Submitted to: North Central Weed Science Society US Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 12, 1996
Publication Date: N/A
A soybean/corn rotation and a continuous corn cropping system were initiated in 1988 and conducted for 6 years on adjacent fields at the Iowa State University Agronomy and Agricultural Engineering Research Center in Boone County, IA. Soil was a Clarion-Nicollet-Canisteo association. Both studies examined the effects of tillage systems (conventional, reduced, and no-tillage) and herbicide application methods (band, broadcast, and none) on weed seed numbers in the soil seed bank. Interrow cultivation was also a treatment from 1988 to 1991. Weed seeds were sampled at 0 to 5, 5 to 10, and 10 to 15 cm and their distributions were compared. Vertical distribution of weed seeds differed among tillage systems in both cropping systems. Seeds were apparently mixed throughout the soil by moldboard plowing in the conventional-tillage system because there were few differences among sampling depths. Reduced-tillage tended to stratify seeds such that their numbers decreased as depth increased. The top 5 cm of soil in no-tillage plots generally contained greater concentrations of weed seeds than deeper sampling depths. Weed seed numbers were often reduced by broadcast herbicide compared to band applied and by interrow cultivation. Management practices that reduced weed seed numbers such as broadcast applying herbicide and interrow cultivating increased crop yield. Vertical distribution patterns of weed seeds were observed most often when large numbers of seeds were likely, such as in plots where weed control in the form of herbicide application was lacking. We conclude that the tendency of various tillage regimes to differentially distribute weed seeds throughout the soil profile could be minimized by management practices used to control weeds and reduce seed production.