Drought stress is the most effective environmental stress on plant growth and yield. On the other hand, climate change and global warming are predicted to have a significant impact on drought and reduced crop yields. Therefore, farmers are looking for management strategies to reduce the harmful effects of climate change on crop growth. Hence, this research was conducted in four different studies. The first study was performed to investigate the effect of two irrigation regimes (normal and deficit irrigation after 55% and 85% depletion of available soil water, respectively) and two levels of nitrogen fertilizer (0 and 112.5 kg N ha -1 in the form of urea, 46% N) On physiological and biochemical traits of fifteen genotypes of sorghum (Pegah, Sepideh, GS4, GS5, GS24, GS25 GS26, GS28, KGS29, KGS33 MGS1, MGS5, SF001, SF002, SF003), an experiment was carried out as a split-split plot based on a randomized complete block design with three replications.The results showed that drought stress caused a significant reduction in biological by decreasing plant leaf area, plant height, F V /F M , chlorophyll content. In contrast, the activity of antioxidant enzymes including catalase, ascorbate peroxidase and peroxidase increased significantly under drought stress conditions. Application of nitrogen under normal irrigation and drought stress conditions led to a significant increase in all traits except chlorophyll a/b ratio and ascorbate peroxidase activity. Among the studied genotypes, SF001, SF002 and MGS5 genotypes had the highest response to nitrogen fertilizer and were the most tolerant to drought stresses for the studied traits. In the second study, the effects of planting date (30June 2016, 10June2017 and 11July2017), irrigation (% and 85% depletion of maximum allowable deficit, MAD) and nitrogen (0 and 112.5 kg N ha -1 in the form of urea, 46% N) on growth of six sorghum genotypes (three forage sorghumincluding SF002, SF001, Pegah and three grain sorghum including MGS5, GS24, GS28) and Maizewere investigated.In this study, early planting date (10June) had higher yields than late planting date (11July). In contrast, delay in planting increased the quality and digestibility of forage. Under normal and deficit irrigation conditions with nitrogen application, biomass and seed yield increased due to the positive effect of nitrogen on leaf area index, plant height, antioxidant enzyme activity, chlorophyll and carotenoid content.In terms of silage quality, crude protein, digestibility increased under normal and deficit irrigations with nitrogen fertilizer, but the effect of nitrogen on normal irrigation was greater than drought stress. The forage sorghum Pegah and the grain sorghum GS24 exhibited higher dry matter yields while they did not show significant differences on total biomass (Biomass + Grain) from that of the Maxima corn under either of the normal or deficit irrigation regimes. Also, Pegah and GS24 genotypes had the highest Irrigation water use efficiency of biomass (IWUE b ) and nitrogen fertilizer use efficiency of biomass (NUE b ) in both irrigation and nitrogen treatments. The best forage quality was related to Pegah and SF002 genotypes with the highest percentage of acetate, isovaleric acid, digestibility and the lowest percentage of Ash, ADF and NDF. In the third study,an open-top chamber experiment was conducted to investigate the growth and biochemical responses of six sorghum genotypes under two irrigation regimes (based on 40% and 75% soil-water depletion) and two N fertilizer levels (0 and 105 kgN ha –1 ), at two atmospheric CO 2 conditions (390±50 and 700±50 µmol mol -1) . The results showed that elevated CO 2 increased dry weight with a positive effect on leaf area, SPAD value, F V /F M , leaf RWC, Phe, DPPH and MSI.With the application of nitrogen, the reduction in DPPH, H 2 O 2 and MDA values was greater under water limited stress rather than control conditions. Hence, we can say that the use of nitrogen fertilizer moderated the effect of water stress on the growth of sorghum genotypes. In the fourth study, calibration and evaluation of grain sorghum model was performed using farm data in two years for two irrigation regimes with nitrogen fertilizer. The results showed that the amount of NRMSE in normal and deficient irrigation regimes was less than 20 and 30%, respectively. Also, the coefficient of determination (r 2 ) was more than 0.97, which indicates that the model is good at simulating biomass and grain yield. In addition, the model output showed that the grain yield of sorghum genotypes will decrease in future climatic conditions (2020, 2030 and 2040) and in both RCPs. Key words lanting date, Drought stress, CO 2 , Silage, Digestibility, Model, Simulation, RCP