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Planting Depth is More Important than you Think...

Introduction

It’s probably a topic that you don’t think about a lot. What is the best corn planting depth? We set our planters and go. But it has a dramatic impact and we would be wise to pay a little more attention to this issue. It is generally agreed on by agronomists that somewhere between 1.5” and 2.5” is optimum. You may take a couple minutes at the beginning of the year to set your depth, or maybe just use whatever depth you left it at last year. And as tempting as that might be, this blog is going to cover the importance of setting your depth appropriately, and the far-reaching effects of corn planted too shallow.


The Temptation…

In years like this year, it’s easy to succumb to the temptation to shallow up. The soil is wet and we think if we plant shallower, we can get in the field sooner. Or maybe we think that if we plant shallower, the plants will come up sooner. Or, maybe if we plant shallower, we can plant a little faster. While these may be tempting, it will result in much more problems later on, than it will save in time. The perceived “extra time” or earlier planting time will not be of benefit.


Issues with Shallow Planting

The University of Nebraska lists the following as possible issues arising from corn planted too shallow:

"

--restricted root development due to compaction

--rootless corn syndrome

--lodging

--lack of surface soil moisture

--variable emergence

--potential damage from pre-plant or pre-emergence herbicides

--potential fertilizer injury”


Each of these issues can have far reaching consequences, much greater consequences than waiting to get into the field, or planting a little deeper.


The main source of these problems is due to the location of the roots. The first nodal roots actually form just above the seed. Because of this, the shallower you plant, the less room available for proper rooting. The nodal roots need about .75” to develop, and that is on top of a normal mesocotyl length of .75”. (See Figure 1) This means we need to plant at least 1.5” deep to allow for proper elongation and plant development. If planted too shallow, these roots will not establish and you will end up with a plant that is only anchored by the main radical root. Seedlings will flop in a stiff breeze, be very quick to fall over, and be more susceptible to lack of soil moisture, and damage from herbicides or fertilizer injury.


Photo from Corn Growth and Development. Abendroth, Elmore, Boyer, and Marlay, Iowa State University

By planting deep enough, we are able to establish a good, strong root system that will help against rootless corn syndrome, and lodging. Additionally, it allows the plant to more efficiently take up water and nutrients and perform better under drought stress.


Finally, a major issue with shallow planting is uneven emergence. When planting shallow, the soil moisture is not even resulting in spots with moisture and spots that are dry. Yield losses can be between 8-10%. Additionally, the moisture present may not be enough for germination. Each seed will absorb 30% of its weight in water for germination. Shallow planting may not be able to supply that kind of moisture for germination.


Difference Between Deep and Shallow Planting

A study from Pioneer tested planting at three different depths, 0.5”, 1.5”, and 3”. Yields were 13-15% greater for the two deeper planting depths than the 0.5” planting depth. At half of the sites, the 1.5” and 3” yields were similar. At one site, the 1.5” depth yielded higher than the 3” depth.


The study was repeated the following year. Results again showed that deeper planting resulted in higher yields, this time, 40% higher.


Across both years, the shallowest depth resulted in reduced final stands and runt plants. Stands were between 62-80% of the stands for the 1.5” and the 3” planting depths.


How Deep Can We Go?

A lot deeper than you think! The plant mesocotyl is capable of elongating at depths past 4 inches. Plants can emerge from deeper than we are capable of planting with our planters. At the mesocotyl approaches the surface, red wavelengths will signal the mesocotyl to quit elongating and for the crown of the plant to form, and the leaves to start growing. This means that the crown of the plant will always be at the right spot, no matter if you plant 1.5” or 3.5”. If soil conditions are dry, don’t worry about pushing it to 3+ inches. The plant is physiologically capable of handling it.


Some people worry that planting too deep will cause the plant to leaf out underground or crusts will prevent emergence. Leafing out underground is generally due to a non-depth related incident such as a seed trench not closed well, herbicide injury, or cold temperature injury. Crusting is generally not depth related. Rather it is a function of moisture conditions at and shortly after planting. Planting deep will not cause crusting. And deep planted corn will have the same amount of energy to push through the crust as shallow planted, and sometimes does even better due to better established root systems.


Changing Soil Conditions

Conditions will change day to day, field by field, and within each field. It is important to continually adjust planting depth for the best seeding conditions. Our first priority is making sure we are planting at least 1.5” deep. Our second priority is to make sure we are getting in to moisture. If there is not moisture at 1.5”, set the planter deeper until you are consistently in moisture.


Summary

While it may be tempting to shallow up in order to plant sooner and faster, don’t make a mistake that will cost you all year. Keep planting depths beyond 1.5” for optimum nodal root development. This will ensure your seedling is rooted correctly and will have the healthy start it needs for the year. Check moisture at planting depth and don’t worry about pushing depth to 3”+ if need be. (Although with our current moisture conditions, that probably won’t be an issue) Finally, check field conditions field to field and make adjustments accordingly.


Resources

https://www.pioneer.com/home/site/us/agronomy/library/planting-depth-and-stand-yields/

http://www.agphd.com/ag-phd-newsletter/2016/03/22/corn-planting-depth/

https://www.pioneer.com/home/site/us/agronomy/library/corn-planting-depth/%20

https://ipm.missouri.edu/IPCM/2016/4/Optimum_Corn_Planting_Depth-Dont_Plant_Your_Corn_Too_Shallow/

https://www.agriculture.com/crops/corn/production/moisture-is-key-to-seed-depth_137-ar47963

https://extension.psu.edu/keep-an-eye-on-planting-depth-in-corn-and-soybeans

https://cropwatch.unl.edu/shallow-corn-planting-can-hinder-root-development

https://cropwatch.unl.edu/proper-corn-planting-depth-critical-successful-season

https://www.agry.purdue.edu/ext/corn/news/articles.00/seeding_depth-0418.html

https://www.agry.purdue.edu/ext/corn/news/articles.12/SeedDepth-0404.html

https://www.agry.purdue.edu/ext/corn/news/timeless/emergence.html

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