Soil Formation and Composition

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

Soil Formation

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

• Three parts to soil formationBegins as bedrock- solid layer of rock

beneath the soilBroken down by weatheringMixes with other materials on the surface

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

Soil Composition

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

• Rock particles and minerals are sand, silt and clay

• Two factors affect the rock particles and minerals found in a soil

- original type of bedrock- type of weathering

EQ: How do you scientifically

describe soil? How is soil formed?

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 plants need to grow:

• nitrogen, sulfur, phosphorus, and potassiumsepup

EQ: How do you scientifically describe

soil? How is soil formed?

Soil Texture• Defined and described by the size of the

particles. • Rubbing soil between your fingers tests the

soil’s texture. • 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?

Soil TextureAll particles as large or larger than pebbles or gravel (diameter greater than 2 mm) are not considered soil, although they will often be found in it.

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

formed?

Soil Texture is:

• grainy if the soil is made up of large-sized pieces and feels gritty, like sand.

• silky if the soil is made of medium-sized pieces and feels powdery, like silt.

• sticky if the soil is made of small pieces and feels gummy, like wet clay.

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

formed?

Rate of Soil Formation

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

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

formed?

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?

Life in soil- organisms mix the soil, create space for air and water make hummus

• 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?

Soil Types in the United States

• Scientists classify soil into different groups based on several factors– Climate– Common plants found in the region– Soil composition

EQ: How do you scientifically

describe soil? How is soil formed?

Class Work and Homework

• Fill In– What did I learn– Confused– Say

Describing Soil ScientificallyMapping US Soils