Effects of Urea, Zinc Sulphate Fertilizers and Azotobacter and Azospirillum Inoculant Application on Grain Yield and Nitrogen Use Efficiency of Rapeseed (Brassica Napus L.)

To study the effects of simultaneous application of urea, ZnSO4 and inoculants, (Azotobacter and Azospirillum), on uptake and nitrogen use efficiency in rapeseed, var. Hyola308, a field experiment with split plot factorial layout based on a randomized complete block design was conducted at the research field of faculty of Agricultural Science, University of Guilan in 2008. Experimental treatments consisted of nitrogen fertilizer in four levels (0, 50, 100 and 150 kg ha-1 in urea form) as main plots and two factors including ZnSO4 fertilizer at two levels (0 and 50 kg.ha-1) and inoculants (with and without inoculants) were arranged in sub plots. Results showed that urea fertilizer, ZnSO4 fertilizer and inoculants had significant effects on uptake and nitrogen use efficiency. Maximum nitrogen use efficiency (38.7) was detected in 50 kgN ha-1+ZnSO4 fertilizer+ inoculant and minimum (27.2) was obtained in 150 kgN ha-1N+ZnSO4 fertilizer+ inoculants. The maximum agronomical nitrogen efficiency (14.9) was obtained in 50 kgN ha-1+ ZnSO4 fertilizer+inoculants and minimum (8.6) was obtained in 100 kgN ha-1+without ZnSO4 fertilizer+without inoculants. Maximum physiological efficiency of nitrogen (34.8) was detected in 50 kgN ha-1+ZnSO4 fertilizer+inoculants. Maximum apparent recovery fraction of nitrogen (52.2) was obtained in 50 kgN ha-1+ZnSO4 fertilizer+inoculants. Maximum oil content (42.8%) and grain yield (2568 kg.ha-1) were observed in zero and 150 kgN ha-1+ZnSO4+inoculants treatments, respectively. With respect to the significant effects of ZnSO4 and inoculants with lower N rate and high nitrogen use efficiency, it seems that the application of inoculants with an additional ZnSO4 fertilizer may lead to better application of nitrogen fertilizer in rapeseed production and minimizing environmental risk.