Soil Types of India — Set 7

Correct Answer: B. Alluvial soil (Bangar)

Alluvial soil, particularly the older Bangar type, is naturally best suited for wheat cultivation in India. The Indo-Gangetic plains where Bangar alluvial soil predominates are India's major wheat-producing regions. The soil's good moisture-holding capacity, adequate mineral nutrients, and loamy texture provide ideal conditions for wheat growth. Punjab, Haryana, and western Uttar Pradesh, all on alluvial soil, are the leading wheat-producing states.

Correct Answer: C. Black soil, because it swells and cracks, churning the soil

Black soil is described as 'self-ploughing' because it swells when wet and contracts and cracks deeply when dry. These wide, deep cracks allow air and organic matter to enter the deeper soil layers, mimicking the effect of ploughing. This self-ploughing property is caused by the high content of montmorillonite clay minerals, which absorb and release water. This unique characteristic is one of the reasons Black soil requires less mechanical tillage than other soils.

Correct Answer: B. Calcareous (limestone) nodules or concretions in old alluvial soil

Kankar refers to calcareous (calcium carbonate or limestone) nodules and concretions found in the older Bangar alluvial soil. These hard lime nodules form through the accumulation and cementation of calcium carbonate at depth, where evaporation concentrates it. Kankar can restrict root growth and reduce soil permeability. The presence of Kankar is one reason why Bangar soil is less fertile than the younger Khadar alluvial soil.

Correct Answer: B. It removes the protective cover that anchors soil and intercepts rainfall, making soil vulnerable to erosion

Deforestation removes the protective vegetation cover that holds the soil in place with roots, intercepts rainfall to reduce its impact, and adds organic matter that improves soil structure. Without forest cover, raindrops hit the bare soil directly (causing splash erosion), and unimpeded water flow erodes the topsoil. Tree roots bind the soil and prevent it from being washed away. Deforestation is one of the primary causes of soil erosion in India, especially in hilly regions.

Correct Answer: B. Removing vegetation cover, compacting soil, and exposing it to erosion

Overgrazing causes soil degradation by removing the protective vegetation cover, which exposes the bare soil to splash and sheet erosion. The repeated trampling of animals also compacts the soil, reducing water infiltration and increasing runoff. Compacted soil has reduced pore space, limiting root growth and microbial activity. Overgrazing is a major cause of land degradation in India's arid and semi-arid regions.

Correct Answer: C. Granular

Granular soil structure consists of small, roughly spherical or rounded soil aggregates (peds). This type of structure is most favourable for agriculture because it provides good aeration, water movement, and root penetration. Granular structure is typically found in the A horizon of fertile soils with good organic matter content. Well-structured granular soils drain well but also retain enough moisture for plant growth.

Correct Answer: C. Flat, horizontal plate-like layers

Platy soil structure consists of flat, horizontal plate-like layers of soil. This structure is unfavourable for agriculture as the horizontal plates restrict water movement downward and root penetration. Platy structure is often found in the B horizon, especially where there is compaction. It can develop from the deposition of fine particles in water or from compaction by heavy machinery.

Correct Answer: C. Vertical column-like aggregates

Prismatic soil structure consists of vertical, column-like aggregates that are taller than they are wide. It is typically found in the B horizon, particularly in subsoils with high clay content. In sodic (sodium-rich) soils, prismatic structure may develop into columnar structure where the tops of the columns are rounded. Prismatic structure restricts horizontal water movement but allows some vertical drainage.

Correct Answer: C. Nitrogen; Alluvial and Black soil

Nitrogen is the most important nutrient for leaf and vegetative growth, and both alluvial soil and Black soil in India are generally deficient in it. Despite the high fertility of alluvial soil, it lacks sufficient organic nitrogen to meet crop demands. Black soil also lacks nitrogen and phosphorus even though it is rich in calcium, magnesium, and potassium. This is why nitrogen fertilizer application is essential for crop production across most Indian soils.

Correct Answer: B. Eluviation (Leaching)

Eluviation or leaching is the process by which soluble minerals, clay particles, and organic matter are washed out of the upper soil horizon (A horizon) by percolating rainwater. The materials removed by eluviation are carried down and deposited in the B horizon in a process called illuviation. Laterite soils are the most leached soils in India, where intense rainfall has removed silica and other nutrients, leaving behind iron and aluminium oxides. Leaching is a major cause of soil infertility in high-rainfall areas.