Changes in Growth and Oil Yield Indices of Rapeseed (Brassica napus L., cv. Hyola 401) in Different Concentrations andTimes of Application of Supplementary Nitrogen Fertilizer

In order to investigate the effect of concentration and time of supplementary nitrogen fertilizer spray on growth indices of rapeseed (cv. Hyola 401), a field experiment was conducted at Rice Research Institute of Iran as a randomized complete blocks design with 16 treatments and 3 replications in 2008-2009. The treatments included concentration of nitrogen fertilizer (urea) at two levels (5 and 10 ppm) in seven levels of application time:1) spraying at 6-8- leaf stage, 2) beginning of stem elongation, 3) prior to flowering, 4) at 6-8- leaf stage + beginning of stem elongation, 5) at 6-8- leaf + prior to flowering, 6) beginning of stem elongation+ prior to flowering, and 7) at 6-8- leaf + beginning of stem elongation+ prior to flowering, which were compared with two control treatments (no fertilizer nitrogen and conventional soil fertilization). Results showed that significant difference was observed between spray treatments including concentration and times of nitrogen application, between controls and between controls with spray treatments, of grain and oil yield, crop growth rate (CGR), leaf area index (LAI) and leaf area duration (LAD). Application of nitrogen (10 ppm) at the beginning of stem elongation+ prior to flowering stages produced maximum grain yield (4221.7 kg/ha) and oil yield (1771.1 kg/ha). Spray treatments produced maximum oil yield index (15.3%) compared to controls. Maximum LAI (6.9 and 5.6 respectively), CGR (15.2 and 14.3 g/m2.10 GDD, respectively) and LAD (1204 and 1029 cm2/10 GDD, respectively) were also obtained from spray application of nitrogen (10 ppm) at the beginning of stem elongation+ prior to flowering stages and at 6-8-leaf stage + beginning of stem elongation + prior to flowering. According to the results of the present investigation, it seems that foliar application of supplementary nitrogen fertilizer at the end growth stages (beginning of stem elongation and prior to flowering) of rapeseed plants may help to enhance growth indices, oil yield index and grain yield.