Relative Date of Wheat Seedling Emergence and Its Impact on Grain Yield

Emergence of wheat ( Triticum aestivum L.) seedlings usually occurs over a period of several days, resulting in nonuniformity among neighboring plants. The impact of nonuniformity in time of emergence on grain yield has not been determined. We determined effect of planting depth on relative date of seedling emergence, and of relative date of emergence on grain‐bearing tillers and grain yield per plant. Large seed (39.8 ± 4.59 mg kernel −1 ) in 1989, and large (41.7 ± 3.83 mg kernel −1 ) and small seeds (24.3 ± 4.56 mg kernel −1 ) in 1990 were obtained from ‘Roblin’ wheat. Seeds were hand.planted at 25‐, 50‐, and 75‐mm depths on Neuborst clay loam (fine‐loamy, frigid, Aquic Haploborolls) at Portage la Prairie, MB. Plants were tagged the day they emerged, and individual plant yield was determined at harvest. Planting depths did not differ for total percent emergence in 1989, but in 1990, increasing planting depth led to decreased total emergence. Gompertz growth model predictions of inflection time, maximum emergence rate, and cumulative percent emergence indicated that seedling emergence rate decreased as planting depth increased, and the decrease was greater with small seed than with large seed. The first date on which seedlings emerged each year was designated as Day 1. Averaged across 2 yr, plants that emerged on Day 1 to 3 produced 1.4 times the yield of those emerged on Day 4 to 6, and 3.2 times the yield of those emerged on Day 7 to 9. Reduced yield of late emerged plants was due primarily to fewer grain‐bearing tillers. This research demonstrates the benefit of shallow placement of large seeds in minimizing variation in time of seedling emergence among plants, and increasing grain yield.