Soil FormationSoil Formation Soil Soil – weathered particles of rock, – weathered particles of rock,

minerals and organic material (from minerals and organic material (from living things)living things)

1. 1. Residual SoilResidual Soil – formed from the – formed from the local bedrock below. Has same color local bedrock below. Has same color and minerals as bedrock.and minerals as bedrock.

2. 2. Transported SoilTransported Soil – brought from – brought from somewhere else (usually by glaciers). somewhere else (usually by glaciers). May have different color and May have different color and minerals than local bedrock.minerals than local bedrock.

Soil colorsSoil colors

Soil HorizonsSoil Horizons A-HorizonA-Horizon = Topsoil; usually dark and = Topsoil; usually dark and

rich. Contains organic matter like rich. Contains organic matter like leaves, twigs and dead grass.leaves, twigs and dead grass.

B-HorizonB-Horizon = Sub-soil; mostly clay- = Sub-soil; mostly clay-sized particles, not much organic sized particles, not much organic matter.matter.

C-HorizonC-Horizon = Partly weathered = Partly weathered bedrock.bedrock.

ErosionErosion ErosionErosion – movement of weathered – movement of weathered

material.material. Natural Agents of ErosionNatural Agents of Erosion

1. Water1. Water 2. Wind2. Wind 3. Ice (glaciers)3. Ice (glaciers)

* All affected by * All affected by gravitygravity – eroded – eroded material moves down hillmaterial moves down hill

Soil Erosion Soil Erosion

How much topsoil is needed to How much topsoil is needed to grow most crops?grow most crops?

25 Billion tons of topsoil is lost 25 Billion tons of topsoil is lost each year worldwide. Where each year worldwide. Where does it go?does it go?

How long does it take on average How long does it take on average for 1” of topsoil to form?for 1” of topsoil to form?

Farming Methods to Conserve Farming Methods to Conserve SoilSoil

Contour Contour FarmingFarming

- Planting in - Planting in horizontal rows horizontal rows across hillsidesacross hillsides

Strip CroppingStrip Cropping

- Planting - Planting alternating alternating rows of crops rows of crops that help that help anchor soil and anchor soil and add nutrients add nutrients to soilto soil

Terrace Terrace FarmingFarming

Cutting steps Cutting steps into hillsides to into hillsides to create flat create flat surfacessurfaces

Wind BreaksWind Breaks - planting a - planting a

barrier of trees barrier of trees around the around the perimeter of perimeter of you fields.you fields.

Dustbowl - 1935Dustbowl - 1935

Characteristics of Eroded Sediments:Characteristics of Eroded Sediments: 1. 1. WaterWater transported sediments are transported sediments are

smoothsmooth and and rounded.rounded. 2. 2. WindWind transported sediments are transported sediments are

small and angular (small and angular (rough edgesrough edges)) 3. 3. Ice (glaciersIce (glaciers) leaves scratches ) leaves scratches

called called striationsstriations on rock surfaces. on rock surfaces. Also Also polishespolishes the surface. the surface.

Glacial StriationsGlacial Striations