Tillage intensity affects weed communities in agroecosystems - Invasive Plants: Ecological and Agricultural Aspects - page 193

trast, the effect of tillage on annual weeds was complex. Winter annual weeds
that emerge in fall and survive cold Canadian winters often became more
prevalent with reduced tillage, perhaps due to the combined effect of less fall
tillage and the insulating effect of increased snow cover facilitated by standing
crop stubble. Summer annual weeds with wind-disseminated seed capable of
germinating on or near the soil surface also were associated with reduced
tillage. However, many other annual weeds were more strongly associated
with conventional than with minimum- or zero-tillage and yet others were
ubiquitous across tillage systems.
The concept of weed functional groups based on responses to tillage system
may have merit as an approach to gain a better understanding of the underly-
ing selection processes, but identification of such weed groups was not
achieved in this study. Greater knowledge of weed biology and ecophysiology
combined with additional data from other studies in different regions of the
world may add to our understanding of tillage effects on weed communities in
agroecosystems.
It should be noted that selection pressures exerted by tillage intensity on
weed populations can at least be partially offset by other cropping practices.
Farmers employing cropping systems that include diverse crop rotations, com-
petitive crop cultivars, green manure and cover crops, altered seed dates, and
timely herbicide use (i.e., sound integrated weed management programs) may
mitigate some of the weed community changes associated with zero tillage
[55, 56]. Indeed, Wicks et al. [57] found at the conclusion of an 18-year study
that the overall weed density was lower with zero tillage than with conven-
tional tillage. Farmers should not be deterred from adopting zero tillage pro-
duction practices because of concerns of increased weed control problems but
rather be aware of potential changes in weed communities and how they may
be effectively managed.
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