It's funny how you diligently defend the Mehlich 3/saturated paste test!!! At best, it is a educated guess through a mathematical equation= Solve for base saturation ratios. How do you know exactly what is locked out through the Mehlich 3/Saturated paste test? How do you know that only 10% of shown phosphorus is available? It's a bunch of guessing. The more that you argue about the "Soil Savvy" test being bunk, the dumber you look!
OK.
First off, Mehlich 3 is a soil testing method, not a soil test. Companies that offer it test base saturation (CEC, sometimes called a "basic soil test") and soil solution (saturated paste) separately. To effectively trouble shoot toxicity/deficiency issues, you need to have the results separate, especially in potted containers, because the soil solution is the source for what's contained on the cation exchange capacity. Toxicity issues will shine like a bright beacon on a saturated paste report. So will deficiencies. The Mehlich 3
base saturation test tells you what's "locked out" just like the Soil Savy test. Base saturation tests not only tell what's "exchangeable" and held by the soil's Cation Exchange Capacity, it also tells what is held by the soil organic matter. This is why anions like Phosphates, Sulfur, and Boron are reported on those tests. Because soil organic matter, specifically the parts of it that lay on the soil solution boundary and are most subject to microbial degradation, has the ability to hold on to both cations AND anions. I will revisit this point in a moment.
If you've only been getting one "Mehlich 3" soil test done to figure out what's wrong with your soil, you're only getting half the picture. If you've been sending in samples to testing companies offering such and providing material for "soilless mixes" instead of telling them that it was potting soil (and sending more "mass") in the "special instructions" box/portion of their form, you're going to get very skewed and inaccurate results.
On to the Soil Savy test. The results provided
combine what is held by the soil's base saturation (CEC and SOM) and what is carried in the soil solution. The terms "available" and "locked up" used by the Soil Savvy folks are thrown about a bit haphazardly, IMO, and seem to have led to some confusion for several growers new to soil testing. "Available" means soluble, in ionic form, and immediately plant available. The largest source for plant available nutrients is the soil solution. "Available" also means exchangeable from the soil colloid, which holds cations, and floats around within the soil solution. As previously mentioned, SOM has the ability to hold both cations and anions by electrostatic charge, just like cations to the soil "CEC". This is what is extracted with the SS test, just like the M3 base saturation/"standard soil test", and what the SS test folks mean when they say "locked out".
What I've been witnessing is blades getting soil tests done, not understanding what soil tests they're getting or what the results actually represent, most likely sending in the wrong amount of material for the wrong kind of test, and then trying to make adjustments by adding more organic matter to their soil mixes in order to "water down" this or that, especially more compost/SPM. This is where I'm guessing the extremely high levels of P are coming from on many of the soil tests that I'm seeing. You know what the funny thing about Phosphates? They're highly insoluble due to their high valence and reactive tendencies. So they are going to bind up micronutrients, cations, and especially micronutrients, which again will require microbial degradation to solubilize the individual ions. I have seen you allude to this, so props for that.
With the SS test, you're not getting ANY information concerning SOM content, Cation Exchange Capacity, or Electrical Conductivity. It combines what's "available" in by both soil phases, so you can't discern whether or not your experiencing toxicity issues, deficiencies, plenty of minerals that are there but "locked out" by too much SOM. What's more your basing your action of remedy upon a suggested "target range" for some mystery agriculture crop/turf application, not growing cannabis in containers. You need as many details as possible to truly ascertain what's happening chemically in the soil, which is why I suggest having one's irrigation water tested when I see high sodium levels show up on soil tests.
This is why I think the M3 tests are better than the SS test. They provide more comprehensive and useful information for troubleshooting "problems". Knowing what's in the soil solution separate from the base saturation is inherently more important for those growing in potted containers. You don't get that with the SS test...
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