| Summary: | In order to evaluate the effect of drought stress and nitrogen (N) fertilizer levels on yield, yield components and protein content of two barley cultivars (Yousef: six-rowed and Nimrouz: two-rowed), field experiments were conducted at the Fars Agricultural Research Center – Zarghan Station, during 2010-11 and 2011-12 growing seasons. The experiment was carried out as split-split plot based on randomized complete blocks design, with 3 replications. Irrigation regimes (full irrigation (W), 75% W; as mild drought stress and 50% W; as severe drought stress) were considered as main plots, nitrogen levels (0, 60 and 120 kg N ha-1) as sub plots, and the barley cultivars as sub-sub plots. In 2011-2012, rainfed treatment was included in the study; however, the other treatments were similar between two years. Results showed that the effect of irrigation regime, N rate and barley cultivar were statistically significant on grain yield, yield components, protein percent and protein yield in both years. Averaged over all treatments, grain and protein yield of the Nimrouz cultivar were higher than the Yousef under severe deficit irrigation and rainfed conditions. In the first year (with year – round 209 mm rainfall), mild drought stress significantly decreased the grain yield of both cultivars (8% and 12% in Nimrouz and Yousef cultivars, respectively). However, in the second year (with year – round 300 mm rainfall), grain yield of the Nimrouz cultivar was not significantly decreased by mild drought stress. There was a significant irrigation × N interaction effect on grain yield in both years. At full irrigation condition, grain yield was increased due to the application of up to 120 kg N ha-1 (28% and 26% as compared to control in the first and second years, respectively), however, at the other irrigation regimes, grain yield was increased due only to the application of up to 60 kg N ha-1. Overall, the Nimrouz cultivar could be recommended for severe drought stress and rainfed conditions. Furthermore, this genotype may receive 60 kg N ha-1 when grown under moderate drought in the years with 300 mm rainfall (such as the second year of this study).
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