SOIL SCIENCE PRINCIPLES
This course explores the fundamental principles of soil science, focusing on the formation, classification, physical, chemical, and biological properties of soils. Students will learn about soil genesis, soil morphology, and soil taxonomy. The course also emphasizes the role of soils in plant growth, water management, nutrient cycling, and environmental sustainability. Practical aspects include soil sampling, analysis, and interpretation of soil data for agricultural and environmental applications.
1. . Introduction to Soil Science
1. Introduction to Soil Science
A. Definition of Soil
Soil is the upper layer of the Earth's crust, formed by the weathering of rocks and the decay of organic materials, which supports plant life.
It is a dynamic natural body composed of mineral particles, organic matter, water, air, and living organisms.
B. Functions of Soil
Soil performs several essential roles in natural ecosystems and human activities:
1. Medium for plant growth – provides physical support, nutrients, and water.
2. Regulator of water supply – controls infiltration, runoff, and groundwater recharge.
3. Recycler of raw materials – decomposes organic matter and recycles nutrients.
4. Habitat for soil organisms – supports a wide diversity of microbes and animals.
5. Engineering medium – foundation for buildings, roads, and other infrastructure.
C. Importance of Soil Science
Supports sustainable agriculture and food production.
Aids in environmental conservation and climate change mitigation (carbon storage).
Critical for land-use planning and infrastructure development.
Helps in pollution control through natural filtration and detoxification.
D. Soil as a Natural Resource
Like air and water, soil is finite and must be managed carefully.
Degradation (e.g., erosion, compaction, salinization) threatens its functionality.
E. Human Impact on Soils
Activities like deforestation, overgrazing, poor farming practices, and industrial waste disposal can negatively affect soil quality and productivity.
CHAPTER TWO
2. Soil Formation (Pedogenesis)
A. What is Pedogenesis?
Pedogenesis is the process of soil formation from parent material through physical, chemical, and biological weathering
Results in the development of soil horizons and unique properties that define a soil type.
B. Weathering Processes
1. Physical (Mechanical) Weathering
Breakdown of rocks into smaller particles without changing chemical composition.
Agents: temperature changes, freeze-thaw cycles, wind, water, root pressure.
Example: Cracking and fragmentation of rocks in deserts or mountains.
2. Chemical Weathering
Alters the chemical composition of rocks and minerals.
Reactions include hydrolysis, oxidation, carbonation, and solution.
Produces clay minerals and releases nutrients like potassium, calcium, and iron.
3. Biological Weathering
Caused by living organisms (plants, microbes, animals).
Includes root expansion, secretion of organic acids, and burrowing activity.
C. Factors of Soil Formation (CLORPT
1. Climate (CL) – Affects rate of weathering, organic matter decomposition, leaching.
2. Organisms (O) – Microbes, plants, animals contribute to mixing and nutrient cycling.
3. Relief/Topography (R) – Influences drainage, erosion, and microclimates.
4. Parent Material (P) – Determines mineral composition and initial fertility.
5. Time (T) – Soils develop and mature over long periods (centuries or millennia).
D. Types of Soils Based on Formation
1. Residual Soils – Form in place from the weathering of underlying rock.
2. Transported Soils – Moved from origin by:
Water (Alluvial)
Wind (Aeolian)
Glaciers (Glacial till)
Gravity (Colluvial)
E. Importance of Understanding Soil Formation
Helps in predicting soil behavior and fertility.
Supports proper land use and conservation practices.
Aids in soil classification and mapping.