By Kyle Poling, Pioneer Hi-Bred Field Agronomist
“Variability” is not a word any farmer wants to use to describe one of their corn fields. While uniformity during the periods of germination, emergence, and nodal root formation is the goal, there are many management practices and environmental conditions that can impact this objective.
Corn germination is triggered by absorption of water. Corn kernels must absorb approximately 30% of their weight in water before the germination process begins. A seeding depth of 2 inches has often been found to provide the most consistent combination of moisture, temperature, and seed-to-soil contact for uniform germination and emergence. Inadequate seed-to-soil contact, a dry seedbed, or a rapidly drying seed zone may provide less than optimum absorption of water, causing the germination process to slow or stop completely. Additionally, corn kernels that absorb excessively cold water (less than 50 degrees F) during the first 24 to 48 hours of germination may experience serious injury or death, resulting in erratic emergence.
Corn typically requires 120 Growing Degree Units (GDUs) to emerge. Plant growth rate speeds up as temperatures increase, leading to more rapid plant growth. Under ideal conditions, corn will emerge in five days, but with cooler soil temperatures the process may take 3 weeks or longer. Between germination and emergence, factors altering soil temperature around each seedling will have significant impact root and shoot growth. Inconsistent seeding depth, variation in soil moisture, changes in soil type/topography, or uneven distribution of crop residue are leading causes for plant growth variability. For example, emergence of seeds planted into heavy residue can take require an additional 30 to 60 GDUs simply because the soils are cooler and slower to warm. Though uniform emergence is important for optimum yield it does not guarantee successful or uniform stand establishment.
Increased farm size, shorter planting windows, and higher yield potential are factors that have caused corn planting dates to trend earlier and earlier. Improved genetics and seed treatments are key components that allow growers to offset the environmental challenges that accompany an early planting date. Cool, moist soils provide an ideal environment for fungal diseases, early season insects, seed rots, and nematodes to infect slow growing plants. Seed treatments offer 10 to 14 days of protection against many of the most common early season pest and pathogens. Direct benefits to the corn crop include increased seedling vigor, healthier plants, improved uniformity, and reduced plant death.
A corn seedling relies on the energy from the seed until the permanent (nodal) root system is established, around the V3 stage. There are enough seed reserves, with the help of the primary roots (referred to in the figure as the seminal roots and radicle), to support the plant for 4 to 5 weeks. Before the nodal root system is well established, a corn plant is susceptible to various early season stresses that cause injury to the seed, primary roots, and mesocotyl (“pipeline” connecting seed and primary roots to the plant). A healthy kernel, primary roots, and mesocotyl are vital until the nodal roots are fully functional.
A slow developing nodal root system increases the window of time for seedling blights, insect feeding, excessively wet/dry soils, seeds rots, and other early season stresses to damage the seed and mesocotyl. Any severe stress that occurs during the time of transition to the permanent root system can cause a corn field that emerged perfectly uniform to go “backwards” in as little as a week’s time. This is also the time when the effects of sidewall compaction or compaction from equipment operations can become apparent.
Uniformity is one of first ingredients necessary to maximize corn yield. Variability in the crop will lead to unfair competition of adjacent plants as they fight for sunlight, moisture, and nutrients. The goal should be for every seed to emerge and every plant to be a mirror image of its neighbor.