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Title: LONG-TERM EFFECTS OF CROP MANAGEMENT ON WEED SEED DENSITY AND VERTICAL DISTRIBUTION IN SOIL

Author
item HOFFMAN, MELINDA - IOWA STATE UNIVERSITY
item OWEN, MICHEAL - IOWA STATE UNIVERSITY
item Buhler, Douglas - Doug

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Conservation tillage crop production systems reduce soil erosion, conserve soil moisture, and reduce energy use; but often increase weed control problems. Conservation tillage consists of reducing or eliminating soil tillage before crop planting. This alters the environment where crops, weeds, and weed control practices interact. Understanding the influence of tillage and crop rotation on weed population development will help the development of more effective weed management systems that require less herbicide. The purpose of our research was to determine the long-term effects of tillage and crop rotation on weed seed numbers and vertical distribution in the soil. We found that both tillage systems and crop rotation affected weed seed behavior in the soil. The more tillage conducted, the more uniform the weed seed distribution in the upper layers of the soil profile. Management practices that reduced weed seed production (herbicide application and interrow cultivation) reduced the effects of tillage systems on vertical distribution. By keeping weed production to a minimum, producers can reduce weed control problems in conservation tillage systems. Results of this research show that tillage and crop rotation interact with weed species, weather conditions, and other factors to determine the nature of the weed seed population in the soil. When conservation tillage systems are used, changes in weed problems and field conditions must be recognized and weed management strategies adjusted accordingly. Producers must combine a knowledge of weed population dynamics with the best control techniques to develop economically viable and environmentally sound weed management for conservation tillage systems.

Technical Abstract: Field experiments were initiated in 1988 and conducted for six years to examine the effects of tillage systems and herbicide application methods on weed seed numbers in the soil seed bank of a soybean/corn rotation and continuous corn cropping system. 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 soil depths 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 the no-tillage plots generally contained greater concentrations of weed seeds than deeper sampling depths. Vertical distribution patterns of weed seeds were observed most often when large numbers of seeds were likely, such as in plots where weed control was poor. Effects on monocot and dicot weeds were similar. Weed seed numbers were often reduced by broadcast herbicide compared with band applied and interrow cultivation. Management practices that reduced weed seed number such as broadcast applying herbicide and interrow cultivation increased crop yields.