Soil Jar Test

danielj_2009July 20, 2014

So I'm not quite getting results as I expected from the jar test... not sure if there is some procedural error, or if this is just what my soil is.

I have two samples, front and back yard. I added some laundry soap (probably too much), a good 2 inches or so of soil, and near filled the bottle with water. I shook each for at least 5 minutes.

I am not seeing any sand settling in 60 seconds. What I see is more like a silt layer settling out in about 2 minutes, with no visible layer of sand settling out more quickly. In other words, either I am looking at a silt layer that settled out in 2 minutes instead of 2 hours, or I am looking at a sand layer that took its good ole time settling out. I don't believe this is sand because I'd have to be at the beach. It looks to me like I have nearly 100% silt. Clay is still settling 2 days later, but it won't amount to that much.

Now, as far as sample method - this is the soil left over from core samples sent to Logan Labs (results due any day now). The core samples were typically 4 inches, sometimes probably closer to 3 inches. I realized this test is useful for drainage questions, so I don't know if 4 inches is really deep enough for that. On the other hand if the test is for soil quality in the root region, then I did the right thing depth-wise?

Check out this quite boring video. The separation becomes clear around 1 min 30 seconds. Total video is about 2 minutes. Anything look strange about this? (OK, brilliant Gardenweb forum software doesn't seem to allow video imbeds. Please copy and paste the link below).

P.S. Check out my next exciting video, "Paint Drying," coming soon!

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dchall_san_antonio(8 San Antonio)

Armed with your cheat to jump ahead to 1:50.

What were you expecting to see? I should say that it is a rare event when someone has the type of soil they thought they had. Almost everyone thinks they have clay. Almost nobody has much clay to speak of.

Yes it looks like you used more than 2 drops of soap. All you need to do is add just a little soap to break the surface tension of the water. Sometimes the soil is hydrophobic; hence the soap.

Generally it is good to use a ruler beside the jar. Measure the height of the soil before you put the water in. That way you know when all the soil is settled out. You can also determine the ratio of one material to another. If you had 3 inches of sand, 1 inch of silt, and the total was 4.25 inches, then you would know that you had 0.25 inches of clay.

Salts can influence your soil but they don't influence this test. For example if you had the wrong ratio of salts, the soil can be very slow to drain like clay. You could also have a quantity of very fine silt which can also resist drainage. And there are some microbes which are hydrophobic and prevent water penetration. These usually occur in highly stressed turf like a golf course might have.

All this is good to know. It will help morph interpret your Logan Labs soil test.

    Bookmark   July 20, 2014 at 7:24PM
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That works for me. I knew I didn't have much clay from the get-go (clay is not common in this area). So much for common wisdom.

I ended up with just under 40% clay. The remainder was silt. I had about six grains of sand in that bottle. My soil is a silty clay loam.

In your case? If it settled before the 2 minute mark, it's sand. Sand grains aren't beach sand, which is rather consistent and pretty big. They can range in size from 1/16th of a millimeter up to 2 mm.

You have a lot of sand if I'm seeing that right. Given the speed of settling, most of that is on the small side. By two minutes, the water is actually starting to clear a bit.

It's not possible yet to make a final determination. But off the cuff I'm saying loamy sand.

What we'll need (as David noted) is the measurements, which will give us the percentages of each type of soil. Although in this case, I'm already saying your percentage of sand is very high, it's always nice to know that you have some other particles to offset that.

I don't strictly-speaking need this for your Logan test, really. They'll report the CEC (cation exchange capacity), which will give me a good read of your soil composition when combined with your organic matter percentage.

Which bears explaining. CEC is the number of positively charged ions the soil can hold (it's more opaque than that, but this is what it boils down to). Each soil type has a differing CEC. Very, very approximately and off the cuff:

Sand: 1 to 8 or so, but it does vary.
Silt: 8 to 15.
Clay: 10 to 100.
Organic material: 50 to 500.

So yes, organic material can hold well over a hundred times the resources that sand can.

That's not necessarily an advantage.

Shortages are easy to correct in sand, but the amounts present are small enough that they need to be corrected often.

Shortages are a nightmare to correct in clay as they require large amounts of material. Once corrected, however, they tend to stay that way for extended periods due to the large amounts of material caught up electrostatically in the clay.

A happy medium is best. CECs in the 10-20 range are good at holding resources, but still fairly easy to change.

CEC is only part of the story. Soil reserves of material (often limestone or the like) can supply ions to the soil solution and the CEC sites. When that happens, we call it an LQC (Limestone Quarry Club) soil. Reducing the pH is usually next to impossible.

And that's only part of the story...but probably the most important part.

    Bookmark   July 21, 2014 at 1:43PM
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dchall_san_antonio(8 San Antonio)

My sand sinks immediately. Of course mine is beach sand, so that's part of it. Grab a hunk of that goo and squeeze the water out of it. Open you hand. Did it stay in the shape of your squeezed hand? Sand will usually collapse into a blob unless there is a lot of silt or salt holding it together.

    Bookmark   July 21, 2014 at 2:09PM
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Interesting stuff, guys. My confusion was that I had predetermined in my mind that I did not have sandy soil because the texture and look just didn't seem like sand. I'm still not convinced, I guess. But at the same time what I thought was silt in my soil wasn't taking 2 hours to settle. So how can silt settle out in only 2 minutes? I guess it can't if you are correct. There is very little of anything else in the sample. The clay hasn't finished settling out, but so far I'm looking at about 95% sand. I dunno, this just doesn't seem right.

Also, I used too much soap because some website said to use a teaspoonful to help break the particles apart into their smallest (actual) particle sizes, not just for surface tension. In my case it doesn't look like it matters.

    Bookmark   July 21, 2014 at 2:11PM
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dchall_san_antonio(8 San Antonio)

The Logan Lab test will lend some insight to this.

    Bookmark   July 21, 2014 at 2:19PM
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>>The Logan Lab test will lend some insight to this.


You can always repeat the test with fresh soil and either no soap or only a single drop of soap. It's faintly possible that the larger silt particles are settling too quickly in the very soapy water since the viscosity isn't what I'm normally used to for a test.

Hint: Almost everybody, including me, is wrong about what kind of soil they have. Contrary to popular wisdom, sandy soils can compact just like clay can (clay is just a little more likely to do it, and when it does it it tends to form sheets of material).

>>So how can silt settle out in only 2 minutes? I guess it can't if you are correct.

In water without soap, it can't. While a very few particles will settle into the sand toward the end of the 2 minute period, silt is simply too light to drop out.

Chemically, sand and silt are identical--they're ground silicon dioxide. Only the particle size differs, and we've set an arbitrary mark at 1/16 mm for that.

Right around 2 minutes, there's a very fine judgement call between sand and silt. Is it really small sand or really big silt? Who knows? It doesn't really matter, so the equally arbitrary 2 minute mark is just fine. At that point, you're either settling really tiny sand particles or really big silt particles.

    Bookmark   July 21, 2014 at 2:41PM
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Speak of the Devil! I just got my lab results. I'm going to post them in a separate thread.

    Bookmark   July 21, 2014 at 6:13PM
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