An experiment was conducted on the field of the Dept. Field Crop Science, College of Agriculture, University of Baghdad during spring and fall seasons of 2004. Using RCBD with four replicates .The objective of the study was to determinate the best level of nitrogen, (100 , 200 , 300 and 400 kg.ha-1 ) that could increase the yield as a result of their effect on some genetic– physiological and morphological characteristics. Characteristics measured includ grain number per ear, grain weight rate, harvest index, yields efficiency, number of days from planting till tassling and silking, number of leaves per plant, number of leaves above the ear, leaf area and leaf area index, and biological yield of the maturity. The dose of 300 kg.ha-1 nitrogen showd the highest grasn yield are reflect of number ears per plant (1.43), number of grain per ear (623.25), number of rows per ear (15.58) and ear length (14.89 cm) that was due to the increase in leaf area (0.487 m2), leaf area index (1.94), plant height (185 cm) and ear height (96 cm) as a result of tasseling and silking (66 and 69). Thus the yield efficiency was highly (199.59 gm.m2¬) during spring season, the treatment N300 did not differ from N400 significantly except in ear length and dry weight which were higher at N400. Studied characters were affected significantly by nitrogen during fall season. Nitrogen increasing resulted in an increase in leaf number (14 leavs), leaf area (0.515 m2), dry weight (430.88 gm) and grain number per row (39.5). At N400, the increase continued in plant height (197 cm), ear high (116 cm), ear length (21.48), number of ear per plant (1.31) and grain weight (0.259 gm) that led to an increase in plant yield and the yield per area unit (10 t.ha-1). There was an increase in the yield efficiency (478 gm.m 2). Nitrogen increasing from N100 to N400 resulted in a ten-day delay in tasseling and silking.