INTERACTIVE EFFECTS BETWEEN IRRIGATION AND NITROGEN TREATMENTS ON YIELD, NITROGEN ACQUISITION AND NITROGEN USE AND AGRONOMIC EFFICIENCIES OF WHEAT PLANT

Field experiments were conducted to investigate the interactive effects between different irrigation treatments and N application rates on grain and straw yields of wheat plants grown on a clay soil and to describe the relationships between irrigation treatments and yield of wheat plants at different N treatments. The factors were nitrogen fertilizer(N): 0(N0), 75(N1), 150(N2), and 225(N3) kg.ha^-1 as urea and four treatments of irrigation(l): fully-irrigation with canal water(l1), 2 times well water + canal water (I2), 4 times well water + canal water (l3), and 6 times well water + canal water (l4). The obtained results indicated that grain and straw yields were significantly increased with increasing application rate of N fertilizer at all treatments of irrigation. On the other hand, grain and straw yields of wheat plants were decreased significantly with increasing number of well water irrigation times. The maximum nitrogen use efficiency (NUE) for grain yield (63.73 kg kg^-1 N) was found with a 75 kg N ha^-1 and h (fully-irrigation with canal water) . In contrast, the minimum NUE for grain yield (19.56 kg kg^-1 N) was found with a 225kg Nha^-1 and l4 (6 times well water,4500 m^3 ha^-1+ canal water, 1500 m^3 ha^-1)for first season. Similarly, irrigation with well water decreased the agronomic efficiency (AE) for grain yield noticeably at all N application rates. The reduction in AE for grain yield of wheat was much higher at U treatment than of that at I2 treatment. The mean agronomic efficiency (AE) for grain yield for the second season confirmed the results of first season and was very close to each other. Future research works should be made by further developing more efficient wheat varieties that could use N more efficiently at lower rates ( 225 kg N ha^-1). It can be concluded that the limited amount of available fresh water should be applied during the initial growth stage and supplemented with well water at later growth stages of wheat plants.