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

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Weathering – breaking down rock into soil Climate(T + water) + biotics Creates erosion PhysicalChemicalBiological

Chemical Weathering

Biotic Weathering Roots Lichens Animals produce CO 2 which diffuses into soil, reacts with H 2 O & forms carbonic acid (H 2 CO 3 )

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

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 Soil semiarid 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 to 8.0 Pygmy Forest in California ( ) 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 Farm Act - subsidy for taking highly erodible land out of production and replanting it with soil-saving plants for 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 , p. 281 Cleanup Prevention 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)

Evaporation Transpiration Evaporation 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.