As corn planting begins, we are faced with another year of watching little corn plants turn into something magnificent. Always in hope of reaching that record high yield. During the season, corn growers, corn specialists, agronomists, and consultants are all trying to diagnose any potential problem that a corn plant may encounter. The first 28 days of a corn plant’s life is a very critical period for its success in life and reaching maximum yield potential. Corn plants are just like any other living thing, they must get a good solid healthy start when they are young, otherwise record yields may be in jeopardy. When scouting or evaluating a newly planted corn field, it is very important to understand the fundamental growth habits of a corn plant and what a small corn plant should look like above and below the soil surface. This newsletter explains four fundamental growth systems that take place from planting through day 28 of a corn plant’s life.
As a kernel of corn germinates the first root of the corn plant emerges from the embryo of the seed. This first root that always extends out from the tip end of the seed is called the radicle. A healthy radicle will extend approximately 2 to 3 inches down and away from the seed into the soil and should resemble a “furry foxtail.” The radicle is extremely vulnerable to fertilizer burn and insect feeding. If the radicle does not look like a “furry foxtail” then further investigation may be needed. The radicle is followed by other seed roots that shoot out the opposite direction. Together, all of the seed roots make up the seminal root system, that feed the plant for approximately 3-4 weeks, until the first nodal root systemgets established.
Soon after radicle emergence, the plumule, the first vegetative structure of the plant, grows out of the embryo as well. As it continues to grow towards the soil surface it develops into what is known as the coleoptile or otherwise known as the spike. The coleoptile is what pushes up and through the soil surface. With adequate moisture and soil temperature, this process generally takes place within 7 days after planting. Inside the coleoptile are the first 5 sets or corn leaves that are bundled up, beginning to grow and ready to emerge after the spike is through the soil surface. Just as the coleoptile emerges through the soil surface and meets sunlight, it splits or opens. This split is the ultimate passage way for those small tightly bound leaves inside to come out and continue to grow. Sometimes the splitting of the coleoptile does not happen easily. Generally two of the main disruptions to growth are either crusted soils or chemical injury. A crusted soil keeps the coleoptile from breaking through the soil surface, but does not eliminate it from splitting. The leaves inside are still able to push their way out of the coleoptile, unfurl, yet still remain under soil surface. These new leaves may eventually emerge through a crusted barrier with rain, yet normally they will break off, ultimately leading to plant death. Chemical injury on the other hand may allow the spike or coleptile to emerge through the soil surface but may not allow it to split or open correctly. When this happens, usually the leaves inside continue to grow and find a way out. When they do, they resemble the look of buggy whips or even shoe strings.
The area between the coleoptile and the seed, lie two other systems of high importance. The mesocotyl and the crown. The mesocotyl is the connecting link between the seed and the crown. The mesocotyl is sometimes referred to as the “umbilical cord,” because again, the small seedling is dependent on the seed and the seed roots for approximately three to four weeks. Any disruptions to the mesocotyl during 3-4 week period, like insect chewing or seedling disease, can be detrimental to the plant. The crown is the area that is referred to as the growing point and is where the first set of permanent nodal roots are developed. The crown, or growing point, will always form approximately 3/4 inch below the soil surface. If planting depth is shallow, 3/4 inch or less, the mesocotyl will have no elongation and nodal root development will take place at or near the soil surface. If planting depth exceeds 3/4 inch then the mescotyl will lengthen and the growing point will remain at 3/4 inch and have plenty of room to establish the small plant’s first set or nodal roots. That is why 1.5 to 2 inches is a desirable planting depth. If a small seedling gets held back for any reason, survival rate depends on nodal root system establishment. At approximately day 28, depending on accumulated heat units, nodal roots must be ready to take over and support the plant. The crown or growing point ultimately reaches the soil surface when the corn plant reaches approximately V6 stage.