Soil Composition Analysis
Drainage & Jar Tests
Drainage & Jar Tests
Garden Tip
TB1468
TB1468
Technical Bulletin Series
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Soil Composition Analysis Drainage & Jar Tests |
Garden Tip TB1468 |
Technical Bulletin Series
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The Importance and characteristics of Soil!
All soil is generally comprised of particles that
fall into three groups. The smallest is clay,
then silt and the largest is sand. Clay compared
to sand is as small as a baseball is to the White
House. Clay tends to drain very slowly while sand
drains too fast. Good "soil" has a mixture of these
that will allow for adequate oxygen throughout,
but also retain water long enough to prevent plant
drought. This is why "silt" is so nice, as a medium
sized particle it has the best of both worlds. 40 %
sand, 40 % silt and 20% clay makes a nice loamy soil.
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Soil Drainage Tests
By performing a "Drain Test" on your soil you can arrive at a good estimate
of the type of soil composition that you have. Though Jar Tests can be more accurate,
many people prefer the simplicity of simply digging a hole - filling it with water
- letting it drain - filling it again, and time how long it takes to drain.
There are two methods for doing this:
Quick Drain (I recommend this)
and the 24 hour Drain. By clicking you will be directed to a page for instructions. |
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If you would like more accuracy and know the percent each of these particles comprise of your soil, try doing A Jar Test Instructions follow
Put enough dirt from your planting area in a quart size jar so that
the level of the jar is about 2/3 full. Then add water until nearly full.
Measuring begins in only 6 seconds. Use a Magic Marker (writes on glass)
to indicate settlement points.
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Measuring is based on TIME of SETTLING. After shaking,
quickly set the jar on a table so you can Mark settling points.
First measurement is at ONLY 6 seconds, so have the Marker ready to go.
The sand will settle (5 seconds) to the bottom. The silt (in 20 seconds) and clay will settle (in 5 minutes or more) on top of that. You will Mark then later Measure the depth point for each and calculate the percentage. In this example we have approximately 7% clay, 20% silt and 73% sand. This is a "sandy loam" and will exhibit excellent mostly rapid drainage. Not a common soil here. |
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At 6 seconds: Use a MARKER and MARK THIS POINT! This represents the amount of SAND in the sample. (in this example 5.5 inches) Now let settle for only 20 additional seconds |
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At 26 seconds from start: Again use the MARKER and "MARK THIS POINT!" this represents the amount of SILT + SAND in the sample. (in this example 7.0 inches) Now let settle for 5 minutes (minimum) from start! At 5 minutes: Again use the MARKER and "MARK THIS POINT!" this represents the amount TOTAL SEDIMENT in the sample. You may want to "re-shake" and measure again. First measure your original Marks. Make new marks, and compare with your first measurement as it is not always clear where the sediment lines actually are. |
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Organic matter (like compost) will mostly float. The percent of compost can't be measured with the jar test. It can however, be measured by a soil laboratory. A bit complicated and expensive. Unless you have added it, organic material is nearly non-existent in our desert soil. Now simply use the "Soil Triangle to find your Soil Type.
Soil characteristics directly affect proper watering and fertilization. In fact; without knowledge of the type of soil being watered IT IS NOT POSSIBLE to provide accurate recommendations for watering. Any watering schedule offered without knowledge of your soil type is really just guessing! |
