1. Soybean Maturity Groups and Selection
Dennis Delaney
Extension Specialist – Soybeans & Conservation Cropping Systems
Crop, Soil & Environmental Sciences
ACES / Auburn University

2. Basics of soybean growth and development
Soybeans are a legume = Glycine max L.
Originally a viny plant from Asia = forage w/ (usually) small black seed
Breeding efforts = large white seed, erect stem, uniform maturity, etc.
Temperature sensitive: optimum = 55 to 85F
USDA-ARS

3. Basics of soybean growth and development
Daylight sensitive = “short-day” ( actually long night)
Classified from MG 000 through X (Canada Prairies/Dakotas through tropics)
Generally, MG IV and under = indeterminate, bloom and grow, height can triple after initial
MG V and above = determinate, bloom and stop, height increase ~ 25%
MG desig. can be “fuzzy” – weather, environment
Others – Long Juvenile and Semi-dwarfs(deter)

4. Preplant considerations:
Maturity and Variety selection:
Match maturity group to rainfall, for timely harvest and conflicts (labor, elevator, hurricanes, etc.)
Typically increase one Maturity Group per 100 miles south

5. Reproductive Stages

6. Initiation of flowering
When daylength is short enough (long night-length), + environmental influences
Not receptive to daylength until at least V1, or abt 3 weeks after emergence, temp. dependent
Determinate usually starts blooming at nodes 8 to 10, abt 3 weeks later
Indeterminate usually starts at nodes 3 to 6
Raceme from axillary bud at node (axil)

7. Daylength, mid-month

8. Daylength, mid-month MG 00 MG V MG VII
Long day/short night inhibit flowering, w/ short enough nights bloom induced, need enough vegetative growth before bloom
MG 00
MG V
MG VII

9. V VI VII Typical Soybean Maturity Groups Planted in Alabama, pre-2005
Usually planted early May through mid-June
Harvest Oct - Dec VI
VII

10. Soybean Production Systems in AL
Now:
Early Soybean Production System (ESPS)
Full Season
Double-cropped / late planted (wheat, etc.)
Different management for each system
Match MG and Row Spacing for system, land and Planting Date

11. Planting date “rules of thumb” for AL:
MG IV: early April through early May
MG V: May 1 through mid-June
MG VI, VII, VIII: May 5 through mid-June
If not optimum time for MG – closer row spacing and higher populations can offset less growth/plant
Optimum weather causes more vegetative growth (moderate temps, moisture)

12. Planting Dates for MG III and IV Soybeans, PBU, 2004
Planting too early for MG results in:
Short plants
Pods set low
Reduced harvest

13. Some “rules of thumb”: In mid-season, one MG = ~10+ days later bloom
Late season, narrows to 3 days difference/MG
Mid-season = maturity ~ 1 day later per day planting delayed
Late planting = stages speed up, 3 days delay might equal only 1 day maturity delay
Length stages vary: Determinate vs Indeterminate, pod-fill = longer w/ Indeter.
See MSU Growth calculator:

14. Example output from MS Growth Calculator: MG 4.0 planted on 15 April
Valid Central MS/AL
Blooming is earlier if same MG moves south, later if northward

15. Why “ESPS” (Early Soybean Production System)?
Matching optimum soybean plant needs to typical Southeastern weather patterns
With typical early May planting:
MG Begin: Bloom Pod-set Seed-fill Maturity
V June 30 July 28 Aug 14 Sep 26
VI July 14 Aug 11 Aug 23 Oct 6
VII July 25 Aug 16 Aug 28 Oct 16
ESPS (mid-April planting):
IV May June 19 July 10 Aug 15

16. Why “ESPS”? $ Early delivery prices
Plant early –while soil moisture is good and soil temps are lower
Plant before cotton, peanuts
Bloom and pod fill before soil moisture exhausted (playing the odds)
Harvest during long, dry days
Early delivery prices $

17. Why Not ESPS?
Can be poorly adapted varieties – need to be breed and tested in Southeast
Diseases: foliar & southern stem canker
Nematode resistance
Late weed control, green leaves & stems
Shattering, late summer rain delays
Conflict with late corn harvest
Must adopt system, not just parts

18. Questions?