Emergence Problems Plague Vermont Corn Fields

Emergence Problems Plague Vermont Corn Fields
Dr. Heather Darby, UVM Extension

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It was a great spring for planting. The conditions were dry and many folks were able to get their corn planted by mid-May. However, dry and cool conditions during planting have resulted in a number of corn fields with less than optimum germination. These stand losses could translate into yield loss at harvest time.
I have been asked by many, what is the penalty for uneven emergence?  Uneven stands will lower yields compared to stands where all the plants look the same. The later emerged corn is at a competitive disadvantage because it must compete with larger plants for moisture, sunlight, and nutrients. The amount of loss from uneven stands or reduced stands is difficult to estimate.  Studies from the Midwest indicate a 6% grain yield loss if a quarter of the plants emerge 1 week later.  A 17% yield loss can be expected if plants emerge 2 weeks later.  If the stands were filled in at this time the yield difference will only be 7%.  A 3 week emergence delay will decrease yields greater than 20%.  In some cases the corn will not emerge at all and yield losses will be higher than from uneven emergence. In fields with losses of ¼, ½, and ¾ of the stand, grain yields will be reduced by 10, 30, and 50% respectively. There have been no studies conducted to measure potential silage loss in uneven or reduced stands.
There are many factors that influenced corn seed germination this spring. Corn needs uniform soil moisture and temperature for rapid, uniform germination and emergence. The most likely culprits of uneven emergence and stand loss were the dry and cool soil! If the soil is too dry at planting, seedlings will emerge at different times.  The emergence times can vary between sections of the field, within rows of the field, and from one plant to the next. The primary factors that influence soil moisture in a field are differences in soil type or topography.  However, I think this year the biggest cause of moisture variation was from secondary tillage passes.  Secondary tillage will impact soil moisture because it will unevenly distribute moist and dry soil particles.  The more tillage trips before planting the more the soil would have dried out.  Many farmers plant corn at a 2 inch depth to ensure seed has adequate moisture to germinate. This year this depth may have been too dry as well. Crops that were seeded shallow would have been a greater risk for poor emergence.
Uneven soil temperature may also contribute to reduced or uneven emergence.  Corn will germinate and emerge slowly and unevenly when soil temperatures are less than 50F. Uneven soil temperatures in the seed zone can also be caused by variable soil type, drainage, seed depth control, and surface residue cover in reduced tillage systems. This year many farmers tried no-till and/or zone-till systems to reduce fuel costs. Uneven residue coverage in these systems causes lower soil temperatures under heavier cover than under barer spots in the field.  It is possible we also experienced uneven seeding depths due to the well worked soil.
Although it maybe too late to replant or fill in the stand, we will hope for an excellent growing season that will bring the existing corn stands to maximum yield potential.

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