G2-2 Soil Formation and Composition EQ: How do you scientifically describe soil? How is soil formed?

G2-2

Soil Formation and Composition

EQ: How do you scientifically describe soil? How is soil formed?

G2-2

Soil Formation

• Soil- the loose, weathered material on Earth’s surface in which plants can grow

• 3 steps to soil formation1)Begins as bedrock (solid layer of rock

beneath the soil)2)Breaks down (weathering)3)Mixes with other materials

EQ: How do you scientifically describe soil? How is soil formed?

G2-2

Soil Composition

• Soil – a mixture of rock particles, minerals, decayed organic material, air and water

• Rock particles- sand, silt, clay• 2 factors affect the rock particles and minerals

found in a soil- bedrock- type of weathering

EQ: How do you scientifically

describe soil? How is soil formed?

G2-2

Soil Composition

• Humus – dark colored substance that forms as plant and animal remains decay– Creates space in soil for air and water– Rich in nutrients for plants:

• nitrogen, sulfur, phosphorus, and potassium

EQ: How do you scientifically describe

soil? How is soil formed?

G2-2

Soil Color

• Color of soil can vary from gray, yellow, deep red brown to black.

EQ: How do you scientifically describe

soil? How is soil formed?

G2-2

Soil Texture• Size of particles. • Rub soil between your fingers to test. • Different names are given to soils depending

on the proportion of sand, silt, and clay.• Every soil on earth is defined as sand, silt, clay.

EQ: How do you scientifically describe soil? How is soil

formed?

G2-2

Soil TexturePebbles/gravel are NOT considered soil!

EQ: How do you scientifically describe soil? How is soil

formed?

G2-2

Soil Texture is:

• grainy -large-sized pieces and feels gritty, like sand.

• silky -medium-sized pieces and feels powdery, like silt.

• sticky -small pieces and feels gummy, like wet clay.

EQ: How do you scientifically describe soil? How is soil

formed?

G2-2

Soil Consistency

• how easily the soil clumps can bebroken apart.

The soil consistency is• loose - soil breaks apart when held.• friable - soil breaks apart with a small amount

of pressure from one finger.• firm - soil breaks apart with a lot of pressure

between two fingers.

EQ: How do you scientifically

describe soil? How is soil formed?

G2-2

Soil Horizons

• A layer of soil that differs in color and texture from the layers above or below it

EQ: How do you scientifically describe

soil? How is soil formed?

G2-2

Soil Horizons

• Scientists classify soil into 3 horizons– A Horizon - topsoil-crumbly, dark brown soil– B Horizon – subsoil- contains clay and other

particles washed down from A. Contains little humus

– C Horizon – contains partly weathered rock

EQ: How do you scientifically describe

soil? How is soil formed?

G2-2

Rate of Soil Formation

• Depends on the climate and type of rock– Warm and rainy climate – soil develops quickly– Cold and dry climate – soil develops slowly

EQ: How do you scientifically describe soil? How is soil

formed?

G2-2

Life in soil- organisms mix the soil, create spaces, make humus .

• Plant “litter”, a loose layer over the soil where plants shed leaves or die

• Decomposers, organisms that break down the remains of dead plants and animals live in the soil

• Bacteria, fungi, earthworms, snails and beetles

EQ: How do you scientifically describe

soil? How is soil formed?

G2-2

Soil Types in the United States

• Scientists classify soil based on:– Climate– Common plants found in the region– Soil composition

EQ: How do you scientifically

describe soil? How is soil formed?

G2-2

Class Work and Homework

• Classwork: Copy questions 1-5 on notebook paper.

• Homework: Questions 1-5 using notes. See page G55.