Lightweight Peat's Mucky Muck soil testing

On CEC/mass:

The simple substitution of lighter weight aeration into the mix would increase my CEC/mass without increasing my CEC/volume. If my soil's CEC-7 is 40cmole/kg and if the remix with lighter aeration weighs .7 of the original, then my CEC-7 would be 57.

CEC per volume wouldn't change. 100 cmoles/kg soil may have equal exchange sites to some 40 cmole/kg soil that has a higher bulk density.

cmole/L or meq/100cm3 is the relevant unit to judge the buffer capacity of my soil vs yours vs anyone else's. cmole/kg or meq/100g is just the raw data from the test.

We must multiply by bulk density (g/cm3) to make it relevant in all soils, "standard" soil just happens to be 1g/1cm3. 1/1=1 multiply the raw data on a standard soil CEC/mass or an elemental ppm-mass test by 1 to get the relevant per volume measurement.

Reporting on the elemental content of any soil other than the 1g/cm3 soils without an accurate bulk density test to go with it seems crazy.

The further away your bulk density is from 1/1, the further down the rabbit hole you go.

Your test devolves from a potentially accurate description of the mass of the Mehlich 3 extractable elements per your volume of plant ready soil into a vague, fuzzy ratio only report on the mass of your elements per the mass of your air dried soil.

Relevant units...it will sink in...

Yeah I gotta get a better grasp on all of this.

Here is another way of putting what you've just written about CEC/mass, CEC/vol:
http://www.pthorticulture.com/en/tr...ion-exchange-capacity-soilless-growing-media/

I keep going back to it but is it possible my mix is 100+ meq/100g or 100-125ish meq/L?with bulk density of .125g/cc? I dont know what would bring down my CEC other than the perlite?

I have done those types of home pH tests in the past, but will re do them soon, I dont doubt I have a high pH, but when I consistently hit high sevens and low eights on the meter I just don't know how to process it.

The AA7.0 direct measure CEC test ( USDA CEC-7), not the AA7.0 cation extraction and summation CEC test. This test should be a big help for you Albrecht BCSR fans.

CEC @ ph 7.0 is what the total CEC calculation formula of brookside/Logan is trying to estimate. If your mix has free carbonates, the Mehlich 3 will overestimate your CEC.

The CEC-7 is solid except in cases of soils with lots of vermiculite ( vermiculite can irreversibly fix NH4, they say) or soil that has enough free carbonates to change the ph of the 7.0 ph buffered solution. This test uses lots of solution to wash out all cations adsorbed and doesn't measure Ca at all. It measures NH4 after saturating and then washing the soil. So I would expect it would be an extreme case for the highly buffered 7.0 ph solution to move with "normal"'levels of free Calcium expected in a mix with a ph below 7, I think we may be good. I'll keep digging on that one.

Directly measure your TCEC !

Pangea said:

Yeah I gotta get a better grasp on all of this.

Here is another way of putting what you've just written about CEC/mass, CEC/vol:
http://www.pthorticulture.com/en/tr...ion-exchange-capacity-soilless-growing-media/

I keep going back to it but is it possible my mix is 100+ meq/100g or 100-125ish meq/L?with bulk density of .125g/cc?

Click to expand...

If your BD is .125g/cm3 your're right in there with 1/2 and 1/2 peat and vermiculite( very light). Your measurement doesn't match your soil's description. Use some accurate measuring cups to measure a liter of field moist soil and then air dry it, weigh it and then oven dry it and weigh it. I would guess its .2g/cm3 or more.( oven dried g /field moist cm3 )

Get the CEC-7 test from a lab that weighs samples with a balance ( this test is 10g of soil, I hope like hell labs don't use a 10g weighing scoop!) and you will have a direct measure of your soil's CEC / mass ( cmoles/kg or meq/100g) @ a ph of 7.0

Get a lab to test your air dry mass/ field moist volume bulk density (BD) or use your own bulk density test to convert your CEC/mass to CEC/volume.

That promix article has just a bit of spin to make their point. First off, almost no one grows in a mix that lightweight. I mean, who grows in 1/2 and 1/2 peat and vermiculite?

They take some pretty high CEC (at 20 meq/100g and 1.3g/cm3 density, it's almost pure clay, I would guess ) mineral soil and give it a nudge with an inflated, very dense,1.3g/cm3 value. At about 1.4 g/cc in clay soils, root growth is restricted. 1.3g/cc, 20 meq/100g clay soil isn't good farm soil. They compare the two extremes. The lightest density mix one could whip up with a wad of some compacted clay.

Let's make it a more reasonable comparision. Let's do a 20 CEC but a bit higher OM and less clay and therefore less dense 1g/cm3 soil ( still probably field soil, not backyard garden density of .9g/cm3 ) in their example. If we do that, it brings the mineral soil example down from 325meq/pot to 250 meq/pot vs 176 meq/pot.

And WTF kind of unit is meq/pot?? is this a professional company?? maybe their own, in house, wizbang Argo-non-amist came up with meq per pot??? WTF???

Let's look at it meq/100cm3 . The mineral soil becomes 20 meq/100cm3 and the peat/vermiculite blend is 14.1 meq/100cm3

At .9g/cm3, the mineral soil becomes 18 meq/100cm3.

Spinning numbers Is what I'm seeing by promix.

A 1g/1cm3 Bulk Density, 14 meq/(100cm3'=per 100g) field soil

or a

14 meq/100cm3 potting mix that is 0.1g/cm3 and also happens to be 176 meq/100g both have equal buffer.

My soil I'm tinkering with ( 40 cmole/kg or meq/100g and .363g/cm3 oven dried BD has an equilivant cation exchange capacity as a 14.5 cmole/kg (or meq/100g or cm3)!mineral soil that is 1g/1cm3 BD. This mix is my lower CEC mix I've been working on.

Pangea said:

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I keep going back to it but is it possible my mix is 100+ meq/100g or 100-125ish meq/L? .

Click to expand...

Meq/100g and Meq/100cm3 only equal each other in soils that are 1g/1cm3 bulk density.

Meq/L is meq/1000cm3

Pangea said:

I have done those types of home pH tests in the past, but will re do them soon, I dont doubt I have a high pH, but when I consistently hit high sevens and low eights on the meter I just don't know how to process it.

Click to expand...

I only check ph when mixing or remixing my soil. I just let it do its thing once planted. It is tricky to get consistent, trust-worthy readings. Take tons of them till you figure it out.

If you have a decently buffered media, the ph shouldn't be an issue during the grow, I'd think.

Pangea said:

I dont know what would bring down my CEC other than the perlite

Click to expand...

Are you referring to a Mehlich 3 test CEC value on this soil? If it was a scooped test, it will be reported low due to the under-measurement of the sample's mass.

If not, then please clarify.

Maybe you might ask:

So, biggy, how much CEC do i want in a mix?

Biggy says the hell if he knows, what you trying to do with your mix?

Dr. T at U.Idaho said in the article I posted earlier that 5 to 10 meq/100cm3 is needed for a consistent cation supply.

I'd say that's the starting point for typical sized containers. Any less exchange capacity than that, you may have to manage ph issues and are really growing more hydroponically than anything else.

So biggy, how much CEC is needed to hold enough charge for a water only mix?

Biggy: how the hell do i know? What size container and how many weeks till harvest? Heavy or light feeding strain?

Biggy does know that if you're gonna talk about your CEC, he only understands your number as relevant if it's in CEC/volume units. cmole/L or meq/100cm3.

If you're in "standard" 1g/cm3 mineral soil, he will give you a pass and let you slide with CEC/mass: cmole/kg or meq/100g

I would like to apologize to all the major soil labs that we all have been using. I too am guilty of sub-par performance many times in my life and I'm sure I will be again in the future. I can relate to your situation. I realize it isn't nice to clown on the ignorant or the delusional, no matter how bad their screw ups are harming folks.

I would like to ask these labs for understanding. I would like them to see my public anger and aggression are born out of compassion for the many folk harmed by all their bad data at full prices.

I ask you, lab guys, please understand the disgust i feel for you is all business and not personal, I promise my beef with you will end and I'd have no hard feelings if you either stop charging hard working lightweight soil farmers full price for grossly mishandled and mis-calculated tests or if you would just tell all non "standard" density soil customers you don't want their soil to test any more due to unwillingness actually weigh any samples.



I promise you, big soil lab, I will understand and forgive your ignorance and/or greed the day you roll out a lightweight soil handing protocol memo to train your staff with or a warning is posted on your website that all non standard density soil customers need not apply.

Deal? Let's be friends, ok?

If your BD is .125g/cm3 your're right in there with 1/2 and 1/2 peat and vermiculite( very light). Your measurement doesn't match your soil's description. Use some accurate measuring cups to measure a liter of field moist soil and then air dry it, weigh it and then oven dry it and weigh it. I would guess its .2g/cm3 or more.( oven dried g /field moist cm3 )

Click to expand...

That is the wet bulk density procedure, Ive done dry bd oven drying to get my number. I take couple liters of my mix and oven dry then measure out 1000cc and weight that. It came out at 125g/1000cc. My mix doesnt have vermiculite but does have 15-25% perlite, the rest is peat moss, composted alfalfa/peat, minerals and humates. Its light weight. I try to bulk it up for outdoor use with cal.bentonite and red lake earth, but have not been able to add as much as I would like.

Meq/100g and Meq/100cm3 only equal each other in soils that are 1g/1cm3 bulk density.

Meq/L is meq/1000cm3

Click to expand...

So It is possible that my meq/100g is 100+ as would be my meq/1000cc

If the lab is under scooping my sample by a factor of 10, 1g scoop is 100mg, would the results be off by the same factor, 10meq/100g would be 100meq?

Pangea said:

That is the wet bulk density procedure, Ive done dry bd oven drying to get my number. I take couple liters of my mix and oven dry then measure out 1000cc and weight that. It came out at 125g/1000cc. My mix doesnt have vermiculite but does have 15-25% perlite, the rest is peat moss, composted alfalfa/peat, minerals and humates. Its light weight. I try to bulk it up for outdoor use with cal.bentonite and red lake earth, but have not been able to add as much as I would like.



So It is possible that my meq/100g is 100+ as would be my meq/1000cc

If the lab is under scooping my sample by a factor of 10, 1g scoop is 100mg, would the results be off by the same factor, 10meq/100g would be 100meq?

Click to expand...

The volume of your wet, field ready, packed like you're about to plant in the container, soil mix is your working volume. The relevant volume.

The mass of that dried soil that fills your working volume when field ready is the bulk density that's relevant.

The Mehlich 3 test will report on mg of extractable elements per kilo of air dried soil.

So that dry soil mass of the mix that filled your field volume when it was "wet"is what you want in g/cm3

Dry mass/field volume

Could your soil be 100meq/100g? : yes

Could your soil be 100meq/L? yes or 10meq/100cm3

Don't try to guess what mass they may scoop, no one knows. The soil is dried and ground well and has a whole new density before scooping. No scoops.

The properly weighed in sample Mehlich 3 test with an accurate mass dry /volume moist bulk density measurement should tell you the mass of the extractable elements per your container.


It should, if no free carbonates or excessive salts exist in the soil solution, provide a CEC meq/100g estimation closely equaling the CEC-7 ( CEC @ ph7.0) test' by adding the meq of Ca, Mg,K, Na, exchangeable acidity and other bases. (TCEC calculated)

I'll find out soon enough, I'm hoping. The sample I sent for testing was last amended about 6 months ago and has been a stable ph 5.7/8 after an initial 3 week "cooking" period.

Happy new year icmag forum people!

Biggreg's new year resolution:

1.To find at least two and hopefully 3 labs that will test our soils using actual mass measurements, actual standard procedures using actual current methods from an actual standard lab manual. ( seems rediculious that's not a given, doesn't it?)

2.To get these labs to report in units most relevant to us.

3. Send 2-3 samples, one to each lab, for every one soil batch I need tested in the future.

4.long list of other stuff.

Think on this one:

Let's say you want 2000ppm Calcium in your container of soil.

What should your test results be in ppm?

Remember that your soil is tested mass per mass ( mg/kg) of air dried soil and NOT mass per volume (mg/L) of field moist in your container soil.

Broke out my spreadsheet for you guys:

A "standard" density 1g/cm3 mineral soil with 2000mg/L Calcium would show 2000mg/kg on the soil test report.

If your soil has a bulk density of 0.2g/cm3, what would your per MASS( mg/kg air dried soil) soil test report have to say to equal 2000mg/L?







Answer: 10,000 mg Calcium per kilogram of air dried soil that is .2g air dried per cm3 of field moist soil = 2000 mg Calcium per liter of field moist soil.

Your soil test would read 10,000ppm in this example.

If you study the spreadsheet you might notice if one mistakes mg/kg for mg/L, the further away your density is from 1g/1cm3, the larger the error becomes, growing in magnitude. Most of us grow in the .2 to .3g/cm3 range ( oven dried g/cm3) in containers, I'm guessing.

Even you mineral soil guys should measure your BD. Look at how much difference .9g/cm3 is from 1g/cm3.

Lots of room for play with Calcium

Run the numbers with Boron or zinc if you want an eye-opener.

Relevant units matter

So biggreg,

How do I measure an accurate bulk density that is relevant.

Biggreg: good question.

You can more accurately measure your field moist volume at home. You know how you pack your containers in your prep to plant your plants.

But

The lab can more accurately measure the mass of that soil air dried, in their dryer, under their conditions and air dried to the same exact level as your soil sample that is weighed into their test on their balance.