Biology Reference
In-Depth Information
enhanced indirectly by tillage, which removes other species and improves the light,
nutrient, soil contact, and temperature environment for seedling establishment.
Over the past 30 years, the adoption of direct-seeding and no-tillage (no-till) crop-
ping systems on the Prairies has steadily increased. Direct seeding refers to planting
a crop directly into the previous crop's stubble; soil disturbance can vary from low
to high levels depending on the planting equipment. No tillage is a subset of direct
seeding with <30% soil disturbance. Such systems protect the soil from wind and
water erosion, conserve soil moisture, and dramatically reduce labour and fuel
costs. Moreover, no-till systems conserve crop residues and soil organic matter,
increasing biological life in soils and contribute to long-term sustainability by
enhancing nutrient cycling (Soon and Clayton 2002), biological diversity (Lupwayi
et al. 1998, 1999), and disease suppression. After a few decades of direct seeding,
we have come to understand that the primary value of tillage was for weed manage-
ment when adequate herbicides and other no-till technology were not available.
In direct-seeding systems where crop residues are left on the soil surface, many
weeds with small seeds are disadvantaged. This conclusion is supported by studies
conducted in the relatively moist subhumid Parkland region of the Prairies
(O'Donovan and McAndrew 2000). Spring seedling populations of green foxtail
[
Setaria viridis
(L.) P. Beauv.], stinkweed (
Thlaspi arvense
L.), wild buckwheat
(
Polygonum convolvulus
L.), and lamb's-quarters (
Chenopodium album
L.)
decreased as tillage intensity was reduced and were lowest under no- (zero) till
(Fig. 8.1). Reduction in these small-seeded weed populations in the no-till system
occurred despite large amounts of weed seeds sometimes present at the soil surface.
Most of these seeds did not germinate. Liebman and Mohler (2001) state that:
70
60
50
Conventional
Minimum
Zero
40
30
20
10
0
T HLAR
CHEAL
POLCO
SET VI
Fig. 8.1
Effect of tillage system on spring weed seedling populations after 4 years of continuous
barley in central Alberta. THLAR, CHEAL, POLCO, and SETVI are five-letter codes for stink-
weed (
Thlaspi arvense L.
), lamb's quarters
(Chenopodium album L.)
, wild buckwheat
(Polygonum
convolvulus
L.), and green foxtail [
Setaria viridis
(L.) P. Beauv.], respectively. Adapted from
O'Donovan and McAndrew (2000)
