Effect of maturity stage on yield, morphological characteristics, and feed value of sorghum [Sorghum bicolor (L.) Moench] cultivars

Sorghum [Sorghum bicolor (L.) Moench] is one of the most important forage crops in arid and semiarid regions, and its yield and nutritive value are affected by the harvesting stage. A 2-year field experiment was carried out during the 2017 and 2018 growing seasons to evaluate the forage potential of sorghum cultivars at different harvesting stages. Experimental factors included four harvesting stages (grain milk stage, grain soft dough stage, grain hard dough stage, and grain physiological maturity stage) and seven sorghum cultivars. The highest dry matter and protein yields (38.13 and 3.11 Mg ha−1, respectively) were obtained from cultivar Mashhad-1 at the grain physiological maturity stage, whereas the maximum relative feed value was recorded in cv. Karaj-16 at the grain milk stage. Moreover, the highest crude protein content (116 g kg−1), digestible organic matter (734 g kg−1), and metabolizable energy (2.73 Mcal kg−1) were obtained at the grain milk stage. The maximum panicle dry matter yield (19.39 Mg ha−1) and panicle ratio (552 g kg−1) were found in cv. Karaj-9 at the grain physiological maturity stage. The results of the principal component analysis also showed that with increasing maturity, forage yield increased, and its quality decreased. Overall, when both high forage yield and quality were considered, forage harvesting between the grain soft dough and grain hard dough stages could be recommended. Among the cultivars, the cv. Mashhad-1 with the maximum dry matter and protein yield and high metabolizable energy, digestible organic matter, and crude protein content could be introduced as the superior genotype.