Throughout the growing season, the corn plant undergoes a series of developmental stages. Cool soil temperatures early in the season increase variability in final stands. As soon as corn seed is planted into soil, having adequate moisture and soil temperatures above 50°F will cause metabolic reactions to begin taking place within the seed. Radical root emergence from the seed is called germination, which occurs after 65 to 80 GDUs have accumulated. Germination is a two-step process.
1st Germination Step: Imbibing Water
- Corn seed absorbs about 30% of its weight in water.
- Radicle root begins to elongate from the corn seed.
2nd Germination Step: Depends on Soil Temperature
- Growth of the radicle root and coleoptile shoot development.
- Temperatures below 50°F: Growth will be very slow increasing insect and disease pressure risk.
Problems Encountered Prior to Emergence
- Yellow, twisted, or seedlings leafing out underground (corkscrewing).
- Reduced vigor and in severe cases seed and seedling death.
- Cloddy soil, herbicide injury, and soil crusting, due to extremely cold soil.
Potential for Frost
- Early planting also exposes seeds and seedlings to increased potential for frost.
- Frost on emerged crops is still possible into early May.
- Frost often affects individual plants differently creating more stand variability.
- Generally, newly emerged corn can withstand 32°F for 4-5 hours since the growing point is below ground and is until V6.
- Corn becomes more sensitive to frost injury when temperatures reach 28°F and below.
Corn Emergence (VE)
- Achieved when the coleoptiles break through the soil surface.
- Requires approximately 100 to 120 GDUs to emerge.
- Delayed several weeks when prolonged cool and/or dry conditions exist.
- Seminal roots are for initial nutrient uptake.