The effects of tracking by tractor wheels on the emergence of common weed species of central Iowa were studied near Ames, IA, in 1996 and 1997. Seedling emergence in tracked and nontracked interrow areas, soil water content, and soil temperature were monitored for 8 to 10 wk after planting of soybean (Glycine max). Compared to nontracked interrow areas, a single wheel-tracking pass at crop planting increased the cumulative number of seedlings of giant (Setaria faberi) and yellow foxtails (S. glauca) by 187%, common waterhemp (Amaranthus rudis) by 102%, and common lambsquarters (Chenopodium album) by 30%. There was little effect of wheel traffic on velvetleaf (Abutilon theophrasti) emergence. After planting, soil water content to a depth of 5 cm was higher in tracked areas than in nontracked areas, but after 6 wk there was no difference. Soil temperature at 4- to 5-cm depth was similar in tracked and nontracked interrows. Compaction from wheel traffic apparently did not create a physical impediment to emergence; rather, it altered micro-environmental conditions in ways that stimulated weed germination and emergence.
