| Summary: | Drought stress is one of the most serious limitations for the growth and yield of wheat worldwide. Under changing climatic conditions, understanding the urea fertilizer requirement for wheat could be helpful for improving the quality and quantity of yield. The effects of different urea fertilizer levels were evaluated for some biochemical and physiological properties of four wheat cultivars under two irrigation regimes. This experiment was conducted in a split-split plot, randomized complete block design, with three replications. The main plots were irrigation (normal irrigation and irrigation terminated at the stem elongation stage). The experimental plots employed four wheat cultivars (‘Shirudi’, ‘Chamran’, ‘Chamran 2’, and ‘Sirvan’) and four levels of urea fertilizer treatment (0, 120, 240, and 360 kg ha−1), at two locations, Khodayan (52°20' E, 29°8' N) and Nasrabad (52°64' E and 29°58' N), Fars Province, Iran. Results from the full analysis of variance across the two locations indicated considerable differences in yield parameters between irrigation, rates of urea application, and cultivars (p < 0.01). Interaction effects of location, irrigation, cultivars, and urea levels were also significant for Chl b, 1,000-seed weight, and seed yield (p < 0.01). The data indicated that termination of irrigation led to a reduction in RWC (20%), total chlorophyll content (30%), carotenoids (19%), 1,000-seed weight (18%), grain yield (29%), and a promotion in ionic leakage (17%) and proline accumulation (4%), in comparison to the controls. According to these results, ‘Chamran’ and ‘Shirudi’ showed the greatest tolerance to reduced irrigation and that using 240 kg ha−1 urea may effectively moderate the adverse effects of this in these and other wheat cultivars.
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