Soil Composition Test How-To

The weather warmed up enough that our soil thawed out, so we thought it would be fun to take a break from our lunar botany experiment do a quick demonstration of a soil composition test. You should do one too, it is easy and doesn't require any special tools! We have a garden bed that I haven't gotten around to amending yet and gets a lot of south-facing sun that has baked it for the past summer, so it is a good candidate to see what the soil is made of.

When we talk about "soil composition", it generally means the percent of sand, silt, and clay (though it can become much more specific than that!) Using these ratios, we can then determine the name of our soil type (for example, clay loam, sandy clay, etc.) and that helps to know how you can amend the soil, how it is going to retain water or nutrients, and what plants would grow well there.

Here’s what you’ll need:

* ~2 cups of the soil you want to test (enough to fill about half of your jar).
* A clear jar with a lid, even and straight sides/bottom, and no label or anything to block your view inside.
* Water (tap water is fine for this!)
* A funnel
* 1tsp dish soap
* 1/2tsp of salt

How to:

1. Clear away any debris from the top of the soil you want to test. Collect your soil from ~6" deep, and a few spots (to make sure it is representative of the whole soil bed rather than just one spot).
2. Pick out and big chunks (sticks, leaves, rocks) and put the soil in your jar. Make sure there's going to be about half the jar filled. The soil is going to settle so use more rather than less. Also, exact measurements don't matter much for this kind of test.
3. Fill the jar with water until it's about 1" from the top. The important thing is that there is enough air to shake and mix the mixture up.
4. Shake it for about a minute, make sure there are no lumps and everything is mixed up.
5. Loosen the lid on the jar as it can ferment and build pressure, possibly breaking your jar!
6. Let the mixture sit overnight or until clear, distinct layers form on the bottom.
7. Measure the overall height of the settled material at the bottom of the jar. Then, measure the height of each individual layer that has formed. Sand is as the bottom and looks fluffy with specks of rocks and sand. Silt is more solid looking and rests above the sand. Clay is usually very light and has chunks of organic material in it at the top.
8. Calculate what percentage each layer represents of the whole settled dirt on the bottom of the jar. You can use https://percentagecalculator.net/ for this (for example, sand was 11mm out of 37mm, so we would put "(11) is what percent of (37)?"
9. Use these percentages and a soil composition triangle to determine where your soil is on this chart: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/?cid=nrcs142p2_054167
10. Soil disposal: Though this soil has some soap and salt in it, it's very dilute. You can spread this around your garden and water it in.