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Proof Soil Temperatures Vary at Different Soil Depths

Proof Soil Temperatures Vary at Different Soil Depths
Sophisticated weather recorders did their job.

The temperature at one inch below the surface, two inches below the surface, and three inches below the surface won't be the same. Duh, you say! That may be so, but it's a big deal to a seed that's waiting to germinate. And it's a much bigger deal if temperatures are relatively warm or cool.

Part of the intent of the Indiana Prairie Farmer/Precision Planting study conducted at the Throckmorton Research Center near Romney, a Purdue University farm, was to determine if there were differences in how corn germinated if planted at 1 inch, two inches, and three inches deep. The logical way to explain those differences, if there were any, was by getting soil temperature recordings at those depths. It only stands to reason that if soil temperature is higher or lower, it will affect germination.

So Spectrum Technologies, Plainfield, Ill., assisted with making automatic weather recording tools available that could record the temperature of t soil at one, two and three inches. These recorders take automatic measurements. The data can then be downloaded into a computer for comparison purposes.

"They worked and collected data, and what we saw was interesting," says Jeff Phillips, Extension ag educator, Tippecanoe County. Phillips has spent 18 years there, doing numerous tests both at Throckmorton and on local farms while there. He also worked in the Purdue Agronomy department as an assistant before taking the Extension position. The bottom line is that he understands research, and how to do it properly.


The problem this year was that the corn wasn't planted until May 27. Having missed the early window, a three-week wet spell at the farm pushed planting date back. Despite that, yields as high as 240 bushels per acre were recorded in the trial.


On the flip side, however, soils were warm, even at the deeper depths, when corn went into the ground. "We saw a difference, probably about to the level you would expect to find between the depths," Phillips says. "The trouble is all depths were warm, ranging form 75 degrees F at three inches deep to 80 degrees at one inch deep.

"When temperatures are that warm, you aren't going to see any difference in emergence just due to temperature. Moisture may factor in, but not temperature. Even the lowest, 75 degrees, is certainly low enough for corn to germinate."

What Phillips hopes is that they can repeat the same trial next year, and use the weather records. Planted a month earlier, if temperatures in the soil are in the 50's or low 60's, temperature alone could effect emergence. That's when having tools to record temperature will be a real plus, he concludes.

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