Tillage intensity affects weed communities in agroecosystems - Invasive Plants: Ecological and Agricultural Aspects - page 192

dubius Scop.) were associated with minimum-zero tillage and rarely occurred
with conventional tillage (Tab. 2).
The association of annual weed species with tillage system was more com-
plex than that noted with biennial or perennial weeds. Of the 39 annual weed
species in these studies, 44% were associated with minimum-zero tillage, 33%
with conventional tillage and 23% were ubiquitous across tillage systems
(Tab. 2). Many of the annual species associated with minimum-zero tillage
have wind-disseminated seed capable of germinating on the soil surface;
examples being annual sowthistle ( Sonchus oleraceus L.), common groundsel
( Senecio vulgaris L.), prickly lettuce ( Lactuca serriola L.) and narrowleaf
hawksbeard ( Crepis tectorum L.). Many of the hard-seeded annuals, such as
mustards, pigweeds, wild buckwheat ( Polygonum convolvulus L.) and com-
mon lambsquarters, were associated with conventional tillage. 11 of 13 winter
annual species were associated with minimum-zero tillage. The prediction that
annual grass species will proliferate with conservation tillage was not sup-
ported in these studies. While downy brome was associated with minimum-
zero tillage, green foxtail ( Setaria viridis (L.) Beauv.) was associated with con-
ventional tillage and barnyardgrass ( Echinochloa crus-galli (L.) Beauv.) and
wild oat were ubiquitous across tillage systems.
Volunteer crops were not necessarily associated with minimum-zero tillage
(Tab. 2). The large-seeded crops such as lentil, pea and sunflower ( Helianthus
annuus L.) exhibited a strong association with conventional tillage, indicating
the need for greater soil-seed contact for germination of these species. Barley
( Hordeum vulgare L.) and rye ( Secale cereale L.) also were associated with
conventional tillage but oilseed rape, linseed, mustard ( Brassica juncea L.),
and wheat were present at similar levels across tillage systems.
Identification of plant functional groups based on response to tillage system
was difficult. A classification based on life cycle alone was not feasible as
exceptions were always found. The predicted association of annual weeds with
conventional tillage [13, 50] often did not occur. The placement of the annual
grass weeds in different response groups and the fact that not all volunteer
crops were placed in the zero tillage response group are more examples of
exceptions to simple classifications and predicted responses to tillage regime.
New classifications were attempted using characteristics such as seed dor-
mancy, seed bank persistence, recruitment depth, dispersal mechanism, and
herbicide tolerance. However, inadequate knowledge of species biology and
ecology relevant to our regional conditions limited development of any mean-
ingful weed functional groups from this study.
Summary
Cropping studies on the Canadian Prairies indicate that tillage intensity is a
strong 'filter' affecting weed communities in agroecosystems. Most biennial
and perennial weeds were associated with minimum- and zero-tillage. In con-