Competitive ability and phytotoxic potential of four winter canola hybrids as affected by nitrogen supply

Low inputs in nitrogen may affect canola (Brassica napus L.) competitiveness and allelopathic potential as well as grain and oil yields. A 2-yr study was conducted to assess nitrogen supply effect on the ability of four canola hybrids to compete with corn poppy (Papaver rhoeas L.) as well as its effect on canola seed and oil yields. Phytotoxic potential of canola hybrids on germination and growth of winter wild oat (Avena sterilis spp. ludoviciana L.), corn poppy, and wild mustard (Sinapis arvensis L.) was also determined using a perlite-based bioassay. At canola blossom, corn poppy plant number in nitrogen-treated plots was 23% less than that in the nitrogen-untreated ones. Canola seed and oil yield was reduced 18.6 and 23.7%, respectively, by the competition of 100 corn poppy plants [m.sup.-2], with 'Elan' and 'Titan' the most productive hybrids. Nitrogen supply did not increase in all cases the competitive ability or the seed and oil yields. In the laboratory, germination of the winter weeds was completely inhibited by the greatest extract concentration (5 g 100 [mL.sup.-1]) of all hybrids. Nitrogen supply did not affect, in most cases, the phytotoxicity of canola hybrids, while phytotoxicity did not significantly differ among hybrids. Conclusively, the hybrids Elan and Titan, cultivated without any herbicide or nitrogen fertilizer, could be viable as a short-term alternative crop system for canola seed and oil production, especially in organic or low-input fields infested by corn poppy. doi: 10.2135/cropsci2009.05.0270