چكيده لاتين :
This study was carried out to evaluate the effects of nitrogen fertilizer levels and plant density on forage yield and nitrogen use efficiency of sorghum bicolor in 2005 at Agricultural Research Center of Jahad-Keshavarzi, Ardabil. The treatments were arranged as split plots based on randomized complete block design of three replications. Treatments consisted of nitrogen fertilizer at three levels (0,75 and 150 kg/ha) and plant densities also at three levels of 6, 12 and 18 plant/m2. The results showed that sorghum can be harvested twice in environmental conditions of Ardabil. The highest forage yield resulted from an application of 150 kg/ha of nitrogen and planting of 18 plants m"2. The results of total forage yield at the two harvests indicated that sorghum forage yield was significantly affected by harvest (being the 1st or the 2nd), nitrogen levels, plant density, nitrogen level* sorghum density, harvest x nitrogen levels, harvest x density. Densities of 12 and 18 plants m"2 resulted in similar yields, however, yeilded more than the 6 plants m"2 treatment. Forage yield of the first harvest was more than the second harvest. Means of comparisons indicated that increasing the application of nitrogen fertilizer decreased nitrogen use efficiency. Nitrogen use efficiency decreased from 16.47 kg/kg for application of 150 kg/kg of nitrogen fertilizer to 14.97 kg/kg for application of 75 kg/ha of nitrogen fertilizer. Nitrogen use efficiency was affected by density, however no significant difference was observed between densities of 6 and 12 plants/m2. Nitrogen use efficiency in the first harvest was observed to be more pronounced than that in the second harvest.
