The Jar test helps to establish the proportion of clay, silt and sand in your soil.
It also visualizes an approximate % proportion of OM (Organic Matter) present in your soil (=floating material).
This can give an overview on the % Carbon content of this soil, namely, how alive and healthy it is.
The more carbon in the ground, the less in the atmosphere!
Take half a jar of soil.
Break up all lumps if necessary.
Remove any large stones (>2mm) or large organic matter (sticks, roots, etc.). Record the approximate percentage of stones in the sample as: less than 5%, 5-20%, or more than 20%.
Using your fingers, pack the soil down as much as possible to reduce pore space and mark the level of soil on the side of the jar with a pen.
Stir in water until ¾ full, then shake well for 3 minutes or until the sample is fully suspended in the water.
Leave for 10 seconds then mark on the side of the jar the top level of settled material —> this is the volume of sand.
Leave for another 10 minutes and mark the top level of newly settled material —> this is the volume of silt (grains are visible). Also mark the bottom and top level of the floating material —> this is the volume of organic matter.
Leave until all particles have settled (this can take over 24 hours) and mark the final top level of settled material —> this is the volume of clay (no structure visible).
Using a ruler, measure the lengths between each marking from the bottom of the jar to the top (excluding the length between the top of the settled material and bottom of the floating organic matter, which is the water volume that we can ignore). From these numbers you can calculate the relative proportion of each component: sand (bottom level), silt (second from bottom), clay (third from bottom), and organic material (floating on top)
Determine the percentage of each component. As an example: You record 5 cm sand, 1 cm silt, 0.5 cm clay, and 0.5 cm organic matter. The total is 5 + 1 + 0.5 + 0.5 = 7. The percent sand is 5/7 x 100 = 71%; The percent silt is 1/7 x 100 = 14%; The percent clay is 0.5/7 x 100 = 7%; The percent organic matter is 0.5/7 x 100 = 7%. Since we rounded the numbers the percentages only add up to 71 + 14 + 7 + 7 = 99%, but that's okay!
<aside> 💡 The table below gives you an indication of soil types: Your soil might fall between these categories!