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Lesson 275 min read
Soil Science
Soil Composition, Texture, pH, Nutrients & Fertilizer Application
In This Lesson
Soil Composition
Ideal Soil Composition
45%
Mineral Matter
5%
Organic Matter
25%
Water
25%
Air
Mineral Matter
- * Derived from parent rock
- * Provides nutrients
- * Determines soil texture
- * Sand, silt, clay particles
Organic Matter
- * Decomposed plant/animal material
- * Humus - dark, stable form
- * Improves soil structure
- * Increases water retention
Soil Texture (Sand/Silt/Clay)
| Particle | Size (mm) | Feel | Properties |
|---|---|---|---|
| Sand | 0.05 - 2.0 | Gritty | Good drainage, poor nutrient retention |
| Silt | 0.002 - 0.05 | Smooth, floury | Moderate drainage and retention |
| Clay | < 0.002 | Sticky, plastic | Poor drainage, high nutrient retention |
Loam - The Ideal Soil
A balanced mixture of sand, silt, and clay:
- Good drainage AND water retention
- Good nutrient holding capacity
- Easy to work/cultivate
- Approximately: 40% sand, 40% silt, 20% clay
Soil Texture Classes
Sandy, Loamy sand
Sandy loam, Loam
Silt loam, Silty clay loam
Clay loam, Sandy clay
Silty clay, Clay
Soil pH
pH measures soil acidity or alkalinity on a scale of 0-14. Most crops prefer a pH of 6.0-7.0 (slightly acidic to neutral).
pH Scale
0-4 Strongly Acidic4-5 Very Acidic5-6 Acidic6-7 Slightly Acidic7 Neutral7-8 Slightly Alkaline8-14 Alkaline
Acidic Soil (Low pH)
- Cause: Heavy rainfall, organic matter decay
- Effect: Aluminum toxicity, nutrient deficiency
- Correction: Apply lime (CaCO₃)
- Acid-loving crops: Pineapple, blueberry
Alkaline Soil (High pH)
- Cause: Low rainfall, calcareous parent material
- Effect: Iron, manganese deficiency
- Correction: Apply sulfur or acidifying fertilizers
- Tolerant crops: Asparagus, beets
Essential Plant Nutrients
Primary Macronutrients (NPK)
N - Nitrogen
- * Promotes leaf/vegetative growth
- * Green color (chlorophyll)
- * Protein synthesis
- * Deficiency: Yellowing of older leaves
P - Phosphorus
- * Root development
- * Flowering and fruiting
- * Energy transfer (ATP)
- * Deficiency: Purple leaves, stunted growth
K - Potassium
- * Overall plant health
- * Disease resistance
- * Water regulation
- * Deficiency: Brown leaf edges
Secondary Macronutrients
Calcium (Ca)
Cell wall structure, root growth
Magnesium (Mg)
Chlorophyll center, enzyme activation
Sulfur (S)
Protein synthesis, enzyme function
Micronutrients
Required in small amounts but still essential:
Iron (Fe)Manganese (Mn)Zinc (Zn)Copper (Cu)Boron (B)Molybdenum (Mo)Chlorine (Cl)Nickel (Ni)
Fertilizers & Application
Inorganic (Chemical) Fertilizers
- Urea (46-0-0): High nitrogen
- Complete (14-14-14): Balanced NPK
- Ammonium Sulfate (21-0-0): N + Sulfur
- Muriate of Potash (0-0-60): High potassium
Organic Fertilizers
- Compost: Decomposed organic matter
- Animal manure: Chicken, cow, pig
- Green manure: Plowed-under crops
- Vermicompost: Worm castings
Fertilizer Application Methods
Basal Application
Applied before or at planting
Top Dressing
Applied during crop growth
Side Dressing
Applied beside the plant row
Foliar Spray
Sprayed on leaves for quick absorption
Soil Management
Soil Conservation Practices
- * Contour farming: Planting along contour lines
- * Terracing: Creating flat steps on slopes
- * Cover cropping: Planting to protect soil
- * Mulching: Covering soil surface
- * Crop rotation: Alternating crop types
Improving Soil Structure
- * Add organic matter (compost, manure)
- * Avoid compaction (minimize machinery)
- * Practice minimum tillage
- * Maintain proper drainage
Key Takeaways
- ✓Ideal soil: 45% mineral, 5% organic matter, 25% water, 25% air
- ✓Texture: Sand (largest) → Silt → Clay (smallest)
- ✓Optimal soil pH: 6.0-7.0 for most crops
- ✓NPK: N=growth, P=roots/flowers, K=health/resistance
- ✓Apply lime to raise pH; sulfur to lower pH