NRES 251 Exam 1

Soil

Dynamic resource that supports plant life. Composed of mineral & organic solids, liquids & living organisms.

Soil Texture

Relative proportion of soil separates in a soil (what % clay, sand or silt it is). How well soil can hold water.

Soil Structure

Is the soil round/irregular/flat/porous? Drainage. Influences surface area. Smaller & flatter particles hold more water. Particles stick together in aggregates.

Bulk Density

Dry weight of soil per unit volume of soil. Mass of solids / Total Volume. Considers both solids & pore space.

Particle Density

Weight of an individual soil particle per unit volume. Only considers mineral solids, not pore space. Expressed in g/cm^3.

Porosity

Amount of pores or open space between soil particles. Volume of Voids (pore space) / Total volume of soil.

Volume Water Content

Volume of water associated with a given volume of dry soil.

Mass Water Content

Mass of water associated with a given mass of dry soil.

5 Soil Forming Factors

Climate, Organisms, Relief, Parent Material, Time.

4 Soil Forming Processes

Transformation, Additions, Losses, Translocation.

Additions

Materials added to the soil (i.e. Organic Matter).

Losses

From wind/water movement or uptake by plants, soil particles can be eroded, or harvested from the soil.

Transformation

Chemical weathering of sand & formation of clay, transformation of coarse OM into humus.

Translocation

Movement of soil constituents (organic or mineral) within the profile and/or between horizons. Moving down or up within soil.

Soil Components

Minerals, organic matter, water, and air (pore space).

Texture Influence on Ecosystem Functions

Holding water: the smaller the particle (clay) the easier for the soil to hold water. Larger particles (sand) drain better. Nutrient holding: finer textured particles retain nutrients easier.

Soil Fertility

Plant nutrient availability. pH, microbes, cycling, symbiosis, organic matter, minerals/parent material.

6 Types of Parent Material

Alluvium, colluvium, locustrine, residuum, aeolian, glacial deposits.

Alluvium

Flowing water (rivers)

Colluvium

Gravity- not sorted at all

Locustrine

Lake sediment- varves/thin layers

Residuum

From bedrock

Aeolian

Wind deposits (loess: wind blown silt) (i.e. sand dunes)

Glacial Till/Drift

Under glacier, gets pushed in front of it. Unsorted.

Glacial Outwash

Glacial melt water. Very sorted, gravelly/sandy.

O-horizon

Organic Matter

A-horizon

Topsoil

Ap-horizon

Plow layer

Ab-horizon

Barried horizon

E-horizon

Leaching zone

B-horizon

Accumulation zone

Bh, Bhs, Bs horizons

Spodic horizon- spodisols

Bt-horizon

Argillic horizon- alfisols

C-horizon

Parent material

R-horizon

Bedrock

Eluviation

Moving out/leaching

Illuviation

Moving in

5 forms of Chemical Weathering

Dissolution, hydrolysis, carbonation, hydration, oxidation/reduction. Common with small particles.

Dissolution

Dissolving- salts/carbonates

Hydrolysis

Water splitting- changing the mineral

Carbonation

Adding CO2

Hydration

Adding H2O

Oxidation/Reduction

Adding or removing electrons