Effects of seed depth and soil aggregates on the emergence of weeds with contrasting seed traits

P>Tillage has a strong impact on weed emergence by burying seeds in the soil and modifying soil structure. Its influence can vary according to seed and seedling characteristics. This article focuses on shoot and radicle elongation in the soil and on seedling mortality caused by soil obstacles. Germinated seeds of nine contrasting weeds were planted in pots and grown in the dark to measure shoot and radicle elongation. Second, the proportion of seedlings blocked under aggregates (20-50 mm) was measured. Shoot growth rate, maximal shoot and radicle lengths were positively correlated with seed mass. Large-seeded species (e.g. Avena fatua) were more likely to emerge from greater depths (exceeding 20 cm deep). Seedling mortality increased with increasing obstacle size for all species; it was greater for monocotyledonous than for dicotyledonous species and decreased with the shoot diameter. Weed seed depth and soil structure influence emergence of weed species differently, depending on seed mass, shoot diameter and taxa. Including the results of this study in a cropping system-weed dynamics model would help to predict responses of weeds species to tillage.