Effects of crop and weed management on density and vertical distribution of weed seeds in soil

Cultural practices used fur crop management ran influence numbers of weed s eeds in the soil seed bank. This paper reports results of field experiments conducted for 6 yr to examine changes in weed seed numbers due to manageme nt practices. We evaluated the effect of tillage, herbicide application, an d interrow cultivation on meed seed numbers in a soybean [Glycine max (L.) Merr.]/corn (Zea mays L.) rotation and in continuous corn. Treatment effect s on meed seed numbers were more repetitive in soybean/corn than continuous corn. Foxtails (Setaria spp.) were the meed class most affected by treatme nts. Weed seeds were uniformly distributed among sampling depths in convent ional tillage and concentrated near the soil surface in reduced tillage and no-tillage. We expected weed seeds to become more numerous in the top 5 cm of soil as tillage was reduced. Tillage, as a main effect, rarely influenc ed weed seed numbers; therefore, we inferred that weed seed losses at the s urface must have increased in reduced-tillage plots. Seed numbers were unif orm among soil depths if herbicides were broadcast, but differed if herbici des were banded or omitted, due to increased seed deposition at the surface . Tillage affected vertical distribution of seeds, while the quantity of we ed seeds in the top 5 cm of soil was regulated by weed control practices. T his indicates that reducing weed seed deposition could be helpful for maint aining weed seeds in reduced-tillage systems at numbers similar to those of intensively tilled systems.