Soil Composition Project

This is your chance to take a closer look at what makes up the soil in farmland as well as in your backyard.

Go outside and dig up some soil. Look at it. What do you see? Now, put some of that soil in a jar so that the jar is about 2/3 full. Then add water, put the lid on and shake. Now, let it sit for a little while.

diagram of layers of soil
Your jar may look something like this, but depending on where you get your soil, it will have different amounts of clay, silt, sand and gravel.
Image by Kirstin Yogg

strawDo you see the layers of clay, silt, sand and gravel?

Soil is made up of clay, silt , sand and gravel. When soil is heavy, it has a lot of clay in it. When soil is light it has a lot of silt or sand in it. The size of the particles that make up the soil is what determines what the soil will be like. Gravel are the largest particles in soil and clay are the smallest.

Eco Info
Most soil is really only half mineral. The rest is air, water and some organic animal and plant residue.

Here are the average sizes of these particles:

  • Gravel: 2 to 64 mm
  • Sand: 0.05 to 2 mm
  • Silt: 0.002 to 0.05 mm
  • Clay: Less than 0.002 mm
Eco Info
The best soil for crops has enough larger particles to be loose, and
enough smaller particles to retain water and dissolve mineral nutrients.

Why do you think it is so important for farmers to know what is in their soil?

Project courtesy of the Ohio State University Agricultural Extension Office Nature

home glossary