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The Planting Depth Debate for Corn

March 23, 2020

by Mike Meier, Regional Sales Agronomist Iowa

What is more important?  Proper Depth or Uniform Depth.  Actually both.

The industry can agree that doing this right the first time is extremely important as it sets up the whole season.  And the industry agrees to disagree on what is optimum for depth as successes have been achieved at different depths as well as failures.

The most adopted depth chosen by the industry professionals and most common advice given from seed companies is historically we’ve been operating between 1.75 to 2.25 inches deep, and pretty much settled on this as the most comfortable range for a long time.  The main factors that affect planting depth outcomes are soil types, tilth, and conditions, equipment setups and execution, seedbed preparations and compaction, to name a few.

Planting too shallow has drawbacks, such as poor emergence due to lack of moisture or dry dirt.  Plants starting from shallower depths have lost potential for ideal root development compromising both larger size root mass and a number of nodal roots left uncovered by soil.  A possible advantage of shallower depth is finding warmer soil temps and improving faster seed germination as well as less chance of soil conditions preventing emergence, however, the shallower we go with the more variable the soil temps.

Planting deeper also has its pros and cons.  Many are cautioned by the question if the plant has enough energy to push through poor and challenging soil conditions and hesitate to error on the side of deeper.  The deeper we go the cooler the soil temps and the more likely we have delayed germination and emergence, however, the deeper we go with the more uniform the soil temps will be.   The upside is if we can manage deeper planted seeds will find more uniform germination timing and we will have more potential to produce a larger root system.

Many agree the consistency of planting depth is more critical than agreeing on which depth.  Even germination with seeds planted at uniform depths is strongly correlated, in other words starting at the same levels with consistent soil temps will positively affect uniform emergence.  Ideally Having all plants out of the ground together allows for healthy competition and not some plants becoming weeds.  The belief is that a neighboring corn plant emerging 3 days later holds the others back—competing and trying to catch up.  Watching planter speeds and using downforce technologies to ensure the same depth across variable soils and conditions can sometimes prove to be the most profitable investment.

The proper way of taking a good measure of seed depth is to first be prepared to check multiple rows.  Be sure to check the rows that best represent the planter speed.  Also, find the soil horizon and surface to gage depth from.  Before you dig the soil will likely settle and you may find yourself needing to tamp or level the soil down before getting an accurate measurement. Remember there will be settling in the soil after tillage, but even with no-tillage there will be some settling from loosened soil in the row possibly due to aggressive row cleaners and closing wheels.

Adjusting your planter depth is a constant variable that demands your attention.  There are times where the weather plays a huge role in deciding what depth should be considered.  Most believe corn genetics really don’t have as much impact on what depth is chosen as compared to basics like soil moisture and temperature at the planting.   Perhaps in addition to a ruler for measuring depth, we should consider using a thermometer and moisture tester of the soil.

When a baseball player has a problem hitting the ball or a pitcher has a problem throwing strikes, what do they always need to go back to, fundamentals. Good fundamental practices when in doubt is a lot of times the simple things we forget.



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