Subscribe and stay up-to-date with the latest news and great offers from DEKALB, Asgrow and Deltapine.
Don't miss out on the latest agronomic news.
Local agronomic alerts.Delivered straight to your inbox.
Soybean seed germination is referred to as “epigeal” because food storage structures (cotyledons) are pulled above the soil surface. In contrast, corn germination is considered “hypogeal” because the storage structure remains below the surface when the seed germinates.
Upon being placed into the soil, the seed begins to absorb or imbibe water and as a result, starts to swell. When enough water (approximately 50% of the seed’s weight) is taken in and with favorable temperatures, the radicle breaks through the seed coat (Figure 1) and rapidly develops into the primary seedling root. Lateral roots quickly emerge from the radicle as it elongates and root hairs grow from the radicle and lateral roots. Root hairs are barely visible and should not be confused with later developing and easily seen branch roots. The root hairs become the main absorbing structures.
Soon after the radicle appears, the hypocotyl starts elongating and forms a hook that pushes toward the surface. The cotyledons are attached to the hypocotyl and progress upward with the growth of the hypocotyl. When the hypocotyl emerges it straightens, and in the process pulls the cotyledons out of the soil (Figure 2). The cotyledons start turning green from exposure to light and as they open, the epicotyl is revealed. The epicotyl contains small leaves, buds, and the main growing point. This is known as the vegetative emergence stage (VE).
After the cotyledons, the unifoliate leaves are the next
leaves to appear (Figure 3). The unifoliate leaves are single,
non-compound leaves that emerge simultaneously and on opposite sides of the
stem. This stage represents the VC stage of growth. The trifoliate
leaves, the first true leaves of the soybean plant, are the next to appear
(Figure 4). The trifoliate leaves are compound leaves made up of three
leaflets and are produced singularly, alternating on opposite sides of the
stem. This represents the V1 stage. The next trifoliate leaf to
appear represents the V2 stage, with each new trifoliate leaf representing a
new V stage.
Moisture. Planting into a moist seedbed with good
seed-to-soil contact is necessary as moisture needs to move into the seed for
germination to occur. If irrigation is required for good soil moisture,
it should be applied ahead of soybean planting and not immediately after
planting. Planting into dry soil with rainfall or irrigation occurring
too soon after can result in soil crusting and poor soybean emergence.
Soil Conditions. Soil crusting can delay or
prevent seedling emergence and cause soybean hypocotyls to become
swollen or break when trying to push through the crust. If the
hypocotyl breaks, the seedling usually dies. Fields with
fine-textured soils, low organic matter, and little surface residue can be
vulnerable to crusting, especially where excessive tillage has taken
Temperature. Soybean seed can begin to germinate when
soil temperatures are less than 55 °F; however, germination is likely to be
slow until soil temperatures warm to the upper 70s. Cold soil
temperatures can cause seeds to remain dormant, increasing their vulnerability
to seed and seedling diseases and feeding by insects and wildlife. When
soil temperatures are between 70 ºF and 90 ºF, seedling emergence should occur
in less than a week. Soil temperatures above 95 ºF can also cause poor
soybean germination and emergence resulting in reduced stands.
Oxygen. Saturated, flooded, and compacted soils can reduce germination and emergence due to the lack of oxygen. Soil pore spaces filled with water reduce the amount of oxygen available for seed respiration. Compacted soil reduces the availability of water and oxygen required for germination, root and plant growth, and nutrient uptake.
Figure 4. Cotyledons, unifoliolate (red arrow), and
trifoliolate leaves (yellow arrow).
Soybean as a crop. Modern corn and soybean production. MCSP, http://www.mcsp-pubs.com. Hoeft, R.G., Nafziger, E.D., Johnson, R.R., and Aldrich, S.A. 2000. Modern corn and soybean production. First edition. MCSP Publications. Champaign, IL. Pedersen, P. 2007. Soybean growth stages. Soybean growth & development. PM 1945. Soybean Extension and Research Program. Iowa State University. http://extension.agron.iastate.edu. Pedersen, P. Soybean planting date. Iowa State University. http://extension.agron.iastate.edu. Web sources verified: 4/16/15. 140513060107