultivated in these areas is affected by drought stress at the terminal of the season. Salinity and drought stress increases the concentration of dissolved solutes in the root environment, increases the osmotic potential of the soil, decreases the absorption of nutrients and decreases the mobility of zinc and iron elements in the soil solution. Elements in the plant can be compensated and tolerance to saline conditions can be increased. Researchers reported that the application of zinc increased the grain yield of wheat and barley cultivars. Researchers reported that the application of zinc increased the grain yield of wheat and barley cultivars. In stress conditions due to reduction of stomatal conductance and limited access to CO2 for carboxylation reactions, the rate of photosynthesis decreases and increasing stomatal resistance is a suitable defense strategy for the survival of wheat and barley. Due to the cultivation of barley in these moderate areas and the role of the micronutrient element zinc in reducing the effects of drought and salinity stress, this research was carried out in different varieties of barley using different amounts of zinc sulfate. This research was carried out in November of the agricultural year 2017-2018 in two areas: 1) Kobutrabad Agricultural Research Station (drought stress by removing water after spike emergence); 2) Rudasht Station (rrigation with salt water 10 dS/m). Planting was carried out by machine planter in November in both regions. In the dry area of Kabutrabad, the plots containing 6 rows of 6 meters with the distance between the rows of 20 cm (the planting area of each plot is 7.2 square meters) with a density of 400 grains per square meter were done. Data analysis and step-by-step regression were performed using SAS9.1 software and mean comparison was performed by LSD test at 5% probability level. If the interaction effect is significant, cutting (slicing) and comparison of means was done by Lsmeans test at 5% probability level. The results showed that barley cultivars under drought stress had higher thousand-grain weight, grain yield and biological yield and lower proline content than under salt stress. Drought stress at the end of the season compared to salinity stress during the growing season had higher thousand-grain weight, grain yield and biological yield and lower proline content. Foliar application of 0.5% zinc sulfate had higher grain yield (4763 kg/ha about 34%) and biological yield (4763 kg/ha about 26%) than without foliar application and is recommended. It should be noted that there was no difference in the amount of proline between cultivars in drought stress, but in salt stress, tolerant and semi-tolerant cultivars had more proline content than the stress-sensitive line. In drought stress, Armaghan (semi drought tolerant) and Goharan (drought tolerant) cultivars had more chlorophyll a in the application of zinc sulfate. It seems that the mechanism of increasing the tolerance and performance of Armaghan and Goharan cultivars under drought stress conditions is the increase in the amount of chlorophyll a due to the application of zinc sulfate. For this purpose, foliar spraying of suitable cultivars (Armaghan and Goharan) is recommended in drought stress conditions.Grain yield had positive correlation with traits of plant height (p = 0.01, r = 0.33), spike length (p = 0.05, r = 0.31), number of grain per spike (p = 0.01, r = 0.35), biological yield (p = 0.01,  r = 0.96), amount of chlorophyll a (p = 0.01, r = 0.44), amount of chlorophyll b (p = 0.05, r = 0.29) and zinc element (p = 0.01, r = 0.39), which is the highest correlation between grain yield and biological yield (r2 = 0.99). In terms of grain and biological yield, Armaghan and Goharan cultivars are recommended under drought stress and Armaghan and Mehr cultivars are recommended under salt stress with a concentration of 0.5% zinc sulfate. In salinity stress, the minimum and maximum grain yield and biological yield were obtained respectively in foliar spraying of 0.1 and 0.5% zinc sulfate in all genotypes. It seems that foliar application of 0.5% zinc sulfate is sufficient for all barley cultivars under salinity stress, and foliar application with a higher concentration of zinc sulfate is not recommended due to the decrease in grain and biological yield in this stress.