In order to study the effects of simultaneous application of nitrogen (N) and ZnSO4 fertilizers and biofertilizer (Azotobacter and Azospirillum) on grain yield and growth traits of rapeseed, Hyola308 cultivar, a field experiment, with split plot factorial layout based on randomized complete blocks design with three replications, was conducted at Research Field of Faculty of Agriculture, University of Guilan, Rasht, Iran, during 2007-2008 growing season. Nitrogen fertilizer at four levels (0, 50, 100 and 150 kg/ha) were the main plot and ZnSO4 fertilizer at two levels (0 and 50 kg/ha) and biofertilizer at two levels (with and without biofertilizer) were arranged in sub-plots. Results showed that maximum and minimum leaf area indices at flowering stage (average of 1.29 and 0.95, respectively) were obtained in 150 kg/ha N+ZnSO4+ biofertilizer and in 50 kg/ha N+ no ZnSO4+ no biofertilizer treatments. Maximum and minimum crop growth rates at flowering stage (average of 5.89 and 3.19 g/m2.GDD, respectively) were obtained in 150 kg/ha N+ZnSO4+ biofertilizer and control treatments. Maximum and minimum grain yields (2568, 2468 and 543 kg/ha, respectively) were obtained in 150 kg/ha N+ with/without ZnSO4+ biofertilizer and control (no fertilizer) treatments. Maximum and minimum oil yields (42.8 and 37.3%, respectively) were measured in 0 kg/ha N+ZnSO4+ biofertilizer and 150 kg/ha N+ no ZnSO4+ no biofertilizer treatments. Since there was no significant difference between 150 and 100 kg/ha N+ZnSO4+ biofertilizer treatments in terms of impact on canola grain yield and growth traits, it seems that application of biofertilizer (Azotobacter and Azospirillum), without any reduction in yield, increased grain production and oil content and saved 50 kg/ha of N fertilizer. Biofertilizer (Azotobacter and Azospirillum), along with zinc and sulfur, produced phytohormones, and N fertilizer increased dry matter accumulation and leaf area index (by increasing carbohydrate conversion to protein), made fertilizer sources available to plants for longer periods of time.

Keywords: Grain yield, Growth index, Savings in fertilizer use

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