Soil: What on Earth is it?
Soil is the thin layer on the crust that is made of weathered rock, water, air, and decayed organic matter (humus). Humus has dead plants, leaves, roots and dead animals. This is great for plants to grow!
There are five properties of soil:
1) Texture: This is how the soil type feels.
2) Particle size: This is how large each particle of the soil type is.
. Diagram of soil’s particle sizes
3) Color: Color tells us about the nutrients in the soil. Soil can be red, brown, yellow, green, black, and even white. Darker soil means more humus/organic matter.
4) Pore space: This is the amount of spaces between soil particles. Water and air move through the pore spaces in soil.
5) Chemistry: This tells the nutrients in the soil. Nutrients must be able to dissolve in water. How well the nutrients dissolve in water depends on the water’s pH. This is the measure of acidity. If a soil is too acidic, plants may have a hard time growing.
Let’s explore three types of soil:
Sandy soil:
Sandy soil’s texture feels rough and gritty. Sand has the largest particles and a big pore space. Air and water can travel easily through the sand. Growing plants in sandy soil is not easy!
Here is an image of what a large pore space looks like! Think of all the water and air escaping!
Silt:
Silt has a smooth texture. Soil rich in silt has smaller particles than sand. It can hold in a good bit of water. That means it has a small pore space.
Clay:
The soil with the finest and smallest particles is clay. The particles are so small; you need a very powerful microscope to see them! Clay’s texture feels sticky to the touch.
Soils with a lot of clay have tiny pore spaces. This means that clay holds in a lot of water!
Here is an image of what small pore space looks like! Think of all the water and air getting trapped in there!
What can affect soil?
Climate can affect soil. Areas with warm and wet weather have rich organic soil. Desert regions with little rain have small amounts of humus which means many plants cannot survive there.
Location can also affect soil. Soil on steep mountain slopes can be washed away by water. A lot of the soil then ends up at the bottom in the valley.
Organisms affect soil. First, bacteria and fungi help to break down dead plants and animals into nutrients. These nutrients help plants to grow! Animals like earthworms, mice, and gophers make their homes in soil. When they make their homes in the soil, they create spaces in the soil. This helps to drain and absorb water. When animals die, they decompose and add nutrients to the soil.
Horizons/Layers: Soil is made in layers, which are called horizons. The layers of soil are made of different types of sediment and nutrients. A Horizon is dark topsoil and high in nutrients. B Horizon is subsoil, lighter in color, and lower in nutrients. C Horizon is weathered bedrock, lightest in color with lower nutrients.