Why sample only 1" of soil?

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Bales9er
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Why sample only 1" of soil?

Post by Bales9er » May 9th, 2022, 7:57 pm

Question I've been sitting on for awhile...why is the recommendation to sample only the inch between 3" & 4" of your soil? I'm assuming that's for an average reading but grass takes up nutrients through all its "hairs" along the roots which obviously run through all of the top 4" of soil so why would you limit the sample to only that small portion of the soil?

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MorpheusPA
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Re: Why sample only 1" of soil?

Post by MorpheusPA » May 9th, 2022, 8:37 pm

Well, for me, the top inch is black with organic material decaying. I really sample from about 2.5" to 4" or so, from where the filtering of OM stops down to the base of the root layer.

I don't want to fool the test with OM that's fairly raw (<1 year old), nor with stuff that's still filtering down and hasn't stabilized yet. I'm aware that higher layers have a higher pH, more P, K, Ca, Mg, and so on, but that's OK. They also have a higher OM percentage than 13%, if you can believe it...

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andy10917
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Re: Why sample only 1" of soil?

Post by andy10917 » May 9th, 2022, 9:54 pm

I'm the perpetrator of the 3" -4" recommendation.

It comes from my frustrations with test results that would bounce around too much each year. Eventually, I came to the conclusion that new nutrients at the upper levels of the soil tended to overstate nutrients, and lower levels of the soil tended to either overstate TEC if there was clay lower,or understate it if sand were below the topsoil. I did several tests of the with different 1" slices, and found that the least "bouncing" happened when I took the 3" - 4" core. It moved closest to what had been done over a few years of nutrient inputs. It took 35 years for me to figure that one out.

It's a recommendation and nothing more. If you've got a spare 35 years, try different levels and see if you agree. When I write up test interpretations, I assume that you're using that 3" -4" zone, and my nutrient recommendations reflect that.

Bales9er
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Re: Why sample only 1" of soil?

Post by Bales9er » May 12th, 2022, 8:25 am

Got it that makes more sense now so thank you for the explanation. Out of curiosity, had any "arguments" with any scholars about that one?

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MorpheusPA
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Re: Why sample only 1" of soil?

Post by MorpheusPA » May 12th, 2022, 1:46 pm

Define argument. Define scholar.


Bales9er
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Re: Why sample only 1" of soil?

Post by Bales9er » May 15th, 2022, 6:54 am

Anyone from university turf programs that teach the stuff for a living. I'm not questioning your expertise I just always find it interesting when the so called professionals aren't up to speed on better information.

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Re: Why sample only 1" of soil?

Post by MorpheusPA » May 15th, 2022, 1:04 pm

That was mostly me being sarcastically funny.

Well, I mean, I've had a few people who claim to teach this stuff for a living bork the chemistry in casual online conversation and claim things like aluminum isn't toxic, iron is more toxic than aluminum (without qualifying statements regarding calcium/magnesium/potassium balances)(and ignoring the previous statement), pot soils can't hold resources at all, the list is nearly endless. So sure, everything gets questioned, by people claiming any number of qualifications.

It's fun to note that those making the claims can, occasionally, be found to have qualifications that are...not even equal to my own "learned it in the gutter while performing unspeakable acts" ones that I'm incredibly happy with. (Particularly the unspeakable acts; I can speak for hours about my unspeakable acts). Note: if I actually quote my qualifications, they're actually not that bad, but I always figure the proof is in the pudding. I've made literal tons of pudding.

There's another great adage that works here, "The dogs bark, but the caravan moves on." I like to collect those. In this case, the above people were dogs. Nothing more.

If you took the slice from 1 to 4" on the average fallow meadow, you'd get a much better representational sample than you would in, say, my lawn or gardens, which are constantly getting slammed with organic matter and Creative Chemistry. Although even there, you'd still get an artificially high (if you think that way) reading on your organic matter--I'd still rather know what's filtered down to the lower layers.

I can, with my little plant stick tester (nearly completely useless in terms of actual pH, but mildly helpful in terms of relative penetration and reasonably helpful to test for dry spots and light levels), see how far my Ca and Mg apps have gone if I kind of ignore the answer and look for relative pH. Before this, all layers were testing at 4.5 (obviously wrong) in the gardens and lawn (actual answers were 6.0 and 5.2). Now, the top inch tests at 7 in both (also completely wrong), but at least I'm kind of figuring my lime's gone down an inch so far. Give or take.

So there's a bit of risk with re-testing too soon after application, but we do rely on the person to tell us things like this. "I just applied 9 pounds of fast lime and 60 pounds per thousand of slow calcitic lime to the garden" would be a required note here (I did that for a quick change and a sustained slow change in the garden to counter the acidic urea-based weekly fertilizer I use).

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