Effects of saline water, foliar application of chelate and nano zinc oxide and their interaction on yield and yield component in barley cultivars

Introduction
Salinity limits production in the world and affects 19.5% of water lands. It is estimated that between 18 and 27 million hectares (10 to 15%) of Iran's land has salinity problems (Mahlooji et al., 2018); therefore, salinity of water and soil resources is one of the most important agricultural problems in Iran. Salinity is one of the major abiotic environmental stresses, which affects almost every aspect of plant life and significantly reduces crop yield and quality. Thus it is a serious threat to agricultural productivity, especially in arid and semi-arid regions. The response of plants to salinity depends on several factors such as growth and developmental stage, severity, duration of stress, and cultivar genetics (Seyed Sharifi et al., 2017). Nutrient availability is decreased in saline conditions because of high concentration of sodium, chloride and sometimes calcium ions in soil solution and plant nutrient balance is changed. These saline water sources reduce absorption, impair growth and deficiency of nutrients in the plant, including zinc. Recent studies have shown that the use of zinc sulfate and zinc nanoxide is effective due to the improvement of photosynthetic pigments and the plant's ability to tolerate salinity stress. Zinc micronutrients under salinity stress conditions increase the activity of antioxidant enzymes, proline accumulation and soluble sugars and chlorophyll content and play an essential role in improving plant growth. As a result, under these conditions, proper and adequate nutrition play an important role in maintaining nutrient balance and crop improvement (Ahmadi et al., 2006). In this regard, the aim of this research was to study the effects of zinc foliar application and saline water on growth indices and grain yield in barley (Hordeum vulgare L.) cultivars.
Materials & Methods
The experiment was conducted in a strip split block design with three replications at Esfahan (Rodasht) drainage and salinity research station in 2012-14. Three water irrigation quality treatments including W1=check, 1-2 dS/m (low salinity), W2=10 dS/m (a common salinity in the region), W3=18 dS/m (high salinity) were evaluated as vertical factor. The horizontal factors were foliar spraying including (Nano zinc-oxide, Chelated zinc, mixture of nano and chelated and water spraying as a check). Three different barley cultivars including (Moroco=moderate semi salt sensitive, Nosrat=moderate salt tolerant and Khatam= salttolerant) were spilted within the vertical factors. Data were analyzed using SAS software and the means were compared by Lsmeans test at 5% probability level.

Results & Discussion
The results showed that with increasing salinity of irrigation water, yield and grain yield components decreased. Foliar application of zinc chelate increased the number of spikes, 1000-kernel weight and grain yield. Khatam cultivar was the most salt tolerant, Nosrat cultivar was semi-tolerant to salinity and Morocco cultivar was more sensitive to salinity. Triple interaction (salinity * foliar application * cultivar) was significant on the all traits in the two years of the experiment (except for number of seeds per spike in the first year). That being the case, effects slicing was performed. With increasing salinity to moderate level (10 dS / m), the advantage of using a mixture of zinc oxide nanoparticles and zinc chelate (in the first year) and zinc chelate (in the second year) became apparent in which it had a positive effect on grain yield of barley cultivars. Under excessive salinity (18 dS / m), no foliar application (in the first year) and the foliar application of zinc chelate (in the second year) were found to be the most appropriate treatments.
Conclusion
It seems that the second year of research was closer to normal conditions (in terms of long-term annual meteorological data) and could be considered more representative of the real condition in the region where the foliar application of zinc fertilizer and the use of salt tolerant cultivar (Khatam) is recommended.