Several factors can contribute to uneven corn emergence and growth early in the season. Replanting is not often justified due to uneven stands; however, understanding why uneven emergence occurred can help minimize the risk in the future. Additionally, consideration should be given to how uneven early growth can affect the implementation of some management tools the rest of the growing season.
Figure 1. Plant-to-plant variability is common in fields that experience unfavorable conditions during emergence.
Potential Causes of Uneven Growth
Soil Moisture Variability in Seed Zone
A corn kernel imbibes approximately 30% of its weight in water during germination2. When kernels within a row are exposed to different amounts of soil moisture, the rate of germination and emergence can vary from plant to plant, resulting in uneven emergence and early growth, or possibly stand loss. Small differences in soil moisture within a row can lead to considerable differences in germination and emergence. Planting deeper to reach uniform soil moisture, managing residue to minimize trash getting wedged into the seed trench, and reducing additional loss of soil moisture can help achieve more uniform emergence and early growth. Tillage completed ahead of planting can rapidly decrease soil moisture, versus no-till fields. Therefore, in dry situations, no-till fields may have more even emergence and early growth compared to fields tilled in a dry spring.
It takes approximately 180 crop heat units (CHU) for corn to emerge, and accumulation may take several days3. Emergence may take 6 to 21 days for corn depending on conditions3. Ideally, the kernel would develop a root system and emerge within much less than 21 days, reducing the dependency on the endosperm. Minor differences in the microenvironment directly around the seeds can magnify the effect of cool temperatures on small seedlings, resulting in uneven early growth in corn.
Planting into damp soils can result in poor seed-to-soil contact in the furrow and thus, uneven emergence and early growth.
Soil conditions that result in crusting can inhibit emergence and contribute to plant-to-plant variability.
Other Potential Causes
Insects, such as white grub or wireworm, or diseases, such as pythium, can result in uneven early corn growth. Herbicide injury is also a potential cause for uneven corn.
Effect on Yield Potential
Yield potential will be affected where larger plants are competing with smaller plants for light, water, and nutrients. A 5% yield loss has been indicated when half the corn stand has a 7-day delay in emergence. Examined from a leaf-stage perspective, a 4-leaf difference in corn plant stage for one in six plants could result in an 8% yield loss3. While uneven emergence in corn is detrimental to yield potential, generally it does not justify replanting in most scenarios1. When two plants differ by two leaves or more, the younger, smaller plant is more likely to be barren or produce small ears (Figure 2).
Figure 2. Later emerging plants often have small ears and incomplete pollination.
Most uneven stands do not justify replanting2. When dealing with uneven stands throughout the growing season, it is important to use recommended herbicide application rates to avoid injuring corn. Apply herbicide based on the most advanced leaf stage in the field.
1 Liu, W. et. al. 2004. Crop ecology, management & quality. Crop Science.vol.44:847-845.
2 Nielsen, R.L. 2000. Corn growth & development what goes on from planting to harvest? Purdue University. AGRY-97-07.
3 OMAFRA Publication 811: Agronomy Guide for Field Crops. Corn development. www.omafra.gov.on.ca (verified 5/19/2014).