Some plants grow well, some are dry, some seem really healthy and fresh. Why is this so? Well, this is because of the type of soil used and its properties. Let us know more about the properties of soil.
Properties of Soil
The upper layer of earth in which plants grow is called soil. It is black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles. The soil has the following special properties:
The texture of the soil depends upon the relative amount of these particles. Clay has the smallest sized particles. Because of very small size, the clay is felt smooth. Silt particles are larger than the clay particles. There size range from0.002 to 0.02mm in diameter. So silt does not feel smooth. Sand particles are largest sized particles of soil. Their diameter is more than0.02mm
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2. Absorption of water
Water holding capacity in different types of soils is different. Soil absorbs water because it is porous. Sandy soil holds less water than clay soil and loamy soil. Clay soil holds more water than sandy soil. Sand absorbs less water than clay. Some plants require more water to grow; they grow well in clay soil and loam soil, since sand hold less water, so less vegetation is found in sandy soil.
- Take three funnels and put some cotton wool in the mouth of each.
- Put equal quantities of sandy, clayey and loamy soils in the funnels
- Keep them in three bottles.
- Pour equal quantities of water over them.
- Observe quantity of water after some time?
Observation: Which bottle contains minimum water?
Texture decides the water holding capacity of the soil. The soil has some amount of water inside it as a moisture. Water is usually present as a thin film around the soil particles. It is absorbed by the roots of the plants. The capacity of a soil to hold water is important for the growth of various crops. Even a dry soil has some water in it.
- Collect some soil and put it in a container.
- Cover the container with a lid and heat it.
- Remove the lid after 5 min.
Observation: We will see that there are small droplets of water on the inner surface of the containers and lid. Where do these droplets come from?
Soils are of different colours. They are red white and black. The red colour of the soil is due to the presence of iron oxide. The black colour soil is rich in minerals and humus. It is good for the growth of wheat and jowar
5. Soil pH
Soil can be acid, alkaline or neutral. Some plants grow in acidic soil (pH below 7) such as potatoes and kumara. Carrots and lettuces prefer soil with neutral pH (7.0). Soil become more acidic over time as minerals are leached away.
6. Percolation Rate
When we sprinkle water on the ground, it is soon absorbed by the soil. This is because water percolates through the soil. The process in which water passes down slowly through the sol is called percolation of water. But water does not percolate at the same rate in all types of soils.
Sandy soil allows maximum percolation of water and clay soil allows minimum percolation of water. Rainwater percolates through the soil and collects above the bedrock. This level of groundwater is called water table. Sandy soil is quite loose, so the percolation rate of water is highest in sandy soil but lowest in the clay soil because it is very compact.
Paddy (rice crops)is planted in standing water in the fields. Hence, the soil with a low percolation rate of water would be the most suitable for growing paddy because it will allow the water to remain in the fields for a much longer time.
7. Soil contains air
Air is present in the space between the soil particles. This air provides the oxygen required for respiration by roots of plants and other organisms. Sand particles are quite large. Sand particles cannot fit closely together, so there is large space between sand particles.
The large space between sand particles is filled with air. Due to this, sandy soil provides much more air to the plant root. But clay particles pack tightly together leaving little space for air. So, clayey soil provides much less air to the plant root which grows in it.
- Fill half a jar with dry garden soil and put it down.
- Gently pour water on the soil until the jug is full.
Observation: We will observe that the water sinks in the soil. The water pushes out the air in spaces. The air comes up in bubbles which burst on the water surface. Therefore, we can say that soil contains air.
Question For You
Q. What is Percolation property of soil?
Ans: When we sprinkle water on the ground, it is soon absorbed by the soil. This is because water percolates through the soil. The process in which water passes down slowly through the sol is called percolation of water. But water does not percolate at the same rate in all types of soils. Sandy soil allows maximum percolation of water and clay soil allows minimum percolation of water.