Depth of seedling recruitment of five weed species measured in situ in conventional- and zero-tillage fields

Differences in the depth of weed seedling recruitment due to agronomic mana gement practices, such as reduced tillage, have implications for weed compe titive ability and management strategies. Depth of seedling recruitment of Avena fatua, Triticum aestivum, Setaria viridis, Polygonum convolvulus, and Echinochloa crus-galli was measured in sim in 1997 and 1998 prior to seedi ng (preseeding) and before in-crop spraying (prespray) in a total of 44 zer o-tillage and 44 conventional-tillage fields located across approximately 3 million ha of southern Manitoba, Canada. For the monocot species, depth of recruitment was measured from the soil surface to the intact seed coats, w hich marked the point of germination. For P. convolvulus, a dicot, greenhou se studies were conducted prior to sampling in the field to identify a reli able morphological marker indicating the point of germination. For all spec ies, mean recruitment depth was found to be significantly shallower in zero - vs. conventional-tillage fields and significantly shallower in the presee ding vs. the prespray period. There were relatively few differences in mean recruitment depth among weed species. Within a sampling period and tillage system, for example, the greatest difference in mean recruitment depth bet ween species was less than 1.2 cm, and the maximum mean recruitment depth a cross species, sampling times, and tillage practice was very shallow (less than 4.2 cm). Locating weed seedling recruitment depth is the first step in characterizing weed seedling recruitment microsites. Results indicate this information should be specific to tillage and sampling time.