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 th e above parameters. Commercially processed, untreated 'Stephens' winte r wheat grains, separated into size-density combinations of large-dens e, large-light, small-dense, small-light, and unsorted, were seeded in to tilled and nontilled soil in the fall of 1990 and 1991. In 1990, wh en seed zone soil moisture was adequate, tillage significantly decreas ed 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 e mergence (15%), number of main stem leaves (11%), seminal roots (4%), root intercepts (3 and 5 cm > 100%), straw yield (17%), and grain yiel d (12%). The only significant effect of seed size and density on above ground parameters was on main stem leaf number, seedling weight, and n umber of heads. Small-light seed had significantly more 3-cm (53%) and 5-cm (39%) root intercepts and 26% fewer disease-pruned roots than ot her size-density treatments. Seed size and density did not significant ly affect grain yield in either year. Therefore, there is not sufficie nt justification to change the current seed processing procedure by us e of a gravity table.