Two cotyledons, a plumule containing two simple leaves, and the hypocotyl-radicle axis are found within the embryo. The hypocotyl is the starting point of the above ground stem, and the radicle is the starting point of the below ground root system.

First to emerge will be the radicle, or primary root, from a break in the seed coat near the micropyle and will grow downwards in response to gravity. This can occur just one or two days after seeding. The radicle, or root, now acts as an anchor in the soil for the developing plant, as lateral roots quickly develop. Shortly after radicle development, the hypocotyl (which connects the cotyledons and the radicle) begins to elongate and the hypocotyl arch pulls the cotyledons through the soil towards the soil surface, in a negative response to gravity. This hypocotyledonary arch provides the leverage, or muscle, to pull the cotyledons to, and above, the soil surface. Once above the soil surface, this arch straightens. Chlorophyll development in the cotyledons is rapid after emergence, and the seedling begins to supplement the stored energy with the onset of photosynthesis.

The cotyledons unfold, and expose the growing epicotyl (young leaves, stem and growing point). The expansion and unfolding of the first leaves (unifoliate) is followed by the growth of all other leaves (trifoliates) as the plant grows onward and upward.

Cotyledons are essentially huge food reserves, and furnish the energy needs of the young plant during emergence and for approximately 7-10 days after emergence, until the leaves take over the energy function entirely. Losing one cotyledon has little or no effect on the young plant, but loss of both cotyledons soon after emergence will reduce yields up to 10%.

A stand is considered established between VC and V1, once it has become obvious that the cotyledons have emerged from the soils and the unifoliate leaves are unfurled.

Cooler soil temperatures at greater planting depths cause slower growth and decreased nutrient availability.

Soil Conditions:
Soil physical conditions can restrict soybean emergence. Soybean emergence from soils with low crust strength decreased 20% as soil moistures decreased. Emergence from soils with high soil crust strengths decreased 40-50% as soil moistures decreased at the same rate. In addition, the ability of the germinating soybean seedling to push through a crusted soil decreases with deeper planting.

Soil compaction can increase mechanical resistance to root and nodule growth. The ability of roots to penetrate the soil is negatively related to soil compaction.

Soil Fertility:
Supply of essential nutrients can affect root and plant growth. Studies have shown that small amounts of fertilizer placed 1-2 inches to the side and slightly below the soybean seed may stimulate early growth if soil temperatures are cool. Fertilizer placement does not attract root growth, so the fertilizer must be placed where roots will intercept it. However, placements of fertilizer too close to the seed will injury the young plants.

Seed inoculation with Rhizobium japonicum bacteria is not generally recommended unless a field has never grown soybeans, or has not grown soybeans for the past 5 or more years.

What’s Next?
Once soybeans have been planted, and germination and emergence has occurred, a myriad of problems are still to be encountered before a successful crop is harvested. Key amongst those problems are the decisions that have to be made if the stand established falls short of our expectations, and/or some external condition such as frost and/or hail damages the stand. The next Technical Resource, due out in a few weeks, will detail how to assess your stands and suggest how to properly calculate options for leaving the stand or for replanting if deemed necessary.

From the radicle, seminal (temporary) roots are formed that will anchor the plant and provide initial nutrient uptake until the permanent root system is formed. The mesocotyl is a stem-like structure between the radicle and the coleoptile that elongates to within ¾" to 1½" of the soil surface. The coleoptile (pointed and quite stiff) forces its way through the soil and when sensing sunlight, signals the mesocotyl to cease elongation and develop a crown at the juncture of the coleoptile and the mesocotyl. All permanent root growth originates from this crown ¾" to 1½" below the soil surface. When seeds were planted at 2", 3", 4" and 5" deep, the crown was always within ¾" to 1½" of the soil surface.

Depth of planting is important here. The mesocotyl, under favorable conditions, can elongate 4-6 inches, meaning that at planting depths deeper than these, the seedling will not be able to breach the soil surface, and will eventually die. Under unfavorable conditions, such as drought stress at planting, elongation of the mesocotyl can cease. Occasionally, with fertility and herbicide interactions, the mesocotyl can loose orientation, and grow in a corkscrew fashion, failing to emerge.

The coleoptile can emerge 6-10 days after planting, but may be delayed by cool temperatures or dry soils. As soon as the tip reaches sunlight, it splits, and the first true leaves emerge rapidly. Within 7 more days, enough new leaves should have emerged, and the root system developed enough to support life, and the seedling will no longer depend on the now nearly exhausted food reserves in the kernel.

Nutrient shortages are not critical at germination, but as the roots take over feeding the seedling, shortages of the major elements can slow growth and development. Phosphorous is especially critical at these early stages of growth.

Seed Treatment:
Once the seed coat is broken, the food rich tissues inside the kernel are open to attack from disease organisms unless the seed has been protected by treatment. In addition, seed corn is treated with insecticides to minimize feeding on the germ or the endosperm.

As the growing point is below ground during the very early leaf stages, it can be affected greatly by soil temperatures, lengthening out the time between leaf stages, increasing the total number of leaves formed, and possibly delaying tassel formation. Cool temperatures at planting will also restrict absorption of nutrients from the soil, and slow growth. Small amounts of banded "starter" fertilizer (containing phosphorus) may eliminate the slow growth.

Early planting should be shallow, to take advantage of warmer soil temperatures near the soil surface. As the season progresses, soil temperatures will warm throughout the planting depth. Additionally, later plantings will have better moisture availability at deeper depths, unless there has been recent rainfall.

When excessively cold and/or wet soils delay emergence and/or germination, the kernel and young seedling are subjected to lengthier exposure to damaging factors such as soilborne diseases, soil insects, injury from preplant, preemergent or carry-over herbicides.

Soil Conditions:
Flooding at any time when the growing point is below the water level can quickly kill the corn seedling in a matter of days, especially if temperatures are high. Inadequate moisture may result in seeds not sprouting, or swelling and sprouting non-uniformly, causing slow and uneven emergence. Stunting and death may occur.

Poor drainage may also result in swelled seeds that do not sprout. Fields that are tilled too wet will result in soil compaction. Soil compaction can result in slow plant death, stunting and discoloration.

Crusting of the soil can cause plants to leaf out below the soil surface. Many times these plants will recover and grow normally once free of the crust.

Successful stand establishment in corn
Quick, uniform germination and emergence of corn is promoted by four simple factors. Anything you can do to ensure the presence of these four factors will greatly enhance successful stand establishment.

What’s Next?
No matter how hard you try to plant properly, there are conditions that will result in a less than perfect stand establishment. This is when replant options need to be considered. Too wet, too dry, hail, frost, insect damage and herbicide injury can all conspire to reduce stands once emergence has occurred, or even cause emergence not to occur.