Cultural practices such as N-fertilizer and plant spacing for each rice variety may differ because of their different genetic background. For obtaining the optimum N-fertilizer and plant spacing requirement of two rice varieties (a local and a breeding variety) a field experiment was conducted in RCB design with four replications. Two varieties were treated with three nitrogen levels (45, 85 and 125 kg ha-1) and three plant spacings (15x15, 22.5x22.5 and 30x30 cm). Effect of variety was significant for all of traits, except for thousand seed weight and biomass weight, totally indicating that varieties respond differentially to cultural practices. Results also showed that fertilizer effect was significant for thousand seed weight, plant height and yield, while spacing effect was significant for all of traits, except for thousand seed weight. Two varieties had different biomass production only at third level of nitrogen. Breeding variety produced more yield than local one with application of 85 kg ha-1 nitrogen, although local variety also produced its maximum yield with 85 kg ha-1 nitrogen. Local variety had an invariable response to different levels of nitrogen, while breeding variety had a variable response. Breeding variety had maximum biomass in 15 cm spacing and local variety did not differentially respond to spacing level. However, biomass of breeding variety was severely reduced with increasing space between hills. Altogether, breeding variety had more harvest index compared to local variety for most combinations of nitrogen and spacing levels, indicating that breeding variety allocated higher material to storage organs and transmitted more products from sources to its sinks (kernels). On the basis of these results, for production of maximum yield local variety must be cultivated with 85 kg ha-1 nitrogen and 22.5 cm transplanting space, while breeding variety must be cultivated with 85 kg ha-1 nitrogen and 15 cm transplanting space.
