Chapter - 9 Soil

·      Soil is one of the most important natural resources. It supports the growth of plants by holding the roots firmly and supplying water and nutrients. It is the home for many organisms. Soil is essential for agriculture.

·      The relative amount of sand and clay depends upon the rock from which the particles were formed, that is the parent rock. The mixture of rock particles and humus is called the soil. Living organisms, such as bacteria, plant roots and earthworm are also important parts of any soil.

·      Different types of soils are found in different parts of India. In some parts there is clayey soil, in some parts there is loamy soil while in some other parts there is sandy soil.

 

FACTORS AFFECTING SOIL:

Soil is affected by wind, rainfall, temperature, light and humidity. These are some important climatic factors which affect the soil profile and bring changes in the soil structure.

FORMATION OF SOIL:

WEATHERING:

It is the process by which soil is formed by the breaking down of rocks by the action of wind, water and climate. The nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.

 

SOIL POLLUTANTS:

·      Polythene bags

·      plastics

·      waste products

·      chemicals

·      Pesticides.

Waste products and chemicals should be treated before they are released into the soil. The use of pesticides should be minimized.

 

SOIL PROFILE:

 

A vertical section through different layers of the soil is called the soil profile. Soil is composed of distinct layers. Each layer differs in feel (texture), color, depth and chemical composition. These layers are referred to as horizons.

 

HUMUS:

 

The rotting dead matter in the soil is called humus. The uppermost horizon is generally dark in color as it is rich in humus and minerals. The humus makes the soil fertile and provides nutrients to growing plants. This layer is generally soft, porous and can retain more water. It is called the topsoil or the A-horizon.

 

This provides shelter for many living organisms such as worms, rodents, moles and beetles. The roots of small plants are embedded entirely in the topsoil.

 

The next layer has a lesser amount of humus but more of minerals. This layer is generally harder and more compact and is called the B-horizon or the middle layer.

The third layer is the C-horizon, which is made up of small lumps of rocks with cracks and crevices.

 

Below this layer is the bedrock.

 

SOIL TYPES:

The soil is classified on the basis of the proportion of particles of various sizes.

 

SANDY SOIL:

 If soil contains greater proportion of big particles it is called sandy soil. Sandy soils tend to be light, well aerated and rather dry.

 

CLAYEY SOIL:

If the proportion of fine particles is relatively higher, then it is called clayey soil. Clay particles, being much smaller, pack tightly together, leaving little space for air. Unlike sandy soil, water can be held in the tiny gaps between the particles of clay. So clay soils have little air. But they are heavy as they hold more water than the sandy soils.

 

LOAMEY SOIL:

If the amount of large and fine particles is about the same, then the soil is called loamy. The best topsoil for growing plants is loam. Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the right water holding capacity for the growth of plants.

 

AERATED SOIL:

If the space between soil particles is filled with air, then the soil is well aerated.

 

PROPERTIES OF SOIL:

 

·      Rate of percolation of water

·      Moisture content

SOIL AND CROPS:

 The climatic factors, as well as the components of soil, determine the various types of vegetation and crops that might grow in any region. Clayey and loamy soils are both

suitable for growing cereals like wheat, and gram. Such soils are good at retaining water. For paddy, soils rich in clay and organic matter and having a good capacity to retain water are ideal. For lentils (masoor) and other pulses, loamy soils, which drain water easily, are required. For cotton, sandyloam or loam, which drain water easily. and can hold plenty of air, are more suitable. Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.