(a) Define soil erosion. [2 marks] (b) List four factors that influence nutrient availability in the soil. [4 marks] (c) Explain two roles of each of the fo...

(a) Definition of soil erosion

Soil erosion is the gradual wearing away and removal of the fertile top layer of the soil from the land surface by natural agents such as running water, wind, or by the activities of humans and animals.

(b) Four factors that influence nutrient availability in the soil

1. Soil pH (degree of acidity or alkalinity)
2. Soil moisture content
3. Soil texture and structure
4. Organic matter (humus) content

(c) Two roles of each factor in soil formation

(i) Climate

• Rainfall causes chemical weathering (leaching, hydration and solution) that breaks parent rock into soil particles.
• Alternate heating and cooling (temperature change) causes expansion and contraction of rocks, leading to physical breakdown.

(ii) Living organisms

• Burrowing animals such as earthworms and termites mix and aerate the soil and bring lower materials to the surface.
• Decomposition of dead plants and animals by micro-organisms adds humus and enriches the forming soil.

(iii) Topography

• Steep slopes encourage rapid run-off and erosion, producing shallow, stony soils.
• Gentle or flat land allows water to sink in and materials to be deposited, producing deep, well-developed soils.

(d) Four problems associated with overhead irrigation

1. High cost of installation and maintenance of the equipment.
2. It wets the foliage and so encourages the spread of fungal and other leaf diseases.
3. Wind causes uneven distribution of water over the field.
4. Much water is lost through evaporation before reaching the soil.