SOIL SCIENCE

1. Soil Formation and Classification

Soil formation is the natural process by which rocks and minerals are broken down and transformed into soil through physical, chemical, and biological processes over time.

1.1. Soil Formation and Classification

a. Climate: Influences weathering rates and organic matter decomposition.

Organisms: Plants, animals, and microbes affect soil structure and nutrient cycling.

Relief (Topography): Affects drainage, erosion, and deposition.

Parent Material: The mineral or organic material from which soil develops.

Time: Soil formation is a slow process; older soils are more developed

1.2. Soil Taxonomy and Classification Systems

USDA Soil Taxonomy: A system based on soil properties like moisture, temperature, and horizons.

FAO World Reference Base (WRB): International system focusing on diagnostic horizons and materials.

Soils are classified into orders, suborders, great groups, etc.

2. . Soil Fertility and Nutrient Management

Soil Fertility refers to the soil’s ability to provide essential nutrients to plants in adequate amounts and proper balance for their growth and development.

Nutrient Management is the practice of optimizing the supply of nutrients to crops to maximize yield while minimizing environmental impact.

2.1. . Essential Plant Nutrients and Their Functions

Macro nutrients: Nitrogen (leaf growth), Phosphorus (root and flower development), Potassium (overall health).

Micro nutrients: Iron, Zinc, Manganese – required in small amounts for specific plant functions.

Nutrient deficiency leads to poor plant growth and yield loss.

2.2. . Soil Testing and Fertilizer Recommendations

Soil Testing: Determines nutrient levels, pH, and organic matter content.

Fertilizer Use: Based on soil test results; includes organic (manure, compost) and inorganic fertilizers.

3. . Soil Physical and Chemical Properties

Definition:
Soil physical properties are the characteristics of soil related to its physical composition and structure, which influence water movement, air flow, root growth, and soil strength. These properties include soil texture, structure, color, density, porosity, moisture, and temperature.

Soil Chemical Properties

Definition:
Soil chemical properties refer to the chemical composition and reactions within the soil that affect nutrient availability, soil fertility, and the soil’s capacity to supply essential elements to plants. These properties include soil pH, cation exchange capacity (CEC), base saturation, salinity, sodicity, organic matter content, and nutrient content.

3.1. Soil Texture, Structure, and Porosity

Texture: Proportion of sand, silt, and clay. Affects water retention and root penetration.

Structure: Arrangement of soil particles into aggregates. Influences aeration and drainage.

Porosity: Space between particles for air and water movement.

3.2. Soil pH and Cation Exchange Capacity (CEC)

Soil pH: Measures soil acidity or alkalinity. Affects nutrient availability. Ideal range: 6.0–7.5.

CEC: Soil’s ability to hold and exchange cations (nutrients). Higher CEC = better nutrient retention.