Download - 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.
