Effect of different N fertilization levels and plant population on agronomic traits and decrease in bolting of autumn-sown onion in Shahdad Region of Kerman, Iran

In order to study the effect of different N fertilization levels and to determine the optimum N level and plant population of onion in autumn cultivation, a split-plot experiment on the basis of a Randomized Complete Block Design with three replications was conducted in Shahdad Region of Kerman, Iran in 2009-2010. Nitrogen fertilization was carried out at four levels of 0, 90, 180 and 270 kg ha-1 and the population was at four levels of 450 000, 550 000, 650 000 and 750 000 plants ha-1. The planting was in the form of transplanting and the studied cultivar of onion was Primavera. It was found that N level significantly affected yield, bolting percent, ring diameter, plant height and corm weight at 1% probability level and population impacted yield, bolting percent, ring diameter and corm weight at 1% level and plant height at 5% level. In addition, the interaction between these two factors was significant for corm weight at 1% level and for ring diameter at 5% level, but it was not significant for the other studied traits. It could be concluded that the application of 180 kg N ha-1 and the population of 550 000-650 000 plants ha-1 in autumn planting of onion in Shahdad Region would result in the best yield with lower bolting percent.