HOW NITROGEN FERTILIZER AND PLANTING DATES AFFECT AUTUMN COLZA YIELD AND YIELD COMPONENTS IN GILAN

A split-plot experiment using randomized complete block design with 3 replications was conducted in the Fashtal village of Siahkal in the cropping year 2013-2014 to study the effects of various rates of nitrogen fertilizer and of planting dates on yield and yield components of the colza (Brassica napus L.) cultivar Hyola401. Four levels of the nitrogen fertilizer (urea at 0, 60, 120, and 180 kg/ha) were the main plots, and 4 planting dates (7, 17, 27 October and 6 November 2013) the subplots. Results showed the effects of the planting dates and rates of urea on biomass, seed yield, plant height were significant at the 1% probability level (p<0.01). The effects of the rates of fertilizer application, but those of the planting dates on harvest index and 1000-seed weight were not. The mutual effects of rate of urea application and planting date were not significant on any of the studied traits except for biomass and seed yield. The maximum yield was observed in the treatment with the 17 November planting date and urea application at 180 kg/ha, but it was not significantly different from the yield obtained by applying urea at 120 kg/ha.