Agriculture Reference
In-Depth Information
Table 12.7
Jointed goatgrass seed-
ling density in the spring and spikelet
density after harvest, partitioned into
harvested grain and the soil seed bank,
after 6 years in a crop rotation study
conducted at Sidney, Nebraska, from
1990 through 1997.
Crop Rotation
a
Seedling Density
Harvested Grain
Soil Seed Bank
Plants m
−2
------Spikelets m
−2
------
WW-Ft
9.6
86
548
WW-Fh
17
95
1,010
WW-F-F
0.01
2.0
0
WW-SF-F
0.15
1.3
0
WW-PM-F
0.07
2.6
0
Signifi cance of contrast
b
2-yr vs. 3-yr
*
*
*
WW-Ft vs. WW-Fh
*
NS
*
Within 3-yr
NS
NS
NS
Source:
Adapted from Daugovish et al. (1999).
a
WW-Ft, winter wheat-fallow with fall tillage; WW-Fh, winter wheat with fall
herbicides; WW-F-F, winter wheat-fallow-fallow; WW-SF-F, winter wheat-
sunfl ower (
Helianthus annuus
L.)-fallow; WW-PM-F, winter wheat-proso millet
(
Panicum miliaceum
L.)-fallow.
b
NS and * indicate not signifi cant and signifi cant, respectively, at the 0.05
probability level.
Seed production of winter annual grass weeds
can be reduced by combining cultural practices.
Feral rye and jointed goatgrass seed production
was reduced by applying nitrogen fertilizer 5
months before wheat seeding, increasing the
wheat seeding rate, and planting a standard height
cultivar (Anderson 1997). Standard height culti-
vars frequently yield less than many semidwarf
cultivars. If a semidwarf cultivar is used, row
spacing can be reduced to help compensate for the
loss in weed competitiveness.
By combining crop rotation, cultural practices,
and herbicides, winter annual grass weeds are
effectively controlled in winter wheat and the
entire cropping system is made more sustainable.
The winter wheat-summer crop-fallow system is
an example of an effective IWM system with
implications beyond weed control.
Table 12.8
Crop production changes in Canada from 1995
to 2005.
Crop or
System
2005
Change from 1995
(million ha)
(%)
Wheat
10
−
20
Canola
5.5
+
55
Barley
5
−
5
Oat
2
−
3
Field pea
1.4
+
250
Corn
1.3
+
3
Soybean
1.1
+
35
Lentil
1
+
190
Flax
0.8
+
40
Canaryseed
0.4
+
45
Mustard
0.25
−
10
Dry bean
0.2
+
110
Sunfl ower
0.1
+
155
Forages
7.5
+
20
Zero tillage
20
+
100
Fallow
4
−
70
Source:
Statistics Canada (2006).
Spring wheat in North America
Zero tillage (no-till) has become a widely adopted
agronomic practice in the spring wheat produc-
tion areas of Canada and the northern US (Table
12.8). Research has shown that some weed species
may become more prevalent with zero tillage, but
overall weed densities decline with time (Derksen
et al., 2002; Anderson 2003; Blackshaw 2005).
Weed seed mortality tends to be greater when
weed seeds are left on the soil surface compared
with when they are buried in the soil with tillage.
Additionally, crop residues on the soil surface
may inhibit weed germination and growth through
physical suppression and/or allelopathic interac-
tions. Thus, zero tillage has contributed greatly
to improved weed management as well as higher
spring wheat yields.
Improved soil moisture conservation with zero
tillage has allowed a greater variety of crops to be
grown in recent years in the semiarid Canadian
