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Post-dispersal weed seed predation in contrasting herbaceous crop systems
F. D. Menalled, A. H. Heggenstaller, and M. Liebman
Department of Agronomy, Iowa State University, Ames, Iowa 50011-1010
[email protected]
Nitrogen Fertility Management and Tillage Practices
2002 crop
Integrated weed management programs combine judicious use of herbicides with
multiple control tactics including crop rotation, cover crops, crop variety, soil
fertilization, and tillage. The goal of these practices is to combine multiple weed
mortality sources that could be individually weak, but cumulatively strong.
2003 crop
2003 Nitrogen inputs
Tillage practices
Soybean 2
Corn 2
110 kg N/ha + 40 kg N/ha
Surface cultivation
Triticale 3
Corn 3
composted manure +
55 kg N/ha + 40 kg N/ha
Moldboard plow
composted manure + 55 kg
N/ha
Moldboard plow
–––
Chisel plow, surface
cultivation
Alfalfa 4
Corn 4
Corn 2
In several natural ecosystems, seed predation is an important mortality factor
affecting plant population and community dynamics. Previous studies have reported
variable rates of weed seed predation in herbaceous annual crop fields (Menalled et
al., in press). However, little is known on the importance of this source of mortality
in the development of multiple-tactics weed management programs.
Objectives
Soybean 2
Corn 3
–––
Soybean 4
• 2. Assess the importance of weed seed predation in determining weed population
dynamics.
Soybean 3
Triticale 3
30 kg N/ha
No tillage
Soybean 4
Triticale 4
30 kg N/ha
No tillage
Triticale 4
Alfalfa 4
–––
No tillage
25
a
20
B
b
b
30
D
25
C
A
15
10
10
5
5
0
0
Soybean
B
20
15
Corn
Weed Management Practices
Crop and system
Corn 2
Corn 3 and 4
Materials and Methods
Mechanical controls
Herbicides
rotary hoe (1x)
PPI: metolachlor, isoxaflutole;
POST, broadcast: nicosulfuron+rimsulfuron,
mesotrione
rotary hoe (1x),
interrow cultivation (2x)
POST, banded: nicosulfuron+rimsulfuron, mesotrione
–––
PPI: metolachlor;
POST, broadcast: bentazon+clethodim,
flumiclorac
rotary hoe (1x),
interrow cultivation (1x)
PPI: metolachlor;
POST, banded: flumiclorac
stubble mowing (1x)
–––
hay removal (3x)
–––
Soybean 2
Three cropping systems were established in Boone, Iowa in 2002
• 2-year rotation: corn–soybean
Soybean 3 and 4
• 3-year rotation: corn–soybean–triticale + red clover green manure
Triticale/clover 3 and
Triticale/alfalfa 4
• 4-year rotation: corn–soybean–triticale + alfalfa–alfalfa hay
Alfalfa 4
Triticale
2-year
C2 C3
-1
% removal day
C2
C4
A4
S3
S2
T3
C3
C2
S4
T4
S4
S3
A4
A4
T3
C4
S2
C2
S4
C3
S3
Jun-03
Jul-03
60
• 2) No exclosures that allowed both vertebrates and invertebrates to
consume weed seeds
30
20
Oct-03 Nov-03
Jun-03
Jul-03
60
Aug-03
Sep-03
Oct-03
Nov-03
Alfalfa
50
40
30
20
40
30
20
10
0
Jun-03
Jul-03
Aug-03
Sep-03
Oct-03
Nov-03
May-03
Jun-03
Jul-03
Aug-03
Sep-03 Oct-03 Nov-03
Alfalfa cutting
Figure 5. Giant foxtail and velvetleaf seed predation through the 2003 growing season.
A population dynamics model indicates that weed seed predation, as a component of
seed mortality, represents an important variable determining weed seedbank
abundance in reduced inputs and diversified crop systems (Fig. 6).
2)
2- and 4-year rotation, without seed predation
T3 = triticale + red clover green manure, 3-year rotation; T4= triticale + alfalfa, 4-year rotation;
4-year rotation with or without seed predation
seed density [#. m-2]
3000
A4 = alfalfa hay, 4-year rotation.
Figure 3. 1) Total exclosure and 2) no exclosure treatments with detail of the seed card
utilized to quantify post-dispersal weed seed predation.
3000
2500
2000
1500
1000
500
0
5
10
15
20
time [years]
A simulation model examined the importance of weed seed mortality,
including post-dispersal seed predation, in determining weed population
dynamics (Liebman et al., 2003).
2500
2000
1500
1000
500
0
0
2-y rotation, lambda = 0.93
4-y rotation, lambda = 1.17
0
5
10
15
20
time [years]
no predation, lambda = 1.17
40% in all crops, lambda = 0.89
23.5% in all crops, lambda = 1
Figure 6: Seedbank abundance in 2- and 4 year rotation systems under different seed predation modeling
scenarios
Results
An ANOVA test on arc-sine transformed data showed that percentage
velvetleaf and giant foxtail seed removal was affected by crop phase.
Rotation length modified velvetleaf seed removal, but had no influence on
giant foxtail removal (Table 2).
Photos: WSSA Web site and Davis, L.W. 1993. Weed Seeds of the Great Plains
Giant foxtail
Triticale cutting Red clover canopy closure
S2 = soybean, 2-year rotation; S3 = soybean, 3-year rotation; S4 = soybean, 4-year rotation;
Figure 2. Weed species utilized in this study.
Sep-03
Triticale
0
May-03
C2 = corn, 2-year rotation; C3 = corn, 3-year rotation; C4 = corn, 4-year rotation;
Setaria faberi
Giant foxtail
40 mg / 100 seeds
Aug-03
10
Figure 1: Aerial photo of the experimental site, Boone, Iowa. Codes refer to crops present in 2003.
Abutilon theophrasti
Velvetleaf
850 mg / 100 seeds
40
0
May-03
50
Block 4
Post-dispersal seed predation was assessed for two weed species commonly
found in the Midwest USA: Setaria faberi (giant foxtail) and Abutilon
theophrasti (velvetleaf). These species were selected because of their different
growing habitats and seed characteristics (Fig. 2).
Velvetleaf
10
May-03
T4
Management practices differed among cropping systems with the 2-year rotation
receiving conventional management practices and the 3- and 4-year rotations
receiving less fertilizer and herbicide (Table 1).
-1
20
50
0
1)
Block 3
% removal day
30
10
Fifty velvetleaf or giant foxtail seeds were placed on individual 12 x 10 cm
cards. Thirteen times between May and October 2003, cards were left in the
field for 48 hs, recovered, and number of seeds remaining on cards was
determined in the laboratory (Fig. 3).
S2
40
Soybean
seed density [#. m-2]
S4
18.3 m
T4 T3
Table 1. Summary of management practices employed at the experimental site.
• 1) Total exclosures that prevented vertebrates and invertebrates from
removing weed seeds and were used to assess the experimental error inherent
in seed recovery
A4
60
Corn
-1
T3
Giant foxtail
% removal day
C3
60
-1
T4
4-year
The two species showed similar temporal patterns of weed seed removal. However,
seed predation rates were crop-specific and closely associated with canopy closure.
While weed seed removal in corn and soybean plots increased during the growing
season as a crop canopy closed, weed seed removal in alfalfa showed periodic peaks
associated with dense canopies prior to mowing. Weed seed removal in triticale
showed a maximum in July 2003 prior to harvest and a secondary peak associated
with the development of a red clover canopy (Fig 5).
% removal day
S2
3-year
Figure 4. Weed seed removal averaged across a) crops and b) cropping systems. Different letters denote
significant differences, P < 0.05. Capitalized letters compare velvetleaf seed predation. Lower case letters
compare giant foxtail seed predation.
Field trials were conducted using two treatments:
Block 2
Block 1
B
A
Alfalfa
50
The experimental design followed a randomized block-design with four blocks and
each crop present every year (Fig. 1).
C4
Chisel plow, surface
cultivation
c
30
b)
35
Velvetleaf
• 1. Compare post-dispersal weed seed predation rates across a range of annual
cropping systems that differ in rotation length and management practices.
C4
Chisel plow, surface
cultivation
Mean Seed Removal
(12 May - 20 November 2003)
a)
35
–––
Soybean 3
Corn 4
Mean Seed Removal
(12 May - 20 November 2003)
Seed removal (% per day)
Introduction
S3
Multiple comparisons indicated that more velvetleaf and giant foxtail seeds were
eaten in alfalfa than in the other crops (Fig 4a). Crop rotation did not affect foxtail
seed removal, but more velvetleaf seeds were eaten in the 4- and 3year rotation
systems than in the 2-year rotation system (Fig 4b).
Giant foxtail
Velvetleaf
Crop
<0.0001
<0.0001
Rotation
0.8908
0.0006
Crop*Rotation
0.4878
0.8517
Block
0.1313
<0.0001
Crop*Block
0.0045
0.8658
Rotation*Block
0.9477
0.7999
Crop*Rotation*Block
0.4817
0.0003
Table 2. Probability values of an ANOVA test on the effect of crop phase, rotation
length, and block on overall percentage weed seed predation.
Conclusions
•Weed seed predation is mainly influenced by crop phase and crop canopy closure.
•Because the 2-yr rotation achieves high levels of efficacy from direct weed control
tactics, it is less reliant on natural weed mortality factors such as seed predation.
•Equivalent weed seedbank densities can be achieved between the 2- and the 4-year
rotations provided that weed seed predation reaches high enough rates in the reduced
input and diversified cropping system.
References
Liebman, M., P. Westerman, F. Menalled, and A. Heggenstaller. 2003. Weed responses to diversified cropping
systems. Symposium on Beyond Thresholds: Applying Multiple Control Tactics in Integrated Weed Management.
Proceedings of the North-Central Weed Science Society meeting. Louisville, Kentucky.
Menalled, F, M. Liebman, and K. Renner. In press. The ecology of weed seed predation in herbaceous crop systems.
In Handbook of Sustainable Weed Management. D. Batish, editor. The Haworth Press, Inc. Binghamton, NY.
.