Soil Formation & Properties – UGC NET Paper 1 (People, Development and Environment)

A set of practice flashcards covering definitions, factors, processes, horizons, and key physical & chemical properties involved in soil formation and classification.

What is the basic definition of soil?

The topmost layer of Earth’s crust, made of rock debris and organic matter, acting as a medium for plant growth and various ecological functions.

Name any three ecological or engineering functions performed by soil.

Acts as a medium for vegetation growth, filters and cleans water, provides habitat for soil organisms, modifies the atmosphere, supports construction foundations, and preserves artefacts.

Which mnemonic summarizes the five classic factors of soil formation?

CLORPT – Climate, Organisms (biota), Relief (topography), Parent material, and Time.

How does relief influence soil formation?

By affecting temperature, precipitation, weathering type, and erosion rates based on altitude and slope.

Give two soil characteristics inherited directly from parent material.

Mineral composition and colour (e.g., black soil from basaltic lava).

Why is climate considered a dominant factor in soil formation over long periods?

Heat and precipitation drive physical and chemical weathering and influence vegetation, which in turn shapes soil profiles.

How do legumes improve soil fertility?

Their root-associated nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia, enriching soil nitrogen content.

Compare young and old soils in terms of thickness and parent-material influence.

Young soils are thinner and more like their parent rock; old soils are thicker and show stronger modification by organic matter and weathering.

What is pedogenesis?

The overall process of soil formation.

Define weathering in the context of soil formation.

The breakdown of parent rock by wind, water, temperature changes, and other denudation agents.

What is leaching and under what climatic conditions is it most common?

Downward movement of water (and dissolved ions) due to gravity; prevalent in hot, humid, water-excess areas.

Differentiate between leaching and capillary action in soils.

Leaching moves water downward with gravity; capillary action moves water upward against gravity, common in dry areas.

Which soil horizon is richest in organic matter and crucial for plant growth?

A horizon (topsoil).

What distinguishes the O1 and O2 sublayers within the O horizon?

O1 contains fresh litter/undecomposed material; O2 contains partially decomposed organic matter transported from elsewhere.

Why is the E horizon typically light in colour?

Because minerals and organic content have been leached out, leaving primarily silica-rich material.

Which horizon is known as the illuvial or accumulation layer and why?

B horizon; it accumulates minerals and organic matter washed down from A and E horizons, often rich in iron oxides and clay.

List the particle-size ranges for sand, silt, and clay.

Sand: 2.0–0.05 mm; Silt: 0.05–0.002 mm; Clay: <0.002 mm.

How does particle size relate to soil’s moisture-holding capacity?

Smaller particles (clay) absorb and hold more moisture than larger particles (sand).

Which soil texture is generally best for plant growth and why?

Loam, because it has a balanced mix of sand, silt, and clay, giving moderate permeability and good nutrient retention.

How can soil colour indicate reducing conditions in humid areas?

Reduced iron gives a bluish tint to the soil.

What pH range defines acidic versus basic soils?

pH < 7 is acidic; pH > 7 is basic.

Name three cations that influence soil cation-exchange capacity and fertility.

Calcium (Ca²⁺), Magnesium (Mg²⁺), and Potassium (K⁺).