YIELD AND YIELD COMPONENTS OF BREAD WHEAT AS AFFECTED BY APPLICATION TIMING OF NITROGEN AND SEEDING RATES

A field trial was conducted at the Experimental Farm, College of Agriculture. Abu Ghraib, Baghdad, Iraq in two winter seasons 2000-2002. The objectives were to investigate the effect of application timing of nitrogen levels and seeding rates on some growth characters, yield and quality of bread wheat, Abu- Ghraib-3, and to identify the most critical stage of growth according to Zadoks etal. For application timing of nitrogen. Seeding rates 80, 120 and 160 kg/ha were assigned in the main plots. nitrogen levels 200, 300 and 400 kg/ha in sub plots and application timing of nitrogen in sub-sub plots. Nitrogen timings included five combinations of growth stages (ZGs21, ZGs32 and ZGs49). The results showed that higher number of spikes/m2 (565) and (643) was found in the first and in the second seasons, respectively, and more grain yield was produced (7.5 t/ha) in the second season only when 160 kg/ha. seeding rate was applied. Nitrogen levels of 300 and 400 kg/ha produced higher number of grain/spike(53) and (55) and yielded higher grain yield (6.31 and 6.22 t/ha), in the first season, but the level of 400 kg/ha produced more spikes/m(2) in both seasons (536 and 627, respectively), grains/spike (56) and higher grain yield (7.22 t/ha) in second season as compared with 200 and 300 kg N/ha. The application timing in (D4) yield [1/2 N at pre-planting+1/4N at elongation stage (ZGs32)+1/4N at booting stage(ZGs49)] was significantly higher in number of grains/spike (57 and 57) and in grain yield (6.62 and 7.70 t/ha) and produced more spikes/m(2) (514) in the first season. A significant interaction between 160 kg/ha seeding rate and 300 kg N/ha gave the highest grain yield in both seasons (6.43 and 7.61 t/ha, respectively). The interaction of 160 kg/ ha and D4 gave higher number of spikes/m(2) (613) in the first season and heavier 1000 grain weight (37.37 g). A significant positive correlation was found between grain yield and spikes/m(2) and grain/spike in both seasons.