Weed Competitive Ability of Green Peas (Pisum sativum L.) Affected by Seeding Rate and Genotype Characteristics

Field experiments were conducted in 1997,1998 and 2000 to investigate the effects of genotype and seeding rate on the competitive ability of green pea (Pisum sativum L.) crops against weeds in organic production. In 1997/98 eight cultivars were tested under three seeding rates (90, 120 and 150 seeds m-2). The dry weight (DW) of the natural weed population at harvest was used to measure competitive ability. In 2000, ten cultivars were tested with one seeding rate (110 seeds m-2) and DW of an in-sown weed crop of winter rape (Brassica napus) plants was used to measure competitive ability. The competitive ability of the pea crop increased significantly when the seeding rate was increased from 90 to 150 seeds m-2 in both years. The reduction in weed DW due to increased seeding rate in 1997 and 1998 was 50% and 30%, respectively, but the increase in yield of peas was only significant in one year. There were significant differences between competitive ability of cultivars in both experiments. Cultivars with high seed weight and with fast early growth tended to be more competitive than small sized peas and slower growing peas. Correlations for seed weight were significant in both years when certain plant types were excluded, but correlations for fast early growth were only significant in one year out of two. Cultivars with high biomass accumulation like Ambassador, Greenshaft, Jaguar, Zelda and DS8903 were highly competitive while the small sized pea cultivars like Dinos, Argona and Wizard were found to have low competitive ability and were therefore unsuitable for organic pea production. The expected lower competitive ability of semi-leafless plant types compared with normal leafed could not be verified in the present work, but needs further studies with near-related genotypes that differ only in leaf type.