Chapter 1 - Intro to Soil Science Flashcards
Functions of Soils (6)
- Medium for plant growth
- Maintains water supply
- Recycle materials
- Habitat for other organisms
- Engineering medium
- Modifier of the atmosphere
Function: medium for plant growth
- Physical support
- Contains nutrients, water
- Ventilation system due to respiration: CO2 vents out, O2 replaces
- Buffer temperatures
Function: maintain water supply
- Filters H2O - cleans it
* Slows H2O movement
Function: recycle materials
- Soil is a big compost pile, decomposes plant and animal materials
- Producers-Consumers-Decomposers-Minerals-Producers cycle
Biomass
- Living mass - organic matter
* Made of CHON (90% of living things)
Function: habitat for other organisms
- Microorganisms
* Macroorganisms (earthworms, moles, etc.)
Function: engineering medium
- Retaining walls to bridges
* Goal is to compact the soil
Function: modifier of atmosphere
- Dry soil, limited plants = creates dust
* Affects temperature with enough dust in the air
Soil
An unconsolidated layer of minerals and OM on the earth’s surface
Regolith
Soil
Soil is composed of
minerals, gases, water, OM, and microorganisms
3 Minerals of soil
Sand, Silt, Clay
Sand attributes
- Largest size, between .05 and 2.0 mm in diameter Primary mineral (not broken down by chemical means, weathering)
Silt attributes
- Primary & secondary minerals, some broken down
- between .05 and .002 mm in equivalent diameter
Clay attributes
- Smallest size, <.002 mm in diameter
Heavy weathering
Organic Matter (OM) - description and functions
- Living or once-living, carbon-based material
- Breaks down and releases elements back to the environment
- Feeds the “producers”, the plants, and all other organisms there
Humus - description
- Dark-colored organic compound
- Very broken-down OM
- Very colloidal in nature
Colloid - description
- A very small particle
- Large surface area vs. volume
- Glue-like, can pull things together
Soil profile
A vertical view of the soil material (to any depth), contains horizons
Soil horizons
Horizontal layers of the soil profile
O Horizon
Organic, topmost layer; feeds the layers below it
A Horizon
Topsoil; “plow layer”; usually a darker material (due to OM breaking down) with the most organisms
E Horizon
Zone of eluviation
Eluviation
Leaching; “the transportation of dissolved or suspended material within the soil by the movement of water when rainfall exceeds evaporation”
B Horizon
Subsoil; less OM; accumulates some leaching; typically more clays than A horizon; lighter color
C Horizon
Coarse layer of materials; limited weathering
R Horizon
Consolidated/solid rock
Influences on horizons
Weather Erosion Parent materials Slopes Plant types Organisms
Soil texture
- Describes the size of the soil particles
- The proportion of SSC (sand/silt/clay) in a soil, usually expressed as percentages
- Hard to change
Loam
Soil having moderate amounts of SSC (a healthy balance, but not necessarily equal)
Soil structure
- Describes the manner in which soil particles are aggregated, and defines the nature of the system of pores and channels in a soil.
- The arrangement of soil particles (SSC, OM) into aggregates, or soil peds
- Can be changed “easily” (such as compaction)
Macropore size and purpose
> .08 mm
- movement of air/gasses and water, plant roots, micro-organisms
- generally found between peds (interpore peds)
Biopores
Macropores that are created by plant roots, earthworms and other organisms
Micropore size and characteristics
t permit much gas movement
