Influence of various levels of nitrogen fertilizer on grain yield and nitrogen use efficiency in canola (Brassica napus L.) cultivars

To evaluate the effect of various levels of nitrogen fertilizer on nitrogen use efficiency and grain yield of canola cultivars, a split plot experiment based on randomized complete block design was conducted in 2007. Factors were: nitrogen fertilizer at four levels (zero, 50, 100 and 150 kg/ha) in the main plots and canola cultivars at three levels (‘Clover’, ‘Opera’ and ‘Okape’) in the sub plots. The results showed that the effects of cultivar and nitrogen levels were significant on grain yield, grain per plant, pod per plant, grain 1000 weight, harvest index and plant height. The interaction effects of cultivars in nitrogen levels were significant on grain yield, grain per plant, pod per plant and plant height. Means comparison showed that with increasing nitrogen levels, grain yield increasing. Response of canola cultivars was different to grain yield. The highest grain yield (1.18 ton/ha) was obtained in Opera cultivar and the least (0.78 ton/ha) of it was in Okape cultivar. Means comparison showed that the highest grain yield, grain per plant, pod per plant and plant height was obtained by the plots which applied 150 kg N/ha with Opera cultivar and the least of it was in Okape cultivar without nitrogen application. However, application of 100 and 150 kg N/ha had similar grain yield in Opera cultivar. Nitrogen use efficiency was significantly as affected by cultivar, nitrogen levels and cultivar × nitrogen levels. Means comparison showed that with increasing of nitrogen, decreased nitrogen use efficiency. Response of canola cultivars was different with nitrogen use efficiency. Maximum nitrogen use efficiency (5.26 kg/kg) was obtained in the plots which 100 kg nitrogen ha-1 with Opera cultivar was used and minimum (2.64 kg/kg) was obtained in the plots which 150 kg nitrogen ha-1 with okape cultivar was used.