soil science: soil science notes

1. Introduction to Soil Science

Soil science is the study of soil as a natural resource, including its formation, classification, properties, and use in agriculture.

2. Soil Formation (Pedogenesis)

Soil forms through the weathering of rocks and the decomposition of organic matter over time. The factors influencing soil formation include:

Parent Material – The original rock material that breaks down to form soil.

Climate – Temperature and rainfall affect weathering and organic matter decomposition.

Organisms – Plants, animals, and microorganisms contribute to soil structure and fertility.

Topography – The shape of the land influences erosion and drainage.

Time – Soil formation is a slow process that can take hundreds to thousands of years.

3. Soil Composition

Soil is composed of:

Mineral Particles (45%) – Sand, silt, and clay.

Organic Matter (5%) – Decomposed plants and animals, which improve fertility.

Water (25%) – Essential for plant growth and nutrient transport.

Air (25%) – Provides oxygen for plant roots and microorganisms.

4. Soil Texture and Structure

Soil Texture – The proportion of sand, silt, and clay particles. It affects water retention, drainage, and aeration.

Soil Structure – The arrangement of soil particles into aggregates (crumb, blocky, platy, granular). It affects root penetration and water movement.

5. Soil pH and Nutrients

Soil pH – Determines soil acidity or alkalinity (scale of 0-14). Ideal agricultural soil ranges from pH 5.5 – 7.5.

Essential Nutrients:

Macronutrients – Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S).

Micronutrients – Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo).

6. Soil Water

Soil water is classified into:

Gravitational Water – Drains quickly and is unavailable to plants.

Capillary Water – Held in pores and available for plant uptake.

Hygroscopic Water – Thin layer around soil particles, unavailable to plants.

7. Soil Erosion and Conservation

Causes of Soil Erosion: Wind, water, overgrazing, deforestation.

Soil Conservation Methods:

Contour farming

Cover cropping

Terracing

Mulching

Agroforestry

Soil Fertility – The ability of soil to support plant growth by providing nutrients.

Fertility Improvement:

Use of organic matter (compost, manure).

Application of fertilizers (organic and inorganic).

Crop rotation and intercropping.