1. SOIL

2. Learning objectives
Recall that soil is the result of weathering of rocks and includes weathered particles: sand, silt and clay

3. What is soil?
Soil is the loose covering of broken rock fragments (regolith) overlying the bedrock of the Earth’s surface
Soil is the result of mechanical and chemical weathering over long periods of time and consists of four major components:
Mineral matter (broken down rock)
Humus (decayed remains of organisms)
Water
Air
During soil development, layers form…
Horizon A
Horizon B
Horizon C
Parent Material / Bedrock

4. Composition by volume good quantity soil
Most soil is composed of mineral matter, organic matter, water, and air
Usually, the mineral and organic matter exist mostly as particles, with the water and air existing in pores between the particles
A soil's texture is determined by the coarseness or fineness of its particles 5%
25%
25%
45%

5. SOIL CHARACTERISTICS
Soil textures are classified by the size of the particle, from very coarse sand to fine clay
Soil fertility is a measure of how well a soil can support the growth of plants
Soil color is determinate of the climate in which it develops as well as the composition of the soil. Color alone is unreliable in determination of fertility of the soil

6. SOIL TEXTURE
Soil texture refers to the proportions of different particle sizes
Sand (large and coarse)
Silt
Clay (small and fine)
Loam (a mixture of all three sizes) is most suitable for plant life
Soil particles “clump” together to give soil it’s ultimate structure

7. Soil Development A Step by Step Process
The primary factors involved in soil development are parent material, time, climate, organisms, and slope
The soil forming process begins when weathering breaks solid bedrock (parent material) into smaller pieces
Pieces then continue to undergo weathering and break down into smaller and smaller pieces
Many organisms (bacteria included) begin to live in these weathered materials
Over time, the organisms die, decay, and add nutrients to the weathered materials to form soil, such as dead fungi, bacteria, and protozoa
In general, soil formation occurs over a long period of time. It can take hundreds of years for only a centimeter of soil to form

8. Soil Composition
While the parent bedrock determines the type of minerals in a soil, the proportion of minerals may not be the same
Differences may occur as the result of chemical weathering, which changes the chemical composition of the soil
The length of time it takes for soil to form also depends on the type of parent rock, as well as the climatic conditions of an area. The longer a soil has been forming, the thicker it becomes.
Soil located above it’s parent material is called residual soil
Soil that has been moved to a location away from its parent bedrock is called transported soil

9. Soil Profiles Soil Profile: Vertical sequence of soil layers
Soil Horizon: A distinct layer within a soil profile
Horizon A - Lots of organic matter, darkest and richest… “topsoil”
Horizon B - Subsoils enriched with clay minerals, red or brown, washed out from Horizon A
Horizon C - Contains weathered parent materials, just above the bedrock
Soils tend to be thin, coarse, and infertile on slopes, and tend to be thick and fertile in valleys

10. Types of soil SOIL TYPES LOCATION CONTENTS Pedalfer
Under Forest Vegetation
Iron oxides and aluminum-rich clays in Horizon B
Pedocal
Drier Grasslands
Calcium Carbonate
Laterite
Hot, wet, tropical Climates
Intense chemical weathering to the top layers of soil

11. Soil erosion Water erodes soil Rates of Erosion Sediment Deposition
Human activities that remove or alter natural vegetation speed up the erosion process
Farming
Logging
Construction
Sediment Deposition
Reservoirs fills with sediment
Sediments are then contaminated with pesticides and fertilizers

12. Controlling Soil erosion
Soil erosion can be lessened by implementing different strategies:
Planting Windbreaks
Terracing Hillsides
Contour Plowing along hills
Crop Rotation