Soil jar test

efeuerOctober 13, 2012

Can you help me interpret the results of this soil jar test? I also sent a sample off to the state lab, but the results won't be back for a little while. I'm hoping to establish a new lawn here next year, ideally with the "no mow" seed from Prairie Nursery. It is mainly sheep fescue, red fescue, and creeping red fescue. The area is is about half part shade and half full sun.

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dchall_san_antonio(8 San Antonio)

You really need several pictures to tell what you have. You need one picture with a ruler next to it before you put any water in. Then you put the water in, shake it, set it down and let it sit for two minutes. Take another picture with the ruler at 2 minutes. The sand and rubble settles first, so the height of the settled sand divided by the height on the dry picture gives you the percentage of sand. Then take another picture after 2 hours. The silt settles on top of the sand. Measure the difference between the top of the sand and the top of the silt and divide that difference by the total. That will give you the percent of silt. The rest is clay. You can let it go for 2 full days to see what settles.

This jar test looks like the sand and silt have settled. Using that assumption to make an example, it goes like this.

Using a ruler up against my screen it looks like you have 2.5 inches of sand and 0.75 inch of silt. Assuming you started with 3.5 inches of soil then the percentages would be as follows

2.5 / 3.5 = 71% sand

0.75 / 3.5 = 21% silt

The rest is clay = 100% - 71% - 21% = 8% clay.

That is if you started with 3.5 inches of soil as measured on my screen.

Then you can use this triangle to figure out what to call your soil.

Move left along the bottom until you get to 71% sand. Then move up diagonally to the left until you get to 21% silt. That's your soil...right between sandy loam and loamy sand.

I suspect you started with slightly less soil than that but this puts you in the ballpark. If you thought you had clay soil, you don't. If you thought you have clay soil, you very likely have high magnesium salts in your soil which does not show up on a jar test and probably will not show up in your university soil test. It would; however, show up in the $20 test from Logan Labs.

    Bookmark   October 13, 2012 at 3:07PM
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Thanks for the details on how to run the test. I will try again following your advice.

I did a soil test from the Rutgers lab on my front yard a few years ago. They described the soil as sandy loam, which is not too different from what you describe.

They said the Mg was above optimum (365) and so was Ca (4030) and K (355.) What is the significance of that?

    Bookmark   October 13, 2012 at 3:52PM
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dchall_san_antonio(8 San Antonio)

There is another forum, not GardenWeb, where the members specialize in interpreting soil tests. Google the following 'logan labs andy morpheus soil test' and you'll find them.

    Bookmark   October 13, 2012 at 5:12PM
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I see probably a lot of sand, a small amount of clay, and almost no organic matter in that sample. The simple soil tests I have told people to do for years state you need about 4 inches of soil for this test.
1) Structure. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. A good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drains� too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

    Bookmark   October 14, 2012 at 6:57AM
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