In order to study the effects of different harvesting dates on yield and agronomic characteristics of forage sorghum cultivars, an experiment was conducted at Experimental station, College of Agriculture, Ferdowsi University of Mashhad. Three the cultivars of forage sorghum namely Ghalami Tabasi (a native cultivar), F1104 and Speed Feed along with five harvesting dates: beginning of flowering, one week, two weeks, three weeks, and four weeks after beginning of flowering were compared in a factorial experiment based on a randomized complete block design with four replications. Results indicated that there were significant differences between different cultivars in terms of plant height, number of tillers per plant and dry matter yield. In spite of similar values for percentage of leaf contribution to dry matter production, there were significant differences between different cultivars in terms of percentage of stem contribution. All characteristics except number of tillers per plant were significantly different among different harvesting date treatments. Two weeks after beginning of flowering, height of plants in all three cultivars were in highest and then remained without any change. Dry matter yield was increased with delay in harvest (at first cutting), but significantly decreased at the final harvesting date. With delay in harvest (at first cutting), percentage of leaf was decreased while percentages of stem and inflorescence were increased. There was no significant difference between F1104 and Ghalami Tabasi in terms of total dry matter yield (sum of first and second cuttings). Speed feed cultivars had the highest total dry matter yield and the other two cultivars the lowest.
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