1. Soil

2. Soil – the loose covering of broken rock particles and decaying organic matter overlying the bedrock of Earth’s surface
Humus – decaying organic matter in soil
Soil results from mechanical and chemical weathering and biological activity over a long period of time

3. Soil Formation Weathering breaks rock into smaller and smaller pieces
Organisms (bacteria, fungi, insects) begin to live in rock pieces
Organisms die, decay, and add nutrients to the rock pieces to form soil

4. The time it takes to form soil is dependent on type of rock and climate
It can take hundreds of years to form one centimeter of soil

5. Soil Profiles Soil profile – the vertical sequence of soil layers
Well developed soils have distinct layers
Poorly developed soils show little distinction between layers
A distinct layer within a soil profile – soil horizon

6. 3 Major Soil Horizons 1) Horizon A – rich in humus, gray to black
2) Horizon B – sub-soils enriched with clay, contain minerals washed out (leached) from the topsoil
Red or brown due to iron oxide

7. 3) Horizon C – weathered parent material directly above the bedrock - All horizons may not be present in all soils

8. Soil Types Tropical soils Intensely weathered, infertile soil
Little humus
Thin Horizon A from high rainfall

9. Temperate soils
High weathering
Grassland – high humus
Forest – less humus, high clay

10. Desert/Arctic soils
Little chemical weathering
Very thin soil
Mostly Horizon C