Earth Systems and Resources

D. Soil and Soil Dynamics: • Rock cycle

• Formation

• Composition

• Physical and chemical properties

• Main soil types

• Erosion and other soil problems

• Soil conservation

Rock Cycle

• Igneous – from heat, pressure (magma)

• Sedimentary – formed when sediments (sand, mud, gravel, shells) are compressed

• Metamorphic – form when sedimentary/igneous rocks are subjected to high pressure and T

Three Types of Rocks

Rock Cycle

http://www.youtube.com/watch?v=sLKXIVHoh54&edufilter=vH8ntV7keCE-ZLl5wRMzNg

Weathering – breaking down rock into soilClimate(T + water) + bioticsCreates erosion

PhysicalPhysical

ChemicalChemical

Biological Biological

Chemical Weathering

Biotic Weathering

• Roots

• Lichens

• Animals produce CO2 which diffuses into soil, reacts with H2O & forms carbonic acid (H2CO3)

• Sand – largest type of soil; visible with the eye• Silt - flour; barely visible• Clay – very tiny, fine; electron microscope• Larger than 2mm in diameter = gravel/stones

(no value to plants)

Soil Composition

Soil Horizons

• O horizon - uppermost layer; organic material (plant decay)

• May be thick or thin (desert, tropical rain forests)

• A horizon – mineral mixed with humus

• O + A = topsoil

Soil Horizons• B – subsoil – clay; rich in Fe, Al compounds (acid

deposition)• Lighter colored• C – rock fragments

• Saturated with groundwater• Usually no roots • Borders parent bedrock

• The percentages (by weight) of different sized particles of sand, silt and clay

• How soil particles are organized and clumped together. (sand, silt, clay)

Soil Texture

• Mature soils are layered

• Infiltration – percolation

• Leaching – dissolving minerals

• Type of soil determines percolation and leaching.

Soil Horizons

• Porosity – volume and space between particles

• Porosity = permeability

• Sand, silt, clay

Soil Composition

http://techalive.mtu.edu/meec/module06/Percolation.html

Mosaic of closely packed pebbles, boulders

Weak humus-mineral mixture

Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts

Alkaline, dark, and rich in humus

Clay, calcium compounds

Desert Soil(hot, dry climate)

Grassland Soilsemiarid climate)

Tropical Rain Forest Soil(humid, tropical climate)

Acidic, light-colored humus – little topsoil

Iron and aluminum mixed with clay

Deciduous Forest Soil(humid, mild climate)

Forest litter leaf mold

Humus-mineral mixture

Light, grayish-brown, silt loam

Dark brown firm clay

Coniferous Forest Soil(humid, cold climate)

Light-colored and acidic

Acid litter and humus

Humus and iron and aluminum compounds

Soil pH

• Determines solubility of minerals

• Most soils - 4.0 to 8.0 • Pygmy Forest in

California (2.8-3.9) • Death Valley, California,

(10.5)

Factors Effecting Soil• Depth - depends on erosion, plant life, etc.

• Color –

• Dark soil, rich, lots of organic matter (leaf decay)

• Light soil (sand) very little organic matter

• Slope – runoff, erosion

• After plowing/harvesting

• 6.4 billion tons of soils per year (U.S.)

• Renewable but recycles slowly

• Unsustainable

• Lowers fertility

• Overloads lakes, rivers with sediments

Erosion

Case Study: Soil Erosion in the U.S.

• 1985 Farm Act - subsidy for taking highly erodible land out of production and replanting it with soil-saving plants for 10-15 years

Reducing Erosion

No-till

Minimum Tillage (reduced tillage)

Reducing Erosion• Terracing• Contour Plowing - plowing across the slope • Windbreaks - also help retain soil moisture,

supply some wood for fuel, and provide habitats for birds

• Strip cropping – a row crop (corn) is alternated in strips with another crop that completely covers the soil:• Helps prevent the spread of pests and plant

diseases

Cover Cropping (alley cropping) – several crops are planted together in strips or alleys between trees and shrubs that can provide shade (which reduces water loss by evaporation) and helps to retain and slowly release soil moisture.

Surface Creep – mountains/sand dunes

Desertification

• About one-third of the world’s land has lost productivity due to desertification

• Drought

• Human activities that reduce or degrade topsoil***

Salinization

• Repeated irrigation causes salt buildup

Fig. 13-15, p. 281

CleanupPrevention

Soil Salinization

Solutions

Reduce irrigation

Switch to salt-tolerant crops (such as barley, cotton, sugarbeet)

Flush soil (expensive and wastes water)

Stop growing crops for 2–5 years

Install underground drainage systems (expensive)

EvaporationTranspiration

EvaporationEvaporation

Waterlogging

Waterlogging:

1.Precipitation and irrigation water percolate downward.

2. Water table rises.

Less permeable clay layer

Soil Conservation

• Fertilizers can help restore soil nutrients, but runoff of inorganic fertilizers can cause eutrophication pollution.• Organic fertilizers: from plant and animal

(fresh, manure, or compost) materials.

• Commercial inorganic fertilizers: Active ingredients contain nitrogen, phosphorous, and potassium and other trace nutrients.

Fertilizers • Organic Fertilizers – animal manure, crop

residues, bone meal, and compost• Inorganic Fertilizers – man-made from chemical

compounds• Benefits – exact compositions are known; they

are soluble & thus immediately available to the plant

• Costs – quickly leach away (pollutes water); doesn’t increase water holding capacity of the soil as organic fertilizers do.