In order to investigate effect of nitrogen fertilizer on yield and quality of three forage sorghum cultivars under Guilan climatological conditions a field study was conducted in 2010 cropping season at Rasht. A randomized complete block design with factorial arrangement with three replications was used. Treatment consisted of four levels of nitrogen fertilizer (0, 50, 100 and 150 kg N ha-1 from urea source) along with three sorghum cultivars (Pagha, Esphidfid, KSF2). Plant characteristics measured were forage yield of dry and forage yield, Stem dry weight, leaf dry weight, Plant height, stem diameter, Crude protein, Dry matter digestibility, Total ash and Acid detergent fiber were calculated. The result showed that nitrogen fertilizer had significant effects on forage yield and quality traits also cultivars had significant effects on forage yield, protein percentage, total dry matter, and Acid detergent fiber (ADF). Maximum forage yield (dry and fresh weight) in sorghum was obtained with 150 kg N ha-1 and KSF2 cultivar. Based on the results obtained from this study in order to increasing forage yield, dry matter percentage and minimum ADF was obtained in KSF2 cultivar should be applied with 100 kg N ha-1 in condition Rasht reign and If our objective is forage quality, was suggested Pagha cultivar with 150 kg N ha-1 in Rasht reign conditions.

Keywords: Dry matter percentage, Forage sorghum, Nitrogen, Protein, Yield.

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