1. The Dirt on Dirt

2. Soil or Dirt?
Most people use the terms soil and dirt interchangeably. Soil is an important natural resource found all over the world. It is the uppermost layer of the crust. When soil gets into places it shouldn’t be, like on our shoes or in our homes, we refer to it as dirt.

3. What is soil?
Have you ever stopped to wonder what soil is made of? Soil is a mixture. Different soils have different components.
Soil can be made of:
crushed rock
sand
silt
clay
humus
minerals
air
water

4. Sand
Sand is one type of crushed rock that is commonly found in soil. Grains of sand are large enough that you can see them. They can be tan, pink, white or even black. Sand feels gritty because its particles are large. Even when wet, particles of sand do not stick together, so water flows through sand easily.
Why do you think sand can be so many different colors?

5. Silt
Silt particles are smaller than grains of sand. They are so small that a hand lens is often needed to see them. Silt is usually a shade of tan or black depending on what kind of rock it came from. Silt feels like powder when it is dry. When wet, it is slippery.

6. Clay
Clay particles are the finest, or smallest of all. They are difficult to see even with a hand lens. Clay is usually gray, reddish-brown or white. Clay drains very slowly, and it gets sticky and heavy when wet. Because of this, clay sticks to things that come in contact with it.

7. Humus
When living organisms like plants and animals die, their remains fall into the soil and began to decay, or break down. Decaying organic matter is known as humus, and is usually found in the uppermost layers of soil. Humus is dark brown or black in color and nutrient-rich. What organic materials can you identify in these soil samples?

8. Minerals
Soil also contains various minerals, such as iron, calcium, lime, sulphur and so on. Often, the minerals present in soil help determine its color. For example, soil that is very red often contains high levels of iron.

9. Air and Water
Air and water are extremely important components of soil. They fill in the spaces between the other components. They also allow plants to grow. A soil’s ability to support plant growth depends largely on how much water it can retain or hold onto.

10. Loam
Soils that are mixtures of sand, silt, clay, and humus, minerals and water are referred to as loam. Loamy soils are often dark brown and they are prized by farmers and gardeners for their ability to grow healthy, robust plants.

11. Observing the Properties of Soil
This week you’re going to do some experiments to determine the properties of soil. Remember, properties tell what something is like – how it looks, feels, smells, tastes, acts, and so on. You will also test soils’ ability to retain water and support plant growth. You will be observing several different soil samples and recording their properties.