Response of yield and yield components of released rice cultivars from 1990-2010 to nitrogen rates

This study examined to compare high-yielding cultivars and respond to N fertilization especially yield component and the aim of this development of rice cultivars suitable for low input requirements. An experiment was arranged in a randomized complete block design with a split-plot arrangement of five rice cultivars, three N rates with four replications in 2011 in Iran. N rates including 0, 69, and 138 kg N/ha as (N0), (N69) and (N138) and rice cultivars including Nemat (C1), Khazar (C2), Neda (C3), Shirodi (C4), and Tarom (C5). The results indicated that all traits response to cultivar and N rates were detected for the parameters examined. The lowest applied N rate had a lower yield than the other two N rates. Grain yields were 5552 for 69 kg N/ha and 6124 for 134 kg N/ha averaged over all cultivars. The grain yield of Khazar and Tarom was independent of the N rate, but the grain yield of Nemat, Neda and Shirodi increased when the N rate was increased from 67 to 138 kg/ha. Panicle density responded to an N rate similar to grain yield. Khazar produced more total spikelet number while Neda had a higher Panicle density. Grain yield and yield components of Nemat, Neda, and Shirodi respond to N rates dependently when planted into high nitrogen. Finally, modern rice cultivars were more efficient at recovering N than older cultivars.