عنوان مقاله [English]
Introduction: Forage sorghum is a valuable plant that tolerates environmental stresses such as drought and heat, which can be used for direct grazing, green forage, dry forage and silage. One of the most important advantages of sorghum is having diverse genotypes that allow the use of appropriate cultivars based on the type of consumption at the time required by the farmer for Their farm animals. Forage quality is highly correlated with fiber components such as NDF (neutral detergent insoluble fiber), ADF (acid detergent insoluble fiber) and lignin (Gholami, 2014; Moore, 1994). To compare forage quality, agronomists and livestock nutritionists use common shortcut units such as RFV (relative value of forage) and RFQ (relative quality of forage), which are highly correlated with the amount of milk and meat produced by livestock. Relative Forage Value (RFV) is a quality comparison index based on digestible dry matter content (DDM) and livestock forage consumption (DMI), which is obtained indirectly from NDF and ADF. Relative forage quality (RFQ) is also a quality comparison index based on total digestible nutrients (TDN) and DMI, which is more accurate than the RFV index due to NDF digestibility (Moore and Andersander, 2000). Due to the production potential and high growth rate in forage sorghum genotypes and also the high resistance of this plant to environmental stresses, this plant seems to have a good ability to produce forage in semi-arid regions. However, there is little information about forage quality in domestic and foreign cultivars and hybrids of forage sorghum in the country and most of the available information emphasizes the quantitative performance of sorghum cultivars; Therefore, the present study was conducted to investigate the potential of forage production in domestic and foreign genotypes of forage sorghum and considering both forage quantity and quality indices to the most suitable domestic and foreign cultivars of forage sorghum for high forage production and nutritional value Be properly identified. Material and methods: Eighteen cultivars, lines and hybrids of forage sorghum were evaluated, planted and harvested at Karaj Seed and Plant Breeding Research Institute. In order to determine the dry matter yield and also to evaluate the quality traits, five plants from each plot were randomly selected and weighed in an oven at 60 ° C until reaching a constant dry weight. Finally, dry matter yield was calculated in the samples. To determine the quality traits, the dried samples were ground. Qualitative traits of forage including crude protein content, ADF, NDF and lignin were determined by the Iranian Institute of Animal Sciences Research by chemical analysis (AOAC, 2002). The digestibility of the samples was determined by the gas test method and the amount of metabolizable energy in the forage was estimated using the amount of gas produced in the twenty-fourth hour and the amount of crude protein (Menke and Steingass, 1988). The means were compared by LSD method at the level of 5% probability. Results and discussion: The results showed that the studied genotypes in terms of plant height, number of tillers and number of leaves per plant were significantly different at the level of one percent probability, while the effect of genotype on stem diameter was not significant. Among the internal genotypes, maximum fresh forage yield (103.84 tons per hectare) was obtained by Pegah cultivar and minimum yield (63.16 tons fresh forage per hectare) was obtained by KFS2 line. The highest dry matter yield (20.61 t / ha) was obtained by Siloking cultivar and the lowest (8.83 t / ha) was obtained by Juicy Sweet BMR SSH.2 cultivar. There was a narrow difference in forage crud protein content, so that the average of crude protein in all studied genotypes was 6.357, internal genotypes was 6.363 and external genotypes 6.354%. The mean NDF in all studied genotypes was 60.36%, internal genotypes 62.06% and external genotypes were 59.51%. Among the studied genotypes, the highest amount of NDF (69.75%) was obtained in Titan cultivar and the lowest NDF content (54.25%) in PHFS-27 cultivar. The average lignin content in all studied genotypes was 1.78, internal genotypes was 1.71 and external genotypes 1.82%. The average metabolizable energy in all studied genotypes was 2.41, internal genotypes 2.33 and external genotypes 2.44 Mcal per kg of dry matter. Juicy Sweet BMR SSH.2 and PFS-21 cultivars had the highest ME levels with 2.67 and 2.64 Mcal of metabolizable energy per kilogram of dry matter, respectively, while Speedfed and Titan cultivars had the highest metabolizable energy ( Produced 2.13 and 2.17 Mcal per kilogram, respectively. The average relative value of forage (RFV) in all studied genotypes was 99.74, domestic genotypes 96.96 and foreign genotypes was 101.13%. The maximum RFV index among external genotypes was obtained by PHFS-27 cultivar (115.75%) and among domestic genotypes by Pegah cultivar (111.38%); While the minimum relative value of forage was observed among foreign genotypes by Titan cultivar (76.28%) and among domestic genotypes by Speedfed cultivar (79.73%). Conclusion: Siloking cultivar, which while producing the most dry matter per unit of area had a high rate of relative forage quality index, is introduced as the most suitable cultivar in terms of quantity and quality of forage. Among domestic genotypes, Speedfed hybrid was able to produce the highest dry matter yield, but was not of good quality. Therefore, planting SpeedFeed cultivar to produce forage will be recommended in situations where only the quantity of forage is important for the farmer. Pegah cultivar, which had good dry matter yield and good forage quality, is introduced as the best domestic genotype for forage production.