Exam 1

Solum

________: horizons above C (not C); the horizons affected by soil forming factors.

Soil

________ binds and detoxifies many pollutants, thus purifying water as it moves towards water bodies.

How are Soil nutrients replenished

by weathering of minerals, degradation of organic residues, and sorption of nutrients that are moving with water through soil.

Regolith

Unconsolidated debris layer

Polypedon

group of similar pedons

Pore space (50%)

contains air and water

Particles/Soil Solids (50%)

contains minerals and organic matter

5 major soil functions

1. medium for plant growth
2. support for buildings and roads (engineering medium)
3. Habitat for organisms
4. Purification of water and regulator of water supplies
5. recycling system for nutrients and organic wastes

How does soil physically support plants?

Supply nutrients, hold water, ventilation, moderates temperature fluctuations, detoxification of substances or microbes

Essential macronutrients for plant growth

Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous, Potassium, Calcium, Magnesium, and Sulfur

Essential Micronutrients for plant growth

Iron, Manganese, Boron, Zinc, Copper, Chloride, Molybdenum, and Nickel

What factors effect soils ability to support roads and buildings?

Bearing strength, compressibility, shear strength, and stability

What factors effect soils ability to support microhabitats?

oxygen, pH, temperature, and water availability

How soil purifies and regulates water

slowing down the flow of water, binds and detoxifies pollutants

Soil recycles animal and plant waste into…

Humus, CO2, and nutrients for plants

Soil is made from

weathered regolith

How is regolith processed?

through biochemical and physical processes like: weathering, erosion, and microbial decay

through synthetic processes like the formation of minerals, organic compounds, and aggregation

5 soil forming factors

1. Climate
2. biota
3. parent material
4. topography
5. time

Active soil forming factors

climate and biota

passive soil forming factors

parent material and time

modifying soil forming factors

topography

define soil with the 5 soil forming factors

A dynamic natural body having properties derived form the combined effects of **climate** and **biotic** activities, as modified by **topography**, acting on **parent material** over periods of **time.**

is there soil on the moon?

no only regolith

What is a soil profile?

Vertical section exposing a set of layers called horizons that extends down to the parent material

what are soil horizons?

Layers of soil, approximately parallel to the soil surface, differing in properties and characteristics from adjacent layers below or above it that vary in thickness and may have irregular boundaries

Features of topsoil

\-layer most affected by soil forming factors

\-darker (more organic matter)

\-more plant roots

\-more porous

\-smaller aggregates

\-usually less clay (more sand & silt)

features of subsoil

\-layers that are less affected by soil forming factors

\-lighter in color (less organic matter)

\-fewer plant roots

\-more dense (less porous)

\-larger aggregates

\-usually more clay

Master Horizons

O, A, E, B, C, R

Horizon O

Horizon of partially or wholly decayed organic materials that may occur over or in place of an A horizon

Horizon A

topsoil mineral horizon

Horizon E

Subsoil horizon that is a zone of eluviation (depletion) \n – Usually loss of clay, oxides, salts, minerals, organic matter \n – Usually white or very light colored

Horizon B

Subsoil horizon that is a zone of accumulation \n – Usually gain of clay, oxides, salts, minerals

Horizon C

Regolith

Horizon R

Rock (not always included in soil profile)

Do all soils have all horizons?

No

Pedon

smallest 3D soil unit with all characteristics of the soil

4 major components of soil

Air, water, mineral, and organic matter

Ideal soil component percentages

Air (25%)

Water (25%)

Mineral (45%)

Organic matter (5%)

how does soil air differ from atmospheric air?

* higher in moisture
* higher in CO2
* lower in O2

Soil water determines…

* organism survival (plants, microbes, small animals)
* quality and quantity of water resources

How does soil water differ from drinking water?

* held by soil particles, which affects its flow
* contains dissolved organic and inorganic substances
* this is where plants get most of their nutrients
* acidity or alkalinity (i.e., pH) affects chemical & biological reactions

pH is considered _______ in soils due to its influence on so many chemical and biological processes

master variable

pH formula

**pH = -log [H+]**

Nutrient availability is tied to what?

nutrients in the soil solutions (soil water)

Plants uptake nutrients through what two processes?

Mass flow and diffusion

what is mass flow?

Ions are carried with the flow of water

what is diffusion

Ions move from areas of high concentration (near soil colloids) to low concentration (area around roots that depleted due to uptake)

How does soil replenish the soil solution?

through weathering, mineral and organic degradation, nutrients released through plant uptake or leaching with percolation**,** and through particles releasing stored nutrients

what are Soil solids?

Mineral (inorganic) constituents of soil called primary particles

What are the Primary particles?

Sand, Clay, and Silt

What are the Features of Sand?

\-0.05-2 mm

\-see with eye

\-low attraction to water and each other

\-low ability to hold chemicals and nutrients

\-tend to act as individuals

\-loose, gritty

What are the features of silt?

\-0.002-0.05 mm

\-see with microscope

\-moderate attraction to water and each other

\-low ability to hold chemicals and nutrient

\-tend to act mostly as individuals, but some groups

\-smooth, powdery, some clods

What are the Features of Clay

\-

How is soil texture denoted?

percentages that describe the relative amounts of primary particles

What is soil structure?

the arrangement or distribution of particles in soil; classified by shape and affects water movement

What are Aggregates?

groups of soil particles that hold together

What are minerals?

homogenous inorganic compounds that have a definite chemical formula

how are primary minerals formed?

as molten lava cools and solidifies

How are secondary minerals formed?

recrystallized or altered forms of primary minerals

What are the three stages of soil organic matter?

living biomass, detritus, and humus

what is the living biomass?

plants and other living organisms that are identifiable

what is detritus?

dead residues from living organisms that are identifiable

what is humus (stabilized soil organic matter)

* very complex mixture of organic compounds that accumulate in soil because they are resistant of decay
* no longer identifiable
* plays a role in soil structure by binding mineral particles together
* holds water, nutrients, and chemicals

Weathering uses what processes to destroy or decompose rock?

biological chemical and physical

weathering usually leads to what?

formation of regolith and formation of soil due to the 5 soil forming factors

physical weathering

abrasion by water ice and wind; temperature; plants and animals

chemical weathering

hydration, hydrolysis, dissolution, acid dissolution, redox, complexation

weathering results in what?

increasingly smaller particles (rock, sand, silt, clay), increasingly more stable particles (gypsum < calcite < dolomite < Al silicates < Fe/Al oxides), release of soluble materials (Ca, Mg, K, Na, SO4)

Types of rocks

igneous, sedimentary, metamorphic

igneous

formed when melted lava cools

sedimentary

deposition and recrystallization of weathering products from other rocks; compacted or cemented weathering products

metamorphic

igneous or sedimentary rocks transformed by high heat or pressure

How does rock differ from mineral?

naturally occurring aggregate of minerals with no definite chemical composition

How does mineral differ from rock?

Naturally occurring substance that has a characteristic composition, highly ordered atomic structure, and specific physical properties with definite chemical composition

What elements are abundant in earth’s crust?

O, Si, Al, Fe, Ca, Mg, Ma, K

what crust elements are acidic?

Al and Fe

what crust elements are basic?

Ca, Mg, Na, K

What crust elements are toxic?

Al and Na

What crust elements are beneficial?

Si and Na

How does rock and soil differ from each other?

soil is higher in Al and Fe, lower in K and Ca

What are the mineral groups?

silicates, oxides, carbon, phosphates, sulfates, halides

Silicates

Quartz; formed from clays: Feldspar, Amphiboles, Pyroxenes, Micas

Quartz

dominate in sands resistant to degradation

oxides

Very insoluble; Hematite (Fe2O3), Goethite (FeOOH or Fe (OH)3), Gibbsite (Al(OH)3)

Carbonates

somewhat soluble; Calcite (CaCO3), Dolomite (CaMg(CO3)2)

phosphates

very insoluble; Apatite (Ca5(OH, F, Cl)(PO4)3)

sulfates

relatively soluble; Gypsum (CaSO42H2O)

Halides

very soluble; Halite (NaCl)Sylite (KCl)

Primary minerals

minerals that have not been altered chemically from their initial formation e.g., from solidification of magma; Most of the silicates, except for the clay minerals smectite, vermiculite, chlorite, and kaolinite, which will be discussed later

Primary mineral examples

quartz, mica, feldspar, hornblende, anorthite, olivine

Secondary minerals

minerals that form near the surface of the earth; recrystallized products from the breakdown and/or alteration of primary minerals; most other minerals including oxides, carbonates, and sulfates

secondary mineral examples

Goethite

Hematite

Gibbsite

Clay minerals- smectite-vermiculite-chlorite-kaolinite

Dolomite

Calcite

Chemical weathering is enhanced by?

water oxygen and acid

dissolution

minerals that dissolve in water

example: gypsum

acid dissolution

weathering accelerated by acid, enhanced by hydration and dissolution reactions

Where do acids for acid dissolution come from?

* water
* root and microbe respiration
* organic acids from roots and decomposition of organic matter
* mineral acids from decomposition of some minerals
* example: pyrite → sulfuric acid

redox

Minerals with Fe, Mn, and S are susceptible to redox reactions which destabilize the crystal structure and cause it to break down

What is a redox reaction?

a chemical reaction where the oxidation state of an element is changed by the transfer of electrons

hydration

intact water molecules can change the structure of minerals

hydrolysis

* water molecules are split into hydroxyl and hydrogen ions at the minerals surface and part is absorbed into the mineral
* Hydro = water
* lysis = separations
* Hydrogen ions often replace the cations