COMPETITIVE ABILITY, YIELD AND YIELD COMPONENTS OF CANOLA (BRASSICA NAPUS L.) CULTIVARS AS AFFECTED BY NITROGEN RATE AND WEED COMPETITION

摘要

A field experiment was conducted at Rice Research Institute in Rasht, northern Iran, to determine the effect of nitrogen (N) rate on competitive ability, seed yield and yield components of canola cultivars. The layout of experiment was a factorial design with three randomized complete blocks. Factors were N rates (0, 100,200 kg ha"1), canola cultivars (Hayola 420, Hayola 308, RGS003 and PF), and weed management regimes (weed-free and weedy conditions, weeded and not weeded throughout the growing season, respectively). The analysis of variance indicated that effects of nitrogen rate, cultivar, weed management regime, and the interaction between nitrogen rate and cultivar were significant (P < 0.01) for seed yield, but the other two- and three-way interactions were not significant. Averaged across cultivars and weed management regimes, seed yield was significantly increased from 667 kg ha"1 to 3106 kg ha*1 as N application rate increased from 0 too 200 kg N ha1. Regardless of N rate and cultivar, canola seed yield was significantly reduced by weed interference. In unfertilized plots and averaged across weed management regimes, the highest and lowest seed yields were recorded for Hayola 420 and PF (832.3 ± 72 and 510.3 ± 61 kg ha-1, respectively).At 100 kg N ha"1 and averaged across weed management regimes, seed yield of Hayola 420 (2322.3 ± 214 kg ha"1) was significantly higher than that of other cultivars and 1.8 times greater than that of in RGS003, which had the lowest seed yield among the cultivars. At 200 kg N ha"1 and averaged across weed management regimes, the seed yield for RGS003 (3616 ± 317) was higher than that of other canola cultivars. Moreover, Main effects of N rate and cultivar were significant (P<0.01) for competitive ability of canola cultivars, but the interaction between them was not significant. Averaged across cultivars, competitive ability was significantly increased (P<0.01) asN application rate increased. Regardless of N rate, the highest competitive ability was recorded for Hayola 420 (6.5), which statistically similar to RGS003 (5.7) and PF (5.6). The lowest competitive ability (3.8) was recorded for Hayola 308. This experiment indicated that cultivars had different competitive ability against weeds and high levels of N favor the crop over the weeds.