Title: Response of seed yield and nitrogen use efficiencies of rice cultivars as affected by N fertilizer rates
Abstract: In order to study the effect of N fertilizer rates on yield and yield components of rice cultivars, a study was carried out in Rice Research Institute of Rasht, Iran in 2008. It was a two-variable factorial experiment based on a randomized complete block design with three replications. The main plot was N fertilization at four rates of 0, 30, 60 and 90 kg/ha and the sub-plot was rice cultivar at three levels of Hashemi, Ali-Kazemi and Khazar. The results of analysis of variance showed that the change in applied N rate significantly affected seed yield, N accumulated in plant and seed and N recovery and physiological efficiencies. Also, the effect of cultivar was significant on seed yield, N accumulated in plant and seed and N agronomical and physiological efficiencies, but the interaction between N and cultivar did not significantly affect any studied traits. Means comparison showed that as N rate was increased from 0 to 90 kg/ha, seed yield and N accumulated in seed increased by 84.5 and 65%, respectively; but as it was increased from 30 to 90 kg/ha, N recovery efficiency decreased by 33.8% and N physiological efficiency increased by 40%. Cultivar Khazar with the average seed yield of 3424.51 kg/ha, N agronomical efficiency of 24.43 kg/kg, N recovery efficiency of 42.11% and N physiological efficiency of 58.97 kg/kg had the highest potential of using applied N among the studied cultivars. In total, the results indicated that cv. Khazar was better to be cultivated accompanied with the application of 90 kg N/ha in order for having the maximum production and minimum lose of applied N under the conditions of the current study.