Seedling vigor and grain yield of 'Roblin' wheat affected by seed size

Commercial spring wheat (Triticum aestivum L.) seedlots contain a small proportion of small-sized seeds. Wheat producers often remove small-sized seeds, attempting to increase seedling. rigor and grain yield. A 3-yr study was conducted from 1989 to 1991 on a Neuhorst clay loam (Aquic Haploborolls) to determine the effect of seed size and proportion of small seeds in a seedlot on emergence, dry matter (DM) production, and grain yield of 'Roblin' wheat. A commercial seedlot containing seeds >2.2 but <3.2 mm in width was designated au the original seedlot and nas divided into 11 sublots: five with uniform seed sizes (2.2-2.4, 2.4-2.6, 2.6-2.8, 2.8-3.0, and 3.0-3.2 mm wide), three with variable seed sizes (2.4-3.2, 2.6-3.2, and 2.8-3.2 mm wide), and three more sublets from which seeds <2.2, <2.4, and <2.6 mm wide were successively removed, with the remaining seeds planted at correspondingly reduced planting density. The use of uniform large seeds increased shoot DM in 1990 and 1991, but not in 1989, Grain yield was increased with uniform targe seeds only for the early planting in 1990, where soil temperature was low. A small proportion of smalt seeds in a seedlot decreased shoot DM in two of sis cases, but in no case decreased percent emergence or grain yield. When small seeds were removed, the remaining seeds, planted at 278 and 236 seeds m(-2), had grain yields equivalent to that of the original seedlot planted at 300 seeds m(-2). There is thus no need to remove small seeds from a seedlot that has been commercially cleaned, and, if uniform large seeds are available for planting, seeding rate can be reduced.