Range

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Range Forest Ecology Soils
What is soil? (from the latin solum meaning
floor) An independent 3-dimensional natural body
occupying the earths surface and capable of
supporting plant growth. Its properties result
from the integrated effect of climate and living
organisms acting upon parent material as
conditioned by relief over periods of time.
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Range Forest Ecology Soils
3 Viewpoints Pedological soil is considered a
natural body emphasis is on geologic history
soil formation process (time scale of 103 to 107
years), with minor emphasis on practical
utilization. Edaphological consideration of
soil from the standpoint of higher plants
emphasis is on properties of soil as they relate
to plant production, e.g nutrient availability,
slope, aspect, moisture, texture (time scale of
100 to 102 years). Ecological consideration of
soil as a component of an ecosystem emphasis on
flows of energy, nutrient cycling dynamics,
microbial activity decomposition (time scale of
101 to 102 years).
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Range Forest Ecology Soils

• Components of Soil (plants perspective)
• Mineral grains provides anchorage, pore space
  (H2O, air), nutrients on exchange basis.
• Organic matter plant animal residues in
  various stages of decomposition, soil organism
  exudates can be source of plant nutrients
  through a microbially-mediated cycling process
  enhances water storage improves soil structure.
• Soil water solvent medium for nutrients
  required by plants.
• Soil air provides oxygen for cellular function
  atmospheric nitrogen for N-fixing organisms
  (atmosphere 78 N2).

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Range Forest Ecology Soils

• The development of soil can be thought of as
  occurring in two phases
• Soil Genesis the weathering of rock substrates
  by
• Mechanical forces expansion contraction due
  to thermal flux erosional forces by wind
  water plant roots can exert sufficient forces to
  cleave exfoliate rock fragments.
• Chemical reactions many principal agent is
  percolating rain water charged with CO2 (weak
  acid solution) which affects carbonates
  (dissolution), feldspars micas (hydrolyze to
  clays release cations) biological processes
  form organic acids.

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Range Forest Ecology Soils

• Continued
• Soil Formation Hans Jenny (1941) characterized
  soil formation (S) as a function of five
  independent variables climate (cl), organisms
  (o), topography (r), parent material (p), time
  (t).
• S ƒ(cl, o, r, p, t)
• Organism include such elements as the soil
  microbial community, litter inputs, vegetation
  type.
• Parent material largely determines chemical
  characteristics of the derived soils.
• ? The interaction of organisms parent material
  with climate produce a soil with characteristic
  features.
• Jenny, H. 1941. The factors of soil formation.
  New York McGraw-Hill.

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Range Forest Ecology Soils
Continued Parent material is the state of the
soil system at time zero for a particular set of
soil-forming environmental factors.
Rocks Minerals In Place Transported Agent Gravity Water Ice Wind Parent Materials Residual Less than ½ of earths surface Colluvial Gravity-induced Alluvial Flood plain Marine Fluctuating sea level Lacustrine Lake deposit Glacial Till, outwash Aeolian - Loess
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Range Forest Ecology Soils
Soil Profile Development Soil formation is
largely a biochemical process, whereby

• Organic material (plant roots, litter inputs,
  soil organisms) mixes with inorganic mineral
  fractions.
• Microbial activity accelerates chemical
  weathering.
• Primary/original minerals are transformed into
  secondary minerals.
• Resulting in development of horizons with
  characteristic color, textural structural
  qualities.

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Range Forest Ecology Soils
Soil Profile Development continued

• Regolith Unconsolidated layer above hard,
  unweathered, bedrock
• Solum Upper portion of the regolith that has
  been altered through biochemical and physical
  processes.  The material between the solum and
  bedrock is referred to as the C horizon.  It is
  slowly changing into solum.
• Pedon A 3-D sampling that displays the full
  range of properties that are characteristic of a
  soil (1-10 m2).
• Soil Profile One vertical face of a pedon. 
• Soil Horizons Horizontal layers,
  differentiated by color or texture, described
  within a profile

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Range Forest Ecology Soils
Soil Profile Development typical horizons
Master Horizons O Organic horizon (gt20 OM by
weight) partly or mostly decomposed OM found in
wetlands, forest litter layers provides
nutrients (nitrogen, potassium, etc.), aids soil
structure (acts to bind particles), enhances soil
moisture retention. A Mineral horizon with
accumulated OM (lt20) typically darker than
other horizons. E Zone of maximum leaching
(eluviation) loss of clays, soluble OM, Fe
oxides common in forest soils light colored. B
Mineral horizon with accumulation (illuviation)
from above usually contains most clays and
fines usually a more dense layer. C Soil
parent material, either in situ or transported
minimal weathering and biologic activity. R
Hard, unweathered bedrock.
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Range Forest Ecology Soils
Soil Profile Development continued

• All master horizons will not necessarily occur
  in a single soil. When they do they are normally
  found in this order
• Master horizons can be subdivided using numbers,
  ex. A1-A2-A3

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Range Forest Ecology Soils
O Horizon
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Range Forest Ecology Soils
A Horizon

1. Humus accumulation in mineral soil
2. Darkened color

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Range Forest Ecology Soils
E Horizon

1. Zone of maximum eluviation loss of organic
   matter, clays, and/or Fe-oxides
2. No humus accumulation lighter color

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Range Forest Ecology Soils
B Horizon
1. Illuviated - accumulation of clays (silicate,
Fe Al oxides), O.M., CaCO3, ... - usually, from
above (A or E) some from sides or below 2.
Complex in highly developed soils - numerous
subdivisions, e.g. color, lime, structure, etc.
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Range Forest Ecology Soils
C Horizon
1. Unconsolidated material 2. Little affected by
weathering processes
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Range Forest Ecology Soils
Physical Properties Texture Structure 1)
Texture Characterization of the solid inorganic
phase of soils refers to the relative
proportions of sand, silt clay called the
soil separates constitute the fine earth
fraction (diameter lt 2 mm) of the soil.
Very Coarse Sand Coarse Sand Medium Sand Fine
Sand Very Fine Sand
Diameter (mm) 2.0 1.0 1.0 0.5 0.5 0.25 0.25
0.1 0.1 0.05 0.05 0.002 less than 0.002
Soil Separate Sand Silt Clay
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Range Forest Ecology Soils

• Physical Properties Texture Structure
• 1) Texture Continued
• Rock fragments (diameter gt 2 mm) are described
  separately on a pedon description modifiers are
  used when rock fragments occupy more than 15
  percent by volume, ex. gravelly sandy loam.
• Organic horizons (Oi, Oe, Oa) are described
  based on the degree of decomposition (fibric,
  hemic, sapric, etc.).

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1) Texture Continued Particle Size
Analysis 1. In the laboratory mechanical
analysis - Sands are determined by sieving - Silt
and clay is determined based on settling time
using Stoke's Law
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Texture Continued 2) Steps to determine soil
texture in the field by feel have been
developed useful for a quick dirty estimate
requires practice (see handout).
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Range Forest Ecology Soils
Physical Properties Texture Structure 2)
Structure Soil structure is the way soil
particles aggregate together into what are called
peds. Peds come in a variety of shapes depending
on the texture, composition, and environment.
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Range Forest Ecology Soils

• Physical Properties
• 2) Structure Continued
• Agents that bind aggregates promote stability
  fungal mycelia, microbial exudates, H Ca ions,
  clays.
• Structural stability is the capacity for the peds
  to retain their shape, i.e. absorb water not
  disintegrate.
• Soil aeration, water movement, plant root
  penetration are greatly enhanced by good soil
  structure.

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Range Forest Ecology Soils
Soil Chemistry Important aspect is the
relationship between the ions (i.e. nutrients)
(a) in soil solution, (b) adsorbed on charged
particles, (c) as constituents of mineral
organic fractions, which tend towards
equilibrium dynamic interaction.
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Range Forest Ecology Soils
Nutrient Uptake by Plants
Exchangeable ions Surface adsorption
Soil Air
Soil Solution
Organic Matter Biota
Solid phases Minerals
Rainfall, Evaporation, Drainage, Addition of
Fertilizer
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Range Forest Ecology Soils

• Soil Chemistry
• The availability of plant nutrients are most
  directly influenced by (1) soil pH, and (2)
  cation exchange capacity (CEC).
• 1) Soil pH
• Strictly, measure of the hydrogen ion
  concentration in solution -log10H H
  concentration (activity) of H
• Neutrality is pH 7 (H OH-)
• As acidity ? , pH ?

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Range Forest Ecology Soils
pH range in soils
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pH vs Availability of Nutrients
Strongly Acid
Strongly Alkaline
Med. Acid
Slightly. Acid
Very Slightly Acid
Very Slightly Alkaline
Slightly Alkaline
Med. Alkaline
Nitrogen
Phosphorus
Potassium
Sulfur
Calcium
Magnesium
Iron
Manganese
Boron
Copper and Zinc
Molybdenum
4.0 4.5 5.0 5.5 6.0 6.5
7.0 7.5 8.0 8.5 9.0
9.5 10.0
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Range Forest Ecology Soils
Soil Chemistry 2) Cation Exchnage Capacity (CEC)
Measure of the number of negatively charged
sites on charged particles that attract
exchangeable cations (via electrostatic charge).
Mineral particle OM fraction (Humus)
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Range Forest Ecology Soils

• Important CEC properties
• Size of CEC determined by soil properties
  (permanent pH-dependent charge)
• Large quantity of nutrients can be held on CEC
  (particularly clay)
• Provides rapid buffering for most cations
• Exchangeable ions held against leaching
• Exchangeable ions readily available through
  cation exchange

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Range Forest Ecology Soils

• Summary
• Components of soil are mineral grains (anchorage
  nutrients), organic matter (nutrient cycling),
  water (solvent medium), air (oxygen
  nitrogen).
• Soil formation is the product of climate,
  organisms, topography, parent material, time.
• Soil profile development encompasses the
  interaction of the above factors to develop
  characteristic soil horizons.
• Soil texture refers to content of sand, silt,
  clay particles.
• The nature arrangements of peds aggregate
  stability are the most significant
  characteristics of soil structure.
• The central concepts in soil chemistry are based
  on the equilibrium of ions in solution.
• CEC is a measure of exchangeable cations on
  negatively charged sites in the soil, is
  influenced by the presence kinds of clay
  minerals humus.