8th Grade: The Dynamic Earth (Module E) Unit 1 Lesson 5 Soil Formation

The Dirt on Soil – Soil Formation Unit 1 Lesson 5 Soil Formation Soil - loose mixture of rock fragments, organic matter, water, and air supports plant growth Soil formation parent rock weathered into smaller pieces to form sediment Plant roots, rain, wind, etc. Decomposers (like bacteria and fungi) break down dead plants and animals into humus Sediment and organic matter mix to form soil Q: What mixes the soil? A: animals (earthworms, moles), rainwater Copyright © Houghton Mifflin Harcourt Publishing Company

Why do soils differ from place to place? Unit 1 Lesson 5 Soil Formation Why do soils differ from place to place? The type of sediment in soil depends on what rocks are in the area. Climate Plants and animals Time Copyright © Houghton Mifflin Harcourt Publishing Company

What factors determine how long it takes for soils to form? Unit 1 Lesson 5 Soil Formation What factors determine how long it takes for soils to form? 1. Rock type: rate of weathering depends on the structure of the rock and minerals that make up the rock 2. Climate: Soil usually develops more quickly in warm, wet areas than in cold, dry areas. 3. Topography: Soils usually develop faster in flatter areas where sediments are not easily eroded. 4. Plants and animals: Without a lot of plants and animals, soil tends to develop slowly. Do page 60 Copyright © Houghton Mifflin Harcourt Publishing Company

Soil horizons Unit 1 Lesson 5 Soil Formation soil profile - vertical section of soil that shows all the different layers Each layer is called a soil horizon Each horizon has different properties Copyright © Houghton Mifflin Harcourt Publishing Company

A horizon - top layer (a.k.a. topsoil) Contains the most humus B horizon - less humus In Leaching, water carried nutrients from A horizon to B horizon C horizon - directly above parent rock Contains the largest rock fragments Usually no organic matter. Unit 1 Lesson 5 Soil Formation Copyright © Houghton Mifflin Harcourt Publishing Company

Soil Properties Used to classify soil Unit 1 Lesson 5 Soil Formation Soil Properties Used to classify soil 1. Soil texture – amount of differently sized soil particles Sand – largest particles (0.05-2 mm) Silt (0.002-0.05 mm) Clay – smallest particles (less than 0.002 mm) Copyright © Houghton Mifflin Harcourt Publishing Company

Soil Properties, con’t Unit 1 Lesson 5 Soil Formation 2. Soil color - depends on minerals and organic matter Iron = reddish/orange Humus = black / brown Grey = area may be wet with poor drainage 3. Soil pH: how acidic (pH 0-6) or basic (pH 8-14) soil is Depends on minerals, sediment & organic matter Determines what can grow in the soil Can be changed by adding stuff to soil Read p. 63 Copyright © Houghton Mifflin Harcourt Publishing Company

Soil Properties, con’t 4. Pore space - the spaces Unit 1 Lesson 5 Soil Formation 4. Pore space - the spaces between soil particles. Water and air are found in the pore spaces of soils. 5. Soil fertility - how well a soil can support plant growth Depends on climate and topography Depends on amount of humus, minerals and nutrients in soil Copyright © Houghton Mifflin Harcourt Publishing Company

What are some properties of soil? Unit 1 Lesson 5 Soil Formation What are some properties of soil? How does the pore space of the soil on the left compare to that of the soil on the right? Copyright © Houghton Mifflin Harcourt Publishing Company

Soil and Climate Desert soil – dry Tropical soils-warm & wet Shallow, not much humus Little rainfall, so chemical weathering & soil development are SLOW Tropical soils-warm & wet Rains wash away and leach soils, not much humus Soil development is FAST Not good for growing

Soil and Climate, con’t. – moderate rainfall & temp Dark colored, rich in organic matter Good for crops Arctic soil – cold & dry No well-developed horizons Many rock fragments