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Different soil results from different labs

Soil test results

I got my soil test results back, and I'll be looking at them in much more depth than you probably want to read about next week (and probably the week after) as a lunchtime series.  However, I thought it was interesting to see how different test results can be from two different labs.
Taking a soil sample
I doubt my soil has changed very much over the last year, since I haven't added any major amendments.  And yet, this year's results show just about everything much lower than last year's results showed, except for the trace minerals, which are mostly higher.

(There are a couple of mitigating factors to consider.  I didn't take any samples from the spots where I spread the gypsum.  But I did take the samples a little differently, testing deeper into the soil profile in 2012 because Solomon wanted a six inch test depth for his analyses.)
Tables


Mule 2011 Mule 2012 CP3 2011 CP3 2012 Back 2011 Back 2012 Front 2011 Front 2012
pH 7.55 6.9 6 5.9 7.3 7.1 7.4 7.3
% OM 17.7 4.87 8.2 5.48 15 7.82 14.6 8.95
P (ppm) 523 494 21 44.5 556 351.78 410 446.38
K (ppm) 774.5 404 351 306.5 615 298 875 487
Ca (ppm) 7555.5 2889 1643 1038 6801 1800.5 5772 2415
Mg (ppm) 989 441 213 175 926 299.5 743 421.5
CEC 70 20 15.6 9.88 56 12.9 47.1 17.63
% Sat. Ca 79 71 64.8 52.56 78.8 69.78 77.7 68.47
% Sat. Mg 16.95 18 13.8 14.77 17.6 19.35 16.4 19.92
% Sat. K 4.25 5 7.1 7.96 3.7 5.92 6.1 7.08
Al 6 215 14 402 6 220 7 247
B 1.5 0.67 0.5 0.29 1.3 0.56 1.1 0.62
Mn 22.2 41 4.5 30 24.4 43 19 47
Zn 8.05 43.57 12.5 6.64 7.5 17.07 8.5 38.34
Cu 1 3.19 0.9 2.03 1 2.8 1 3.46
Fe 2.15 248 2.2 153 2.1 215 1.7 236
S 126.5 24 33.8 19 109 20 100 19

Since these two labs used different extraction techniques, it's not terribly surprising their results varied.  But you'd think there'd be one right answer to how much sulfur (and everything else) there is in the soil.  I guess this is why Solomon recommends picking a lab and sticking to it if you want to be able to tell the changes in your soil over time.

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Hi Anna,

You can find on the web several inter-lab tests where the 'same' soil was sent to a variety of labs. Even when the soil was well mixed, etc. the results are quite different.

You probably only want to compare the actual lab measurements between labs. This is made much harder in that percentages given are NOT what was measured.

I could go on and on. It's a real problem without an easy answer.

And the micro-trace elements that really matter aren't usually measured at all.

John

Comment by john Sat Jan 12 15:14:23 2013

A measurement value by itself is almost meaningless. At the very least the (standardized or otherwise published) method by which it was carried out should be mentioned.

If the methods used by the two labs are different it will be very hard to compare the numbers, unless you know both methods and have enough knowledge of chemistry to be able to estimate the effect of both.

Comment by Roland_Smith Sun Jan 13 09:41:20 2013

Hi Anna,

I would have thought you would have collected some real comments by now.

A good book to start with is Mike Astra's "The Ideal Soil Handbook". In some minerals you need enough like Calcium. In other cases the ratio is important. Zn to Cu and a lesser known Zn to Cd. And enough boron. Boron should be about 1/1000 of Ca. But high boron often inhibits germination.

You should check levels of Se for your health. There are many minerals that plants don't care about, but are very necessary for animals and humans. A little sprinkle can make a HUGE difference.

As I said earlier, there is quite a variation among consultants to make matters even more confusing. Pay attention to what the vets say. They are in general MUCH better informed than most MDs about what works for animal health. Read and listen to what Joel Wallach, DVM, MD has to say as a pretty good introduction to what really matters.

I always enjoy what you have to write. NICE JOB :).

John

Comment by john Sun Jan 13 17:09:21 2013

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