1. Count leaves when the collar shows. Three Leaf Plant The round tipped leaf is No. 1 (1).
2. Corn has approximately 20 days food reserve in the seed (2).
3. The seed’s food reserve provides energy and supports the plant through the three leaf stage or about ten days after emergence. Within this time:
a. When the shoot hits light, the secondary root system and growing point will be about 1-1/4 – 1-1/2″ below the soil surface.
b. At the growing point, the primary ear has been initiated. The number of rows and approximately the first 14 kernels of each row are also determined.
With these basic principles, let’s review some variations which can influence plant stands.
4. Planting too deep (4) places stress on seed food reserve and can relate to leafing out below the ground. If the shoot does emerge, this early stress may carry on to the harvest as a tall thin plant with a nubbin ear. Planting deeper does not move the secondary roots down; the mesocotyl (5) only becomes longer.
5. Planting too shallow (6) can move the secondary root system closer to the surface. Two primary concerns are:
1. The secondary root is closer to concentrations of surface incorporated chemicals.
2. If surface soils dry out, the young plant will show the classic stress symptoms of purple and/or yellowing. Planting in a depression when soils are mellow can result in the same symptoms and potential chemical stress as planting too shallow. If the depression is filled in by dragging, wind or water moving soil, it changes the relative position of the seed to the soil surface. As a result:
a. More stress is on the seed for reserve to push the shoot to the soil surface.
b. Visualize where chemicals are (herbicide or banded insecticides) in relation to the secondary root system which is 1-1/4 – 1-1/2″ below the shoot when it breaks the soils surface. The secondary root can be very close to herbicide and insecticide concentrations. Insecticides which are phytotoxic can increase the potential stress.
c. Under these conditions, you should expect to see hybrids react differently.