Effect of different amounts of potassium and nitrogen fertilizers on yield and yield components of rapeseed after rice cropping

In order to determine the appropriate amounts of potassium and nitrogen fertilizers to achieve high grain and oil yields of rapeseed (Hyola 401) in paddy fields, a field experiment was conducted at Rice Research Institute of Iran (Rasht) in a factorial experiment based on the complete randomized block design with 3 replications in 2008-2010. The first factor was the amounts of potassium fertilizer in three levels (100, 150 and 200 kg.ha-1) and the second factor was nitrogen fertilizer values in the four levels (zero, 180, 240 and 300 kg.ha-1 from urea resource). The results of the combined analysis of variance showed that significant difference between potassium levels, according as application of 150 and 200 kg.ha-1 potassium had the highest of grain yield. Between the levels of nitrogen, application of 240 and 300 kg.ha-1 produced the highest grain yield. The control treatment with average of 43.92%, showed the maximum oil precent. In general, 150 kg.ha-1 of potassium and 240 kg.ha-1 nitrogen level are recomended due to less fertilizer consumption and prevention of destroying effect on the environment.