Interaction effect of plant spacing and nitrogen on growth and yield of rice (Oryza sativa L.) under different Barnyardgrass (Echinochloa crus-galli) densities

In order to evaluate the interaction effects of plant spacing and nitrogen on growth and grain yield of rice, an experiment was conducted in Kushkak agricultural research center in 1998 cropping season. The experimental design was split-split plot in which nitrogen was assigned to main plots, plant spacing to sub-plots and weed density to sub-sub plots. With increase in rice plant spacing from 2020 to 2525 cm, rice grain yield increased. Among yield components, the number of panicle per plant (11.7vs 13.7) and number of grain per plant (782.2 vs 1202.7) significantly increased. The increase in Barnyardgrass weed density significantly reduced rice grain yield (from 4328 to 2587 kg ha-1). Rice grain yield increased by increasing nitrogen rate (from 2818 to 3802 kg ha-1) but there was no significant difference between 80 and 120 kg/ha-1. Nitrogen fertilizer efficiency decreased when the rate of nitrogen increased. Harvest index reduced by increasing the rate of nitrogen, but this reduction was not significant.