The weed-competitive ability of Canada western red spring wheat cultivars grown under organic management

Competition from weeds can reduce grain yields in both conventional and organic systems. Plant height, tillering, and elevated photosynthetically active radiation interception are some of the traits thought to help confer competitive ability in cereal grains. Crop cultivars developed before the advent of modern, high-input agriculture may be better suited to lower soil nutrient levels and elevated weed competition. Twenty- seven spring bread wheat (Triticum aestivum L.) cultivars, representing 114 yr of Canadian wheat breeding, were grown at conventionally and organically managed sites in north central Alberta over a 3-yr period. Average conventional yields were 63% greater than organic yields, and average overall weed biomass was significantly greater under, organic management. Earlier flowering and maturity were more important for achieving high grain yield in organic fields than in conventional fields. Greater numbers of spikes m(-2) were associated with increased grain yield inorganic fields but were not in conventional fields. In organic fields, increased plant height and early maturity were associated with reduced weed biomass, while strong early season vigor was related to increased yield, increased spikes m(-2), and reduced weed biomass. A competitive crop ideotype for organically grown spring wheat in northern growing regions of the Canadian Prairies should include taller plants, with fast early season growth, early maturity, and elevated fertile tiller number.