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

The adoption of soil-conserving management systems in dryland soft whi te winter wheat (Triticum aestivum L.) production areas is limited by concerns that seedbed residues contribute to suboptimal stand establis hment. Field trials were seeded in 1990 (Trial 1) and 1991 (Trial 2) n ear Pendleton, OR, to ascertain seedbed crop residue, seed size, and c ultivar effects on emergence, early growth and development, and yield of soft white winter wheat. Seedbeds were much drier in Trial 2 than i n Trial 1. Seed-soil contact was probably reduced in high residue cove r, but emergence rate was reduced by seedbed residue in Trial 2 only w hen seed zone water content was <120 g kg(-1). Consequently, plant gro wth and development were responsive to seedbed residues only in Trial 2. Final stand density and grain yield were not sensitive to seedbed r esidue level in either trial. Seed size had no effect on laboratory ge rmination, but seedlings from large seed emerged more rapidly in the f ield. 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 pro duced 4.2% greater grain yield than from small seed in Trial 2. Cultiv ar performance was determined by genetic potential, seed size, and see d quality, and was not differentially influenced by seedbed residue le vel. Emergence was influenced by coleoptile length which differed amon g cultivars, but coleoptile length was not related to seed size. Highe r levels of seedbed surface residues required to reduce soil erosion i n dryland crop production systems do not reduce stand establishment or yield of soft white winter wheat.