Soybean Production and Management in

Kentucky

Jim Herbek Grain Crops SpecialistUniversity of Kentucky

SOYBEANSOYBEAN

Growth Growth

StagesStages

► How a Soybean Plant Develops, Special Report No. How a Soybean Plant Develops, Special Report No. 5353

► Iowa State University PressIowa State University Press► $2.00$2.00

Extension Distribution CenterExtension Distribution Center119 Printing and Publications Building119 Printing and Publications BuildingIowa State UniversityIowa State UniversityAmes, Iowa 50011-3171 Telephone: (515) 294-5247Ames, Iowa 50011-3171 Telephone: (515) 294-5247Fax: (515) 294-2945Fax: (515) 294-2945

http://www.extension.iastate.edu/Pages/hancock/http://www.extension.iastate.edu/Pages/hancock/agriculture/soybean/bean_develop/agriculture/soybean/bean_develop/

The information in the presentation comes from Iowa State Special Report No.53. This is an excellent resource for any producer or agronomist.

Vegetative StagesVegetative Stages Reproductive StagesReproductive Stages

VE – emergenceVE – emergence R1 – beginning bloomR1 – beginning bloom

VC – cotyledon (unrolled VC – cotyledon (unrolled unifoliolate leaves)unifoliolate leaves)

R2 – full bloomR2 – full bloom

V1 – first trifoliolate*V1 – first trifoliolate* R3 – beginning podR3 – beginning pod

V2 – second trifoliolateV2 – second trifoliolate R4 – full podR4 – full pod

V3 – third trifoliolateV3 – third trifoliolate R5 – beginning seedR5 – beginning seed

V(n) – nth trifoliolateV(n) – nth trifoliolate R6 – full seedR6 – full seed

R7 – beginning maturityR7 – beginning maturity

R8 – full maturityR8 – full maturity

Soybean Growth StagesSoybean Growth Stages

When staging a soybean field , each specific V or R stage When staging a soybean field , each specific V or R stage is defined only when 50% or more of the plantsis defined only when 50% or more of the plants in the in the field are in or beyond that stage.field are in or beyond that stage.

* A fully developed trifoliolate * A fully developed trifoliolate leaf node has unrolled leaf node has unrolled leaflets.leaflets.

Young Soybean Plant (Seedling)

Time Between Soybean Growth Stages

► Specific time between stagesSpecific time between stages, number of , number of leaves developed, and plant height leaves developed, and plant height may varymay vary according to varieties/maturity groups, according to varieties/maturity groups, seasons, locations, planting dates, and planting seasons, locations, planting dates, and planting patterns.patterns.

► An An early-maturing varietyearly-maturing variety may develop fewer may develop fewer leaves or progress through the stages at a leaves or progress through the stages at a faster rate.faster rate.

► Late-maturing varietiesLate-maturing varieties may develop more may develop more leaves or progress through stages more slowly.leaves or progress through stages more slowly.

► Late planting datesLate planting dates will progress through will progress through stages at a faster rate.stages at a faster rate.

Time Between Soybean Growth Stages (2)

► Rate of plant development is Rate of plant development is directly related to directly related to temperaturetemperature..

Length of time between stages will vary as temperature Length of time between stages will vary as temperature varies (both between and within growing seasons).varies (both between and within growing seasons).

► Stressful conditionsStressful conditions may lengthen the time between may lengthen the time between vegetative stages and shorten the time between vegetative stages and shorten the time between reproductive stages.reproductive stages.

► Soybeans at high populationsSoybeans at high populations grow taller; produce grow taller; produce fewer branches, pods and seeds per plant; and set pods fewer branches, pods and seeds per plant; and set pods higher off the ground higher off the ground than soybean at low populationsthan soybean at low populations..

► Soybean has Soybean has great compensation abilitygreat compensation ability to adjust to adjust (branches, pods, seeds) to populations, injury and (branches, pods, seeds) to populations, injury and stress.stress.

Development and timing of vegetative growth, Development and timing of vegetative growth, flowering, pod development, and seed filling.flowering, pod development, and seed filling.

Days of R Stages

R Stage

(node and leaf development)

Soybean Growth Habits

► In general, soybean has In general, soybean has two types of growth habits.two types of growth habits.

► Indeterminate:Indeterminate: characterized by a continuation of characterized by a continuation of vegetative growth after flowering begins.vegetative growth after flowering begins. Lower V(n) prior to bloom (R1).Lower V(n) prior to bloom (R1). Flowers, pods and new leaves occur on plant at same time.Flowers, pods and new leaves occur on plant at same time. Most varieties in maturity groups 00 to IV.Most varieties in maturity groups 00 to IV.

► Determinate:Determinate: characteristically finishes most of its characteristically finishes most of its vegetative growth before flowering begins.vegetative growth before flowering begins. Flowering occurs about the same time in top and bottom of Flowering occurs about the same time in top and bottom of

plant. (pod and seed development are similar on same plant. (pod and seed development are similar on same plant).plant).

Higher V(n) prior to bloom (R1).Higher V(n) prior to bloom (R1). Terminal node has a long flowering raceme (stalk with pods).Terminal node has a long flowering raceme (stalk with pods). Most varieties in maturity groups V to IX.Most varieties in maturity groups V to IX.

Due to photoperiod sensitivity, soybean varieties are adapted for

growth in a relatively narrow latitude range.

Areas Where Maturity Groups of Soybean are GrownAreas Where Maturity Groups of Soybean are Grown

Group 00 = earliest maturityGroup IX = latest maturity

Soybean varieties are classified into maturity groups (00 to IX) according to the range in latitudes in which they are adapted and are most productive.

Regions of adaptability are long east to west but relatively short (100- 150 miles) north to south.

Soybean Vegetative (V) Stages

► Begins with seedling emergence and ends with last Begins with seedling emergence and ends with last V(n) prior to beginning bloom (R1).V(n) prior to beginning bloom (R1).

► VE VE = Emergence= Emergence

► VCVC = Cotyledon (unrolled unifoliolate leaves) = Cotyledon (unrolled unifoliolate leaves)

► V1 – V(n)V1 – V(n) = Fully developed trifoliolate leaf node = Fully developed trifoliolate leaf node stagesstages

► Except for VE and VC stages, all other vegetative Except for VE and VC stages, all other vegetative stages are defined and numbered according to the stages are defined and numbered according to the uppermostuppermost fully developed trifoliolate leaf nodefully developed trifoliolate leaf node..

► New V stages appear about every 5 days (from VC-New V stages appear about every 5 days (from VC-V5) and every 3 days (from V5 to shortly after R5).V5) and every 3 days (from V5 to shortly after R5).

VEVEVEVE

VE (Emergence) = Cotyledons above the soil surface.

VE

VC

V1

•Soybean seed begins germination by absorbing ~50% of its weight in water.

•Although soybean can germinate at minimum temperature of 50°F (or less), field emergence is more rapid (~7 days) and uniform if soil temperature is above 65°F.

““Poking through”Poking through”

hypocotyl

VCVC (Cotyledon) = Unifoliolate leaves unrolled sufficiently so the leaf edges are not touching.

•Nutrients and food reserves in the cotyledons supply the young plant during emergence and for about 7-10 days after VE (or until about the V1 stage).

•Unlike corn, where the growing point is protected beneath the soil for several weeks, the growing point of soybean moves above the soil surface at emergence. Thus, the plant is susceptible to damage (hail, frost, insects) or anything that cuts the plant off below the cotyledons (lowest axillary buds).

Determining Soybean Leaf Node Stages

► Following VC, the V stages are numbered according to Following VC, the V stages are numbered according to the the uppermostuppermost fully developed trifoliolate leaf node fully developed trifoliolate leaf node..

► Fully Developed Trifoliolate Leaf NodeFully Developed Trifoliolate Leaf Node:: A fully A fully developed leaf node is one that has developed leaf node is one that has unrolled leafletsunrolled leaflets (i.e. the (i.e. the two edgestwo edges of of each leafleteach leaflet have separated have separated (unrolled) and the two edges are no longer touching).(unrolled) and the two edges are no longer touching).

► Start at the bottom of the plant and count upwards all Start at the bottom of the plant and count upwards all nodes with fully developed trifoliolate leaves.nodes with fully developed trifoliolate leaves.

► The uppermost leaf node counted with a fully The uppermost leaf node counted with a fully developed trifoliolate leaf is the V stage.developed trifoliolate leaf is the V stage. (i.e., 5 fully developed trifoliolate leaves = V5 (i.e., 5 fully developed trifoliolate leaves = V5

stage)stage)

Uppermost trifoliolate leaf with folded (rolled) leaflets (Leaflet

edges touching each other).

NOT a fully developed trifoliolate leaf node

NOT a fully developed trifoliolate leaf node

leaflet edges touching

leaflet edges touching

Identification of the Uppermost Node with a Fully Developed Trifoliolate Leaf

Uppermost node

counted Uppermost node

counted

V1V1

V1 = One fully developed trifoliolate leaf node.• The two edges of

each leaflet have unrolled and the two edges are not touching.

V1

V2V2V2 = Two fully developed trifoliolate leaf nodes

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•Rhizobia bacteria have infected roots and nodules become visible shortly after VE.

•N-fixation begins at V2 to V3 stages.

•Lateral roots are growing rapidly into the top 6 inches of soil.

•Lateral roots are growing rapidly into the top 6 inches of soil.

Root Nodules(including a sliced nodule)

Root showing nodulesActive nodules have an

internal pink colorActive nodules have an

internal pink color

NodulesNodules

V3V3

V3 = Three fully developed trifoliolate leaf nodes.

V4V4V4 = Four fully developed trifoliolate leaf nodes.

The upper junction between the main stem and a leaf petiole is called an axil.

Each axil has an axillary bud.

An axillary bud may develop into: 1) A flower cluster2) A branch3) Remain dormant

The upper junction between the main stem and a leaf petiole is called an axil.

Each axil has an axillary bud.

An axillary bud may develop into: 1) A flower cluster2) A branch3) Remain dormant

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11

Axillary BudsAxillary BudsStem ApexStem Apex

Axils of the unifoliolate and trifoliolate leaves and cotyledons all have axillary buds.

Young Soybean PlantGrowing Point

Trifoliolate leaf node

Trifoliolate leaf(3 leaflets)

Unifoliolate leaf

Main stem

Cotyledon

Unifoliolate node

Petiole

*Axillary buds

*The upper junction between the main stem and a leaf petiole is called an axil. In each axil there is an axillary bud. This bud usually developes a flower cluster, but may remain dormant, or may develop into a branch.

*The upper junction between the main stem and a leaf petiole is called an axil. In each axil there is an axillary bud. This bud usually develops a flower cluster, but may remain dormant, or may develop into a branch.

Young Soybean Plant

V5V5 V6V6Apex

(Growing Point)

The total number of nodes that the plant may potentially produce is set at V5-V6.

Branch

Stem Apex and Axillary Buds

► The The axillary buds allowaxillary buds allow a tremendous a tremendous capacity for the capacity for the soybean plant to recoversoybean plant to recover from damage (such as hail) and thin plant from damage (such as hail) and thin plant stands.stands.

► The The stem apexstem apex (tip growing point) (tip growing point) exhibits exhibits dominancedominance and supresses axillary bud and supresses axillary bud development during vegetative growth.development during vegetative growth.

► If the If the stem apex is damagedstem apex is damaged, axillary buds , axillary buds will produce many will produce many branchesbranches..

► The The plant is killedplant is killed if broken off below the if broken off below the cotyledonary node. No axillary buds occur cotyledonary node. No axillary buds occur below this node.below this node.

If the growing point is broken off during vegetative growth stages, the remaining axillary buds are allowed to branch so the plant can recover from damage or thin stands.

During reproductive stages, the ability of the soybean plant to recover from damage is not as great.

If the plant is broken off below the cotyledon node (lowest axillary buds), the plant will not recover.

Young Soybean PlantGrowing Point

Trifoliolate leaf node

Trifoliolate leaf(3 leaflets)

Unifoliolate leaf

No plant recovery

Cotyledon

Unifoliolate node

Petiole

*Axillary buds

What Vegetative (V) Stage is this Plant?What Vegetative (V) Stage is this Plant?

V6V6V6 = Six fully developed trifoliolate leaf nodes.V6 = Six fully developed trifoliolate leaf nodes.

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1133

New V stages are now appearing every 3-5 days.

50% leaf loss at V6 reduces yield

~3%.

50% leaf loss at V6 reduces yield

~3%.

Unifoliolate leaves and cotyledons may have matured and fallen from the plant at this time.

Root system expands at its fastest rate from V6 to

R2

Determining Soybean V(n) Stage When Lowest Leaves are Missing

► Unifoliolate leaves (and lowest trifoliolate leaves) may Unifoliolate leaves (and lowest trifoliolate leaves) may be lost through injury or natural aging.be lost through injury or natural aging.

► The The unifoliolate nodeunifoliolate node produces unifoliolate leaves on produces unifoliolate leaves on directly opposite sidesdirectly opposite sides of the lower stem (on short of the lower stem (on short petioles).petioles).

► The cotyledonsThe cotyledons (modified leaf storage organs) also are (modified leaf storage organs) also are directly oppositedirectly opposite on the stem on the stem just belowjust below the unifoliolate the unifoliolate node.node.

► All other nodesAll other nodes produce true leaves that are produce true leaves that are trifoliolate trifoliolate leavesleaves (on long petioles). (on long petioles).

Produced Produced singularlysingularly (from different nodes). (from different nodes).

AlternateAlternate (from side to side) on the stem. (from side to side) on the stem.

Young Soybean PlantGrowing Point

Trifoliolate leaf node

Trifoliolate leaf(3 leaflets)

Unifoliolate leaf

Main stem

Cotyledon

Unifoliolate node

Petiole

*Axillary buds

*The upper junction between the main stem and a leaf petiole is called an axil. In each axil there is an axillary bud. This bud usually developes a flower cluster, but may remain dormant, or may develop into a branch.

Trifoliolate leaf nodes: Trifoliolate leaves appear singularly (different nodes) and alternate (side to side) on the stem.

Unifoliolate leaf node: Two unifoliolate leaves are directly opposite on lower stem.

Cotyledonary node: Two cotyledons are directly opposite on the lower stem.

When leaves fall off, a scar is left on the stem where the leaf petiole was attached.

Leaf Node Locations

Identifying Soybean V(n) Nodes

► If lower leaves are lost, the V(n) stage can be If lower leaves are lost, the V(n) stage can be determined by determined by locating the position of the locating the position of the unifoliolate nodeunifoliolate node..

► The The two two oppositeopposite leaf scars leaf scars (slight indentations) on (slight indentations) on the lower stem (where the leaf petioles were the lower stem (where the leaf petioles were attached) permanently mark where the unifoliolate attached) permanently mark where the unifoliolate leaves had grown.leaves had grown.

► The unifoliolate leaf scars are The unifoliolate leaf scars are located just abovelocated just above the two opposite scars that mark the cotyledonary the two opposite scars that mark the cotyledonary node.node.

► Any leaf scars Any leaf scars aboveabove the unifoliolate scars appears the unifoliolate scars appears singularlysingularly and and alternatelyalternately on the stem, and mark on the stem, and mark node positions where trifoliolate leaves had grown.node positions where trifoliolate leaves had grown.

Soybean Reproductive (R) Stages

► Begins with flowering and ends with full maturity.Begins with flowering and ends with full maturity.

► R1R1 - - - Beginning Bloom (flowering) - - - Beginning Bloom (flowering)► R2R2 - - - Full Bloom - - - Full Bloom

► R3R3 - - - Beginning Pod - - - Beginning Pod► R4 R4 - - - Full Pod- - - Full Pod

► R5 R5 - - - Beginning Seed- - - Beginning Seed► R6 R6 - - - Full Seed- - - Full Seed

► R7R7 - - - Beginning Maturity - - - Beginning Maturity► R8R8 - - - Full Maturity - - - Full Maturity

R1 – Beginning BloomR1 R1 = One open flower at any node on the main stem.= One open flower at any node on the main stem.

Indeterminate varieties:At R1, plants are in the V7 to V10 stage. Flowering begins on the third to sixth node (depending on V stage at flowering) and progresses upward and downward.

Vegetative growth continues after flowering begins. At R1, less than half of the nodes on the main stem have developed and plants have achieved less than half their final height.

Determinate varieties:Vegetative growth is complete before flowering begins. Most or all of the nodes on the main stem have developed and plants grow very little in height after R1.

Flowering occurs at the same time in the top and bottom of the plant. R1 and R2 may occur simultaneously.

*******************Soybean flowers are self-pollinated with less than 1% natural crossing. Pollination occurs at or just before flowers open.

Flowers are purple or white

(variety)

Open Flower

Planting Soybean Maturity Group

Date MG II MG III MG IV MG V

Predicted First Flowering Date

  mean1 SD2 mean SD mean SD mean SD

  (±) (±) (±) (±)

1-May 3-Jun 2 8-Jun 4 17-Jun 4 25-Jun 5

15-May 15-Jun 2 21-Jun 2 29-Jun 3 8-Jul 3

29-May 27-Jun 2 5-Jul 1 12-Jul 1 19-Jul 2

12-Jun 10-Jul 1 16-Jul 1 23-Jul 1 29-Jul 1

26-Jun 24-Jul 1 29-Jul 1 2-Aug 1 8-Aug 11 Average of 29 years of weather data, Spindletop Farm, Lexington, KY.2 Standard deviation: measurement of variation.Flowering dates generated from CROPGRO and verified from field data by Dr. Dennis Egli.AGR-184 --- Predicting Soybean First Flowering Date.

Predicted first flowering date

Predicted Number of Days to First Flowering

0

10

20

30

40

50

60

70

28-Apr 8-May 18-May 28-May 7-Jun 17-Jun 27-Jun 7-Jul

Planting Date

Da

ys

MG II

MG III

MGIV

MGV

AGR-184 --- Predicting Soybean First Flowering Date.Average of 29 years of weather data, Spindletop Farm, Lexington, KY.Standard deviation: measurement of variation, expressed by bars.Flowering dates generated from CROPGRO and verified from field data by Dr. Dennis Egli.

R2 – Full BloomR2 = Open flower at one of the two uppermost nodes on the

main stem with a fully developed trifoliolate leaf node.

The rapiddry weight accumulation initially starts in the vegetative plant parts but then gradually shifts to the pods and seeds between R3 and R6.

50% defoliation at R2 reduces yield about 6 percent.

R2 marks the beginning of a period of rapid and constant (linear) dry weight accumulation by the whole plant which continues until shortly after the R6 stage.

Axillary buds in stem Axillary buds in stem axils develop into axils develop into flower clusters called flower clusters called racemes.racemes.

A racemeA raceme is a short is a short stem-like structure stem-like structure that produces that produces flowers that develop flowers that develop into pods.into pods.

Determinate Determinate varieties generally varieties generally have a longer raceme have a longer raceme (flowering stalk) (flowering stalk) than indeterminate than indeterminate varieties.varieties.

Raceme

R2R2

Well-nodulatedWell-nodulatedplantplant

Well-nodulatedWell-nodulatedplantplant

Major Major lateral lateral root growthroot growth is is now verticalnow vertical (downward). (downward). They (and the They (and the taproot) taproot) continue to continue to elongate deep elongate deep into the soil into the soil until late R6.until late R6.

Major Major lateral lateral root growthroot growth is is now verticalnow vertical (downward). (downward). They (and the They (and the taproot) taproot) continue to continue to elongate deep elongate deep into the soil into the soil until late R6.until late R6.

Soybean roots can achieve depths of 5-6 feet by R6.Soybean roots can achieve depths of 5-6 feet by R6.Soybean roots can achieve depths of 5-6 feet by R6.Soybean roots can achieve depths of 5-6 feet by R6.

R3 – Beginning PodR3 = Pod is 5 mm (3/16 inches) long at one of the four uppermost

nodes on the main stem with a fully developed trifoliolate leaf node.

About 60 to 75 percent of all flowers produced typically abort.

• ~ half of this abortion occurs before flowers develop into pods.• Other half is due to young pod abortion.• Stress causes higher abortion rates.

pod 3/16inch long

R4 – Full PodR4 = Pod is 2 cm (¾ inches) long at one of the four uppermost

nodes on the main stem with a fully developed trifoliolate leaf node.

R4 is start of the most critical period for yield determination.

From R4 through R6, stress (moisture, light, nutrients, frost, lodging, defoliation) reduces yield more than any other period.

Yield reductions at R4 result mainly from fewer pods per plant.

Stress can cause pods to abort.

Period of rapid dry weight accumulation by the pods (R4 to middle of R5).

¾ inchlong pod

Sequence of Young Pod Development

R3 = Pod is 5 mm (3/16 inch) long.R4 = Pod is 2 cm (3/4 inch) long.

R3 R4

R5 – Beginning Seed

R5 = Seed is 3 mm (1/8 inches) long in the pod at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node.

Seed yield depends on dry weigh accumulation (rate and length of time).

Period of rapid seed growth.

Between R5 and R6 dry weight accumulation redistributes to the developing seed.

Stress at R5 will abort seeds.

Yield loss in late R5 to R6 occurs mainly from fewer pods per plant and fewer seeds per pod. Also somewhat from smaller seed size.

R6 – Full Seed

Dry weight accumulation still rapid in seeds, but begins to slow shortly after R6.

R6 = Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed trifoliolate leaf node.

“green bean” stage

Stress reduces seed size (weight)

Sequence of Seed Development (R5 R6)

R5R5R6R6

R5 = Seed is 3 mm (1/8) longR6 = Green seed fills pod cavity

R7 – Beginning Maturity

R7R7 = One normal pod on the main stem has = One normal pod on the main stem has reached its mature pod color (normally reached its mature pod color (normally brown or tan).brown or tan).

At R7, the plant is essentially at physiological maturity. No additional dry weight will accumulate in the seed.

Physiological maturity occurs when the seed (and pod) turns yellow (lost all green color).

Seed at physiological maturity is ~60 percent moisture.

Stress at R7 essentially has no effect on yield.

R6 R7 R8

Sequence of Color and Size Changes of the Soybean Pod and Seed (R6 R8).

Soybean Pods and Seeds (R6 R8)

(R8)

(R7)

(R6)

R8 – Full Maturity

Five to ten days of drying weather are required after R8, before the seed contains less than 15 percent moisture.

Ideal seed moisture content at harvest and for storage is 13 percent.

Harvest can begin above 15 percent moisture:

•drying costs.•seed damage if

very high.

Harvest delayed below 13 percent moisture:

•field shatter loss.

•harvest shatter loss.

•seed damage (split seeds).

R8R8 = 95 percent of the pods have reached their mature pod color. = 95 percent of the pods have reached their mature pod color.

Components of Soybean YieldComponents of Soybean Yield

Soybean yield is determined by Soybean yield is determined by 3 major 3 major componentscomponents.. Number of pods per plant.Number of pods per plant. Number of seeds per pod.Number of seeds per pod. Weight per seed (seed size).Weight per seed (seed size).

Yield increases or decreases result from an Yield increases or decreases result from an increase or decrease in one or more of the yield increase or decrease in one or more of the yield components.components.

A reduction in one component may be A reduction in one component may be compensated for by another component.compensated for by another component.

Soybean Yield EstimatesSoybean Yield Estimates

Estimates can be made. Reliability/variabilityEstimates can be made. Reliability/variability depends on accuracy of estimating yield depends on accuracy of estimating yield components.components.

The following publications provide information The following publications provide information and guidelines for estimating soybean yield in and guidelines for estimating soybean yield in the field prior to harvest.the field prior to harvest.

Estimating Soybean Yields (AGR-188).Estimating Soybean Yields (AGR-188). Kentucky Integrated Crop Management Manual for Kentucky Integrated Crop Management Manual for

Field Crops. Section in “Soybean” manual (IPM-3).Field Crops. Section in “Soybean” manual (IPM-3).

Criteria for Estimating Soybean Yield

Criteria for Estimating Soybean Yield

Variability in yield components will alter yield estimate Variability in yield components will alter yield estimate reliability. Some assumptions are made.reliability. Some assumptions are made.

More locations/samples; the better the estimate.More locations/samples; the better the estimate.

Best to estimate after seed fill is complete.Best to estimate after seed fill is complete.

Estimate the Estimate the following componentsfollowing components:: Population (plants/acre).Population (plants/acre). Pods per plant.Pods per plant. Seeds per pod.Seeds per pod. Seed size (seeds/lb).Seed size (seeds/lb).

The “Remarkable” Soybean (1)The “Remarkable” Soybean (1)

Soybean has a great ability to Soybean has a great ability to adapt (+ or -) to adapt (+ or -) to it’s environmentit’s environment. Ability to compensate in both . Ability to compensate in both the vegetative and reproductive stages.the vegetative and reproductive stages. Important feature of the soybean.Important feature of the soybean. Best ability of all major row crops.Best ability of all major row crops.

Vegetative Stages

Great capacity to compensate for reduced Great capacity to compensate for reduced stand, plant loss, or stem and leaf damage.stand, plant loss, or stem and leaf damage.

Axillary buds at lower nodes produce branches Axillary buds at lower nodes produce branches (with new leaves). (with new leaves).

The “Remarkable” Soybean (2)The “Remarkable” Soybean (2)

Ability of the soybean plant to recover from Ability of the soybean plant to recover from vegetative (foliar) injury is vegetative (foliar) injury is much lessmuch less during during reproductive stages (particularly late R stages).reproductive stages (particularly late R stages).

However, the soybean has the ability to However, the soybean has the ability to adjust adjust it’s reproductive componentsit’s reproductive components (flowers, pods, (flowers, pods, seed #, seed size) in response to environmental seed #, seed size) in response to environmental conditions (stress or no stress).conditions (stress or no stress).

Increases or decreases in one or more of the Increases or decreases in one or more of the yield components will yield components will affect yield (+ or -)affect yield (+ or -)..

Reproductive Stages

The “Remarkable” Soybean (3)The “Remarkable” Soybean (3)

StressfulStressful conditions conditions will abortwill abort flowers, pods, seeds and flowers, pods, seeds and decrease seed size.decrease seed size.

A reduction in one yield component may be A reduction in one yield component may be compensated for by another component.compensated for by another component.

Which yield component decreases (stress) or increases Which yield component decreases (stress) or increases (good conditions) (good conditions) depends on the R stagedepends on the R stage when when stress/non-stress occurs.stress/non-stress occurs.

A short period of stressA short period of stress allows the next R stage to allows the next R stage to compensate as conditions improve.compensate as conditions improve.

The “Remarkable” Soybean (4)The “Remarkable” Soybean (4)

An extended period of stressAn extended period of stress decreases the opportunity decreases the opportunity for R stage components to compensate each other.for R stage components to compensate each other.

As the soybean plant progressesAs the soybean plant progresses from R1 to R6, it’s from R1 to R6, it’s ability to compensate after a stress decreases.ability to compensate after a stress decreases.

At later R stagesAt later R stages, potential yield loss from stress , potential yield loss from stress increases.increases.

Stress from R4 to R6 reduces yield more than stress at other R Stress from R4 to R6 reduces yield more than stress at other R stages.stages.

VegetativeVegetative

FloweringFlowering

Soybean Compensation Ability by Soybean Compensation Ability by Growth StageGrowth Stage

Vegetative Flowering Podding Vegetative Flowering Podding No. of Seeds No. of Seeds Seed SizeSeed Size

Optimum stand branching ability reducedOptimum stand branching ability reduced Reduced stand increased branchingReduced stand increased branching Plant damage increased branchingPlant damage increased branching

No stress maintain more flowersNo stress maintain more flowers Stress more flowers abortStress more flowers abort

Flower and Pod TriviaFlower and Pod Trivia

About 60 to 75 percent of all soybean flowers About 60 to 75 percent of all soybean flowers produced abort and don’t contribute to yield.produced abort and don’t contribute to yield. About half (30-40%) of this abortion occurs before About half (30-40%) of this abortion occurs before

flowers develop into young pods.flowers develop into young pods. The other half (30-40%) is due to pod abortion.The other half (30-40%) is due to pod abortion.

If soybean maintained all its flowers, yield If soybean maintained all its flowers, yield potential would be 250 bu/acre.potential would be 250 bu/acre. Present soybean plant not capable.Present soybean plant not capable.

Overproduction of flowers and pods is good. Overproduction of flowers and pods is good. Allows flexibility for early stress periods.Allows flexibility for early stress periods.

Seed NumberSeed Number

Seed Fill (weight)Seed Fill (weight)

No stress increase seed size (weight)No stress increase seed size (weight) Stress decrease seed size (weight)Stress decrease seed size (weight)

PoddingPodding

No stress more seeds developNo stress more seeds develop Stress seeds do not develop or seeds Stress seeds do not develop or seeds abortabort

No stress maintain more podsNo stress maintain more pods Stress more pods abortStress more pods abort

Soybean PopulationsSoybean Populations

U.K. Recommended Seeding RatesU.K. Recommended Seeding Rates

Higher than neededHigher than needed for most situations. for most situations. Contain a Contain a seeding rate rangeseeding rate range for each for each row widthrow width.. Recommendations are Recommendations are “buffer”“buffer” seeding rates. seeding rates.

Insurance in the event of poor emergence, stand loss, Insurance in the event of poor emergence, stand loss, etc.etc.

GrowersGrowers are are not acceptingnot accepting lower seeding rates. lower seeding rates. Soybean seed costs:Soybean seed costs:

Relatively low seed costs 10-20 years ago.Relatively low seed costs 10-20 years ago. Comparatively higher seed costs today with Comparatively higher seed costs today with

technology trait soybeans (i.e. RR).technology trait soybeans (i.e. RR).

U.K. Recommended Seeding RatesU.K. Recommended Seeding Rates

Row Width (inches)

Seeding RateSeeding Rate

Expected* plants/acre

Seeds/foot Seeds/acre

77 2 to 32 to 3 149,000 to 149,000 to 224,000224,000

119,000 to 119,000 to 179,000179,000

1515 5 to 65 to 6 174,000 to 174,000 to 209,000209,000

139,000 to 139,000 to 167,000167,000

3030 8 to 108 to 10 139,000 to 139,000 to 174,000174,000

111,000 to 111,000 to 139,000139,000

*Assuming 80% emergence of planted seed.

AGR-130 --- Soybean Production in Kentucky (Part III).

Seeding Rate Final PopulationSeeding Rate Final Population (Plants) (Plants)

What can we expect?What can we expect? Average % emergenceAverage % emergence = 80-85% = 80-85% RangeRange = 70% or less to 95% = 70% or less to 95%

FactorsFactors influencing final stand achieved. influencing final stand achieved. Seed qualitySeed quality (germination and vigor). (germination and vigor). Seedbed conditions (tillage, residue).Seedbed conditions (tillage, residue). Planting environmentPlanting environment (soil temp. & moisture). (soil temp. & moisture). Weather after planting (crusting, moisture).Weather after planting (crusting, moisture). Planting equipmentPlanting equipment (depth, seed coverage). (depth, seed coverage). Post-emergence (hail, pests, chemicals). Post-emergence (hail, pests, chemicals).

Seeding Rate BasicsSeeding Rate Basics

Base seeding rate on Base seeding rate on number/unit areanumber/unit area (seeds/acre); (seeds/acre); notnot volume/area volume/area (pounds/acre).(pounds/acre).

Reason: Reason: Seed size will varySeed size will vary.. VarietyVariety (genetics). (genetics). Environment:Environment: Affected by growing season (weather Affected by growing season (weather

during seed-fill).during seed-fill).

Seed size can vary from:Seed size can vary from: 2500 seeds/lb or less 2500 seeds/lb or less (large seed)(large seed) 3500 seeds/lb or more 3500 seeds/lb or more (small seed)(small seed)

Seed Size / Seeding Rate Seed Size / Seeding Rate ExampleExample

Fifty pound bag of seed contains:Fifty pound bag of seed contains: Small seedSmall seed (3500 seeds/lb) = 175,000 seeds (3500 seeds/lb) = 175,000 seeds Large seedLarge seed (2500 seeds/lb) = 125,000 seeds (2500 seeds/lb) = 125,000 seeds

differencedifference = 50,000 = 50,000 seeds/bagseeds/bag

Seeding rate of 60 pounds/acre:Seeding rate of 60 pounds/acre: Small Small (3500 seeds/lb) = 210,000 seeds/A(3500 seeds/lb) = 210,000 seeds/A LargeLarge (2500 seeds/lb) = 150,000 seeds/A (2500 seeds/lb) = 150,000 seeds/A

differencedifference = 60,000 seeds/A = 60,000 seeds/A

How Seed Size Affects Seeding RateHow Seed Size Affects Seeding Rate

No. of SeedsNo. of Seeds

in a 50 lb. in a 50 lb. BagBag

Lbs. of Seed Required at:Lbs. of Seed Required at:

Seed Size Seed Size (seeds/lb)(seeds/lb)

180,000 180,000 Seeds/acreSeeds/acre

120,000 120,000 Seeds/acreSeeds/acre

20002000

25002500

28002800

30003000

35003500

40004000

100,000100,000

125,000125,000

140,000140,000

150,000150,000

175,000175,000

200,000200,000

9090

7272

6464

6060

5151

4545

6060

4848

4343

4040

3434

3030

Soybean Plant PopulationsSoybean Plant Populations

StudiesStudies: : Yields do not vary greatly within a Yields do not vary greatly within a wide rangewide range (100,000 – 220,000 plants/A). (100,000 – 220,000 plants/A).

South:South: < 100,000 plants/A have equal yields. < 100,000 plants/A have equal yields.

A common goalA common goal is 150,000 plants/A. is 150,000 plants/A. Seeding rates of 175,000-200,000 seeds/A.Seeding rates of 175,000-200,000 seeds/A.

Most producers Most producers overseed than underseed.overseed than underseed.

Considerations?:Considerations?: Variety (maturity group)Variety (maturity group) Planting datePlanting date

Question:Question: Why can soybeans produce equivalent yields Why can soybeans produce equivalent yields

at a wide range of plant populations?at a wide range of plant populations?

Answer:Answer: Soybeans have a tremendous ability to Soybeans have a tremendous ability to

compensate compensate ( (branchingbranching, pod number, seed , pod number, seed number).number).

High populations:High populations: plants do not sense a need to plants do not sense a need to branch.branch.

Low populations:Low populations: plants branch to fill in space. plants branch to fill in space.

Young Soybean PlantGrowing Point

Trifoliolate leaf node

Trifoliolate leaf(3 leaflets)

Unifoliolate leaf

Main stem

Cotyledon

Unifoliolate node

Petiole

*Axillary buds

*The upper junction between the main stem and a leaf petiole is called an axil. In each axil there is an axillary bud. This bud usually developes a flower cluster, but may remain

dormant, or may develop into a branch.

*The upper junction between the main stem and a leaf petiole is called an axil. In each axil there is an axillary bud. This bud usually develops a flower cluster, but may remain dormant, or may develop into a branch.

Young Soybean Plant

17,400

34,800

70,000

121,800

192,000

Seeding Rates:Live Seeds per Acre

•Spindletop Farm, Lexington, KY•15-inch rows•2 planting dates (full season and double crop)•Three yrs (2003, 2004, 2005)•No-Till (2003, 2004) Reduced Till (2005)•Glyphosate herbicide for weed control•Live stand counts were taken prior to harvest. •Study conducted by Chad Lee, Dennis Tekrony, and Dennis Egli (Univ. of Kentucky).

Plants acre-1(1000's)

0 20 40 60 80 100 120 140 160 180

Yie

ld (

bu

acr

e-1)

0

20

40

60

80

100

120

Low VigorHigh Vigor

CF492 Early 2004

y = 16.0558 + 52.4492(1 - e0.0383x)

Plants acre-1 (1000's)

0 20 40 60 80 100 120 140 160 180

Yie

ld (

bu

acr

e-1)

0

20

40

60

80

100

120

Low VigorHigh Vigor

CF 461 Early 2004

y = -24.7245 + 124.1175(1 - e0.0320x)

Plants Acre-1 (1000's)

0 20 40 60 80 100 120 140 160 180

Yie

ld (

bu a

cre-1

)

0

20

40

60

Low Vigor High Vigor

B336 Late 2004

y = -1.9197 + 56.7899(1-e-0.0307x)

Plants Acre-1 (1000's)

0 20 40 60 80 100 120 140 160 180

Yie

ld (

bu

acr

e-1)

0

20

40

60

Low Vigor High Vigor

B336 Early 2004

y = 15.9972 + 44.9757(1 - e-0.0370x)

Minimum plant densities required for optimum yieldMinimum plant densities required for optimum yield

Seeding Seeding DateDate11 CultivarCultivar MaturityMaturity Minimum Plant PopulationMinimum Plant Population22

plants/acreplants/acre

24 April 24 April 0303 FSFS

StresslanStresslandd 4.54.5 42,50042,500

24 April 24 April 0303 FSFS CF 461CF 461 4.64.6 53,40053,400

24 April 24 April 0303 FSFS CF 492CF 492 4.94.9 49,80049,800

21 May 21 May 0404 FSFS B283B283 2.82.8 92,30092,300

21 May 21 May 0404 FSFS B336B336 3.33.3 72,10072,100

21 May 21 May 0404 FSFS CF461CF461 4.64.6 85,80085,800

21 June 21 June 0404 DCDC B283B283 2.82.8 91,40091,400

21 June 21 June 0404 DCDC B336B336 3.33.3 93,10093,10011 FS = full season; DC = double crop. FS = full season; DC = double crop.2 2 Exponential rise to maximum, 3 parameter model: density required for 95% of yield that Exponential rise to maximum, 3 parameter model: density required for 95% of yield that was achieved at maximum plant density.was achieved at maximum plant density.

Lexington, KY, 2003 and 2004

Table 2. Table 2. Minimum plant densities required for optimum yield as defined by two Minimum plant densities required for optimum yield as defined by two regression equations.regression equations.

Linear-PlateauLinear-Plateau22 ExponentialExponential33

Seeding DateSeeding Date11 CultivarCultivar MaturityMaturity Minimum Plant PopulationMinimum Plant Population

plants/acreplants/acre

24 April 0324 April 03 FSFS StresslandStressland 4.54.5 42,10042,100 42,50042,500

24 April 0324 April 03 FSFS CF 461CF 461 4.64.6 42,90042,900 53,40053,400

24 April 0324 April 03 FSFS CF 492CF 492 4.94.9 39,70039,700 49,80049,800

21 May 0421 May 04 FSFS B283B283 2.82.8 66,80066,800 92,30092,300

21 May 0421 May 04 FSFS B336B336 3.33.3 47,80047,800 72,10072,100

21 May 0421 May 04 FSFS CF461CF461 4.64.6 49,80049,800 85,80085,800

21 June 0421 June 04 DCDC B283B283 2.82.8 79,80079,800 91,40091,400

21 June 0421 June 04 DCDC B336B336 3.33.3 69,90069,900 93,10093,10011 FS = full season; DC = double crop FS = full season; DC = double crop22 Linear-plateau model: Minimum plant density required for maximum yield. Linear-plateau model: Minimum plant density required for maximum yield. 33 Exponential rise to maximum, 3 parameter model: Density required for 95% of yield that was Exponential rise to maximum, 3 parameter model: Density required for 95% of yield that was achieved at maximum plant density.achieved at maximum plant density.

Soybean Population SummarySoybean Population Summary(Lexington, KY ---- 2003 & 2004)(Lexington, KY ---- 2003 & 2004)

Maximum yieldMaximum yield was obtained at populations was obtained at populations between between 42,000 and 93,000 plants/acre42,000 and 93,000 plants/acre (more (more conservative exponential regression model) or conservative exponential regression model) or between between 40,000 and 80,000 plants/acre40,000 and 80,000 plants/acre (linear (linear plateau model).plateau model).

Maximum yieldMaximum yield obtained withobtained with <100,000 <100,000 plants/acre plants/acre (in all situations).(in all situations).

Early maturitiesEarly maturities (MG II and early MG III) and (MG II and early MG III) and later planting dateslater planting dates (after June 1) (after June 1) may needmay need slightly higher populationsslightly higher populations (70,000 to 90,000 (70,000 to 90,000 plants/acre).plants/acre).

Soybean Population Study- - (2005)Soybean Population Study- - (2005)((Earlier VarietyEarlier Variety (3.9 RM) --- (3.9 RM) --- EarlyEarly Planting Date) Planting Date)

Seeding RateSeeding Rate(viable seeds/A)(viable seeds/A)

Avg. Final StandAvg. Final Stand(Plants/A)(Plants/A)

Soybean YieldSoybean Yield(Bushels/A)(Bushels/A)

50,00050,000 44,00044,000 70 70 aa

75,00075,000 61,00061,000 70 70 aa

100,000100,000 81,00081,000 72 72 aa

125,000125,000 101,000101,000 71 71 aa

150,000150,000 117,000117,000 73 73 aa

175,000175,000 142,000142,000 73 73 aa

200,000200,000 168,000168,000 71 71 aa

225,000225,000 184,000184,000 70 70 aa

Location: UKREC (Princeton, Ky)Location: UKREC (Princeton, Ky) Variety = Pioneer 93M90Variety = Pioneer 93M90 Planted May 25, 2005. Row spacing = 15 inches.Planted May 25, 2005. Row spacing = 15 inches.

Soybean Population Study- - (2005)Soybean Population Study- - (2005)((Later VarietyLater Variety (4.7 RM) --- (4.7 RM) --- EarlyEarly Planting Date) Planting Date)

Seeding RateSeeding Rate(viable seeds/A)(viable seeds/A)

Avg. Final StandAvg. Final Stand(Plants/A)(Plants/A)

Soybean YieldSoybean Yield(Bushels/A)(Bushels/A)

50,00050,000 45,00045,000 72 72 aa

75,00075,000 68,00068,000 74 74 aa

100,000100,000 92,00092,000 76 76 aa

125,000125,000 119,000119,000 73 73 aa

150,000150,000 145,000145,000 73 73 aa

175,000175,000 162,000162,000 75 75 aa

200,000200,000 183,000183,000 76 76 aa

225,000225,000 210,000210,000 74 74 aa Location: UKREC (Princeton, Ky)Location: UKREC (Princeton, Ky) Variety = Pioneer 94M70Variety = Pioneer 94M70 Planted May 25, 2005. Row spacing = 15 inches.Planted May 25, 2005. Row spacing = 15 inches.

Soybean Population Study - - 2005Soybean Population Study - - 2005(Avg. of 2 Varieties --- (Avg. of 2 Varieties --- Early Planting DateEarly Planting Date))

Seeding RateSeeding Rate(viable seeds/A)(viable seeds/A)

Avg. Final StandAvg. Final Stand**(Plants/A)(Plants/A)

Soybean YieldSoybean Yield****(Bushels/A)(Bushels/A)

50,00050,000 45,00045,000 73 73 aa

75,00075,000 65,00065,000 72 72 aa

100,000100,000 85,00085,000 75 75 aa

125,000125,000 110,000110,000 73 73 aa

150,000150,000 130,000130,000 74 74 aa

175,000175,000 150,000150,000 74 74 aa

200,000200,000 175,000175,000 74 74 aa

225,000225,000 195,000195,000 72 72 aa

**Avg. approx. final stand of two varieties.Avg. approx. final stand of two varieties.****Avg. of two varieties (3.9 RM and 4.7 RM). Varieties were not significantly different.Avg. of two varieties (3.9 RM and 4.7 RM). Varieties were not significantly different. Planted May 25, 2005. Row spacing = 15 inches. Location = UKREC.Planted May 25, 2005. Row spacing = 15 inches. Location = UKREC.

Soybean Population SummarySoybean Population Summary(Princeton, KY ---- 2005)(Princeton, KY ---- 2005)

Statistically,Statistically, equivalent soybean yield equivalent soybean yield was obtained at populations ranging fromwas obtained at populations ranging from 45,000 to 200,000 plants/acre.45,000 to 200,000 plants/acre.

The lowest population ofThe lowest population of 45,000 45,000 plants/acreplants/acre was sufficient to obtainwas sufficient to obtain maximum yield.maximum yield.

Occurred for both soybean varieties/maturities Occurred for both soybean varieties/maturities (3.9 RM and 4.7 RM).(3.9 RM and 4.7 RM).

Lower Soybean Populations: Lower Soybean Populations: (+ and -)(+ and -)

BenefitsBenefits No yield lossNo yield loss Lower seed costsLower seed costs Less lodgingLess lodging

Possible negativesPossible negatives More difficult to harvest?More difficult to harvest?

Large, low branchingLarge, low branching Low pod heightLow pod height Go slow; go lowGo slow; go low

More Weed pressure?More Weed pressure?

Maximum Soybean YieldsMaximum Soybean Yields

can be achieved atcan be achieved at

Lower Soybean PopulationsLower Soybean Populations

as a result ofas a result of

Lower Seeding RatesLower Seeding Rates

which result inwhich result in

Lower Seed CostsLower Seed Costs particularly true for soybean seed that has particularly true for soybean seed that has higher higher

costs associated with technology traitscosts associated with technology traits (i.e. RR). (i.e. RR).

SeedingSeeding

RateRate

(Seeds/A)(Seeds/A)

No. of **No. of **

50 lb.50 lb.

Bags/ABags/A

Seed***Seed***

CostCost

($/Acre)($/Acre)

SeedSeed

SavingsSavings

($/Acre)($/Acre)

175,000175,000** 1.251.25 $37.50$37.50

150,000150,000 1.101.10 $33.00$33.00 $4.50$4.50

125,000125,000 0.900.90 $27.00$27.00 $10.50$10.50

100,000100,000 0.700.70 $21.00$21.00 $16.50$16.50

75,00075,000 0.550.55 $16.50$16.50 $21.00$21.00

Soybean Seeding Rates and Seed CostsSoybean Seeding Rates and Seed Costs

*Average seeding rate being used (based on yield contest entries).

**Based on seed size of 2800 seeds per pound.

***Based on average seed cost (RR seed) of $30 per 50 lb. bag.

Soybean PopulationSoybean PopulationConclusions (1)Conclusions (1)

Appears thatAppears that populations for populations for Full-Full-Season soybeansSeason soybeans can be lowered can be lowered (from (from present populations commonly being present populations commonly being used) and still obtain maximum yields.used) and still obtain maximum yields.

ResultsResults in reduced seeding rates and lower seed in reduced seeding rates and lower seed costs/acre.costs/acre.

How low can we go?How low can we go?:: 120,000 --- 100,000120,000 --- 100,000 80,000 --- 80,000 ---

50,000??50,000??

More researchMore research needed to more clearly define needed to more clearly define population/yield response parameters.population/yield response parameters.

Soybean PopulationSoybean PopulationConclusions (2)Conclusions (2)

Comparatively higher populations Comparatively higher populations may may likely be needed for:likely be needed for: Late plantingsLate plantings (D.C. soybeans). (D.C. soybeans). Early maturity varietiesEarly maturity varieties?? More research needed to clarify.More research needed to clarify.

Different environments Different environments may alter may alter soybean population/yield response.soybean population/yield response. Growing season (weather).Growing season (weather). Stress or non-stress.Stress or non-stress.

Soybean Variety Soybean Variety SelectionSelection

Soybean Variety Selection Criteria (1)

• Yield potential • Multi-location and multi-year tests.

• Standability (lodging).

• Pest resistance.• Diseases (SCN, foliar, others).• Insects? (future development).

• Technology (GMO) traits.• Herbicide tolerance (RR trait).• Future pest traits? (insects, diseases)• Future food/health traits.

Soybean Variety Selection Criteria (2)

• Shattering. • Great improvements, Mat. Group differences.

• Markets (price; premiums).• Commodity soybean (oil and meal).• Specialty soybeans (specific uses/traits). (AGR-180)• Non-GMO.

• Management reasons.• Soils, harvest mgt., cropping system, planting date.

• Maturity Group(s)

Which Maturity Group(s) is Best to Use?

Due to photoperiod sensitivity, soybean varieties are adapted for

growth in a relatively narrow latitude range.

Areas Where Maturity Groups of Soybean are GrownAreas Where Maturity Groups of Soybean are Grown

Group 00 = earliest maturityGroup IX = latest maturity

Soybean varieties are classified into maturity groups (00 to IX) according to the range in latitudes in which they are adapted and are most productive.

Regions of adaptability are long east to west but relatively short (100- 150 miles) north to south.

Yields by Maturity Group

MG 2003 2004 2005 Avg.

------------ Bu/A ------------

II 40.7 31.3 30.9 34.4

III 46.4 39.9 35.8 40.9

IV 51.7 45.9 38.8 45.4

V 40.2 37.1 43.4 40.3

LSD (0.05) 5.0 3.7 5.7

Field: Spindletop Farm, Lexington, KY (Chad Lee)Tillage: No-Till

2003 & 2004 = Adequate moisture throughout season.2005 = Dry early (M,J.J); some rain in August; dry late.

Maturity Group Study Results

• Based on data for three years (2003-05)– MG IV was highest yielding– MG III and MG V were about 10% less– MG II was about 20% less

Results

KY Soybean Variety Trials

2003 2004 2005

Bu/A

III 56.7 66.8 47.5

IV 61.8 68.7 55.8

V 59.7 59.9 59.0

Average yield of maturity groups across 5 locations.

2003 2004 2005

% Difference

III - 8 - 3 - 15

IV 0 0 0

V - 3 - 13 + 6