Apr 20, 20232 min read

Testing Clay Content in Subsoil for Rammed Earth

How to Conduct a Jar Test for Optimal Plant Growth and Rammed Earth

Clay is a soil type that is formed by the weathering of rock over time. It is a crucial component of healthy soil, and the amount of clay in the subsoil can significantly impact plant growth and other applications like building rammed earth structures. In this article, we'll explore the levels of clay content in the subsoil and how to test for it using a jar.

Clay content is typically expressed as a percentage by weight of the soil sample. The level of clay content in the subsoil can vary greatly from one location to another. So, before starting any project that requires a particular clay content, it is important to test the soil for its clay content. One common method to do this is by using a jar test.

To conduct a jar test, you'll need a clear jar with a lid, subsoil samples, water, and a ruler. Begin by collecting a sample of subsoil from the desired location. It's recommended to take samples from different spots to get a more accurate representation of the subsoil's clay content. Next, remove any large stones, twigs, and roots from the soil sample.

Fill the jar with approximately one-third of the subsoil sample, then add water until the jar is almost full. Tighten the lid on the jar and shake it vigorously for several minutes until the soil is completely suspended in the water. Allow the jar to sit undisturbed for at least 24 hours, allowing the soil to settle in layers.

After 24 hours, you'll see three distinct layers. The bottom layer will be sand, the middle layer will be silt, and the top layer will be clay. Measure the height of the clay layer with a ruler and calculate the percentage of clay in the subsoil sample.

Generally, soil with 7% or less clay content is considered sandy, while soil with 30% or more clay content is considered heavy clay. Soil with clay content between these levels is considered loamy.

In conclusion, the clay content in subsoil is an essential factor in soil health, and it's important to test the soil before starting any project that requires a specific clay content. Conducting a jar test is a simple and effective way to determine the clay content in the subsoil. By doing so, you'll be able to make more informed decisions about what plants to grow or how to construct rammed earth structures.