EFFECTS OF TILLAGE SYSTEMS AND WEED MANAGEMENT ON WEED POPULATIONS INGRAIN-SORGHUM (SORGHUM-BICOLOR)

Field research was conducted from 1987 to 1991 to evaluate the influen ce of four weed management systems on weed population and species dyna mics in conventional-tillage and no-tillage grain sorghum production. These weed management systems included zero, low, medium, and high inp ut systems. The weed seedbank increased faster in zero and low input w eed management systems than in the high input weed management systems because of differences in weed control. Tillage influenced weed seed d ensities as well. Common ragweed, common lambsquarters, horseweed, and sicklepod seed densities often were greater in no-tillage than conven tional-tillage plots. Common cocklebur and large crabgrass seed densit ies were usually greater in conventional-tillage than no-tillage plots . Smooth pigweed seed densities were not affected by tillage. Increasi ng weed management inputs diminished differences between tillage syste ms. Smooth pigweed dominated the weed populations after 4 yr in both t illage systems even in high input systems.