The influence of weed removal, cultivar, and row spacing on soybean [Glycine max (L.) Merr.] yields was determined for 3 yr at the western edge of the soybean production area in the Great Plains in order to establish the critical weed-control periods. Early weed removal aided soybean stand establishment, and there was an inverse relationship between soybean stand and production of weed top-growth. Soybean seed weight and numbers per plant both increased as weed growth decreased. The soybean variety ‘Amsoy 71’ was more competitive than ‘Beeson’ to both early and late emerging weeds. Soybeans weeded at 2 through 4 weeks after planting did not show significantly reduced soybean yields from later emerging weeds. Thus, weed control the first month after planting is the most critical in obtaining high soybean yields.

Soybeans [Glycine max (L.) Merr.] were planted in an untilled, stale seedbed and conventionally tilled seedbed of Sharkey clay (Vertic Haplaquept) at Stoneville, Mississippi, in 1979 and 1980 to determine the feasibility of the stale -seedbed approach for soybean production in the Mississippi River Delta. Chemical weed control included applications of preplant, preemergence, and postemergence herbicides. Prickly sida (Sida spinosa L.) was the dominant weed in all tillage and weed-control systems. Perennial species were observed at harvest mostly in the stale - seedbed plots. Preemergence herbicides reduced the total weight of weeds per plot. Conventional seedbed preparation caused delays in planting of 3 weeks or more. In the presence of adequate soil moisture, yields of ‘Bedford,’ ‘Tracy’, and ‘Bragg’ cultivars from the stale - seedbed planting and areas that had been treated preemergence were always equal to or greater than yields from the tilled - seedbed plantings and areas that had been treated postemergence. In 1980, the hot, dry conditions of the growing season apparently negated any effect from either earlier planting or preemergence vs. post-emergence weed control.