الفهرس 
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Abstract
Two field experiments were conducted at Abazah Village, Faqous District, Sharkia Governorate, Egypt during 2013/2014 and 2014/2015 growing seasons, to study the effect of three sowing dates (November, 10th, November 30th and December 20th), three nitrogen fertilizer levels (60, 90 and 120 kg N/fad.) and four wheat cultivars (Gemmizea 11, Sids 12, Giza 168 and Misr 1) on yield and yield attributes of wheat under sandy soil conditions. Each experiment included 36 treatments, which were the combinations of three sowing dates, three nitrogen fertilizer levels and four wheat cultivars. A split-split plot design with three replicates was used where; the main plots were devoted to sowing dates, while the sub plots were occupied by nitrogen fertilizer levels and wheat cultivars were allotted in the sub-sub plots. A. Wheat growth: The obtained results indicated that sowing on November, 30th appeared to produce the highest values of plant height, plant top dry weight at heading (AH), 10 and 20 days after heading (DAH), flag leaf area and total chlorophyll content at heading and crop growth rate during growth periods AH-10 DAH and 10-20 DAH, while days to 50% heading increased with early sowing at November, 10th.
Application of 120 kg N/fad., tended to produced the highest values of plant height and plant top dry weight at heading, 10 and 20 days after heading, flag leaf area, total chlorophyll content at heading and days to 50% heading and crop growth rate for both growth periods AH-10 DAH and 10-20 DAH.
The results indicated that the superiority of both Misr 1 and Gemmizea 11 cvs., in plant height and plant top dry weight at heading, 10 and 20 days after heading, flag leaf area and total chlorophyll content at heading, days to 50% heading and crop growth rate at both growth periods AH-10 DAH and 10-20 DAH followed by Sids 12, then Giza 168 cv. B. Wheat yield and yield attributes: The obtained results revealed that plant height , number of tillers and spikes /m2, spike length, number of spikelets/spike, number of grains/spike, spike grain weight , 1000-grain weight and grain, straw and biological yields/fad., were significantly higher at November, 30th sowing as compared to November,10th and December, 20th., while harvest index was not significantly affected.
Nitrogen fertilizer level appeared to be significantly affected all studied traits. Increasing N level up to 120 kg N/fad., significantly increased each of plant height, spike length, number of spikelets/spike, number of grains/ spike and grain, straw and biological yields/fad., however, 1000-grain weight significantly decreased. On the other side, number of tillers and spikes /m2, spike density and spike grain weight significantly increased due to application of nitrogen up to 90 kg N/fad.
Misr 1 cv. recorded the maximum plant height, number of spikes/m2 as well as grain, straw and biological yields/fad., but without significant differences than Gemmizea 11 cv in grain and biological yields. On the other side, Sids 12 cv gave longer spike length, higher number of spikelets/spike, spike density, number of grains/spike, spike dry weight, 1000-grain weight, while Giza 168 cv. produced the highest values of harvest index.