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Mass confusion on Ph, soil tests and fertility
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SimpleJoe
Posted 11/20/2025 08:26 (#11440850 - in reply to #11440675)
Subject: RE: Mass confusion on Ph, soil tests and fertility


NW Illinois		Just finishing my 32 year in retail and like you, could kill pages on here with horror stories. We were the first to start "Precision Ag" in our county in 1996 here. I have to admit after all these years and staring at 100,000 plus acres of testing data, pretty colored maps, and million plus acres of VR spread maps for Lime, P and K, I am tone deaf and numb to this.
Where I live and work, unfortunately don't farm instead farm rougher soil types another county away. Quad Cities area, some top tier dirt. Osco/Muscatune soils that do transition into B and C class soils. 3 to 4.5 OM, CEC 17-26 mostly. Large areas have been no tilled for 25 plus years in corn/soybean rotation. Average year can raise 250+ corn without irrigation and single nitrogen apps.
95% plus of all test cores have been pulled manually by all companies local over the last 30 years. Here's a couple trials I've done since I'm now the owner and test puller. One is a stratification test. I grid sample and pull cores from a single 15' circle roughly at the center of the grid. So I will pull a standard 10-12 cores test and then I go right back into the same circle and pull same number of cores but I cut off the bottom 3-6" of the core and only send the upper "surface to 3 inch depth" as a separate sample. I don't tell anyone, not even the lab. Done this multiple times and results for here are if standard 0 to 6 test says 25 ppm of P, 180 ppm of K the strat test is mostly 50% higher. So it will say something like upper 30's ppm P, mid 200's ppm K. So we have stratification. I'm not an agronomist or a scientist and can't tell you if that's all the commercial fertilizer sitting on the top, or decaying OM from previous crop being recycled. But I do know there is a numeric difference displayed on test result. The other test I do is checking to see if where I test is affecting test results. So same grid point, same 15' circle scenario. I believe it's important to test in the middle of the harvested crop rows "30 inch rows here" and avoid pulling tests within a couple inches of the harvested crop rows. Results from those tests are roughly 20% lower numbers on P & K from my test pulled within and/or on the harvest row vs staying roughly in the middle of the row.
Point is from all I just typed, I know I can alter the test numbers for P & K by altering where I test in the field or the depth I choose to test to. Do random sub contractors or seasonal hires understand it though.
To the OP, google "Midwest labs buffer PH" and that lab has a short 3 minute You tube video that explains pretty easy how PH testing is done and what buffer PH means.
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