Abstract

In cereals, the main source of nitrogen for grains is nitrogen remobilized from vegetative parts shown to be depended on environmental and genotype factors. Field experiments were conducted to study the effect of various N rates on four Iranian wheat cultivars which have been released at different periods. The experimental design was split plots, arranged in randomized complete block with three replications. Results showed that cultivar differences in dry matter and nitrogen translocation efficiencies were related to nitrogen and biomass accumulated in plant reserve parts at both anthesis and maturity. Cultivar dry matter translocation efficiencies ranged from 17.9 in Zagros to 35.4% in Dena, nitrogen translocation efficiencies from 73.8 in Zagros to 86.7% in Dena and contribution of pre-anthesis assimilates to grains from 29.3 in Zagros to 69.8% in Dena. It has to indicate that all of them were greatest in the modern wheat cultivar. Increase in N application, decreased the contribution of pre-anthesis assimilates to grains and increased the N gain. Highest N losses were obtained at both 0 and 150 kg N ha^-1 in the modern wheat cultivar. Results indicated that in high N application level, modern cultivar (i.e. Dena) had the best grain yield because of the greatest dry matter translocation efficiency; contribution of pre-anthesis assimilates to grains with better nitrogen use and translocation. Therefore, the modern subtropical wheat cultivar was shown the best responses to highest N fertilizer applications.

Key words: Nitrogen, wheat, dry matter, cultivar, efficiency.