Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/1998
Publication Date: N/A
Interpretive Summary: Conservation tillage crop production systems reduce soil erosion, conserve soil moisture, and reduce energy use, but often increase weed 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 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 reduced weed seed numbers in the soil and 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 using conservation tillage systems, farmers need to recognize changes in weed problems and field conditions and adjust weed management strategies accordingly. Armed with an improved knowledge of weed population dynamics, farmers can develop economically viable and environmentally friendly weed management for conservation tillage systems.
Technical Abstract: Arable cropping systems are managed using practices that influence density and distribution of weed seed banks. This paper reports results of two field experiments conducted for 6 years to examine changes in weed seed numbers due to effects of and interactions among management practices. Effects were more uniform in a rotation than in continuous corn. In treatments where weed seed numbers increased, foxtails increased disproportionately to other species. Therefore, any treatment differences were caused by increases in foxtail. Weed seeds were uniformly distributed among sampling depths by conventional tillage and concentrated near the soil surface by reduced tillage. Although weed seeds in the top 5 cm of soil were expected to increase as tillage decreased, seeds were rarely affected by tillage, so weed seed demise at the surface must have increased in reduced-tillage plots. Effects of herbicide application method on weed seeds were similar to those of tillage; seed numbers were uniform among soil depths if herbicides were broadcast but differed if herbicides were banded or not applied due to increased seed deposition at the surface. The effects lacked interactions in the soybean/corn rotation, so neither tillage nor interrow cultivation adequately controlled escapes, but conventional tillage and interrow cultivation sometimes mitigated these effects in continuous corn. While tillage affected vertical distribution of seeds, weed control practices had more influence on weed seeds in the top 5 cm of soil and could be helpful to maintain weed seeds in reduced-tillage systems at numbers similar to intensively-tilled systems.