The 11 th Conference of Agronomy, Agron. Dept., Fac. Agric., Assiut Univ., Nov. 15-16, 2005 ٥١ YIELD AND NITROGEN USE EFFICIENCY AS INFLUNCED BY RATES AND SOURCES OF NITROGEN FERTILIZERS OF SOME WHEAT VARIETIES Nasser Kh. B. El-Gizawy Agron. Dept. , Fac. Agric., Moshtohor, Zagazig Univ., Banha Branch. ABSTRACT Two field experiments were conducted at the Research and Experimental Center of Moshtohor Faculty of Agriculture, Zagazig Univ., Banha Branch, during 2002/03 – 2003/04 seasons. The objective of this experiment was to determine the effect of rates and sources of nitrogen fertilizers on nitrogen use efficiency (NUE), yield and its components of some wheat (Triticum aestivum L.) varieties. Three wheat varieties (Gemmeiza 5, 7 and 9) were evaluated at four nitrogen rates (25 , 50 , 75 and 100 kg N/fed) and two nitrogen sources (Ammonium nitrate and Urea). A split split plot in a randomized complete block design was used. The results indicated significant differences among wheat varieties in all studied traits, except spike length ,number of spikelets/spike and grain N content in both seasons also No. of tillers and spike/m 2 in the 2 nd season only. Gemmeiza 9 surpassed the other two varieties in grain yield. Increasing N fertilizer rates significantly increased all studied traits in both seasons. Grain yield/fed was increased by 38.6, 50.9 and 58.7 % due to increasing the rates of N from 50, 75 and 100 kg N/fed. in the 1 st season, respectively and by 40.1, 56.6 and 64.9 % in the 2 nd season compared with 25 kg N/fed. While, NUE decreased with increasing N rates. Nitrogen addition as ammonium nitrate showed a favorable significant effect in improving most studied traits. Significant interaction between varieties and N rates was detected for number of grains/spike and grain yield/fed in both season and significant interaction between N rates and N sources was detected for grain yield and NUE in the 2 nd season only. The maximum net return was achieved by 100 kg N/fed as ammonium nitrate with Gemmieza 9. Key words: Wheat, N rates and N use efficiency INTRODUCTION Wheat (Triticum aestivum, L.) is one of the most important cereal crop in terms of area and production. Also, wheat is considered the first leading cereal crop in the world due to its position as a staple food for the majority of the world population. In Egypt, wheat is the most important food crop and provides almost 35 % of the total food calories of the Egyptian people. Regarding wheat varietal differences, many workers found significant differences between wheat varieties in growth traits, yield and its components. El–Sayed et al. (2000) found that the tested wheat cultivars Gemmeiza 5,7,and 9 showed significant variations in all studied traits . Gemmeiza 9 surpassed the other two cultivars in number of spikes/m 2 , number of grains/spike , grain weight/spike, 1000- grain weight , grain and straw yields/fed followed by Gemmeiza 7 , while Gemmeiza 5 recorded the lowest values . Toaima et al. (2000) indicated that Sids 1 wheat cultivar surpassed significantly the other wheat cultivars (Gemmeiza 5 and Sakha 69) in plant height , spike length , number of grains/spike, weight of spike , grain weight/spike , number of spikes/m 2 ,grain and straw yields/fed. Abd El-Maksoud