Agriculture Reference
In-Depth Information
(A) Conventional
(B) No-till
*
AMARE
250
250
GRASS
*
CHEAL
AMARE
+
*
GRASS
150
150
*
+
+
**
+
+
Crop
+
+
+
+
Soybean
Wheat
Corn
+
+
CHEAL
+
50
50
+
+
+
*
*
OTHER
OTHER
-50
-50
-50
50
150
250
-50
50
150
250
(C) Reduced Input
(D) Biologically Based
250
250
GRASS
*
OTHER
*
150
150
+
++
+
+
+
+
+
+
+
+
+
+
CHEAL
+
*
AMARE
*
+
+
+
+
*
+
+
+
+
50
+
+
50
+
+
AMARE
+
+
+
*
+
*
+
+
CHEAL
*
OTHER
GRASS
-50
-50
-50
50
150
250
-50
50
150
250
DCA Axis 2
Figure 7.1
. Variation in weed species composition in relation to crop grown in the four
annual cropping systems of the Main Cropping System Experiment (MCSE). Plot scores are
from detrended correspondence analysis (DCA) of weed species composition from 1990-
2002 for each crop in A) Conventional, B) No-till, C) Reduced Input, and D) Biologically
Based systems. Symbol legend for all panels appears in panel A. Asterisks indicate scores
for the four dominant weeds used in the ordination. AMARE =
Amaranthus retroflexus;
CHEAL =
Chenopodium album;
Other = Other dicots; Grass = all grass species. Modified
from Davis et al. (2005).
forbs and C
4
grasses, while fall tillage (coinciding with the winter wheat planting)
favored winter-annual forbs and C
3
grass species (Smith 2006). The importance
of tillage timing in determining weed species composition is indicated by strong
similarities in species composition between corn, soybean, and the spring fallow
treatment (spring tillage) as well as between wheat and the fall fallow treatment
(fall tillage) (Fig. 7.3).
In the MCSE Early Successional system, a small area (20 × 30 m) at the north-
ern border of each replicate plot has been annually tilled to maintain dominance by
annual weeds as part of the Disturbance by N-Fertilization Experiment. Although
the species composition of the annually tilled plots has varied over time (Grman
et al. 2010), they are consistently dominated by giant foxtail (
Setaria faberi
;
Table 7.4), a C
4
annual grass that is a common weed in corn and soybean in the
