Grain yield response index of bread wheat cultivars as influenced by nitrogen levels

Two field experiments were conducted at Giza Agric. Res. Station, Agric. Res. Centre during the two seasons of 2009/2010 and 2010/2011. The study aimed to investigate the productivity of four bread wheat cultivars, namely Giza-168, Sakha-94, Gemmeiza-10, and Sids-12 under different nitrogen levels i.e. 0, 25, 50, 75, 100, and 125 kg N/fad. The strip-plot design in three replicates was used. The obtained results showed significant differences among the tested wheat cultivars in the two seasons for number of spikes/m2, spike length, kernels number/spike, kernels weight/spike, weight of 1000 kernels, and grain and straw yields/fad. Gemmeiza-10 along with Sids-12 produced the highest weight of 1000 kernels surpassing the other cultivars in the second season only. Gemmeiaza-10 was the superior cultivar for producing higher grain yield, but statistically leveled with Sakha-94 in the 1st season and with Sids-12 in the 2nd one. Moreover, straw yield of Giza-168 was higher than each of other cultivars in the 1st season, while Gemmeiza-10 along with Sids-12 gave the maximum straw yield in the 2nd season. Increasing N up to 75 kg/fad increased yield and its attributes of wheat in both growing seasons. All yield attributes significantly influenced by the interaction between wheat cultivars and N levels in both growing seasons, except kernels number/spike in the 1st season and spike length in the 2nd one. The maximum agronomic efficiency (AE) was recorded with Gemmeiza-10 and with application of 50 kg N/fad. Grain yield response index showed that each of Giza-168 in 2009/2010 and Sids-12 in 2010/2011 was belonging to efficient-responsive group.