Chapter 5: Forest Soils Flashcards
This is the upper, unconsolidated layer of earth surface
Soil
What are the two main components of soil?
Organic and mineral parts
What three things does soil provide to plants?
Support, water, nutrients
What are five types of organisms that make up soil communities?
Bacteria, fungi, protists, invertebrates, and vertebrates
Generally, what percent of soil is mineral?
45%
Generally, what percent of soil is water?
25%
Generally, what percent of soil is air?
25%
Generally, what percent of soil is organic matter?
5%
What is the term for soil creation?
Pedogenesis
What are the five factors of soil formation?
Parent material, climate, biota, topography, time
Parent material is the source of this soil component
Mineral component
What are the two main sources of parent material?
Decomposed bedrock and transported material
What three aspects of soil does parent material affect?
Fertility, soil depth, and development rate
This type of soil formation is deposited by ice/glaciers
Morainal
What 5 elements make up morainal soils?
Boulders, stones, sand, silt, clay
This type of soil formation is deposited by flowing glacial meltwater
Fluvioglacial
What two elements make up most of fluvioglacial soils?
Sand and gravel
This type of soil formation is deposited by lake water
Lacustrine
What two elements make up most of lacustrine soils?
Silt and clay
This type of soil formation is deposited by stream water
Alluvial
What three elements make up most of alluvial soils?
Sand, silt, clay
This type of soil formation is deposited by wind
Eolian
What two elements make up most of eolian soils?
Very fine sand and silt
This type of soil formation is deposited by gravity
Colluvial
What three elements make up most of colluvial soils?
Sand, silt, bedrock fragments
What are five influences of climate on soil?
Weathering parent material; Erosion/transport of soil; Decomposition rates; Soil organic matter inputs; Decomposer biota
This is the breakdown of parent material; the first step in soil formation
Weathering
What are three ways soil biota affect soil formation?
Source of organic component; Organisms affect SOM accumulation; Organisms decompose and mix SOM
This topographical feature modifies other factors in soil formation
Relief
Are soils deeper and wetter on ridges?
No
Are soils deeper and wetter in depressions?
Yes
These topographical features restrict drainage
Shallow water tables
Which slope aspect is wetter, northern or southern?
Northern
Which slope aspect has lower organic matter, northern or southern?
Southern
What are two effects of topographic relief on soils?
Erosion and transport
Do soils take a short time to develop?
No
Do physical and biological properties of soils change with age?
Yes
Soils develop this as they age
Layered structure
What are soil layers called?
Horizons
What are the four horizon-forming processes?
Additions, losses, translocations, transformations
What are five examples of soil additions?
Sediments, SOM, water, air, solar energy
What are three examples of soil losses?
Evapotranspiration, erosion, leaching
What are three examples of soil translocations?
SOM movement, particle movement, movement of nutrients between layers
What are two examples of soil transformations?
Chemical changes and physical changes within layers
On what basis do soil scientists classify different soils?
Horizons
What soil horizons do capital letters identify?
Master horizons
What do lowercase and numeric suffixes denote in soil horizons?
Additional traits
This soil horizon is made up of surface litter, an organic layer of decaying plant and animal tissue
O horizon
This soil horizon is the mineral horizon below O, and is made up of humified SOM mixed with mineral material
A horizon
What is the A horizon also known as?
Topsoil
This soil horizon is the zone of leaching, and is made up of leached minerals and organic matter
E horizon
What is the E horizon also known as?
Eluvial zone
In what type of soils is an E horizon found?
Older, developed soils
This soil horizon is a zone of clays and minerals leached from above
B horizon
What is the B horizon also known as?
Subsoil
This soil horizon is made up of unweathered parent material (decomposed bedrock or transported material), and has little soil formation
C horizon
What is the C horizon also known as?
Substratum
What is the C horizon/substratum the source of?
Geological components of soil
This horizon is hard bedrock
R horizon
What are three soil color forming factors?
Mineral content, SOM, drainage/soil moisture
What does brown soil indicate?
High SOM
What does red soil indicate?
Well drained, high iron
What does grey soil indicate?
Poorly drained
This is used to classify color
Munsell color chart
This describes the mix of soil mineral particles
Soil texture
What are the three classes of particles that make up soil texture?
Clay, silt, sand
This soil particle is between 0.000 and 0.002 mm
Clay
This type of soil particle is between 0.002 and 0.050 mm
Silt
This type of soil particle is between 0.050 and 2.000 mm
Sand
This describes the physical arrangement of soil particles
Soil structure
What two things does soil structure affect?
Drainage and fertility
From what five factors does soil structure arise?
Chemistry; SOM; Organisms; Wetting/drying; Freezing/thawing
What are four characteristics of sandy soils?
Larger pores, low total porosity, dry, infertile
What are four characteristics of silt and clay soils?
Smaller pores, higher total porosity, wetter, more fertile
What soil type is the optimal mix of the three soil particles?
Loamy soils
Loamy soils have the best mix of these two soil characteristics
Porosity and fertility
What are five shapes produced by soil structure?
Granules, blocks, prisms, columns, plates
What are four functions of organic matter in soils?
Creates soil structure; Improves aeration/drainage; Source of soil nutrients; Energy source for soil food web
Most SOM comes from this
Litter
Litter is broken down into these two molecules
CO2 and H2O
The breakdown of litter releases these two things into the soil
Energy and nutrients
Tree litter is high in these two substances
Cellulose and lignin
How do cellulose and lignin affect the decomposition rate of tree litter?
Both slow decomposition rate
Litter decomposition creates this
Humus
What is humus?
The dark, amorphous end product of decomposition
For how long can humus persist?
Millenia
What are two reasons why humus is essential to soils?
Acts as a cement for soil structure; Source of soil nutrients
Soil acts as a reservoir for this
Water
What are the 7 roles of soil water?
Plant resource; Transport; Soil consistency; Aeration; Soil temperature; Soil biota; Erosion/deposition
What are five factors that influence soil moisture?
Climate; Vegetation; Soil permeability; Soil storage capacity; Topography
What are three factors that determine soil water holding capacity?
Soil texture; Soil structure; Organisms
How does soil texture affect soil water holding capacity?
Texture affects porosity
What is soil porosity?
Gaps of air between grains in a soil
Is the porosity of clay soils greater than sandy soils?
Yes
How does soil structure affect soil water holding capacity?
Soil particles aggregate, creating large pores/seams
What are two ways organisms affect soil water holding capacity?
Burrowing animals create tunnels; Tree roots create channels
What are the three fractions of soil water?
Gravitational water; Capillary water; Hygroscopic water
This type of soil water is held in cavities/large pores after rain, and is drained by gravity
Gravitational water
This type of soil water is held in small pores against gravity
Capillary water
What is capillary water also known as?
Available water
This type of soil water adheres strongly to soil particles and is unavailable to plants
Hygroscopic water
What are the three quantities of soil water storage?
Saturation point; Field capacity; Permanent wilting point
This soil water storage point happens when all pores and cavities are filled with water
Saturation point
What is the equation for the saturation point?
SP = Gw + Cw + Hw
This soil water storage point is the remainder after large pores drain
Field capacity
What is the equation for field capacity?
FC = SP - Gw
This soil water storage point is the fraction after available water is exhausted and leads to plant wilt
Permanent wilting point
What is the equation for the permanent wilting point?
PWP = FC - Cw
What type of soil has the highest available water?
Loamy soils
In what two U.S. areas is soil moisture highest?
Mississippi Valley and Great Plains
These soil organisms are over 20mm long and include moles, rabbits, and rodents
Megafauna
These soil organisms are 2-20mm long and include worms, beetles, centipedes, slugs, and ants
Macrofauna
These soil organisms are 100um-2mm and include mites and springtails
Mesofauna
These soil organisms are 1-100um and include bacteria, fungi, protists, and nematodes
Microfauna/flora
Soil biota are crucial for this process
SOM decomposition
These two types of soil organisms fragment, shred, and mix SOM
Macrofauna and mesofauna
These soil organisms respire SOM for energy and mineralize nutrients
Microfauna/flora
This process converts organic minerals to inorganic form
Mineralization
These microbes outnumber bacteria in forests and are more tolerant of low soil pH
Fungi
These fungi are root mutualists that aid in uptake of water and nutrients
Mycorrhizae
These fungi feed on dead organic matter
Saprophytic fungi
These microbes are also important decomposers, and are more abundant in grasslands than fungi
Bacteria
What are three roles that tree roots play in forest soils?
Source of SOM (from sloughing tissue during growth); Create channels that aid water movement and root growth; Grip and stabilize soils to reduce erosion losses
This is the zone around roots
Rhizosphere
What three microbes are found in high concentrations in the rhizosphere?
Bacteria, fungi, protists
What are three ways roots exert influence on soil chemistry?
Exuding sugars/proteins; Releasing H+ to solubilize nutrients; Releasing allelopathic chemicals
This is the acidity or alkalinity of soil solution
Soil pH
What are two things that soil pH affects?
Biology and nutrient availability
Do grassland soils have a lower pH than forest soils?
No
Why do trees release H+?
To free soil nutrients
Do conifer soils have a lower pH than broadleaf soils?
Yes
Do wet soils tend to be acidic?
Yes
What are five examples of cations that are key plant nutrients?
Ca2+, Mg+, Fe3+, K+, NH4+
What is the source of cations?
Breakdown of SOM and minerals
Cations are highly mobile in this part of soil
Soil water
Are cations not attracted to any soil particles?
No
This is a measure of soil fertility, the capacity of soil to retain cations
Cation exchange capacity
What are two factors that influence cation exchange capacity?
Surface area and surface charge
What surface area do sandy soils have?
Very low
What surface area do clay soils have?
Low to high
Can humus exceed high clays in surface area?
Yes
These two soil types have negative charge
Clays and humus
Do high CEC soils lose nutrients?
No
Does soil CEC decrease as the amount of clay rises?
No
Does soil CEC increase as the amount of humus rises?
Yes
Does soil CEC decrease as soil pH increases?
No
Cations are displaced from clay-humus by these
H+ ions
What is the order of cation attachment strength for five major cations?
H+>Ca2+>Mg2+>K+>Na+
This mixes with soil water to produce carbonic acid
CO2
These displace nutrients from soil particles
Acids
This describes how “full” the soil surface is
Base saturation
These six macronutrients are needed in large quantities by plants
N, P, K, Ca, Mg, S
These eleven micronutrients are needed in small quantities by plants
Fe, Mn, B, Cu, Mo, Zn, Cl, Co, Ni, Na, Si
Soil classification is based on these two factors
Formative factors and soil properties
What are the six levels of soil classification used by the USDA?
Order, suborder, great group, subgroup, family, series
What are three examples of soil orders named for their unique parent materials?
Andisols, Histosols, Vertisols
What are three examples of soil orders named for their unique environments?
Aridisols, Gelisols, Oxisols
What are three examples of soil orders named for their age of development?
Entisols, Inceptisols, Ultisols
What are three examples of soil orders named for vegetative influence?
Alfisols, Mollisols, Spodosols
What are the four important forest soil orders?
Oxisols, Ultisols, Alfisols, Spodosols
These soils are old, leached, and infertile, with <35% base saturation
Ultisols
What are two types of forests where Ultisols are found?
Southeastern pine and pine/oak forests
These forest soils have relatively high fertility and >35% base saturation
Alfisols
What are two types of forests where Alfisols are found?
Oak-hickory forests and northern hardwood forests
These are sandy, acid forest soils found in cold, humid climates
Spodosols
What are three types of forests where Spodosols are found?
Northern hardwood forests, Great Lakes hardwood forests, and boreal forests
These are intensely weathered soils that are leached and nutrient poor
Oxisols
In what type of forests are Oxisols found?
Tropical forests
What are Ultisol E and B horizon characteristics?
Yellow E and red clayey B
What are Alfisol E and B horizon characteristics?
Grey E and brown clayey B
What are Spodosol E and B horizon characteristics?
Grey E and reddish brown B
Spodosol B horizons are often high in this
Humus
What are Oxisol soil horizon characteristics?
Red and highly oxidized
