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Low pH Tests Might Be Worth Testing Again

Low pH Tests Might Be Worth Testing Again
You can't afford for pH to slip too low.

The past six months have been a nightmare for soil consultants worried about doing an excellent job of soil testing. Samples pulled during the vary dry spell from August through early November could show a lower pH reading that is actually in the soil. The question becomes if your soils were sampled then and your pH tests are low, can you afford to assume it's a mistake?

How much dry weather affects sampling is up for debate. Jim Camberato, soil fertility specialist at Purdue University, says the difference may not be that great. However, Betsy Bowers, a certified crop agronomist and crops consultant with Ceres Solutions, Terre Haute, says data from the University of Kentucky says it can amount to at least a half point swing. Soil pulled from dry conditions tests lower. For example, if the actual pH is 6.0 but the soil was extremely dry, it could possibly test 5.5 or even lower.

Some theories hold it's because salts accumulate that affect pH readings. A good rain washes out the salts and the pH reading returns to normal. The problem for those who had samples pulled while it's dry is in determining whether the pH reading was low, and if it was, was it due to dry weather, or is the pH in that field or a spot within the field truly headed toward low pH values? If pH is truly low, variable lime application with GPS-based equipment to put lime where it is needed most might be the best solution.

One option is to retest soils now that soil moisture has returned to the surface, assuming conditions become right for testing. Danny Greene, a soils consultant from Franklin, Ind., operating Greene Consulting, Inc., notes that there is some variation from fall to spring in sampling for pH anyway. If sampling drifts into the spring before it can be completed, there may be natural variation in pH compared to if readings were taken in a normal fall.

The risk is what may happen in terms of crop yields if pH readings are truly lower, and not a mirage. If they're truly lower, they would be expected to react positively with a yield increase to lime applications. If the pH is so low that you can see it visibly in the plants, then yield is definitely being impacted.

Here's another 'freebie' question from the Indiana Prairie Farmer/Beck's Hybrids Crops Knowledge Quiz. See the full quiz either in the December issue, page 21, or find it in the December issue online under 'More Prairie Farmer,' and 'Magazines online.' Answer the 10 questions correctly and enter by January 15, either by sending in the printed form or emailing the answers to: tbechman@farmprogress.com.  You'll be eligible to win free seed by entering the contest.  Over half of the answers have been revealed this week in Web stories. Look for the rest of the answers next week.

The question is: Corn grows slowly, stalks are spindly, soybeans have few nodules. The problem is likely: a) pH above 6.5, b) pH 5.8 to 6.5, c) N deficiency, d) pH below 5.0. The answer is 'd,' pH below 5.0.

While this may seem extreme, specialists say there are still areas within fields, especially on red clay hills in southern Indiana or on sands in other areas that can fall into this trap.  Lime is the remedy.

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