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Some soil sampling guidelines for dry fall

You’re on a soil testing program. Perhaps you test soils every two years, maybe every four years. Maybe your local fertilizer dealer offers a soil consulting service. Whatever the case, you’re at a crossroad. What do you do about soil testing since fall was so dry?

Some consultants who normally pull samples waited during the long, dry stretch because soils in their area were so hard they couldn’t consistently sample to the 8-inch depth. Suppose samples could be pulled. Current wisdom says potassium levels will be lower, phosphorus levels unaffected and pH levels perhaps lower. Now what?

“We believe the bottom line was to take advantage of the early harvest and dry soil conditions, and continue soil sampling,” says Jim Camberato, Purdue University Extension specialist. “Then fertilize and apply lime where needed.

Key Points

Some experts suggest sampling if you can do it properly.

At least one major co-op called off sampling during very dry weather.

Consider options carefully when deciding when and how to sample again.

“Just remember that most of the K taken up by the crop, especially the corn crop, remains in residues, so don’t be alarmed if soil test K levels are lower than expected. ”Camberato also believes that due to good rainfall and normal fertilizer uptake earlier in the season, there may be fewer salts left behind to lower pH than some think.

A different approach

Ceres Solutions in west-central Indiana elected not to have consultants pull samples during the driest stretch. Why? “Our No. 1 concern was getting a consistent 8-inch sampling depth,” says Betsy Bower, Ceres agronomist, Terre Haute. Even though Ceres consultants drive vehicles equipped with automated probes, early sampling attempts indicated they weren’t hitting the 8-inch depth consistently.

“Soil testing is an art and a science,” Bower says. “We believe it’s very important to sample at the same depth to remove the variable of inconsistent sampling depth. ”That’s left customers at the crossroad described above.

“If they didn’t have immediate plans to apply fertilizer, we could wait for rain and better conditions,” Bower says. “We suggested that those who didn’t want to wait use mapped yield data or a yield goal and follow a one-year crop removal fertilizer program, and then test next fall.”

Specific situations

A few farmers who took advantage of the dry October to apply fertilizer wonder if samples can be pulled once soils moisten up.

“We wouldn’t do that because sampling could pick up applied fertilizer, and lead to erroneously high results,” Bower says. “Wait until next fall to sample.”

Some farmers asked about sampling next spring. “We can, but then you ought to stay on spring sampling,” she says. “Switching from fall to spring can lead to differences in soil test results. If you want to keep a field on fall sampling, I would wait until next fall.”

On the flip side, some asked about waiting two years on a field due to be sampled this fall to get back on rotation. “We wouldn’t recommend waiting two more years,” she says. “That could be up to six years since a sample, and soil pH can change too much. Low pH can certainly reduce yields.”

This article published in the December, 2010 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.