TILLAGE, SEED SIZE, AND SEED DENSITY EFFECTS ON PERFORMANCE OF SOFT WHITE WINTER-WHEAT

Conservation tillage systems, which leave residues on or near the soil surface, can suppress soft white winter wheat (Triticum aestivum L.) emergence, early development of seedlings, and grain yield. This field study evaluated effects of tillage, seed size, and seed density on the above parameters. Commercially processed, untreated 'Stephens' winter wheat grains, separated into size-density combinations of large-dense, large-light, small-dense, small-light, and unsorted, were seeded into tilled and nontilled soil in the fall of 1990 and 1991. In 1990, when seed zone soil moisture was adequate, tillage significantly decreased seminal root intercepts at 3 cm (16%) and 5 cm (24%) below the seed. There was no significant effect of seed size-density. When seed zone soil moisture was marginal in 1991, tillage significantly increased emergence (15%), number of main stem leaves (11%), seminal roots (4%), root intercepts (3 and 5 cm > 100%), straw yield (17%), and grain yield (12%). The only significant effect of seed size and density on aboveground parameters was on main stem leaf number, seedling weight, and number of heads. Small-light seed had significantly more 3-cm (53%) and 5-cm (39%) root intercepts and 26% fewer disease-pruned roots than other size-density treatments. Seed size and density did not significantly affect grain yield in either year. Therefore, there is not sufficient justification to change the current seed processing procedure by use of a gravity table.