Morphology

Habitat:

• Grown in areas where the summer is hot and rather damp; withstand excessive heat or severe winters; grown on a wide range of soils.




Habit:

• Erect, bushy pubescent annual with grey hairs on all parts of the plants; some are prostate and twining, a tendency which increases with shade; determinate cultivars develop terminal inflorescence; indeterminate cultivars shows axillary inflorescence.



Roots:

• Taproot, nodules small spherical sometimes lobed.



Stem:

• Branched; buds in axils of cotyledons. The primary leaves do not normally develop unless tip damaged.



Leaves:

• Alternate, trifoliate, rarely five foliage; petiole long narrow, cylindrical; stipules, small lanceolate, stipels minute; leaflets ovate to lanceolate, usually palea green in colour, base rounded; apex acute or obtuse; lateral leaflets often slightly oblique; most cultivars drop leaves when pods begin to mature.



Inflorescence:

• Short clustered axillary raceme; terminal if determine type.



Flowers:

• Small, bracteoles two, ovate, acute.



Calyx:

• Hairy, persistent, united for half-length with two upper and three lower lobes.



Corolla:

• White or lilac; standard ovate, emarginated (notched at the extremity); wings narrow, obovate; keel shorter that wings, not fused along upper surface.



Androecium:

• Stamens monadelphous; vexillary stamens free at the base; anthers uniform, globose.



Gynoecium:

• Hairy sessile, few ovuled, style curved, glabrous, stigma capitate.



Fruit:

• Pod; borne is cluster on short stalks; pale yellow, grey or black; slightly curved.



Seed:

• Globose; testa straw yellow; green, brown or black or blotched and mottled in combination of these colours, hilum small; cotyledon yellow or green.



Pollination:

• Self-pollination is the rule. Flowers open in the early morning and pollen is shed just before or at the time of opening and is shed directly onto the stigma. Bees and other insects visit flowers so that cross-pollination can take place, but is usually less than one per cent.

Growth Stages

• The soybean is a dicotyledonous plant that exhibits epigeal (above the surface) emergence.
• During germination, the cotyledons are pushed through the soil to the surface by an elongating hypocotyl.
• Because of the energy required to push the large cotyledons through heavy soils, soybeans generally emerge best if they are planted no deeper than 2 inches.
• After emergence, the green cotyledons open and supply the developing leaves with stored energy, while capturing a small amount of light energy.
• The first leaves to develop are the unifoliolate leaves. Two of these single leaves appear directly opposite one another above the cotyledons.
• All subsequent leaves are trifoliolates comprised of 3 leaflets.
• Soybean development is characterized by two distinct growth phases.
  • The first is the vegetative stages (V) that cover development from emergence through flowering
  • The second is the reproductive ( R ) stages from flowering through maturation

Vegetative stages

a) Germination Stage

• The radical, or primary root, is first to emerge from the seed. Shortly afterward, the hypocotyl (stem) emerges and begins growing toward the soil surface pulling the cotyledons (seed leaves) with it.
• This hook-shaped hypocotyl straightens out once emerged and as the cotyledons unfold.
• Emergence normally takes five to ten days depending on temperature, moisture conditions, variety and planting depth. During this time, lateral roots are also beginning to grow from the primary root.

b) Cotyledon Stage

• In this stage unifoliolate leaves are fully expanded.
• The cotyledons supply the nutrient needs of the young plant (for about seven to 10 days).
• The cotyledons will lose about 70% of their dry weight to this nutrient reallocation.

c) First trifoliolate

• The first trifoliolate is fully emerged and opened.

d) Second node

• Plants are 6-8 inches tall and have three nodes with two unfolded leaflets. Active nitrogen fixation from the bacteria is just beginning to occur.
• Most of these root nodules are within 10 inches of the soil surface with millions of bacteria in each nodule.
• Nodules that are pink or red inside are active in nitrogen fixation. White, brown or green nodules are not efficiently fixing nitrogen and are probably parasitic on the plant.

e) Third to Fifth nodes

• Soybean plants are about 7-9 inches tall with four nodes (three unfolded leaflets). The number of branches seen on the plant may increase at this point.
• At this stage the plant normally has axillary buds in the top stem that will develop into flower clusters (racemes).

f ) Sixth node

• Plants are often 12 to 14 inches tall at this stage with seven nodes with unfolded leaflets.
• The unifoliolate and cotyledons may have senesced from the plant.
• New stages are quickly unfolding every two to three days.
• Lateral roots have crossed over the row underground in any rows 30 inches or less
  

Reproductive Stages

a)Flower Initiation

• At least one flower is located on the plant at any node on the main stem. Plants have lengthened to 15-18 inches tall.
• Soybean flowering always initiates on the third to sixth node on the main stem depending on vegetative stage when flowering begins.
• This flower initiation will progress up and down the plant. Branches eventually also flower.
• Within each raceme, the flowering will occur from the base to the tip, so basal pods are always more mature.

b)Full Bloom stage

• Soybeans are around 17-22 inches. An open flower is seen at one of the two top nodes of the main stem.
• At least one of these two upper nodes shows a fully developed leaf.
• At this stage, the soybean has accumulated about 25% of its total dry weight and nutrients and has obtained about 50% of its mature height.

c)Pod Initiation

• Plants can be up to 23-32 inches tall. A pod on the upper four nodes is 3/16 inch long.
• Temperature or moisture stress at this time can affect yield through total pod number, bean number per pod or seed size.

d) Full Pod

• This stage shows rapid pod growth and the beginning of seed development at the beginning of the full pod stage.
• This stage is the most crucial period for seed yield.

e) Seed Initiation

• Seed filling during this stage requires much water and nutrients from the plant.
• Redistribution of nutrients in the plant occurs with the soybean providing about a half of needed N, P and K from the plant's vegetative parts and about a half from N fixation and nutrient uptake by the roots.

f) Full Seed

• This stage is also known as the "green bean" stage or beginning full seed stage, and total pod weight will peak during this stage.
• Growth rate of the beans is rapid

g) Initial Maturity

• This stage begins with one normal pod on the main stem which obtains the mature color (brown or tan).
• Dry matter begins to peak in individual seeds. This is visually seen when all green color is lost from both the seeds and pods (they appear yellow).
• Seeds contain about 60% moisture at physiological maturity.

h) Full Maturity

• On the soybean plant, 95% of the pods have reached their mature color and only five to 10 days of good drying weather after this stage will be required to have the soybeans at less than 15% moisture, or harvest moisture.