Soil Science: Formation, Types, Properties and Conservation
Soil is a three-phase natural body - mineral matter, organic matter, water and air - formed by the weathering of rock under climate, relief, organisms and time. The paper tests formation factors, the soil profile, soil types of India and Uttar Pradesh, physical and chemical properties, and conservation measures.
Formation and profile
- Physical weathering (temperature, frost, wind, water), chemical weathering (hydrolysis, oxidation, carbonation) and biological weathering by roots and microbes.
- Horizons: O (litter), A (topsoil, humus), B (subsoil, illuviation), C (weathered rock), R (bedrock).
- Five soil-forming factors: parent material, climate, relief, organisms and time.
Soil types
Alluvial soil dominates the Indo-Gangetic plain and UP: deep and fertile but low in nitrogen and humus. Black (regur) soil is clayey, moisture-retentive and cracks on drying. Red soil comes from granite, laterite from heavy leaching, desert soil from Rajasthan; saline-sodic patches in UP are called reh or usar.
Properties
Texture (sand, silt, clay), structure, porosity, water-holding capacity, pH and organic carbon. Most UP soils are neutral to alkaline (pH 7.5–8.5); sodic soils need gypsum, while acidic soils need lime.
Worked example
A sample has 40% sand, 40% silt and 20% clay. Sand plus silt is 80% and clay is below 27%, so the soil is a loam - good for wheat and sugarcane. If clay rose above 40%, it would be a clay loam with poor drainage; the remedy is organic matter and avoiding tillage when wet.
Traps that cost marks
- Claiming alluvial soil is rich in nitrogen; it is usually deficient.
- Treating reh as a crop rather than a salt-affected soil.
- Mixing laterite (leached, acidic) with red soil.
- Forgetting conservation practices: contour bunding, terracing, strip cropping, mulching, green manuring, check dams and afforestation.