Soil Types: The 'Self-Mulching Soil' Explained

The soil commonly known as 'self-mulching soil' is Black soil.

Reasoning for Self-Mulching Property

Black soils are rich in clay, specifically montmorillonite. This clay content gives them unique properties:

• Swelling and Shrinking: When black soil gets wet, it swells significantly due to the clay absorbing water.
• Cracking: As the soil dries out, it shrinks, forming deep vertical cracks.
• Self-Mulching Action: This continuous cycle of swelling when wet and shrinking/cracking when dry churns the soil naturally. It brings deeper soil particles to the surface and buries surface material, similar to the effect of artificial mulching. This process helps conserve moisture and improve soil aeration without external intervention.

Summary of Options

The key characteristic of self-mulching defines the soil type:

• Grey soil: Generally lighter, less clay.
• Red soil: Rich in iron oxides, often less fertile.
• Brown soil: Variable composition, typically good drainage.
• Black soil: High clay content, exhibits swelling/shrinking, leading to the self-mulching characteristic.

Therefore, black soil is the correct answer.