What is soil? What are the kinds of soil? The layers of soil, information about soil.
What is the most valuable and useful material on earth? Perhaps you think it is gold or silver, but actually it is soil. Living things must have soil for their existence. Plants get water and mineral salts directly from the soil in which they grow. People and other animals eat plants, so soil is of vital importance to us all.
In time rock surfaces get broken up by rain, wind, snow and frost into smaIl pieces. This process is called weathering.
The upper layer of soil in which plants grow is called top soil. This layer contains organic matter, roots of plants, organisms such as worms, insects and bacteria that break down organic matter (decomposers) into humus. The decayed organic matter is called humus. it gives soil its dark color and it enriches the soil. Humus is important to the growth of healthy plants because it can absorb and hold the water needed by plants. Top soil is formed very slowly. It takes between 500 and 1000 years to produce 2.5 cm of top soil. The layer of soil under the top soil is called subsoil. Subsoil contains little humus. It contains larger rock partides and less organism. There are some roots in this layer. Plants do not grow well in subsoil.
There are three different kinds of soil; sand, dayand humus.
- Sandy soil: This allows water to pass through easily, so most plants do not grow in sandy soils. The cactus can grow in sandy soil because it needs a little water. Desert soils are sandy.
- Clay soil: This contains very small rock partides which stick together. This makes it difficult for water and air to enter the soil. Clay soils are not good for growing of most crops.
- Humus: This is formed from dead bodies of plants and animals. When plants die, their roots, leaves and stems decay and mix with the soil. Humus is fertile soil in which plants grow easily.