Perennial weeds
in a crop rotation perspective
Ilse A. Rasmussen
Dept. of Integrated Crop Protection
Danish Institute of Agricultural Sciences
Research Centre Flakkebjerg
Archived
at
20 cm
60 cm 40 cm
Tussilago farfara
Sonchus arvensis
Elymus repens
50 cm
100 cm
Cirsium arvense
I
II
III
IV
V
I: Initial growth
II: Emergence of first shoot
III: Dry weight minimum of the whole plant
IV: Dry weight minimum of subterranian parts
V: Dry weight of subterranian parts larger than at I
1: Original vegetative propagation organs
2: New vegetative propagation organs
I
II
III
IV
V
I
II
III
IV
V
I
II
III
IV
V
Integrated approach
Crop, grain
Suppressive
catch crop
Autumn ploughing
(20 cm)
Strategy I: ”Integrated light”
Early August,
mechanical
disintegration
Shallow
ploughing
Roterende
P.t.o.-driven rotary
cultivation
Mechanical disintegration
Strategy I: ”Integrated light”
E. repens
biomass (g m
-2
)
a
a
b
c
d
0
20
40
60
80
100
120
140
Untreated
Shal. Pl.
Rot. cul.
Stub. cul.
Kvik-Up
Effects recorded close to spring barley harvest the following year
Strategy I: ”Integrated light”
3
3.5
4
4.5
5
5.5
6
0
50
100
150
200
No catch crop
Radish/ryegr.
Cl./vetch
E. repens biomass (g m
-2
)
Grain yield (t ha
-1
)
Integrated approach
Silage crop
Suppressive catch crop
1’st July, shallow
ploughing (10 cm)
Following season,
ploughing (20 cm)
prior to next crop
Early August,
ploughing (20 cm)
Strategy II: ”Integrated intensive”
Fallow, tine
cultivation
Long fallow period
Silage Crop
1’st July, shallow
ploughing
Strategy III: ”Half fallow”
Fallow, tine cultivation
Autumn ploughing
(20 cm)
Traditional
Crop, grain
Autumn ploughing
(20 cm)
Early August, onset
of post-harvest
cultivation
Strategy IV: ”Traditional strategy”
Post-harvest tine
cultivation
Results from 4 experiments
Integrated
intensive
Half fallow
Traditional
November
July
June
0
50
100
150
200
250
E. repens
shoots
m
-2
Results from 4 experiments
a
b
b
0
0,5
1
1,5
2
2,5
3
3,5
4
4,5
5
Gr
a
in y
ie
ld (
t ha
-1
)
Integrated
intensive
Half fallow
Traditional
Spring barley grain yield the following year
Repeated hoeing in spring barley
with undersown clover
Year one: treatments
Hoeing in crop
May - July
Suppressive
catch crop
Autumn ploughing
(20 cm)
Crop: spring
barley.
Year two: counts/weights + yield
Hoeing: mid-May – mid-July
Repeated hoeing
Number of hoeings
0
1
2
3
4
5
6
A
b
ov
e
g
round bioma
s
s
(g/m
2
)
0
10
20
30
40
50
60
Harvest 2002
Harvest 2003
Repeated hoeing
Hoeing: medio May-medio July
Number of hoeings
0
1
3
5
Yield (100 kg
/ha)
0
10
20
30
40
50
Harvest 2002
Harvest 2003
Repeated mowing in clover or
without crop
Crop: spring barley.
Year three: counts/weights + yield
Year one: establishment
Crop: spring
barley
Suppressive
catch crop
No catch crop
Mowing in
clover/weeds May - July
Suppressive
catch crop
Autumn
ploughing
(20 cm)
Year two: treatments
No
catch
crop
Before
After
Before
After
Number of mowings
0
1
2
3
4
5
6
7
A
b
ov
e
g
round biom
a
s
s
(g/m
2
)
0
50
100
150
200
250
300
350
With out catch crop
With catch crop
Repeated mowing
Harvest 2002
Number of mowings
0
2
4
6
Yi
eld
(100kg/
h
a)
0
10
20
30
40
50
60
With out catch crop X
With catch crop Y
Repeated mowing
Harvest 2002
Mowing: mid-May - late July
a
b
ab
ab
Number of mowings
0
1
2
3
4
5
6
7
A
b
ov
e
g
round biom
a
s
s
(g/m
2
)
0
20
40
60
80
100
With out catch crop
With catch crop
Repeated mowing
Harvest 2003
Number of mowings
0
2
4
6
Yi
eld
(100kg/
h
a)
0
10
20
30
40
50
60
With out catch crop X
With catch crop Y
Repeated mowing
Harvest 2003
Experimental factors
• Crop rotation (level of cereals)
• Catch crop (without/with catch crop)
• Manure (without/with)
Crop rotations
Four-year crop rotations are used.
The level of cereals and pulses
increases from rotation 1 to rotation
4:
1: 1.5 grass-clover + 1 pulse
2: 1 grass-clover + 1 pulse
3: 1 grass-clover
Weed control - perennials
•
Elymus repens
:
– stubble cultivation:
• without catch crops > 5 shoots m
-2
• with catch crops - none
Weed control - perennials
•
Elymus repens
:
– Rotations with and without catch crops with severe
problems:
• Grass clover plowed early (June)
• Repeated harrowing
Weed control - perennials
•
Cirsium arvense
:
– cut below ground and pulled at the anthesis of the cereals
– stubble cultivation
• Others (
Artemisia vulgaris, Rumex crispus
etc.):
– pulled up at sight
Nitrate leaching with or without catch
crop in rotation with grass-clover
Leaching of nitrate-N (kg/ha/y
ear)
0 20 40 60 80 100 120
Without catch crop
With catch crop
Coarse
Loamy
Sandy
N-leaching on coarse sandy soil with or
without catch crops and stubble cultivation
Leaching of nitrate-N kg ha
-1
0
20
40
60
80
100
120
140
+CC
-CC - Stubble cult.
-CC + Stubble cult.
From
E. repens
shoots m
-2
0
20
40
60
80
- CC + Stubble cult.
+ CC - Stubble cult.
E. repens
shoots in spring barley on coarse
sandy soil with and without catch crops
Fres
h w
e
ight
of
C.
arv
ens
e
(g m
-2
)
0
10
20
30
40
50
60
-CC + Stubble cult.
+CC - Stubble cult.
C. arvense
biomass on sandy loam in different
crop types with and without catch crops
Summary
• Catch crops should be included in systems with
grass-clover to reduce nitrate leaching when possible,
especially on sandy soils
– but use of catch crops precludes stubble cultivation
• Stubble cultivation should be used to reduce
E. repens
infestations
– but not after pulses
• Stubble cultivation did not seem to reduce
C. arvense
1997
1998
1999
2000
2001
2002
2003
Concentr
a
ti
on af
ni
trate-N (m
g/l)
0
10
20
30
40
50
No summer fallow
Summer fallow
Concentrations of nitrate-N on coarse sandy soil.
Mean of 4 crops, without catch crop, with manure
First crop
Second crop
E. repens
shoots m
-2
0
5
10
15
20
25
No fallow
Fallow
E. repens
shoots on coarse sandy soil
after grass-clover with or without summer fallow
1997 1998 1999 2000 2001 2002 2003
E. re pens shoots m -2 0 20 40 60 80
- CC + Stubble cult. + CC - Stubble cult.
From
Summary
• Summer fallow could be used to reduce
E. repens
infestations
– mainly the first year after fallow
– increases risk of nitrate leaching on sandy soil
Nitrate leaching with or without catch crop
in rotations with or without grass-clover
Leaching of nitrate-N (kg/ha/y
ear)
0
10
20
30
40
50
60
Without catch crop
With catch crop
Loamy
Sandy
Loamy
Sandy
With grass-clover
Without grass-clover
From
Fresh w
e
ight of
C. arvense
, g m
-2
