Soils & Soil Physical PropertiesUnit 2.1 | Part 2 –7
Lecture 1: Soils—An Introduction
Lecture 1: Soils—An Introduction
Pre-Assessment Questions
- What are some of the functions that soil serves?
- What are some of the factors involved in soil formation?
- What are the components that make up soil?
A. Introduction
- What is soil?
a) Definitions
i. Different concepts = different definitions. How soil is defined depends on who is
using the word.
- Edaphological (in relation to plant growth)
A mixture of mineral and organic material that is capable of supporting plant life
- Engineering (in relation to supporting structures)
Mixture of mineral material (sands, gravels, and fines [very small particles]) used as
a base for construction
- Pedological (looking at soil as a distinct entity)
The unconsolidated mineral or organic material on the surface of the earth arising
from a particular parent material that has been subjected to and shows the effects
of climate macro- and microorganisms, the topography of its location in the
landscape, and time. It is at the Geosphere-Biosphere-Hydrosphere-Atmosphere
interface.
b) Functions of soil
i. Supports growth of higher plants
ii. Primary factor controlling fate of water in hydrologic systems
iii. Nature’s recycling system for nutrients
iv. Habitat for organisms
v. Engineering medium
B. How Soil Is Made
- Soil-forming factors
At one time, people thought that soils were static. In the late 1800s, Russian soil scientists
introduced the concept that soils are dynamic—that any one soil developed into the soil
it is now and that it continues to evolve. The scientists came up with five soil-forming
factors that influence how soils turn out the way they do. The idea is that if all five of the
soil-forming factors are the same, then the soil will be the same. The technical term for soil
formation is pedogenesis. The five soil-forming factors are:
a) Climate: Temperature, precipitation, and how they are distributed across the seasons
b) Biotic factors: Plants, animals, fungi, bacteria, and other microorganisms
c) Topography: Slope position, aspect, and shape
d) Parent material: Rock, alluvium (wind- or water-deposited material)
e) Time: How long the soil has been forming