NRES 251 exam 4 review

Lecture 13: Physical Properties

soil taxonomy

a soil classification system consisting of six hierarchical categories based on observable soil characteristics. The system recognizes 12 soil orders.

hue

intensity of yellow/red (pages)

value

brightness (up/down)

chroma

saturation (side to side)

hydrometer

An instrument for determining the density of solids and liquids by flotation.

stoke's law

An equation relating to the terminal settling velocity of a smooth, rigid sphere in a viscous fluid of known density and viscosity to the diameter of the sphere when subjected to a known force field. It is used in the particle size analysis of soils by the hydrometer method

macroaggregates

Soil particles joined together to form larger discrete particles of various shapes and sizes, visible to the naked eye. (0.25-5 mm)

microaggregates

Intimate association of soil particles, often clay-humus, not visible to the naked eye. (0.002-0.25 mm)

Flocculation

the process by which colloidal (i.e. clay-size) particles join together

Shrink and Swell

soil swells with moisture and shrinks when dry

soil density

weight of a unit volume of soil expressed on either a wet basis (including soil and water) or on a dry basis (soil only, most common)

bulk density

The mass of dry soil per unit volume, including the air space, and organic matter

particle density

the mass per unit volume of the soil particles, only including solids

most common mineral particle density

2.65 g/cm3

porosity

The percentage of the total volume of a rock or sediment that consists of open spaces.

Lecture 14: Soil Water

capillary flow

Water moves up hill (or in any direction) due to the forces of adhesion and cohesion - movement under tension or negative pressure

soil water potential

measures the energy status of water

-more negative: water is held tight

-less negative: water isn't held tight

water tends to move from high potential (less negative) to low potential (more negative)

gravitational potential

Potential energy that depends on the height of an object

matric potential

the potential energy generated by the attractive forces between water molecules and soil particles

hydrostatic potential

Energy due to the weight of the water at a given elevation and pressure

osmotic potential

The tendency of water to move across a semi-permeable membrane into a solution

tensiometers

instrument used to measure soil moisture

Bulk Density equation

dry mass/volume

Particle Density equation

dry mass (g) of soil / volume of soil particles

saturation

all pore spaces filled with water (max retentive capacity)

field capacity

after gravitational water drains

wilting point

water held tightly by micropores, no longer available for plants

hygroscopic coefficient

remaining water no longer considered liquid phase

Lecture 15: Cation Exchange Capacity

soil colloids

smallest fraction of soil particles, composed of clays and humus

Cation Exchange Capacity (CEC)

the ability of a particular soil to absorb and release cations

tetrahedron (SiO4)

silicon shares half the charge from its 4 oxygens

octahedron [Al(OH)6, Fe(OH)6]

aluminum/iron share half the charge from its 6 hydroxyls

Tetrahedral sheets

composed of 4 oxygen atoms in a tetrahedron with a silicon atom in the center

-si tetrahedra share basal oxygen

-apical oxygens shared with octahedral sheets

Isomorphous substitution

the replacement of one atom by another of similar size in a crystal lattice without disrupting or changing the crystal structure of the mineral

low pH= -log [H+]

low pH-> a lot of protons (hydrogen)

humus

large irregular organic molecules; varied composition

Lecture 16: Soil pH

alkalinity

capability to resist acidification (buffering)

Cation weathering

Ca-silicate + 2H -> H4SiO4 + Ca

Carbonate inputs

CO3 + H -> HCO3 + H -> H2CO3

Soil pH influences

acidifying:

-precipitation, and leaching

-plant and microbial activity

-accumulation of OM

alkalizing:

-cation weathering

-carbonate inputs

exchange of H+ to help maintain pH

CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+

weathered Al causes hydrolysis

Al + 3H2O -> Al(OH)3 + 3H

nitrification

NH4 + 2O2 -> H2O + 2H + NO3

sulfur oxidation

2FeS2 + 7O2 + 2H2O -> 2FeSO4 + 4H + 2SO4

Additions of Elemental Sulfur (Treating Basic)

2H2O +3O2 + 2S -> 2SO4 + 4H

Lime Added to soil (Treating Acidic)

CaMg (CO3)2 + H2O -> Ca + Mg + 2HCO3

HCO3 + H -> H20 + CO2

NH4 additions (Treating Basic)

2O2 + NH4 -> NO3 + H2O + 2H

Lecture 17: Soil Biology, Organic Matter, and Best Management Practices

Living Biomass

bacteria, fungi, fine plant roots

What is soil organic matter?

all carbon compounds in soil that are/were components of a living organism

identifiable dead tissue

detritus

humic substances

irregular complex polymers, resistant to breakdown

nonhumic substances

identifiable byproducts of soil microbial activity

soil biota

organisms that spend all or a portion of their lifecycle within the soil or on its immediate surface

bacteria and fungi

most abundant organisms within soil, 80-90% of soil metabolic activity

herbivores

feed on living plants

detritivores

feed on dead plant tissue

predators

feed on smaller organisms

Actinomycetes

need aerobic conditions, decompose complex organics, furthering humus development, sensitive to low pH and high water content, produce over 2/3rds of all antibiotics

Saprophytic fungi

effective at degrading large organic compounds using extracellular enzymes, litter decomposers, brown-rot, white-rot fungi, abundant in upland soils, more resistant to desiccation and low pH than bacteria

litter decomposers

ephemeral substrates

brown-rot fungi

cellulose, not lignin

white-rot fungi

lignin and cellulose

Mycorrhizae

act as an extension of plant root system, contribute soil nutrients (especially phosphorus), and add water to plant in exchange for carbon, 90% of all plant species have some relation (except agriculture)

ex: ectomycorrhiza, arboscular mycorrhiza

Microfauna

Small, often microscopic animals, especially those that live in the soil.

Nematodes

predatory roundworms, 4-100 micrometers in diameter, activity releases more plant available nutrients via predation on bacteria

Protozoa

one-cell organisms that feeds on soil bacteria and have free movement via cilia or flagella

Earthworms

create burrows that leave behind casts, OM mixed and shredded as it passes through gut

-no native earthworms in northern US

Epigeic, Endogeic, Anecic

Earthworm sizes in order

Rise in CN =

decrease in Nitrogen, and increase in Carbon

Lowering of CN =

increase of CN

Libile

Changing rapidly and often (repeating compounds like Hemicellulose, cellulose, chitin, and starch)

recalcitrant

hard to break down, ex: lignin

humus made up of =

lignin