The Soil

The science of the study of the soil is called Pedology. Soil formation and development of soil is called Pedogenesis. Soil is an important material resource that acts as an interface, connecting climate with vegetation. Soil determines human well-being & food security as it directly controls agricultural production and productivity.

Processes & Factors Controlling Soil Formation

Climate

It is the most important factor involved in the formation of soil. The factors controlled by climate are is rate of weathering of rocks which determines the faster whereas hard rocks weather slowly. For example, Quartzite – Hard rock is weathered slowly to form Red Soil which is thin, devoid of nutrients but rich in Iron Oxide. The red soil is thin & shallow, incapable of sustaining agriculture. Their comparison to Basalt is as under

Slope

Slope controls the balance between the formation and erosion of soil. On steep slopes, the soil is thin-as the process of erosion is rapid. On a gentle and low slope, erosion is extremely slow and hence the soil is thick.

Time

The maturity of the soil is determined by time. In a mature soil, the soil profile is well developed. For the maturity of the soil, there must be a stable atmosphere and land conditions for a longer duration of time. For example, in India’s Great Plains we have two types of alluvium soil viz:

Soil Horizon & Soil Profile

A soil horizon is a layer of soil with a unique formation. Soil profile on the other land is a vertical arrangement of soil horizons. A typical soil profile is as under –

1.3. Bacterial Activity: Tropical and temperate humid climate favor bacterial activity which is why it is faster here than in cold & dry areas.

1.4. Translocation: Transport & transfer of materials across soil horizons (Soil layers) is called translocation. This movement could be downward or upward.

 

2. Parent Rock: These are weathered to form finer particles which are the basis of soil. The nature of the parent rock determines the following. The thickness of soil, Soil texture, Soil Color, and Soil minerals.

Soil Properties

1. The thickness of Soil: The hardness & softness of parent rocks determines the thickness of soil.

2. Texture: It indicates the composition of soil with respect to the composition of soil particles. It indicates the absorption of moisture in the soil and its retention. Clay & silt rich soil have high absorption and retention capacity of water. eg: Black soil which is an organic soil Sandy soil are poor in terms of absorption and retention capacity of water since pore size is large. E.g: Red soil in the plateau of Karnataka & Andhra Pradesh which needs additional fertilizers and manure for agriculture.
3. Structure Of Soil: Structure is the aggregation of soil particles and that determines the ease in tilling of the soil. For instance, Loam Soil which has a crumb structure is considered the best for tilling or plow. It has an equal proportion of Clay, Silt & Sand. In stark opposition is sand which has a single grain structure due to which there is no cohesiveness in sandy soil, making it very difficult to till/plow. Again manuring is required.
4. Color of Soil: The color of the soil is determined by the mineral content of soil and the presence of humus. Iron oxide – Red; Mg/Al – Black; Humus – Dark in Color / Black.
5. Ph Value of Soil: It determines the acidic/basic nature of the soil. PH < 7 is acidic soil; PH > 7 is basic soil. Soil with PH = 6.5 is considered Best for Agriculture.

SOIL DEGRADATION

Adverse changes in soil with a decline in fertility and thickness are described as soil degradation. Soil degradation is an outcome of two factors, viz.

Natural Hazards

Stages of Fluvial erosion of soil

• Splash Erosion
• Sheet Erosion
• Rill Erosion
• Gully Erosion

Splash Erosion: Impact of the momentum of raindrops as they strike the soil. Soil breaks down and gets fragmented. Forest & Grassland cover is recommended to reduce this.

Sheet Erosion: Flow of water along a slope where the fertile top layer is removed. Forest & Grassland cover is recommended to reduce erosion.

Rill Erosion: Starts with the formation of rivulets.  With this soil erosion is further increased since the movement of soil in the water is going to be in a suspended state. This is called Rill Erosion.

Gully Erosion: It is the worst form of soil erosion. Here deep, steep and narrow trenches are developed by Rivulets and streams. Such en erosion results in the formation of landforms known as Ravines or Badlands which makes the area infertile for agriculture. E.g: Chambal River (M.P). The best way to prevent this is by plugging of rivulets.

Wind Erosion

Wind erosion is dominant in Semi-Dry & Dry regions. Deflation is the main process of wind erosion in which wind takes – away from the upper layer of the soil. Aforestation i.e., increasing forest cover and grassland cover is the recommended procedure to prevent this. Mulching is another technique (used in Rajasthan) where crop-residue is used to cover the soil so that the soil retains its moisture. Strip Farming is another technique wherein crops are grown in rows and columns so as to break the effect of wind.

Tsunami

These are seismic sea waves flooding the coast as there is a massive and sudden rise in the sea level resulting in

1. Flooding
2. Salt deposition upon the retreat of seawater which makes the soil infertile.

Landslides

This can be seen in the mountains where there is a rapid downward movement of rocks and soil. It is responsible for large scale removal of fertile topsoil.

Avalanches

This can be seen in mountains where there is a rapid downward movement of rocks, snow, and soil. It is responsible for large scale removal of fertile topsoil.

Human Interferences Responsible For Soil Degradation

1. Deforestation
2. Degradation of grasslands
3. Monoculture: extensive growth of a given crop multiple times in a given year.
4. Overuse of land & water resources.
5. Excessive use of chemical fertilizers, pesticides & insecticides
6. Leakage of water & water logging seen in areas with canals where leakage results in increasing the alkalinity (CO₃^{2 –} ions) and salinity (Cl^– ions) of the soil. Eg: Haryana & Punjab.

Soil Conservation

Soil conservation needs a comprehensive and integrated approach. Some techniques are:

1. Contour Ploughing: Ploughing at Right Angles to the slope is called contour plowing.
2. Terrace Farming: Useful in mountain terrain. It is also known as Step Farming.
3. Mulching: Covering the soil with CROP RESIDUE.
4. Strip Farming: Growing crops in rows and columns.