Rock Cycle and Soil

Minerals

Elements or inorganic compounds that occur naturally and are solid

Usually have crystalline structure

Almost all of Earth’s crust made of minerals

Rock Cycle

Interaction of processes that change rocks from one type to another

Recycles material over millions of years

Slowest of the earth’s cyclic processes

The Rock CycleThe Rock Cycle

Three Classifications of Rock

Igneous

Sedimentary

Metamorphic

Igneous Rocks

Form from molten rock material (magma) near the surface

Underground igneous rocks are called igneous intrusions, granite

Magma that reaches the surface & cools is called extrusive igneous rock, basalt or pumice

Sedimentary Rocks

Weathered materials that has been deposited in layers and has undergone compaction

Make up 75% of earth’s surface, such as limestone, sandstone, bituminous coal

Metamorphic Rocks

Preexisting rock that have been altered by high temperature, high pressure, or chemically active fluids

For example: graphite, slate, or marble

Soil Terms to Know:

Soil

Soil Horizons

Soil Profile

Humus

Soil Structure

Four distinct physical parts:Mineral particles

Organic matter

Water

Air

Inhabitants include:Plants, animals, fungi, & microorganisms

Soil Horizons

Obtained by taking a core sample (soil profile)

O horizonSurface-litter layer

Rich in organic matter(dead plant material, animal waste, fungi, etc.)

A horizonTop-soil layer

Porous mixture of humus

Soil Horizons---cont.B horizon

SubsoilZone of illuviation or accumulation (area where minerals leached out of topsoil & surface litter)Typically rich in Fe and Al

C horizonContains weathered pieces of rockBelow the extent of most roots & is often saturated with groundwaterLies on top of unweathered bedrock

Soil Texture

Determined by the amounts of different sizes and types of mineral particles (clay, silt, & sand)

Loams have roughly equal portions of clay, silt, sand, & humus and is best for growing crops.

Texture, porosity, permeability determine water-holding capacity, aeration, and workability

Soil Texture—cont.

Soil porosity: measure of the spaces per volume of soil & average distances between those spaces.

As particle size increases porosity decreases, holds less water and nutrients

Soil permeability: rate at which water & air move from upper to lower soil layers

As particle size increases permeability increases, infiltration increases

Properties of Soils with Different Textures

Soil Texture

Nutrient-Holding Capacity

Water Infiltra-tion Capacity

Water-Holding Capacity

Aeration Worka-bility

Clay Good Poor Good Poor Poor

Silt Medium Medium Medium Medium Medium

Sand Poor Good Poor Good Good

Loam Medium Medium Medium Medium Medium

Soil Acidity and Plant Growth

pH of soil influences ability of plants to take in soil nutrients

H+ bind to negative sites in the soil which allows cation plant nutrients to move through the soil

Acid deposition can result in loss of soil fertility

Soil Tests

Chemical tests: pH, Salinity, Ion exchange capacity

Physical tests: water-holding capacity, percolation rate/permeability, soil texture to determine soil type

SOIL TEXTURAL TRIANGLE

PERCENTAGE OF CLAY

Read Numbers on This Side

Read Numbers on This Side

PERCENTAGE OF SILT

Read Numbers on This Side

PERCENTAGE OF SAND

How much clay, silt and sand are in the soils indicated by stars below?

Erosion

Movement of soil from one place to another

Most is caused by moving water

Types of water erosion:Sheet—wide sheet of water moves

Rill—water forms small channels

Gully—small channels join together & get wider

Water Erosion

Desertification

Conversion & loss of marginal semi-arid or arid land to desertCauses:

OvergrazingDeforestation with no reforestationSurface mining with no reclamation\Eroding/salt-concentrating (salinization) irrigation techniquesBad farming practicesSoil compaction Poisoning of soils by pesticides/chemicals

Soil Conservation & Regeneration

Conservation tillageResidues from previous crops are left in soilResidues cover & help hold soil in place

No tillageLeaves the soil undisturbed prior to planting, special machines cut a narrow furrow in the soil for seeds Increases organic material in soils & improve water-holding capacity

Preserving Soil Fertility

Two main types of fertilizer:Organic—from natural materials, complex, slow-acting, long-lasting

Inorganic—from manufactured chemical compounds• Adv: easy to get, soluble, immediately available to plants,

increases soil fertility and speeds up growing process

• Disadv: short-lived, doesn’t provide micronutrients, lacks organic material which decreases water-holding capacity, over-application impacts plants, water, and human health

Organic Fertilizers

Animal manure

Green manure: fresh or growing vegetation plowed into the soil

Compost

Spores of mushrooms, puffballs, and truffles: attach to plant roots and help absorb moisture & nutrients

Other Options for improving Soil

Adding different soils to adjust water-holding capacity

Apply lime for acidic soil

Apply sulfur for alkaline soil

Burn crop residue to add potassium

Plant legumes or apply manure to increase nitrogen

Humus: nutrients, water-holding capacity, aeration, helps root growth