اثر غلظت و زمان محلول‌پاشی کود نیتروژن به عنوان مکمل تغذیه خاکی بر انتقال مجدد ماده خشک و عملکرد دانه و روغن کلزا (Brassica napus L.)

In order to evaluate the effect of concentration and time of foliar spraying of nitrogen fertilizer as complementary of soil nutrition on dry matter remobilization and seed and oil yield of rapeseed (Hyola401), an experiment was conducted in complete randomized block design with 16 treatments and three replications in two years (2008-2010) in Rice Research Institute of Iran (Rasht). In this experiment, nitrogen concentration (from urea source) at two levels (5 and 10 ppm) and application time in seven levels including 1-seedling stage at 6-8 leaves 2: beginning of stem elongation, 3: prior to flowering, 4: 6-8 leaves + stem elongation, 5: 6-8 leaves + prior to flowering, 6: stem elongation+ prior to flowering, 7: 6-8 leaves + stem elongation+ prior to flowering plus two control treatments including zero nitrogen fertilizer and conventional fertilization (180 kg.ha-1) at seed sowing, stem elongation and prior to flowering in equal rates, were considered. Results showed that foliar application of nitrogen (10 ppm) in 6-8 leaves+stem elongation+prior to flowering stage had the highest dry matter remobilization (612.2 g.m-2), current rate of photosynthesis (3074 g.m-2), and grain yield (3686.2 kg.ha-1). Calculation of regression coefficients showed that dry matter remobilization had linear and positive relationship with grain yield (r2=0.95**). According to the results of the present experiment, it seems that foliar application of nitrogen (10 ppm) at 6-8 leaves + stem elongation+ prior to flowering stage and stem elongation+ prior to flowering stage increases dry matter remobilization, seed and oil yields.