Submitted to: Iowa Academy of Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/1999
Publication Date: N/A
Interpretive Summary: Despite extensive efforts to eliminate them from agricultural lands, weeds continue to plague farmers. An important characteristic that allows many weeds to survive is their ability to produce seed under adverse conditions and the ability of those seeds to survive in the soil from year to year. The weed seed reserve in the soil is commonly referred to as the weed seedbank. Since cropping practices influence the ability of weeds to produce seeds and the survival of those seeds, it is important to understand the influence of different cropping practices on the weed seedbank and subsequent weed populations. The objective of our research was to improve the understanding of the effects of crop rotation on the weed seedbank and weed populations. We found that the number of weed seeds in the soil was lower with a three-crop rotation that included an oat/forage crop than the commonly practiced corn/soybean rotation. These differences were reflected in lower weed densities in the succeeding crops. This research showed that intensifying crop rotations can be an effective means of reducing the densities of economically important weeds and can be employed as a component of integrated pest management. Since herbicides represent the majority of pesticide used in corn and soybean production, development of integrated management systems that reduce pesticide use must focus on weeds. When farmers look for methods to reduce herbicide use, appropriate crop rotation should be considered as an option. Changes in Iowa cropping systems may result from a better understanding of these system dynamics.
Technical Abstract: Weed populations in agronomic settings are, in part, a reflection of the cropping system utilized. The goal of this project was to gain an understanding of the weed population dynamics in a narrow strip intercropping (NSI) rotation by assessing the weed seedbank, weed emergence, and seedling establishment over the growing season for a corn-soybean (two-crop), and corn-soybean-oat+berseem clover (three-crop) system. Field research was conducted in 1994 and 1995, near Nashua, IA and each crop was grown in 4.6 m wide strips. Giant foxtail and total weed seed densities were significantly lower in the three-crop NSI rotation system than the two-crop system. NSI rotation system affected total preplant weed emergence. Preplant density ranged from 103 to 433 weeds per sq. m in the two-crop system, while density ranged from 3 to 99 weeds per sq. m in the three-crop system. There were no consistently significant differences in total weed seedling emergence after crop planting due to NSI rotation system when individual species were examined. Changes in Iowa cropping systems may result from a better understanding of these system dynamics.