Soil has some characteristics that form the basis for its classification into various types, and also the types of crops that are grown in it.
These properties are,
• Absorption of water
• Moisture in the soil
• Percolation rate of water in soil
Absorption of water: The capacity of the soil to hold water before it starts dripping is called its water absorption capacity. All types of soil do not absorb water in the same way.
This property of soil can be understood by performing an activity using plastic funnel with filter paper. A dry powdered soil is poured in the funnel. Now pour water drop by drop on the soil. Pour water evenly over the soil; continue pouring till the water starts dripping.
The percentage of water absorbed is calculated by using the following formula
U= Initial weight of water
V = Final weight of water
Moisture in the soil: Soil moisture is the water content present inside it as moisture and it is available for evaporation.
Moisture content of the soil is mainly depends on the type of soil. Soil moisture plays a major role in the plant growth because plants always depend on the moisture content available at roots. The moisture content in the soil can be observed by heating a little bit of soil in a boiling tube.
Types of soil: Soil is not similar everywhere. Soil is classified into various types based on the appearance and proportion of particles.
Percolation rate of water in soil: The phenomenon of absorption of water by soil is termed as percolation. The rate of absorption is different for different types of soils. The rate of absorption of a soil depends on its composition. A soil with more percolation rate can hold water for longer time. On the other hand a soil with poor percolation rate will hold water for shorter time. Percolation rate helps in selection of suitable soil for crop growth.
• Sandy soil
• Clay soil
• Loamy soil
Sandy soil: Sandy soil is made of greater proportion of big particles like sand. They cannot fit closely together. So, there are large spaces between them. These places are filled with air. Therefore, in this type of soil, water absorption is very high as the water passes quickly through these spaces. These soils are light, well aerated and dry.
Clayey soil: Clayey soil is made of a relatively higher proportion of fine particles. Unlike sandy soils, these soils have very less space between particles. Because the particles are smaller in size, water can be trapped in the tiny gaps between them. Clay soils are heavy and hold more water.
Loamy soil: Loamy soil is a mixture of sand, soil and silt. Silt particles are present between sand and soil particles. It also contains humus, and is, therefore, considered the best for the growth of plants. The percolation rate is between that of sandy soil and clay soil.
Soil and crops: Climatic factors as well as the components of the soil determine the types of vegetation and crops that grow in a particular area.
• Cereals like wheat and gram are grown in clay and loamy soils, because these soils have better water retention capacity.
• Soils rich in clay and organic matter with good water retention capacity are ideal for paddy.
• Loamy soils, which drain water easily, are suitable for lentils and other pulses.
• For cotton, loamy or sandy soils are more suitable, because of their water draining and air logging capacity.
• Clay soils are rich in humus and fertile. These soils are very good for wheat.
Activities & Simulations
Nationalzoo.si.edu has developed an interactive simulation. The simulation goes in interesting manner in explaining the properties of soil using both physcial and chemical tests.
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Glencoe.com has developed an interactive simulation regarding the properties of soil. This simulation is based on testing of different soils like sand, silt and clay. The test is based on water absorption capacity of these soils.
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