Soils and Soil Conservation: notes

Soil

• Formation: weathering of parent rock plus humus from dead plants and animals, over a long time.
• Profile: topsoil (dark, rich in humus), subsoil, weathered rock, bedrock.
• Texture: sand (loose, drains fast, poor in nutrients), clay (sticky, holds water), loam (a good mix, best for crops).

Erosion

• Causes: overgrazing, ploughing up and down slopes, removing trees, heavy rain on bare soil.
• Effects: loss of fertile topsoil, gullies, silted dams and rivers, lower yields.

Conservation

• Contour ridges: ridges along the slope's level lines slow run off.
• Terracing: steps cut into a hillside.
• Mulching: a cover of grass or crop residue protects the soil.
• Crop rotation: changing crops keeps fertility. Afforestation: planting trees holds the soil.