Germination process and soil temperature on Corn
Seed absorbs about 30 percent of its weight in water; temperature does not affect that process. But temperature does affect growth of both the radicle (first root) and coleoptile (shoot). With soil temperatures below 50 F, seeds readily absorb water but do not initiate root or shoot growth. This opens up opportunities for insects and pathogens to attack seeds resulting in poor emergence especially if poor seedbed conditions are prolonged.
Problems associated with corn in cold soils Cool soil temperatures early in the season increase variability in final stands. We want to give every precious seed the chance of survival unless we intend to overplant to compensate for seed viability lost before emergence.
Cool soil conditions early in the season also lead to more unevenness in growth and development from one plant to another. In addition, once the seed begins to germinate, a significant change in soil temperature can cause problems for mesocotyl growth. To maximize yield, manage corn to reduce plant-to-plant variability.
In addition to the effects of early planting on seed development and growth, early planting also exposes seeds and seedlings to increased potential for frost. We know that since a corn seedling's growing point is below ground until V6 — the sixth leaf stage — it can withstand freezing temperatures when plants have emerged until the V6 stage. Indeed that fact has saved a lot of replanting and the associated costs over the years.
What we don't always say — or for that matter understand — is that frost often affects individual plants differently resulting in more variability from one plant to another. That variability can result in unequal interplant competition and lower yield potential. Depending on the potential date of replant though, keeping the surviving stand — albeit of variable plant heights and development — may still be the best option.
In addition to the impact on seedlings, extreme cold snaps can refreeze soils down to seeding depths. This can and does kill seeds and growing points, reducing stands and forcing a complete replant.
Republished from Iowa State University Extention and Outreach. Written by: By Roger Elmore, Department of Agronomy.