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Stick to a consistent soil sampling season

All experts don’t agree about the best way to sample a field or how many cores to pull. Most agree on one thing, however: Do it consistently.

If you typically pull soil samples in the spring, and wet soils prevented the job from being finished last spring, should you complete it this fall? Here’s what various agronomists suggest.

Andy Awald, with Farm Fertilizers & Seeds, Hamlet, and an Indiana Certified Crop Adviser, is a strong believer in pulling in the same season all the time. “It’s important to always stick with one soil testing time frame,” he insists. “Seasonal variations occur with the major nutrients, largely due to temperature and soil moisture variations.

Key Points

Once you sample in the spring, always sample in the spring.

Soil fertility test results trend somewhat higher in the spring vs. the fall.

If you sample fields this fall normally sampled in the spring, don’t compare.

“If you begin testing these fields in the fall now, it would be impossible to look at historical trends because the spring vs. fall results would vary. If you’re a spring sampler, wait until next spring and pull samples from those fields.”

An alternative view

Steve Gauck would take a different tact if he was advising someone who samples in the spring but couldn’t complete sampling in 2011. Gauck, with Beck’s Hybrids, Greensburg, thinks it’s important to get some knowledge about soil fertility in these fields without waiting until next spring.

“You should go ahead and sample this fall so those acres don’t get behind in your sampling program,” Gauck advises.

Many times a fall sample will read lower in phosphorus and potassium, as fodder hasn’t yet decayed and let nutrients move into the soil, he explains. Take that into account if you sample this fall, and you normally sample in the spring.

“Use fall samples to plan until next time around, and you will have kept your soil fertility in check,” he advises.

Third opinion

These two opinions mesh together in David Taylor’s suggestion. He’s an agronomist with Harvest Land Co-op in east-central Indiana, based at Portland. “The quick answer is you can sample these fields [you didn’t get to sample last spring] in the fall,” he begins. “But if you want to make any comparisons to your past soil samples, you should wait and sample in the spring. When sampling timing changes, say from spring to fall, the results can look quite a bit different, with spring results often somewhat higher than fall results.”

Fall results tend to be a little lower, he notes. Taylor cites work by Ted Peck, agronomist at the University of Illinois, who showed that nutrient availability through the year is very cyclic. Soils contain lower nutrient loads in the fall and a higher nutrient load in the spring, according to Peck’s results.

“This is why most agronomists say once you choose your season to sample, you should continue to sample during that season,” Taylor concludes.


Consistency pays: Agronomists say to sample in the same season, and sample at the same depth each time. Here, this person marks the probe so it’s always inserted to the same depth.

This article published in the November, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.