MixSeeded Soybean as a

1
Mix-Seeded Soybean as a Weed Management Tool
in Roundup Ready Soybean
Jason Norsworthy Clemson University
2

• Broadcast mix-seeding of Roundup Ready and
  conventional soybean is an effective tool for
  managing weeds on silt loam, but not silty clay
  soils.
• (Norsworthy and Oliver 2000)
• Soils of the Southeast are prone to extensive and
  prolonged drought stress due to the high sand
  content of these soils.

3
Conclusions

• Success with the broadcast mix-
• seeding technique was highly
• contingent on timing of early-season
• rainfall.
• Choice of cultivar had little effect on
• weed management and no effect on
• soybean seed yield.

4
Soybean Seed Yield(Planting Date Effect)
LSD(0.05)
Yield (kg/ha)
Planting Date
5
2000
Planted
6
2000
Rainfall (cm)
2001
Month
7
End-of-Season Soybean Height(Planting Date
Effect)
Height (cm)
Planting Date
8
Questions?
9
Objectives

• To evaluate the effectiveness of
• a weed management system
• utilizing a broadcast RR/Conv.
• soybean seed mix under varied
• planting dates and cultivar
• maturity groups on a loamy
• sand soil.

10
Materials and Methods

• Split plot
• Planting date (main factor)
• late-May, mid-June, early-July
• Roundup Ready cultivar (subfactor)
• Pioneer 95B41, DPL 6880,
  Hartz 7550, Hartz 8001
• Glyphosate Application
• V4 to V6 soybean
• 0.84 kg ae/ha
• 94 L/ha, 4.8 km/h

11
Materials and Methods

• Planted Treated
• May 31 July 10
• June 16 July 18
• July 1 August 7
• Weed Growth Stages (at treatment)
• Palmer amaranth, 15 to 33 leaves, 33 to 45 cm
  tall
• morningglory spp., 6 to 9 leaves, 16 to 56 cm
  vines

12
Materials and Methods

• Data Recorded
• Soybean groundcover
• Weed control
• Weed and soybean densities
• Soybean and weed biomass
• Soybean height
• Soybean yield
• Statistical Analysis
• ANOVA, LSD (0.05)

13
Planting Method
broadcast
incorporated
14
Palmer Amaranth Density (Planting Date Effect )
LSD(0.05)
Density (plants/m2)
Planting Date
15
Morningglory spp. Density(Planting Date Effect)
LSD(0.05) NS
Density (plants/m2)
Planting Date
16
Palmer Amaranth Biomass(Planting Date Effect)
LSD(0.05)
Biomass (g/m2)
Planting Date
17
Morningglory spp. Biomass(Planting Date Effect)
LSD(0.05) NS
Biomass (g/m2)
Planting Date
18
Conclusions

• Planting date influenced Palmer amaranth density,
  but morningglory spp. density did not vary prior
  to treatment with glyphosate.
• Rainfall differences among planting dates most
  influenced soybean growth, weed management, and
  soybean seed yield.

19
Volumetric Water Content at Treatment(Planting
Date Effect)
LSD(0.05)
Volumetric water content
Planting Date
20
Morningglory spp. Control(Planting Date Effect)
LSD(0.05)
Control
Planting Date
21
Soybean Groundcover at Treatment (Planting Date
Effect)
LSD(0.05)
Soybean groundcover
Planting Date
22
Palmer Amaranth Control(Planting Date Effect)
LSD(0.05)
Control
Planting Date
23
late-May, H 7550, 38 DAT
24
Morningglory Density(Cultivar Effect)
Density (plants/m2)
Cultivar
25
End-of-Season Soybean Height(Cultivar Effect)
LSD(0.05)
Height (cm)
Cultivar
26
mid-June, P 95B41, 29 DAT
27
early-July, H 7550, 11 DAT
28
early-July, P 95B41, 11 DAT
29
mid-June, P 95B41, 29 DAT
30

• Seed yield maximized at 200,000 Roundup Ready
  seed/A plus 200,000 conventional seed/A.
• (Norsworthy and Oliver 2000)
• Strong correlation between early-season
• weed suppression and soybean groundcover.

31
Conclusions

• Suppressed soybean yields may
• be attributed to interference with Palmer
  amaranth emerging after the glyphosate
  application, regrowth of uncontrolled
  morningglory spp., and prolonged periods of
  inadequate rainfall.
• Weed control was directly dependent
• on early-season soybean groundcover with
  soybean groundcover influenced
• by rainfall following planting.

32

• Redroot pigweed emergence varied over one of two
  growing seasons, with emergence not related to
  precipitation.
• (Moore et al. 1994)
• Pitted morningglory continually emerges
• throughout the growing season, with
• temperature most influencing the extent of
  
• seed germination.
• (Lovelace et al. 2001)

33
Conclusions

• Late-season control of Palmer amaranth and
  morningglory spp.
• was at least 85 when soybean was seeded in
  early-July.

34
Soybean Seed Weight(Planting Date Effect)
Seed weight (g/100 seed)
Planting Date
35
(No Transcript)
36
Soybean Seed Weight(Cultivar Effect)
Soybean weight (g/100 seed)
Cultivar
37
Lodging10/18/00
38
Morningglory spp.
Palmer amaranth
39
(No Transcript)
40
(No Transcript)