Agriculture Reference
In-Depth Information
Temporal Dynamics in Weed Communities
The seed bank is an important source for weed infestations in agricultural fields
(Buhler et al. 1997). Although the linkage between composition of the weed seed
bank and weed pressure can be difficult to gauge (Davis 2006), understanding the
factors affecting the persistence and species composition of weed seed banks in
arable soils is important for weed management (Buhler 2002, Davis 2006).
When the MCSE was established, weed seed banks in all four annual row-crop
systems were dominated by
Chenopodium album
(lambsquarters), likely reflect-
ing its ability to persist with the previous 20 + years of herbicide use typical of
weed management in conventional row-crop agriculture (Davis et al 2005). Over
time, the composition of the weed seed banks in the four annual row-crop systems
diverged in response to management (Menalled et al. 2001, Davis et al. 2005). In
the Conventional and No-till systems, seed banks shifted to dominance by annual,
C
4
grasses (mainly
Panicum dichotomiflorum
(fall panicgrass) and
Digitaria san-
guinalis
(large or hairy crabgrass), and some
S. faberi
, whereas the Reduced Input
and Biologically Based systems became dominated by small-seeded dicot species
(Fig. 7.2) such as
Stellaria media (
common chickweed),
Veronica perigrina
(purs-
lane speedwell), and
Arabidopsis thaliana (
mouse-ear cress). Despite the impor-
tant role that seed banks play in determining weed communities and the observed
divergence in weed seed bank composition (Fig. 7.2) and differences in emergent
weed biomass (Table 7.3), there is little divergence in the weed species composi-
tion among annual systems (Fig. 7.1; see also Davis et al. 2005). This suggests
that interannual variation in these communities is strongly controlled by cropping
system management (Davis et al. 2005) and climatic variation (Robinson 2011).
The timing of tillage and the use of cover crops can have dramatic effects on the
composition of the emergent weed community in row crops (Smith 2006, Smith
and Gross 2007), which may result from interactions between the disturbance
regime (e.g., whether and how tillage or herbicides are used to control weeds) and
the source of N (legume cover crop vs. inorganic fertilizer). Both the type (herbi-
cides vs. interrow cultivation) and timing of weed management disturbances can
alter the composition of the weed community, which in turn affects its response to
differences in N availability.
Temporal Dynamics in Successional Communities
Within 4-5 years after abandonment from agriculture, the MCSE Early Successional
system underwent a typical shift in species composition from initial dominance by
annual weeds to dominance by herbaceous perennials (Huberty et al. 1998, Gross
and Emery 2007). Although species composition initially differed among the six
replicate plots, within 5 years all plots converged to a similar composition (Fig. 7.4)
and were dominated by perennial forbs and relatively few grasses (see also untilled
treatment, Table 7.4).
Although native species are relatively rare in these communities (Table 7.4),
they produce about 50% of the aboveground biomass (Gross and Emery 2007).
The low number of native species in these fields probably results from the lack
