The first 28 days of a corn plant’s life (~ 350 GDUs), is a very critical period in its overall success and setting it up to reach maximum yield potential. When scouting a newly planted cornfield, it is important to understand the fundamental growth habits and what the plant should look like above and below the soil surface. Here are the four fundamental growth modules that take place from planting through day 28 of a corn plant’s life.
MODULE 1 - THE SEMINAL ROOT SYSTEM
As the kernel germinates the first root that extends out from the tip end of the seed is called the radicle. A healthy radicle will extend approx. 2-4 inches down & away from the seed (into the soil) & should resemble a “furry foxtail.” The radicle is followed by other seed roots that shoot out the opposite direction, these are known as the lateral seminal roots. Together, all of the seed roots make up the seminal root system that feeds the plant for the next 3-4 weeks, until the first nodal root system is established.
The seminal root system always grows downward because of gravity. At this time, the radicle is extremely vulnerable to fertilizer burn & insect feeding.
MODULE 2 - THE COLEOPTILE
The coleoptile (or spike) is what pushes up through the soil surface. This process generally takes place within 7 days of planting, but requires ~125 GDUs. Extremely warm soil, PGRs, or starter fertilizer can speed up this process. Inside the coleoptile are the first sets of corn leaves waiting to emerge. As the coleoptile pushes through the soil surface & meets sunlight, it opens / splits, allowing the first set of leaves to emerge.
There are 2 key vulnerabilities at this point — crusted soils & chemical injury. Crusted soils can keep the coleoptile from breaking through the surface. Chemical injury can keep the spike from splitting correctly. Both disruptions can result in corn leafing out under the ground.
MODULE 3 - THE MESOCOTYL
The mesocotyl, sometimes referred to as the “umbilical cord,” is the tubular, white, stem-like tissue connecting the seed & the coleoptile. It is very important to the plant’s health because it is the link between the seed & the crown.
Any disruptions to the mesocotyl during this 3-4 week period, like insect chewing or seedling disease, can be detrimental to the plant. The plant is still living off the seed (mother) and has not yet been weaned.
MODULE 4 - THE CROWN
The crown is the area that is referred to as the growing point & where the first set of nodal roots are developed. The crown will always form approximately ¾-inch below the soil surface. That’s why 1.5-2 inches are desirable planting depths. Once the nodal root system is established, the plant weans itself from the seed (mother) and continues to grow in a self-sufficient manner. At this point, the role of the mesocotyl, seed, and seminal root system is finished. If a small seedling gets held back for any reason, the survival rate depends on good nodal root system establishment.
If planting depth is shallow (¾-inch or less) the mesocotyl will have no elongation & nodal root development will take place at or near the soil surface.
Disclaimer - This content is intended to be a quick and easy reference when evaluating new corn seedlings. The modules outlined in this article are through the eyes of AgriGold agronomy’s years of learning and in-field experience. We believe that new corn seedlings go through a weaning process and use that as an analogy. Some content may or may not be supported by university experts. For deeper and more analytical details of this process please visit the university website of your choice.