Weed seedling emergence and seed survival: Separating the effects of seed position and soil modification by tillage

Tillage causes both vertical redistribution of weed seeds and changes in soil physical properties. These two factors are rarely distinguished in studies of the impact of tillage on seedling emergence or seed survival. In this study, seeds of Chenoponium album L., Amaranthus retroflexus L., and Abutilon theophrasti Medik. were planted at particular depths in pots of undisturbed or stirred soil to separate these effects. Emergence and survival data were analysed by non-linear regression to determine the nature of significant differences between treatments. Emergence increased with slight burial and then decreased exponentially at greater depths. Average emergence over all depths was generally greater in tilled soil than in untilled soil, particularly for C. album and A. retroflexus. Seed survival approached a maximum with increasing depth. Average survival of seeds that did not produce emerged seedlings was greater in tilled soil than in untilled soil for C. album and A. retroflexus. Thus, tillage affects emergence and seed survival of weeds through changes in soil conditions independently of effects resulting from redistribution of seeds in the soil profile.