Abstract: In order to estimate extinction coefficient (EC or K), radiation use efficiency (RUE) and dry matter accumulation (DMA) in canola (Brassica napus L.), a factorial experiment was conducted based on randomize complete block design (RCBD) with four replications in 2013-2015, at Gonbad Kavous University, Iran. Treatments consisted of four canola cultivars (Hyola 401, Zarfam, Hyola 308 and RGS003) and three levels of nitrogen fertilizer (0, 50% (75 kg/ha urea) and 100% (150 kg/ha urea) of N fertilizer recommendation). Results showed that nitrogen fertilizer had a significant impact on light extinction coefficient, especially in the second year. The obtained figures of extinction coefficient for the cultivars ranged from 0.4 to 0.8, with the lowest at 100% recommended nitrogen for RGS003 in the second year. The amount of RUE was different during the two years in terms of nitrogen fertilizer for cultivars. The highest RUE (1.2 g MJ-1) was obtained at 100% nitrogen fertilizer for RGS003 in the second year. There was a significant effect of treatments on dry matter (P<0.05). The highest and lowest dry matter production were 1032.4 and 371.9 g m-2 day-1 at zero and 100 percent of N fertilizer recommendation and for Hyola 308 and RGS003, respectively.
Keywords: brassica napus l., fertilizer, leaf area index, radiation use efficiency