STAND ESTABLISHMENT RESPONSES OF SOFT WHITE WINTER-WHEAT TO SEEDBED RESIDUE AND SEED SIZE

The adoption of soil-conserving management systems in dryland soft white winter wheat (Triticum aestivum L.) production areas is limited by concerns that seedbed residues contribute to suboptimal stand establishment. Field trials were seeded in 1990 (Trial 1) and 1991 (Trial 2) near Pendleton, OR, to ascertain seedbed crop residue, seed size, and cultivar effects on emergence, early growth and development, and yield of soft white winter wheat. Seedbeds were much drier in Trial 2 than in Trial 1. Seed-soil contact was probably reduced in high residue cover, but emergence rate was reduced by seedbed residue in Trial 2 only when seed zone water content was <120 g kg(-1). Consequently, plant growth and development were responsive to seedbed residues only in Trial 2. Final stand density and grain yield were not sensitive to seedbed residue level in either trial. Seed size had no effect on laboratory germination, but seedlings from large seed emerged more rapidly in the field. Plants grown from large seed were taller, heavier, and had more tillers than plants grown from small seed. Planting large seed had no effect on grain yield in Trial 1, but plants grown from large seed produced 4.2% greater grain yield than from small seed in Trial 2. Cultivar performance was determined by genetic potential, seed size, and seed quality, and was not differentially influenced by seedbed residue level. Emergence was influenced by coleoptile length which differed among cultivars, but coleoptile length was not related to seed size. Higher levels of seedbed surface residues required to reduce soil erosion in dryland crop production systems do not reduce stand establishment or yield of soft white winter wheat.