Effects of different rates of nitrogen fertilizer on fertilizer use efficiency, yield and forage quality of sorghum (Sorghum bicolor L.) at different cutting

In order to study of effects of different rates of nitrogen fertilizer on fertilizer use efficiency, yield and forage quality of sorghum (Sorghum bicolor L.) at different cutting, a split plot in time experiment based on randomized complete block design was conducted with three replications in 2010. Experiment factors were included: different rates of nitrogen fertilizer in four levels (0, 60, 120 and 180 kg.ha-1) in the form of urea in main plots and different cutting in two levels in sub plots. Means comparison indicated that in both cuts, maximum of quantitative and qualitative yield were obtained with increasing nitrogen rates. Of course, nitrogen application had more effects on the first than the second cut. Leaf-stem ratio decreased with increasing of nitrogen fertilizer in the first cut but it increased in the second cut. Maximum of nitrogen use efficiency was obtained in application of 60 kg N.ha-1 in the first cutting and the least of it was in application of 180 kg N.ha-1×the second cutting. Based on the results, sorghum can be harvested twist in environmental conditions of Ardabil. It seems that that application of 180 kg urea.ha-1 can be recommended for increasing of forage yield and qualitative traits such as leaf and stem protein, phosphorus and calcium percentage in the study area.