effect of nitrogen application on some characteristics of drought tolerance in spring barley

according to the drought as the most important environmental factor that limiting agricultural products and using nitrogen as the most consumed nutrition element in farming system, in this study investigates examined the effect of nitrogen on drought tolerance characteristics, including changes in total chlorophyll content, total protein content, leaf area, phosphorus and peroxidase enzyme activity under water stress on spring barley. experiment as factorial was conducted with three replications based on completely randomized design in greenhouse of the faculty of agriculture, university of mohaghegh ardabil in 2012. water deficit imposed at three levels: 35% (severe stress), 60% (mild stress) and 85% (control) field capacity by gravimetric method (treatment of water deficit was applied, a week after taking the first dose of fertilizer) and three levels of nitrogen 40, 80 and 120 kg per hectare )including two million kilograms per hectare in the soil( was applied in the form of urea on ebytw-11 spring barley genotypes. the results showed that the water stress accelerated aging of leaves and decreased the total chlorophyll content, total protein, phosphorus, leaf area and grain yield, whereas the peroxidase enzyme activity increased. severe stress (35% of field capacity) than mild stress (60% of field capacity) and control (85% of field capacity) showed the greatest impact on these parameters, so that the lowest traits (except for peroxidase enzyme) was observed in severe stress. nitrogen application significantly improved plant tolerance at all levels of water stress. grain yield was 66% decreased in severe stress and consumption of 40 kg nitrogen per hectare than control. nitrogen application showed severe reduction during stress than the control condition, so that in the severe stress decreased 69% yield with consumption of 120 kg nitrogen per hectare. correlation between the studied parameters showed that there was a significantly positive correlation between the grain yield and leaf area, protein, chlorophyll and phosphorus, and the highest correlation was belonged to crop yield and leaf phosphorus content (r=0.994*). correlation was a significantly negative between the peroxidase enzyme activity and other traits include protein content, phosphorus, leaf area and total chlorophyll, in other words with reduce the amount of these traits. peroxidase enzyme activity was increased during drought stress. with increasing water stress, chlorophyll concentration and leaf area were reduced which leads to decrease the yield in plant. one of the visible effects of decline in yield is reduced of leaves area. a physical and molecular implication occurs such as analysis chloroplasts, reduction in photosynthesis and protein breakdown.