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Little River, TX | Really the Labs provide reasonably good consistency of results. With the samples we send they dry with hot circulating air, then they grind the soil to a powder, then they stir and mix the resulting sample. Then they pull a sub sample from the what we sent and run their magic on it. If tomorrow you ask for them to run the same sample again the next sub sample will have some differences from the originally tested sub sample. I am amazed that there is any validity to soil testing.
Through in the complications of high, neutral, and low pH, and heavy clay to almost pure sand. Different labs even using the same chemistry will produce different results, though each will be consistent with their own standards. Tissue analysis results from strange to each other labs will be very comparable.
Personal Opinion follows: Our University System have bought into the idea that soil testing is better than nothing. This is more or less true. Problem has been soil testing as we know it is not reliable for much more than pH, Organic Matter.
If you are willing to spend the money they can tell us the real honest CEC value of our soil, with a 90% Confidence Factor. They do this by washing all the cations out of the sample with a different strong cation. Then this is rinsed out. Then they re inoculate the sample with calcium and measure how much is taken up.
For a smaller fee they will determine how much calcium is loose in the soil and not attached to soil particles. Again with a 90% confidence factor.
The confidence factor for P, K, Mg. or Ca. is maybe 60% or even 70%, while our confidence for Sulfur and all the micronutrients is at best 50%.
The Key Words are Confidence Factor.
Edited by Hay Wilson in TX 11/2/2008 06:40
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Zone Sampling - Revisited
