Topic 5 Part 1Topic 5 Part 1

soilsoil

What is soil and why do we care about it?

What is soil and why do we care about it?

complex mixture: weathered mineral

materials from rocks partially decomposed

organic molecules Ecosystem services

complex mixture: weathered mineral

materials from rocks partially decomposed

organic molecules Ecosystem services

Soil formationSoil formation Many factors contribute to this LONG process

ClORPT Help determine soil type

Many factors contribute to this LONG process ClORPT

Help determine soil type

Temperature and Moisture influence the speed of chemical reactions, which in turn, control how fast rocks weather and dead organisms decompose.

Soils develop fastest in warm, moist climates, and slowest in cold and arid ones.

The shape of the land and the direction in faces makes a difference in how much sunlight the soil gets, and how much water it keeps.

Deeper soils form at the bottom of a hill than at the top because gravity and water move soil particles down the slope.

Just like you inherited some characteristics from your parents, every soil inherits traits from the material from which it formed.

Soils that form in limestone bedrock are rich in calcium, Soils that formed from materials at the bottom of lakes are high in clay.

Time

Older soils differ from younger soils because they have had longer to develop

EXAMPLE: In the Northern U.S., soils tend to be younger, because glaciers covered the surface during the last ice age, which kept soils from forming. In the southern U.S., there were no glaciers. There, the soils have been exposed for a longer time, so they are more weathered.

Soil Texture Soil Texture Ratio of soil particle size determines some soil

properties Ratio of soil particle size determines some soil

properties

Determining soil typeDetermining soil type

% I

ncre

asin

g C

lay

Soil Properties: Porosity Soil Properties: Porosity Affects water infiltration, water holding capacity,

aeration, workability Affects water infiltration, water holding capacity,

aeration, workability

Soil Properties: Chemical Soil Properties: Chemical Cation exchange capacity (aka nutrient holding

capacity) Cation exchange capacity (aka nutrient holding

capacity)

SOIL ProfileSOIL Profile

Weak humus-mineral mixture

Mosaicof closelypackedpebbles,boulders

Dry, brown toreddish-brown, with variable accumulationsof clay, calciumcarbonate, andsoluble salts

Desert Soil(hot, dry climate)

Grassland Soil(semiarid climate)

Alkaline,dark,and richin humus

Clay,calciumcompounds

Soil Profiles in Different BiomesSoil Profiles in Different Biomes

aridisolsmollisols

Acidiclight-coloredhumus

Iron andaluminumcompoundsmixed withclay

Forest litterleaf mold

Humus-mineralmixture

Light, grayish-brown, silt loam

Dark brownfirm clay

Tropical Rain Forest Soil(humid, tropical climate)

Deciduous Forest Soil(humid, mild climate)

Soil Profiles in Different BiomesSoil Profiles in Different Biomes

oxisols alfisols

Soil Properties: BioticSoil Properties: Biotic

surface = algae top few cm of soil =

bacteria & fungi roundworms, segmented

worms, mites, insects farther down: burrowing

animals--gophers, moles, insect larvae, worms

even farther: some plant roots

surface = algae top few cm of soil =

bacteria & fungi roundworms, segmented

worms, mites, insects farther down: burrowing

animals--gophers, moles, insect larvae, worms

even farther: some plant roots

Soil CommunitySoil Community

Soil Community -- MycorrhizaeSoil Community -- Mycorrhizae

Redwood seedlings with (right) and without (left) mycorrhizae.

Pine seedling showing how mycorrhizal roots from one tree spread to inoculate other tree roots.

mycorrhizal symbiosis - mutualism between plant roots & fungi