Wheat-weed interactions at variable seeding rates in organic farming systems

Many organic producers seed spring wheat (Triticum aestivum L.) at higher rates than conventionally recommended. By increasing seeding rate, the crop is expected to become a stronger competitor against weeds. A two-year study assessed the response of spring wheat to variable seeding rates (1X conventional, 1.25X, 1.5X and 2X) in a plot experiment in Nova Scotia and on organic farms across Canada. Weed biomass and weed nitrogen uptake was reduced at higher wheat seeding rates. Weed suppression corresponded with an increase in light interception at higher seeding rates midseason, as well as increased crop height and biomass and accelerated maturity. Highest yield was obtained at a double seeding rate in 2003 and at the 1.25X, 1.5X and 2X seeding rates in 2004, although crop plant density was similar at these rates due to poor emergence in 2003. On organic farms, a 1.25X seeding rate was sufficient to maximize yield.