Causes of Uneven Stands, Part 2

Gary Geske
Paintbrush strokes dividing page

Submitted by John Toft
CCA, Tekamah, Nebraska

Yesterday, I blogged about the importance of determining the causes behind uneven corn stands in the field.  Things to consider included: planting conditions at the start of the season, possible excessive planter speed over rough soil or residue, planting in unfit soils, shallow or excessive planting depth, failure to close the furrow or worn planter parts.  I also provided a link to help make planter adjustments that promote those “picket fence” stands in your field.

But what if everything I mentioned in yesterday’s post was done properly and you still end up with uneven corn?  Dig up those poorly performing plants!  Nearly all unevenness results from a problem under the soil surface.  Some potential culprits to check for include:

  • Insect damage by pests such as wireworms, seed corn maggots, white grubs, sod webworms and black cutworms.
  • Seedling diseases and/or rotted kernels.
  • Fertilizer injury, including Anhydrous ammonia or the subsequent nitrate salt formed in the ammonia injection band.  This injury can be eliminated by applying ammonia in good soil conditions and not planting directly into the ammonia injection band.
  • Varying amounts of residue cover in a field, which can affect soil temperature and soil moisture.
  • Cooler soil temperatures not only affect plant growth but also microbial activity responsible for nitrogen and/or sulfur mineralization and the micorrhizal fungal activity instrumental in phosphorous acquisition from the soil. It’s not uncommon to observe soil temperature under varying amounts of residue differing by as much as 10 to 12 degrees Fahrenheit into June.
  • Soil Compaction.
  • Patchy weed growth left to compete too long within a field often results in uneven corn.
It’s not uncommon for fields to emerge and appear even until the plants reach the V2 stage of growth.  Until V2 a young plant survives mostly upon food storage in the kernel and water and nutrients received through its primary root system.  At approximately V2, the plant’s photosynthetic area has increased in size until it provides significant food and energy and the secondary root system (main plant root system) has developed enough to gather significant water and nutrients. 

Plants at V2 that have lost or diminished primary root systems and underdeveloped secondary root systems will become smaller, poorer doing plants when compared to the increasing growth of their unimpaired neighbors.  As time goes on, the healthy, rapidly growing plants accentuate the unevenness as they “grow away” from the poor performing plants.  Fields emerging the same day but exhibiting unevenness prior to V2 usually contain plants with rotted kernels or have lost their primary root systems.

A large number of uneven corn stand cases are always tied back to unfit soils at planting time and resulting soil compaction.  Having mentioned that, I’ll leave you with a link and the Top Ten Reasons to Avoid Soil Compaction as provided in a recent issue of Corn and Soybean Digest.

Top 10 Reasons to Avoid Soil Compaction

  1. Causes nutrient deficiencies
  2. Reduces crop productivity
  3. Restricts root development
  4. Reduces soil aeration
  5. Decreases soil available water
  6. Reduces infiltration rate
  7. Increases bulk density
  8. Increases sediment and nutrient losses
  9. Increases surface runoff
  10. Damages soil structure