Yield and Nitrogen Use Efficiency of Rapeseed (Brassica napus L.) Influenced by Nitrogen Rates and Irrigation Regimes

This research was carried out during two years 1394 and 1392 in order to investigate the effect of nitrogen rates on quantitative yield and nitrogen use efficiency of rapeseed in different irrigation regimes in Qazvin. The factorial experiment was conducted as randomized complete block design with three replications. The irrigation factor at three levels , normal irrigation, cut off irrigation at stem elongation and cut off irrigation at flowering stage) and nitrogen rates in five levels (0, 40, 80, 120 and 160 kg N.ha-1) were considered in experimental blocks. The results of combined analysis showed that the effect of irrigation levels, nitrogen and their interaction were significant on grain yield. The results of the mean comparison indicated that the highest grain yield in normal irrigation regimes and the lowest grain yield related to irrigation cut at flowering stage. Treatments of 120 and 160 kg.ha-1 pure nitrogen in normal irrigation conditions had the highest seed yield (3780 and 4054 kg.ha-1), respectively. The results showed that increasing nitrogen up to 160 kg N. ha-1 caused to increase grain yield significantly under normal irrigation regime. However, in these conditions, a significant increase in grain yield was observed up to 120 kg N. ha-1, and there was no statistically significant difference between treatments of 120 and 160 N. ha-1. In terms of irrigation interruption in flowering and stemming stages, increase in nitrogen consumption up to 120 N. ha-1increased grain yield and then decreased somewhat. In general, in the absence of water during flowering and stemming, consumption of 120 160 N. ha-1 and in the presence of sufficient water, consumption of 160 N. ha-1 is recommended.