Agronomy Talk

Agronomy Update

E. Indiana and Ohio: Planting Time and Depth

Published on Tuesday, April 22, 2014

Should I Be Planting Yet?
The calendar says we should be planting, the soil moisture level in many areas says we should be planting, but the forecast calls for cool weather into next week. In Fort Wayne, IN the forecast calls for highs in the 50’s and lows in the 40’s through next week. What should you do? Although we can’t determine for certain what would happen, there are a few things to be aware of.

Both corn and soybeans require 3 things in order to germinate- the right temperature, the right moisture, and oxygen. Let me run through what happens to the seed once you place it in the ground.

The first thing a seed will do is imbibe (or absorb) water. Soybean seeds need to imbibe about 50% of its weight in water, whereas corn seed requires ~30 of its weight in water. This imbibition will happen at any temperature above freezing. Once the seed has taken up enough moisture (which usually happens within a day), then the seed starts to respire (breathe), and this requires oxygen. If a heavy rain event happens soon after planting, this will cut off the oxygen to the seed causing uneven emergence or the death of the seed. Many replant situations occur when corn and soybeans are planted prior to a large front coming through. 

 

                   

 

Temperature is important for the seed to continue metabolic activities. Fifty degrees Fahrenheit is the generally accepted temperature at which these processes begin to occur and it usually requires 90 GDU’s for soybeans to emerge and 100-120 GDU’s for corn to emerge. Based on the forecast, the seed may be sitting in the ground for a while, exposing it to more of the elements such as insects, diseases, and more weather events. This will probably reduce the overall stand, but by how much we can’t determine.

Wide swings in soil temperatures (>27º F) can also affect emergence. Sandy soils don’t buffer soil temperatures as well as clay soils, so we will often see plants that unfurl underground, have a corkscrew shape or look like the mesocotyl switches direction like the plants pictured below.

 

                       

 

                                  

 

If you decide to plant, be aware that these things will probably happen:
---Corn and soybeans may take 3 weeks or longer to emerge (depending on temperatures of course!)
---Corn and soybeans will probably be more uneven coming up (but don’t shallow up planting depth on corn!)
---Expect more stand loss the longer the crops stay in the ground
---Expect more purple corn plants

How Deep Should I Plant Corn?
As mentioned in the previous article, the weather is predicted to stay below normal for the next week. If you decide to plant, should you plant shallower due to the colder weather? The short answer is no.

Uniform emergence is important to achieve top end yields and this can only be achieved with deeper planting. The deeper you plant the more uniform the temperature will be. The air temperature in Wood County, Ohio on April 20th varied from 31 to 75º F, greater than a 40 degree swing. At the 2” soil depth, the actual soil temperature varied 27º F, whereas at the 4” depth it only varied 14º F. I am not suggesting that you plant 4” deep, but you should be planting at least 2” deep.

 

                       

                                        Air temperatures in Wood County, Ohio, April 20-21, 2014.

 

In addition to temperature, moisture will be more uniform as well. This will cause seeds to begin respiring at the same time resulting in more uniform emergence. Plant stand counts are generally higher with deeper planted corn.

Shallow planting can cause several other problems including a greater chance for herbicide injury, a less developed root system or “rootless corn” (causing root and stalk lodging), smaller ear size, less drought tolerance and reduced yields. Many farmers set their planters for a depth of 1.5”, and are often amazed to find out later in the season that the seed is shallower than they thought. Loose seedbeds cause seed to be planted shallower, especially after a rain that settles the soil. Fast planting often causes a planter to lift up, resulting in a shallower seed depth.
Bottom line- Keep your planting depth the same no matter when you plant.

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Mark Apelt
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Mark Apelt

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