The Best Time to Test Soil Is Now

It’s the season for soil testing. The best time to collect soil samples is before fall fertility applications when soil is in a depleted nutrient condition.

“Now is a great time to do it with the crop off and no rush to get tillage done,” says Dave Mowers, a consulting agronomist based in Illinois.

Farmers are able to specify which nutrients or micronutrients they want to test for with their laboratory. Tests should tell farmers their soil PH, and the levels of phosphorous and potassium in different areas of the farm. Knowing whether soil fertility is high, medium, or low can be a “fantastic money management tool” in terms of fertilizer purchases, Mowers said.

“Why would you spend large dollars on an expensive crop input without a guideline on what you really need to have?” Mowers said.

Although Mowers believes there is more soil testing being done than is realized, he is confident that not enough farmers are taking the time to test their soil. Exactly 70% of farmers that responded to an agriculture.com poll reported that they are soil testing this fall.

Soil samples should be made up of a solid column of soil that collects from the soil surface to nearly 7 inches in depth. To get the most accurate results, Mowers suggests stratification testing.

The most convenient way to take a sample is with a soil probe. However, it’s important to check for any clogs or air pockets that would return less accurate results.

“It’s important that they take denser samples and more from the area to get a better soil fertility reading and recommendation,” Mowers said.

A shallow sampling can provide inaccurate results since nutrients tend to be brought up to the topsoil layers through plant foliage. Also beware of soil compaction when collecting samples. It’s crucial to collect a full column of soil, and compaction can hinder a farmer’s ability to get the proper depth needed.

Over the last few years, Mowers has seen lower levels of potassium in soil samples in his trade area. Growers should know that with crops that are very resilient to decomposition, sometimes it’s hard for those nutrients to escape the plant and get back into the soil. Test results may reflect some nutrients coming up short, which is helpful for farmers to understand what they need to apply to compensate.

The lab Mowers works for suggests taking one sample for every 2.5 acres. Their fee is $8.25 per acre, but that cost can vary with whether or not a farmer wants fertilizer recommendations made.

“If I were farming, I would be sampling more,” said Mowers. “I would collect one sample for every acre knowing what I do now.”

In the future, Mowers hopes research will lead to farmers taking deeper samples — up to 1 foot in depth. By testing more of the rooting medium, he believes farmers will benefit from more data about their soil.