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Impact of plant density on the canopy area index and weed infestation depending on different cultivars of winter oilseed rape (Brassica napus L., ssp. oleifera Metzg.)

One way to increase the competitiveness of crop plants against weed infestation is to adjust crop density. Introduction of new (“semi-dwarf”) cultivars of winter oilseed rape triggers a need for research in this field. A two-factor experiment evaluated the effect of plant density and winter oilseed rape (WOSR) cultivars on the canopy architecture and weed infestation of a WOSR crop as well as on the correlation between these traits. During the 2010–2012 study period, the average plant density was 38.0; 29.4; and 22.9 plants m-2 (three row spacings were used: 33, 44, and 55 cm). The oilseed rape cultivars were as follows: conventional, hybrid and “semi-dwarf” hybrid. Experimental factors did not cause significant differences in the number of weeds and their mass. However, there was a clear trend of decreasing total number of weeds in the span of 33 cm spacing than in the 44 and 55 cm. Hybrid cultivar resulted in increasing of total number of weeds in comparison to the conventional one. The differences in the assimilation area of WOSR plants per unit of ground area were significant between row spacings until the end of the flowering stage and between cultivars until the flower bud development stage. During the growth stages from the beginning of flowering until the end of pod development significant negative correlations were found between the assimilation area and the number of weeds, while the correlations between the assimilation area and the weed weight were insignificant. Insignificant correlations also occurred between the number of oilseed rape plants per unit area and the mass of weeds. The results indicate the possibility of reducing the demand for seed sowing, without requiring additional costs for weed control. 
 