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Water scarcity is a major obstacle to forage crop production in arid and semi-arid regions. In order to improve food security in these areas, it is imperative to employ suitable irrigation management techniques and identify drought-tolerant cultivars. A 2-year field experiment (2019–2020) was conducted in a semi-arid region of Iran to assess the impact of different irrigation methods and water deficit stress on forage sorghum cultivars’ yield, quality, and irrigation water-use efficiency (IWUE). The experiment involved two irrigation methods, i.e., drip (DRIP) and furrow (FURW), and three irrigation regimes supplied 100% (I100), 75% (I75), and 50% (I50) of the soil moisture deficit. In addition, two forage sorghum cultivars (hybrid Speedfeed and open-pollinated cultivar Pegah) were evaluated. This study revealed that the highest dry matter yield (27.24 Mg ha−1) was obtained under I100 × DRIP, whereas the maximum relative feed value (98.63%) was achieved under I50 × FURW. Using DRIP resulted in higher forage yield and IWUE compared to FURW, and the superiority of DRIP over FURW increased with the severity of the water deficit. The principal component analysis indicated that, as drought stress severity increased across all irrigation methods and cultivars, forage yield decreased, while quality increased. Plant height and leaf-to-stem ratio were found to be suitable indicators for comparing forage yield and quality, respectively, and they showed a negative correlation between the quality and quantity of forage. DRIP improved forage quality under I100 and I75, while FURW exhibited a better feed value under the I50 regime. Altogether, in order to achieve the best possible forage yield and quality while minimizing water usage, it is recommended to grow the Pegah cultivar and compensate for 75% of soil moisture deficiency using drip irrigation.

Sorghum (Sorghum bicolor (L.) Moench) is the fifth important cereal considered a drought-tolerant crop. However, its reduction of grain yield considerably occurs in a shortage of water. In the current study, 10 sorghum genotypes were assessed for their grain yield under normal irrigation and water deficit irrigation. As well, the efficacy of several drought indices was evaluated for the selection of high-yield and drought-tolerant genotypes. The experiment was conducted as a split-plot considering three irrigation levels as main-plot and 10 genotypes as sub-plot. Correlation among the indices, clustering of the genotypes along with principal component analysis was employed. Yield production was significantly and positively correlated with indices MP (mean productivity), STI (stress tolerance index), GMP (geometric productivity), HM (harmonic mean), and YI (yield index) in all the irrigation levels. Therefore, these indices are more effective in the selection of high-yielding genotypes under different water conditions. Rank means of stress indices for each genotype revealed that genotype TN-04-79 in mild deficit irrigation and genotypes KGS23 and TN-04-79 in severe deficit irrigation were the most tolerant.

The current research aimed to perceive the effect of water deficit irrigation and plant density on yield and yield components of promising lines of grain sorghum. The experiment was conducted in the form of split-plot factorial design with three replications at the Seed and Plant Improvement Institute (SPII) for two years (2015–2016). Irrigation was considered as the main factor (60, 120 and 180 mm evaporation from pan class A) and plant spacing on the row (8, 12 and 15 cm) and lines (KGS23, KGS32 and KGS36) were considered factorial. The combined analysis of variance indicated that there was a significant difference between the lines in terms of grain yield (p ≤ 0.01). The lines KGS23 and KGS36 exhibited the highest grain yield with 5333 and 4645 kg ha−1, respectively, while line KGS32 produced the lowest grain yield of 4011 kg ha−1. The results indicated different reaction of the grain sorghum lines to irrigation. Under water deficit irrigation, the line KGS23 had a significant advantage in comparison to the other two lines in terms of high yield, morphological characteristics, and adaptation to drought stress conditions. Grain yield was positively correlated with panicle weight, biological yield, and 1000-grain weight. Additionally, line KGS36 performed better than KGS32 in terms of grain yield and drought tolerance. The highest grain yield (7964 kg ha−1) was observed for line KGS23 under normal irrigation and plant space on the row of 12 cm in the second year. Moreover, the effect of plant density on grain yield was not significant (p ≤ 0.05).