Did you collect soil samples in our dry fall?

first_imgShare Facebook Twitter Google + LinkedIn Pinterest We had an interesting discussion recently about how dry it was collecting soil samples this fall. It was so dry that the folks who sell soil probes are having a run on sales this fall because of the bent and twisted ones used in our hard, overly dry soil.This may have an impact on your soil test results. We learned in graduate soil chemistry class that dry clays can collapse around potassium (K) ions and trap nutrients there and away from crop roots — and away from a soil test. But here in Ohio I would never worry about such concerns before. We are usually wet, and the past several falls it has even been a bit difficult to get harvest finished before Christmas.Some field work always brings clarity to me — not just what happens in a lab. Nearby in Kentucky they had an opportunity to check out this soil sampling concern (http://www2.ca.uky.edu/agc/pubs/agr/agr189/agr189.pdf). Lloyd Murdock and Dottie Call found that pH and potassium are most affected by dry soils such as we see in the fall. They collected soil samples every two weeks throughout the growing season to track changes. They found that pH can dip as much as half a point in a dry season and may take until late fall to recover as the soil moisture rebuilds. For potassium, the difference can be as much as 50 to 100 pounds per acre reduction from a test in a wet season verses a dry season. And because so much potassium is tied up in residue, until we get fall rains to leach K back out of the residue, levels will be lower. Phosphorus (P) also dropped throughout the growing season as the crop pulled available P out of the soil solution, then recovered in the fall, just not as dramatic a change as for K.Their recommendation for the best way to estimate what your crop nutrients will have for the growing season is to pull soil samples in the spring. If you pulled samples as I did this fall, that’s OK, just be consistent in your sampling timing. And did this fall dry spell affect your results? If yes, then double check these results against past soil tests before you make any major change to your nutrient management plans.last_img

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