Rock cycleSoil formationSoil compositionPhysical and chemical properties of

soilMain soil typesErosion and other soil problemsSoil conservation

groups: igneous, sedimentary, metamorphic

Igneous – from melted rock that has cooled/solidified (Ex. granite) Rarely has fossils, crystals

Sedimentary – formed on surface (land/water) from layered sediment broken from rock (Ex. limestone, shale) Most rock, fossils, visible layers

Metamorphic – other rock that changes due to heat/pressure (ex. slate and marble) Rarely has fossils, may have layered crystals

THE ROCK CYCLE !

Holds nutrients and waterCleanses and filters water as it flows

through soilAffects the amount of water that

returns to atmosphereNamed for physical and chemical

properties EX: texture, pH

IT TAKES A YEAR TO MAKE 1 mm TOPSOIL

Formed from weathering, takes TIME TIME (rocks broken into smaller and smaller bits) Physical weathering – alternate freezing and

thawing, wind/water erosion, ocean waves Chemical weathering – carbonic acid in soil

(from CO2 and H2O) Biological weathering – lichen produce acid

several factors influence the soil formed: Parent material – rock/mineral it came from Living organisms – decompose litter and

recycle nutrients (Ex. Rhizobium, fungi, insects, worms, snails)

1. Mineral Particles (45%) Weathered rock Provides essential nutrients for plants

2. Organic Material (5%) Litter, animal dung, dead remains of plants and

animals Increase water-holding capacity Humus – decomposed org. matter, binds

nutrients/water3. Water (25%)4. Air (25%) PERCENTS ARE FOR A

TYPICAL/HEALTHY SOIL

Pore space air- good for

aeration (O2, CO2, N2)

water- provides water to roots

O-horizon Rich in plant litter/organic

matter A-horizon

Topsoil (organic matter and humus), plant growth, leached

E B-horizon

Lighter colored subsoil, illuviation, high inorganic

C-horizon Somewhat weathered

parent material, groundwater, no organic

Bedrock - unweathered

There are millions of microorganisms in 1 tsp of fertile agricultural soil

Soil organisms provide ecosystem services

Examples Decaying and cycling organic material Breaking down toxic materials Cleansing water Soil aeration (especially done by

earthworms)

Nutrients are cycled between plants, organisms and soil

Example Bacteria and fungi

decompose plant and animal wastes

They are transformed into CO2, soil nutrients and water

Soil Texture Relative proportion of sand, silt and clay Sand: 2mm-0.05mm (large) Silt: 0.05mm-0.002mm (medium) Clay: less than 0.002mm (small)

Soil texture affects soil properties Coarse textured soil (sandy)

Will not hold water well- flows through easily

Fine textured soil (high in clay) Due to negatively charged surface, able to

hold onto important plant nutrients (K+, Ca2+)

Poor drainage Low oxygen levels in soil

Loam Combo all textures – 20% clay, 40%

sand and silt Ideal for agriculture▪ Sand holds air/water▪ Clay holds nutrients

Nutrients: Nitrogen, potassium (potash), phosphorus

Soil Acidity Measured using pH scale▪ 0-7 = acidic ; 7 = neutral ; 7-14 = basic

pH of most soils range from 4-8 Affects solubility of certain plant nutrients Affects leaching of nutrient minerals▪ Ex: acidic soil doesn’t bind positive ions as well

Optimum soil pH is 6-7▪ plant nutrients are most available to plants▪ Soil amendments (ex: lime) can be used to achieve this

pH

Physical and chemical properties of soil

Soil vocab: clay, silt, sand, loam, humus, topsoil

coniferous forests O-horizon

composed of needles

Not good farmland- too acidic

Temperate Deciduous Forests

Precipitation high enough to leach most organics and nutrients out of O-, A- and B-horizons

Soil fertility maintained by leaf litter

temperate, semi-arid grassland

Very fertile soil Soluble nutrients

stay in A-horizon due to low leaching

arid regions Low precipitation =

no leaching, no vegetation = not much org. matter

tropical and subtropical areas with high precipitation

Very little organic material accumulation due to fast decay rate

B-horizon is highly leached, acidic, and nutrient poor

Nutrient minerals in plants, not soil

Soil Erosion Def: wearing away of soil from the land Caused primarily by water and wind

Why a problem? less soil grow less plants Decrease amount of nutrients need

more fertilizers Sediment into surface water that

decreases quality of fish habitat

Erosion causes: natural, but anthropogenic activities

make it worse:▪ Poor agricultural practices▪ Removing natural plant communities when building roads (plant cover holds soil)▪ overgrazing

Great Plains have low precipitation and subject to drought 1930-1937 severe

drought No natural vegetation

roots to hold soil in place▪ Replaced by annual crops

Winds blew soil as far east as NYC and DC.

Farmers went bankrupt

Nutrient Mineral Depletion

Soil Salinization Def: gradual accumulation of salt

in the soil Often in arid and semi-arid

areas The little precipitation that falls is

quickly evaporated Leaves behind salts most plants die

Soil remediation Dilution,

bioremediation/phytoremediation

Desertification Def: degradation of once-

fertile land into nonproductive desert

Typically a human-induced condition

Ex: African Sahel; possible solution: Agroforestry to plant crops and Acacia trees (nitrogen-fixing + decomposing leaves)

Conservation Tillage Residues from previous

year’s crops are left in place to prevent soil erosion

Includes no tillage Con: weeds

o Crop Rotation (polyculture)• Planting a series of different crops in the same field

over a period of years• Lessens pest and insect disease• Replenish nitrogen• Ex: corn soybeans oats alfalfa (soy and alfalfa

= legumes)

Contour Plowing Plowing around hill

instead of up-down Rows catch water

Strip Cropping Alternating strips of

different crops on steep slopes ; prevents erosion by naturally damming water

Terracing Creating terraces on

steep slopes to prevent erosion

Strip Strip CroppingCropping

TerraciTerracingng

Organic fertilizers Animal manure, crop residue, worm castings, and

compost (individual and municipal) Nutrients available only as material decomposes▪ Slow acting and long lasting▪ Could contain disease-causing pathogens if not

properly composted.

Inorganic fertilizers Made from chemical compounds Soluble▪ Fast acting, short lasting

Bad for environment▪ leach and pollute groundwater and surface run-off▪ Produced using lots of fossil fuels

Use soil without depleting fertility and amount so it’s productive enough for future generations

Food Security Act (Farm Bill) Food Security Act (Farm Bill) 19851985 Required farmers with highly erodible

soil to incorporate erosion-control practices or are at risk of losing subsidies

What physical test could you do to soil?

What chemical test could you perform on soil?

What are the layers of soil horizons, but top down?

What is the ideal pH for most plants?

Having a pH lower than 7 makes a substance a ____.

What is loam?Why does clay bind readily to some

ions?What inorganic soil particle is the

largest?What inorganic soil particle is the

smallest?

What happens to the quantity of organic material as you move down the horizons?

Which soil horizon is the illuviation zone?

Which soil horizon is where the topsoil is located?

What does leaching mean?

Does rain affect leaching?Other than organic matter and

inorganic particles, what else constitutes soil?

What does anthropogenic mean?What does sustainable mean?

In typical soil, is there more organic matter or inorganic particles?

Why is air space important for soil?What is humus?What part of soil increases its water

holding capacity?Where do the inorganic particles of

soil come from?

Name the 3 types of rockWhich rock is from cooled lava?Which rock forms from layer upon

layer of other rock particles and dead organisms?

What rock forms when either of the other 2 are exposed to high heat and pressure enough to change them?

Granite is an example of what type of rock?

Marble is an example of what type of rock? Limestone and sandstone are examples of

what type of rock? Why is soil important? What are the 3 types of weathering

processes? What role do earthworms play in forming

soil?

How does carbonic acid form?What does it do to rock?Give an example of physical

weathering. Give an example of biological

weathering.Where is bedrock located?

What are the consequences of erosion?

What are causes of erosion?What is desertification?What is soil salinization? How do you remedy it?What causes it?