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🌱 SOIL SCIENCE – MODULE 1 NOTES
1. Introduction to Soil Science
Soil science is the study of soil as a natural resource.
It focuses on soil formation, classification, morphology, physical and chemical properties, and how soil supports plant growth.
2. Definition of Soil
Soil is the upper weathered layer of the earth’s crust that supports plant growth.
It contains minerals, organic matter, water, air, and living organisms.
3. Components of Soil
1. Mineral matter (45%) – sand, silt, clay
2. Organic matter (5%) – decayed plant/animal remains
3. Soil water (25%)
4. Soil air (25%)
5. Organisms – bacteria, fungi, earthworms
4. Soil Formation (Pedogenesis)
a) Factors of Soil Formation
1. Parent material
2. Climate
3. Topography
4. Biological organisms
5. Time
b) Processes of Soil Formation
Weathering (physical, chemical, biological)
Addition of materials (organic matter deposition)
Loss (leaching, erosion)
Translocation (movement of clay, nutrients)
Transformation (decomposition, mineral alteration)
5. Soil Profile
A vertical section of soil showing layers (horizons).
Horizons:
O – Organic layer
A – Topsoil (rich in organic matter, most plant roots)
B – Subsoil (accumulation of leached materials)
C – Parent material
R – Bedrock
6. Soil Texture
Refers to the proportion of sand, silt, and clay.
Sandy soil: large particles, drains quickly
Clay soil: fine particles, holds water, poorly drained
Loam soil: balanced texture, best for agriculture
7. Soil Structure
Arrangement of soil particles into aggregates (crumb, blocky, platy).
Good structure improves aeration, water infiltration, and root penetration.
8. Soil Colour
Indicates properties such as organic matter, drainage, mineral content.
Dark soils → high organic matter
Red/yellow soils → iron oxides
Grey/blue soils → poor drainage
9. Soil Water
Types of water:
Gravitational water – drains freely
Capillary water – available to plants
Hygroscopic water – not available to plants
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🌾 SOIL SCIENCE – MODULE 2 NOTES
1. Soil Chemistry
Study of chemical composition and reactions in soil.
a) Soil pH
pH = measure of soil acidity or alkalinity.
Acidic soils (pH < 7) → apply lime
Alkaline soils (pH > 7) → apply sulfur, organic manure
pH affects:
nutrient availability
microbial activity
crop growth
b) Essential Nutrients
Macronutrients:
Nitrogen (N) – growth and chlorophyll
Phosphorus (P) – root development
Potassium (K) – disease resistance
Calcium (Ca), Magnesium (Mg), Sulfur (S)
Micronutrients:
Iron, Zinc, Boron, Manganese, Copper, Molybdenum, Chlorine.
2. Soil Fertility
Soil fertility is the ability of soil to supply nutrients in adequate amounts.
Determined by:
organic matter content
nutrient levels
pH
soil structure
cation exchange capacity (CEC)
Improving Soil Fertility
Organic manure
Green manure
Fertilizers (NPK)
Crop rotation
Liming acidic soils
3. Soil Organic Matter (SOM)
Consists of humus and decomposing residues.
Functions:
Improves soil structure
Increases water holding capacity
Enhances nutrient availability
Supports microorganisms
4. Soil Biology
Soil hosts millions of organisms:
Bacteria
Fungi
Actinomycetes
Earthworms
Arthropods
Functions:
Breakdown organic matter
Nitrogen fixation
Aeration of soil
Nutrient cycling
5. Soil Erosion
Removal of topsoil by water, wind, or human activity.
Types of Erosion
Splash erosion
Sheet erosion
Rill erosion
Gully erosion
Wind erosion
Control Measures
Terracing
Contour farming
Windbreaks
Mulching
Cover crops
Strip cropping
6. Soil Conservation
Protecting soil against degradation.
Techniques:
Minimum tillage
Agroforestry
Water harvesting
Proper grazing management
7. Soil Sampling and Testing
Helps determine soil fertility and pH.
Steps:
1. Collect samples across the field
2. Mix to form composite sample
3. Air dry
4. Send to lab
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