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So,
which tests are appropriate for our peaty, lightweight, organic soils?

Good question. In Florida and North Carolina it seems the Mehlich 3 is used on organic muck soils. In Michigan it's bray and A.A. for mucks. I don't know this answer but I've been using the Mehlich 3.


Got word today that https://www.rockriverlab.com/ will actually weigh in the sample for a M3 with an actual balance for no extra charge unless it's over 200 samples.

I'd like to get a list of labs going that get that you can't weigh these soils with a spoon.

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Here is one of the research paper on vegetable production in peaty muck ( histosiols) and testing via Mehlich 3 I found. There are quite a few to be found with google. Keyword histosol and Mehlich 3 .pdf. If I had access to all the scholar papers, I could find tons more research on managing peat for agriculture.

To the lab that told me that the Mehlich 3 isn't appropriate for "un-natural" soils, i and Florida and North Carolina organic soil researchers disagree. Also the soil sciences society of America says peat is a natural soil.

https://www.soils.org/discover-soils...ypes/histosols

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Here's another one:

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The Diffrences between organic, lightweight, peaty, mucky mucks and mineral soils when it comes to soil testing so far:

Bulk density!

Severe volume shrinkage after drying and grinding for the lab test making volumetric style testing of a known volume problematic.

No, mineral soil calibrated automatic weighing scoops don't correctly measure mass of organic soils. Sorry labs. Require your sample to be weighed in

Ppm soil mass ( mg per Kilo) is not the same as ppm volume ( mg per L) as it is in mineral soil @ 1g per cc.

The Mehlich 3 is an acceptable test for histosols. As are others. These soils are real soils.

What are some more diffrences between these two types of soil as it pertains to testing?

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How about the differences in nutrient availability organic soils vs mineral at various ph? Organic matter behaves and holds elements differently than the clay fractions in mineral soil. How does this affect our ph strategy?

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Another list of diffrences:

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And we must consider organic soils that have clay added. Maybe that chart would be in between those two previous charts? It would be dependent on the amount of clay added, I'd suppose.

Anyone here had luck adding calcium bentonite to their peaty muck mixes? Maybe some clay would help with Mn uptake? The stuff clears up koi ponds and improves the fish's color. Sounds good to me.

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Here is a redneck soil experiment for ya:








1. Took a gallon of field moist soil packed in just as if I were planting, oven dried it bone dry and weighed it and converted to cc .363g per cc.

2. Took a 240ml cup and weighed the oven dried soil. .445g per cc

3. ground soil in soil ninja, measured a 240ml cup. .698g per cc.

If a lab were to scoop a known volume of dried, ground, ready to test organic soil, the test results in mg per Liter would be skewed high by 2x maybe. You'd be testing 2xthe mass of soil in the volume as the same volume of field ready soil.

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Back to the diffrences between organic vs mineral soil as it pertains to soil testing and interpretations.

Organic soil exchange capacity derives almost exclusively from organic matter humus.

Mineral soil exchange capacity derives mostly from clay and some humus.

Organic soil has a ph dependent variable CEC. Goes up rapidly with ph.

Mineral soil has a fixed to just slightly variable exchange capacity at various Ph levels.

How does this fact affect us?

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CEC tests A.A. 7.0 and 8.2 are buffered at those ph levels and report CEC at that PH. Due to variable ph dependent CEC of organic matter, CEC is higher at 8.2ph than at 7.0ph.