In order to investigate the effect and efficiency of nitrogen levels on quality and quantity of yield and yield components of two cultivars of spring rapeseed , an experment was conducted in a split plot design with four replications in the year 2000-2001 at the expermental farm of faculty of Agriculture, Chamran University of Ahwaz.Two cultivars,PF7045.91 and Hyola308 were assigned in the main plots and four nitrogen levels ,100,150,200 and 250 KgN/ha in sub plots.Traits under study were, yield ,yield components ,seed protein percentage and also pattern of nitrogen uptake in whole plant . Results indicated significant differences among cultivars, nitrogen levels and their interactions for most of the traits. The study of nitrogen uptake pattern in` fertilizer levels showed that Hyola 308 hybrid had lower fertility range, compared to PF7045.91 cultivar , while,it has the higher nitrogen use efficiency. Results of interactive effects indicated that the highest grain and oil yield of PF7045.91 and Hyola308 cultivars were obtained at the fertilizer levels of 250 KgN/ha and 150KgN/ha ,respectively.Same result were observed for yield components, except 1000 kernel weight in PF7045.91 cultivar. Among yield components, number of pods per plant and number of grains per pod, indicated significant positive relations with grain and oil yield, while a significant negative relation was detected between 1000 kernel weight and number of grains per pod. Also, a high correlation coefficent of grain yield with oil yield showed that selection of cultivars and N levels could be conducted based on oil yield.
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