Effects of Nitrogen and Potassium Fertilizer Levels on Nitrogen Use Efficiency and Yield of Rapeseed (Brassica napus L.) as a Second Crop after Rice in Gilan Region

In order to evaluate the effects of different levels of potassium and nitrogen on nitrogen use efficiency (NUE) and yield of rapeseed (Hyola 401), a field experiment was conducted at Rice Research Institute of Iran (Rasht) in a factorial experiment based on a complete randomized block design with 3 replications for two years (2008-2010). The first factor was pure potassium fertilizer in three levels (40, 60 and 80 kg.ha-1) from sulfate potassium source and the second factor was pure nitrogen fertilizer rates in four levels (zero, 180, 240 and 300 kg.ha-1) from urea source. In this experiment, nitrogen use efficiency, nitrogen agronomic efficiency (NAE), oil content, grain and oil yields were studied. The results of the combined analysis of variance showed significant differences between potassium and nitrogen fertilizers rates for NUE, NAE, grain and oil yield and oil content. Application of 60 and 80 kg.ha-1 of potassium produced maximum NUE with average of (10.39 and 10.20 kg. ha-1 respectively), NAE (6.92 and 6.73 kg. ha-1, respectively) and grain yield (2699 and 2641 kg.ha-1, respectively) and were not significant. Among nitrogen fertilizers, application of 180 and 240 kg.ha-1 produced maximum NAE with average of 8.92 and 9.07 kg. ha-1, respectively. Maximum oil content was observed for application of 40 kg.ha-1 potassium (42.17%). Based on the results of present experiment, it seems that application of 60 kg. ha-1 potassium and nitrogen rate of 240 kg. ha-1 provide fertlizer requirement and increase the yield and nitrogen fertlizer use efficiency of rapseed.