Conflicting soil test results

bcsteeveJuly 21, 2014

Pretty basic stuff... I'm just trying to determine the physical soil type I'm working with.

I assumed it was very sandy based on drainage. Drains like there's nothing there. Never any puddles. I empty the kid's pool and it is dry in under a minute. Sand, right? But I'm never one to assume... not when I'm spending money.

I'm wanting to switch from sprinkler's to sub-surface drip irrigation and the emitter and row spacing depends on the soil type (narrower for sandy, wider for clay, etc). So I want to confirm. In the drip line instructions, they detail the jar method (ie. put a cup of soil in a jar, fill with water, shake and let settle... measure the strata). The result of this test was... confusing. It was homogenous. I didn't get strata at all. If you looked really closely, MAYBE there was a tiny layer at the top which would indicate it was like 99% sand or silt and 1% silt or clay (with 2 layers instead of 3, you can't be certain what the layers are). So a bit inconclusive, but this seemed to confirm that its almost entirely sand.


Not quite satisfied, I watched a good video on the "feel" test. Take a lump of sand, add some water, squish it up... can you form a ball or not? If you can't, it is sand. But... I could! Quite easily! A very nice, compact, round ball. Wait a minute, that suggests clay! Then I did the ribbon test and I could make a 5cm+ ribbon which seemed to confirm I'm working with clay-clay, not sand. Not even loamy clay, but just... well, clay.

But if its clay, then why does it drain so fast?

What do I do next?

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The easiest way to determine the requisite dripper spacing is to put a full 2 liter or gallon container with a small hole out on the ground you are irrigating and observe the wetted volume after the container empties. After all, no matter what any other test shows, if you are not placing your drippers at the right spacing based on wetted volume, you are not getting the roots wet (or are way overwatering the intersecting volumes). From your description of your soil, my first guess is that there is not much lateral movement of water in your soil, so drippers will need to be placed closer together.

    Bookmark   July 21, 2014 at 7:33PM
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OK. Let's assume you're right and there isn't much lateral movement... can the soil be amended to correct for that? The goal here is to reduce water usage and I don't want to be in a situation where I'm having to over-water with drip vs over water with sprinklers :)

    Bookmark   July 21, 2014 at 9:14PM
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If the soil is very sandy and there is little lateral movement of water, then you would put the drippers closer together in your design, and run the system for less time when watering. If there is a lot of lateral movement, the drippers would be farther apart, so each would need to put out more water to achieve the same total effect, so you would water for a longer time. The net effect in either case should be so many gallons/sq,ft of bed--the same regardless of the dripper spacing.

    Bookmark   July 21, 2014 at 11:00PM
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ferroplasm Zone 7b

Post a picture of your ribbon.

    Bookmark   July 21, 2014 at 11:40PM
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jean001a(Portland OR 7b)

Mixing in lots of compost is the answer for both sand and clay.

    Bookmark   July 22, 2014 at 3:58AM
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The jar test shows the soil you have. If there is no strata, division of soil types, you have none. Most likely what you have is sand, and the spaces between the sand particles promote quick drainage. To slow that drainage that soil needs organic matter which will fill in the spaces between the soil particles and help retain moisture as well as nutrients. Once the soil has adequate amounts of organic matter in it then proper spacing of those emitters can be determined.

    Bookmark   July 22, 2014 at 6:34AM
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Where do you live?

Place emitters based on how fast water runs through the dirt.

I have no clue why you would be getting a 5cm ribbon AND fast-draining soil, unless you took soil from a different spot and hit a small nodule of clay.

To minimize water waste ... water short times, but more often. Use a moisture meter to make sure you are wetting the soil deeply wnopugh for the roots

Add organic material ... compost like crazy and add it.

MULCH! thick mulches.

    Bookmark   July 22, 2014 at 9:17AM
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ferroplasm Zone 7b

bcsteeve, post a few pictures of your soil. If you're in the US, map your location on the "Web Soil Survey" (google it) to get a very rough idea of the types of soil you may have.

    Bookmark   July 22, 2014 at 9:25AM
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Thanks for the posts all.

I'm in West Kelowna in British Columbia, Canada. Now, I know a lot of people read "Canada" and think "cold", but this region is actually considered "semi arid" and its more close in climate to California's Napa Valley than it is to most of Canada. It is hot (usually 90 to 95 degrees) and dry in the summer, and cold (down to about 5 degrees) and dry in the winter.

I took three samples from around the yard, split each sample into two and conducted both the jar and feel tests. I was shocked that I could form nice neat balls and ribbons because I was sure I had sand. But... maybe I did the tests wrong to start with. I read somewhere to "pulverize the sample" for the feel test so that's what I did... so did I just go ahead and make clay?

As for posting pictures... as luck would have it, we've just been on evacuation order for the last week and living out of a hotel room. I just got back and have no idea where we put the camera. I tried with my phone but its not even worth uploading. I'll try to get pictures soon.

Regardless, I think the first job is bringing in organic material... did I have it right? Should I be tilling to about 8"?

    Bookmark   July 22, 2014 at 12:16PM
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ferroplasm Zone 7b

Here's a link to a feel-test method for soil texture.

No, you can't make clay just by manipulating the soil with your hand. It's either there or it isn't. The texture won't change no matter how much you work it with your hand.

    Bookmark   July 22, 2014 at 12:43PM
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That is the video I followed, however I began with pulverized soil I don't recall where, exactly, but somewhere I read that it should be pulverized before testing. So that's what I did... mechanically, first with a hammer and then with a rolling pin. Is it possible that I smashed it enough to change the particle size? I doubt it, but it sure seems strange that it is behaving like his "sandy clay" (clay with a gritty texture) but I have what I would call "extreme drainage" and the jar test indicated a homogeneous sample (and it settles fast, indicating sand, not clay).

But rather than wondering if the pulverizing caused this... I did another feel test without pulverizing. This time it didn't make as nice and neat of a firm ball, but I was still able to form a ball. I couldn't get it to ribbon this time but I think perhaps I used too much water. I'll try again later.

And I repeated the jar test again, this time in a graduated beaker rather than a simple mason jar. After a couple of minutes, most of the particles settled to the bottom. It has now been about 4 hours and the water above is still murky but it looks like I'm probably going to get the same result with just a very tiny layer on top of an otherwise homogeneous sample. Now.. one thing I should mention is that I'm vigorously stirring the sample rather than shaking it (I didn't have anything with a lid handy). Perhaps that's ruining the test?

    Bookmark   July 22, 2014 at 1:49PM
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mad_gallica(zone 5 - eastern New York)

Just because you are Canadian doesn't mean you can't play games with soil surveys.

Here is a link that might be useful: BC soil surveys

    Bookmark   July 22, 2014 at 3:24PM
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Sure, interesting reads... but - forgive my ignorance - does it really pertain to anything? This isn't farmland. I'm not tilling a natural plot of land. This is a construct of man. They took the side of a mountain, raped it of its natural flora and fauna (and yes, I have since absorbed guilt over our decision to buy into this), and shaped it to their will using whatever the cheapest process available to them at the time was. In other words, surely whatever soils they were testing in 1984 before anyone dreamed of building houses on mountain out yonder, has next to nothing to do with what is in my backyard, right?

Soil here, in general, must be very fertile. We're the envy of much of the world for the quality and abundance of fruit bearing trees, grapes, and nut varietals. We have more species of apples than most people know exist. So I'm sure, as a whole, the soil in my area is perfectly wonderful. I just personally don't define what is in my backyard as "soil".

From earlier advice and my own reading, I'm pretty sure I have a handle now on what I need to do. I'm going to strip off a few inches (just so I'm not raising the finished grade) and replace with "GlenGrow" (a locally produced product from the city... plant based compost)... and then till it all so I'm not going to run into interfacing issues.

THEN, I'll evaluate the soil again and choose drip spacing appropriate to what I end up with. Re-dig (for trenches), lay pipe, backfill, compact, seed, etc.

    Bookmark   July 22, 2014 at 5:22PM
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nil13(z21 L.A., CA (Mt. Washington))

"Soil here, in general, must be very fertile."

That is a terrible assumption unless you are living on a farm in the middle of the agriculture region. The west coast is very geologically active and as such you will find a great variety of soil types.

    Bookmark   July 22, 2014 at 8:05PM
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That was exactly my point.

    Bookmark   July 22, 2014 at 8:40PM
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I wonder if it's sandy clay? That would have a rather sandy appearance but when wet it acts like clay. Just a thought.

You already know what sand looks like - everybody does. When it's dry, put some in your hand and smear it out with your thumb. You can feel and see the sand. Are there smaller particles (silt), or powdery stuff (clay) mixed in?

    Bookmark   July 23, 2014 at 11:10AM
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To me it looks, feels, and (most importantly) behaves like sand (at least in terms of drainage)... but I can definitely form a ball with it and it ribbons, which is a clear indication of clay. No, I don't detect any silt or clay by feel or appearance. And like I said before, the jar test settles to a nearly homogeneous sample of sand with a very tiny layer of either silt or clay. There is no 3rd layer to tell which it is, but I think its silt and the cloudy remains in the water (after > 24 hours) is clay.

So in my latest jar (graduated beaker) I have 42 mm of sand and 4 mm of probably silt and I doubt the clay layer, if I can ever even measure it, would come to a single mm.

That works out to 90% sand, 9% silt and 1% clay. Fully consistent with the behavior I see with drainage and what I've always thought I had. As I said in the beginning of this thread... I'm just confused because trying to confirm that with a feel test gives me an indication of the complete opposite.

It makes me wonder if there's some 4th factor... some mineral or something, that perhaps is heavy like sand (so it settles and drains) but binds the particles when wet. I have no idea really.

Again, I guess it really doesn't matter. It needs compost as a first step. Then I can start over.

    Bookmark   July 23, 2014 at 1:25PM
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Well, keep us posted. Are there any other gardeners in the area you can talk with? Or are you out in the middle of BC with no other civilization for miles? I know there are a lot of just miles and miles up there. ;-]

    Bookmark   July 24, 2014 at 10:38AM
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I'm not in the middle of nowhere, no. But I've found that I'm just as likely, or more likely, to get good advice from strangers online that I am from someone local that thinks they know what they're talking about.

I've had the worst advice from "professionals". An irrigation "specialist" at the garden center told me to increase my water pressure by using smaller pipes (if anyone thinks that is correct... we can explore that if you'd like). A "master gardener" told me to use a local product called OgoGrow in my veggy garden (OgoGrow is a compost from biosolids, which includes human excrement and, potentially, flushed medical waste and is really not safe to use for food growing). Most recently, I was discussing my soil with a landscape contractor and I mentioned "organic material" and he looked at me blankly and asked, "what's that". Sigh.

In an unregulated industry, I think the best we can do is to become self educated because its so hard to pick the good "professionals" from the bad.

    Bookmark   July 24, 2014 at 11:54AM
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Wow, that's rough! A landscape guy oughta know what organic matter is... :-o

    Bookmark   July 29, 2014 at 12:07PM
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To me it looks, feels, and (most importantly) behaves like sand (at least in terms of drainage)... but I can definitely form a ball with it and it ribbons, which is a clear indication of clay.

So ... for gardening, it's sand.

IGNORE THE SQUEEZE test if the drainage test shows fast drainage.

    Bookmark   July 29, 2014 at 12:30PM
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Well, that's fine in simple terms of drainage. But, as I mentioned above, I'm wanting to install sub-surface tubing. The spacing and specs of which depends on the soil type. Different types have varying degrees of capillary action of the soil, which determines the AREA of wetting per emitter. That's different than the retention capability of the soil, isn't it? Maybe its not. Maybe I'm over-thinking this.

    Bookmark   July 29, 2014 at 1:00PM
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The real test is just to do a test and see how wide the wet zone is after a certain amount of run time.

    Bookmark   July 30, 2014 at 11:09AM
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