Soil
· Soil is considered as one of the most important natural resources.
· Soil is mixture of rock particles and humus .
· It gives anchorage to the plants and supplies water and nutrients.
· Soil is the native (home) for many organisms.
· Soil is essential for agriculture which provides food, clothing and shelter for all.
Soil Profile
· Soil is composed of many different layers.
· Rotting dead matter in the soil is known as humus.
· Soil is formed by the process of weathering which involves breaking down of rocks by the action of wind, water and climate.
· The nature of soil depends upon the rocks from which it has formed and the type of vegetation that grows in it.
· Soil profile is a vertical section through different layers of the soil .
· Each layer differs in chemical composition ,feel (texture), colour and depth .
· These layers are known as horizons. Soil is fertile and provides nutrients to growing plants.
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A
A-horizon: A-horizon layer is generally soft, porous and can retain more water. It is known as topsoil or the A-horizon.
· The next layer is called the B-horizon or the middle layer,Which has a lesser amount of humus but more of minerals. This layer is generally harder and more compact .
· The C-horizon is the third layer of soil , that is made up of small lumps of rocks with cracks and crevices.
· Bedrock which is hard and difficult to dig with a spade. It is bottom layer of soil.
Soil types
· Weathering of rocks results production of small particles of various materials. which include include sand and clay.
· The proportion of sand and clay depends upon the rock from which the particles were formed, that is the parent rock.
· Living organisms( bacteria, plant roots and earthworm ) are also important parts of any soil.
· The soil is classified on the basis of the ratio of particles of various sizes.
· If soil containing greater proportion of big particles it is called sandy soil.
· If the ratio of fine particles is relatively higher, then it is called clayey soil.
· If the amount of large and fine particles is same, then the soil is called loamy.
· Thus, the soil can be divided in categories as sandy, clayey and loamy.
Sandy Soil
· The size of the particles in a soil has an affects on its properties.
· Sand particles are quite large.
· They cannot fit close together, so there are large spaces/gaps between them.
· These spaces/gaps are filled with air.
· Sand is well aerated due to spaces between the particles.
· Due to this water can drain quickly through the spaces between the sand particles.
· sandy soils tend to be light, well aerated and rather dry.
Clayey Soil
· Clay particles are much smaller, pack tightly together, leaving little space for air.
· It can be held water in the tiny gaps between the particles of clay.
· Clayey soils have less air.
· It are heavy as they hold more water than the sandy soils.
Loamy Soil
· It is the best topsoil for growing plants is loam.
· It is a mixture of sand, clay and another type of soil particle known as silt.
· The loamy soil also contains humus in it.
· It has the enough water holding capacity for the growth of plants.
Silt
· Silt occurs as a deposit in riverbeds.
· The size of the silt particles is between sand and clay.
Properties of Soil
Percolation rate of water in soil
· The property of absorption of water by soil is called percolation . Amount of water absorbed by soil is called as percolation.
· The amount of water absorbed by soil in a given interval of time is known ass percolation rate. And it’s formula is :-
For example, suppose that for a certain sample, it took 20 minutes for 200 mL to percolate.
Moisture in Soil
· Moisture is measured by the quantity of water present in the soil. Even though dry soil contains a small amount of moisture. Clayey soil retains the highest amount of moisture.
Absorption of water by Soil
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· How much Soil absorbed can be found by :-
Initial volume of water in the measuring cylinder = U mL
Final volume of water in the measuring cylinder = V mL
Volume of water absorbed by the soil = (U – V) mL
Weight of water absorbed by the soil = (U – V) g
(1 mL of water has weight equal to 1 g)
Soil and Crops
· Different types of soils are found in different region of India.
· In some regionss there is clayey soil, in some parts there is loamy soil while in some other parts there is sandy soil.
· Soil is influenced by wind, rainfall, temperature, light and humidity.
· The climatic factors and the components of soil, determine the different types of vegetation and crops that might grow in any region.
· Clayey as well as loamy soils are both suitable for growing cereals like wheat, and gram. This kind of soils are good at retaining water.
· For paddy crop, soils rich in clay and organic matter and having a good retaining capacity of water are ideal.
· loamy soils, which drain water easily, are good for lentils (masoor) and other pulses.
· Sandy or loam, which drain water easily and can hold plenty of air, are more suitable for cotton.
· Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.
