For some, it's instinctive – longer days and warmer weather bringing out the itch to get to the fields and start planting. But a Kansas State University agronomist cautioned farmers to take a small step first that could mean the difference between bountiful yields or a thin crop.

"As we're gearing up for spring planting, we need to be mindful of soil temperatures," said Dale Fjell, crop production specialist with K-State Research and Extension. "We are tending to plant earlier and earlier and the earlier we get, the more important checking the soil temperature becomes."

Fjell suggested that growers take the temperature at a 2-inch depth in various parts of the field and that the temperature not be taken first thing in the morning.

"In fact, the best time to take soil temperature is 10 a.m. to 12 p.m.," he said.

Soil thermometers are often available from farm supply stores and seed dealers.

It's also important that the soil be at the minimum temperature or above for at least two or three consecutive days before planting. The minimum temperature depends on which crop is being planted.

Fjell provided these guidelines for minimum soil temperatures:

• Corn - 50 F. degrees minimum.
• Soybeans - 55-60 degrees minimum.
• Grain Sorghum - 65-70 degrees minimum.
• Sunflowers - 50-60 degrees minimum.
• Cotton - 65-70 degrees minimum, but "the warmer, the better," Fjell said.

What happens if farmers plant when it's too cool?

Microbes that live in the soil feed on seed, the agronomist said. So once the seed is in the ground, it's a race between if the microbes will have enough time to feed on the seed and damage or destroy it or if the seed germinates and the plant strengthens as it grows.

"But microbes don't start getting active until the soil temperature is around 50 degrees," he said.

For that reason, planting corn fairly early is usually safe. If the seed sits in the soil for a while, microbes likely will not harm it, because under 50 degrees, they aren't active either. And once the soil temperatures reach 50 for long enough periods, the seed will start growing and fend off microbial damage.

Other crops are another story, however. If grain sorghum, for example, was planted when the soil temperatures were around 50, but the seed doesn't germinate until 65 or 70 degrees, that could give soil microbes plenty of time to feast on the sorghum seed.

"The result can be a thin stand," Fjell said.

"Another way to help protect the seed is to either buy treated seed or treat it yourself before planting," he said.

K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus in Manhattan.