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

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

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)

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

Reproductive Stages

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)

Daylength, mid-month

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

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

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

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)

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

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: http://msucares.com/deltasoy/gsModelFrame.htm

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

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 29 June 19 July 10 Aug 15

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 $

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

Questions?