SoilsSoilsEarth’s Changing Earth’s Changing

SurfaceSurface

ReviewReview

Weathering – breaks down rockWeathering – breaks down rock– MechanicalMechanical– Chemical Chemical

Erosion – removes the rock particlesErosion – removes the rock particles

What is soil?What is soil?

The loose, weathered material on The loose, weathered material on Earth’s surface in which plants can Earth’s surface in which plants can grow.grow.

SoilSoil

Bedrock - the solid layers of rock Bedrock - the solid layers of rock beneath soil. beneath soil.

Soil CompositionSoil Composition

Mixture of rock particles, minerals, Mixture of rock particles, minerals, decayed organic material, water, and decayed organic material, water, and airair

Humus – decayed organic material in Humus – decayed organic material in soil soil

SoilSoil

Fertility of Soil – measures how well Fertility of Soil – measures how well the soil supports plan growth. the soil supports plan growth. – Rich in humus has high fertility Rich in humus has high fertility

Why does fertility of soil matter?Why does fertility of soil matter?

Soil TextureSoil Texture

What does soil feel like? What does soil feel like? Sand feels coarse and grainySand feels coarse and grainy Clay feels smooth and silkyClay feels smooth and silky

Soil texture depends on the size of Soil texture depends on the size of soil particles. soil particles.

Soil Particle sizeSoil Particle size

ClayClay SiltSilt Sand Sand GravelGravel

Less than Less than 1/256 mm1/256 mm

Less than Less than 1/16 mm1/16 mm

Less than Less than 2 mm2 mm

2 mm and 2 mm and largerlarger

LoamLoam

Soil that is made up of about equal Soil that is made up of about equal parts of clay, sand, and silt is called parts of clay, sand, and silt is called loam. loam.

Soil FormationSoil Formation

Forms as rock is broken down by Forms as rock is broken down by weathering and mixes with other weathering and mixes with other materials on the surface.materials on the surface.

Soil FormationSoil Formation

Soil HorizonsSoil Horizons– A layer of soil that differs in color and A layer of soil that differs in color and

texture from the layers above or below texture from the layers above or below it. it.

Soil Horizons Soil Horizons

A HorizonA Horizon

Topsoil – a crumbly, dark brown soil Topsoil – a crumbly, dark brown soil that is a mixture of humus, clay, and that is a mixture of humus, clay, and other minerals.other minerals.

Develops as plants add organic Develops as plants add organic material to soil and plants weather material to soil and plants weather rock.rock.

B HorizonB Horizon

Subsoil – clay and other particles Subsoil – clay and other particles washed down from the A horizon, but washed down from the A horizon, but little humus. little humus.

Soil TypesSoil Types

Thousands of different types of soil in Thousands of different types of soil in U.S. aloneU.S. alone

Classified based on climate, plants, Classified based on climate, plants, and soil composition. and soil composition.

Living Organisms in SoilLiving Organisms in Soil

Some soil organisms make humusSome soil organisms make humus Some soil organisms mix the soil and Some soil organisms mix the soil and

make spaces in it for air and water. make spaces in it for air and water.