Nitrogen is the first element whose deficiency is
encountered in arid and semi-arid regions which is
resulted from the deficiency of organic matter as the
main source of N storage (Malakouti and Gheibi, 2003). It
is very important to achieve the optimum fertilization
rates because the responses of the plants to these rates
are translated into their optimum yield. Neisani et al.
(2011) reported that N fertilization increased forage
yield of forage maize by improving leaf area index and
leaf, stem and ear weight. In a study on forage sorghum,
Pourazizi and Fallah (2013) revealed that higher N
fertilization resulted in linearly higher forage yield under
chemical N and cattle manure fertilization treatments
and that it was rooted in significant increase in leaf, stem
and spike fresh weight and stem diameter.