Pedology: Study of Soil and Horizons

Pedology: The Study of Soil

• Pedology is the study of soil.
• Soil is formed from the weathering of rocks, organic matter, and the remains of living organisms.
• Soil formation is a long and complex process.

Soil Horizons

• Soil horizons are layers of soil.
• The O horizon is the uppermost layer, composed primarily of organic matter.
• The O horizon is also known as the humus layer.
• The A horizon is the layer below the O horizon, and it is rich in organic matter and minerals.
• The B horizon is the layer below the A horizon, and it is characterized by the accumulation of clay and other minerals leached from the A horizon.
• The C horizon is the layer below the B horizon, and it consists of weathered parent rock material.
• The R horizon is the bedrock.

Soil Profile

• A soil profile is a vertical section of soil that shows all the horizons.
• The soil profile is used to classify soils.

Types of Soil in India

• The Indian Council for Agricultural Research (ICAR) has classified soils in India into eight major categories.
• These include:
  • Alluvial soils
  • Red soils
  • Black soils
  • Laterite soils
  • Mountain soils
  • Desert soils
  • Acidic soils
  • Alkaline soils

Alluvial Soils

• Alluvial soils are the most widespread soils in India.
• They are formed by the deposition of sediments by rivers.
• Alluvial soils are generally fertile and suitable for a variety of crops, including wheat, rice, sugarcane, and cotton.

Red Soils

• Red soils are formed by the weathering of igneous and metamorphic rocks.
• Red soils are known for their red color due to the presence of iron oxide.
• They are generally less fertile than alluvial soils but can be made suitable for agriculture with proper irrigation and fertilization.

Black Soils

• Black soils are formed from the weathering of basalt rock.
• They are known for their black color due to the presence of iron and magnesium compounds.
• Black soils are highly fertile and are known as "regur soils."
• They are rich in calcium, magnesium, and iron.
• They have good water-holding capacity and are ideal for cotton cultivation.

Laterite Soils

• Laterite soils are formed in areas of high rainfall and temperature.
• They are characterized by their reddish-brown color due to the presence of iron oxides.
• They are generally infertile as they lack nutrients due to leaching. However, they are utilized for the production of tea, coffee, and spices.

Mountain Soils

• Mountain soils are found in the mountainous regions of India.
• They are influenced by the altitude, climate, and vegetation of the region. These soils are generally infertile.

Desert Soils

• Desert soils are found in the arid and semi-arid regions of India.
• They are characterized by their low organic matter content, high salt content, and poor water retention.
• They are suitable for the cultivation of drought-resistant crops such as barley and millet.

Acidic Soils

• Acidic soils occur in regions where there is high rainfall and leaching of nutrients. This leads to an increase in the concentration of hydrogen ions and reduction in pH. These soils are not suitable for most crops.

Alkaline Soils

• Alkaline soils have a high pH due to a high concentration of calcium and magnesium. These are found in regions where there is limited rainfall, resulting in the accumulation of salts.

Soil Fertility

• Soil fertility is the ability of the soil to support plant growth.
• Soil fertility depends on the amount of nutrients, organic matter, and water-holding capacity of the soil.
• The three major nutrients required for plant growth are nitrogen, phosphorus, and potassium.
• These nutrients are often depleted from soils due to intensive agriculture.
• Farmers often use fertilizers to replenish these nutrients.

Importance of Soil Conservation

• Soil conservation is important to protect soil fertility and prevent soil degradation.
• Soil degradation is the process of deterioration of the soil.
• Soil degradation can be caused by various factors including erosion, salinization, and compaction.
• Soil conservation practices include crop rotation, cover cropping, contour farming, and no-till farming.