SOIL - NOTES

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

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

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

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!

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)

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.