For many of us, the calendar says it's time to plant corn. Yield data from years of testing by various companies and research groups say early-planted corn yields best over the long term. So what are you waiting for?

Corn Illustrated 4/7: When is the best time to plant corn? Here's a novel way to know

Odds are you're looking at when to plant corn based on the soil thermometer – in the ground on bare soil about 4 inches deep. You're looking for 55 degrees F, the temperature at which corn will germinate and grow.

If you want uniform emergence and even stands, it's best to plant every corn seed at the same depth, where moisture levels and soil temperatures are the same.

Corn Illustrated: Farmers who know when to plant corn will have their equipment ready when soils are sufficiently dry and warm.

A soil thermometer may not be standard equipment in every planter toolbox, but there are those who think it should be. You can gamble on when to plant corn if the temperature is on the line and warmer weather is forecast.

Related: For Planting Corn, Soil Temperature Of 50 Degrees Is Magic Number in Iowa

Planting corn when the soil temperature is 55 F or lower and there are cooler days in the forecast means you're probably stepping out on a thin limb, more or less on faith.

Bob Nielsen has long maintained that the soil temperature needs to be 55 degrees F for corn to germinate and grow uniformly. Nielsen is the Purdue University Extension corn specialist.

No-till soil temps
Whether the soil temperature reaches 55 degrees F as quickly in no-till as in conventional till is a question you can find debate arguments for all over the board.

Many who claim no-till warms up as quickly also preach spreading out residue evenly behind the combine spreader in the fall. Otherwise, the areas covered by combine residue is likely to be cooler and warm up more slowly because the soil is not bare – it is covered by residue, but only in spots.

Don't overlook spring planter preparation – if you skip it, you could be subject to the bottom-line implications of not minding the details. For helpful tips, download our free report: Planter Preparation Tips: Best Practices for Minimizing Breakdowns this Spring

So throw a soil thermometer in your pickup or tool box before you head to the field. If it helps you determine the best time to plant corn, it might just turn out to be the most valuable thing on the truck that day.