1. SOIL - NOTES

2. Soil Formation Soil is a mixture of:
Weathered rock and mineral fragments.
Decayed organic matter, HUMUS.
Water and air spaces.
Organic matter (dead plants & animals) decomposes and changes into HUMUS.
Soil composition : how well a soil holds water, important for plant growth

4. Factors Affecting Soil Formation
CLIMATE: affects weathering.
(Hot humid tropics vs. cold regions)
SLOPE of the Land: gravity moves soil downhill
soil is thinner at the top of hills, and thicker in low spots and valleys
TYPES OF ROCK: minerals in the original rock weather differently
PLANTS: hold soil and decay into HUMUS
TIME: how long rock has been weathering

5. SOIL PROFILES SOILS have different characteristics.
Soil layers are called HORIZONS.
Soil Horizons contain different mixtures of material.

6. Like a Drip Coffee-maker!
LEACHING
How minerals (and chemicals) get carried by water from Horizon A down to Horizon B.
Like a Drip Coffee-maker!

7. Most SOILS have 3 HORIZONS
(Some soils have HORIZON O -
organic matter on the surface)
Horizon A: topsoil
more HUMUS, less rock particles, usually darker & more fertile
Horizon B: subsoil
less organic matter (HUMUS), more rock, minerals leached down from Horizon A
Horizon C: substrate
partly weathered rock, little humus
(Horizon R: Solid ROCK not weathered)

8. Sciencesaurus Go to page 191.
Draw a picture of each layer on the front flap of your foldable.
On the inside of the flap:
Define each layer
In Horizon A, define HUMUS as well.
What is included in each layer.
Answer the questions on the back.