Chapter 6 Factors and the Fundamental equation

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• Chapter 6- Factors and the Fundamental equation
• S or s f (cl, o, r, p, t, )
• Where S soil or s soil property
• f function of
• cl climate factors
• o organic factors
• r topographic factors
• p parent material factors
• t time

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• Important subfunctions
• Cant solve this equation for everything at one
  time if they all vary.
• get around this by letting 1 of the 5 factors
  vary and holding the others as constant or known
  factors
• Climofunction climate is variable
• Biofunction biological input is variable
• Lithofunction parent material is variable
• Topofunction topography is variable
• Chronofunction time is variable

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Considering a factor as constant Two ways 1- the
range of the factor is quite small in the given
region or aspect e.g., climate in the tri-state
region is considered the same everywhere 2- the
variation of the factor has a negligible effect
on the soil profile development
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Climate (cl) Mean annual precipitation and
temperature for the region Occasionally local
climatic effects as well e.g., north facing
alpine slopes vs south facing temperature or east
vs west facing alpine slopes moisture Affects
the chemical and physical weathering processes
and the transportation of materials through the
profile these are sometimes measured as leaching
indices
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Topography (r) Shape of slope e.g., Convex or
Concave up Steepness of slope e.g., Vertical vs
horizontal Thin soils due to erosion on upslope
locations Cumulic soils in toe slope
positions Aspect of slope e.g., North, South,
East, West Groundwater and surface water related
to slope e.g., where does water accumulate or
discharge
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Biological factors (O) typically restricted to
plant material how much and what types are
growing nearby profound effect on chemical
processes Can include animals bioturbation
agents are primary Typically report the type of,
and amount of veggies growing in region
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Slope shapes can also include concavity or
convexity going side to side as well
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Parent material (p) All materials from which the
soil is formed Can include rock, e.g. granite,
quartzite, limestone sandstone shale sediment,
e.g. loess, alluvium, colluvium soils, previous
ly formed soils that are subjected to alternate
soil forming conditions vegetation (peat) mostly
organics can form soils with minor additions of
mineral matter
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Time (t) The time since the soil started
forming time since deposition e.g., loess, till,
alluvium, colluvium time since conditions became
favorable for soil formation the concept of a
soil forming interval e.g., Sangamon geosol time
since exposure (bedrock) e.g., granite, sandstone
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The problem with the equation Cannot be solved
using quantitative data to predict the resulting
soil adequately. Does that mean we cant use it?
Also, many soils had multiple factors which
varied during their formation Monogenetic soils
-soils that had limited variability in soil
forming factors during the interval in which they
formed Polygenetic soils- soils that formed
during multiple episode during which time the
factors influencing formation varied enough to
cause perceptible changes in the soil
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Other equations- evolution model S f (P,
R) Where S soil development P progressive
pedogenesis steps forward R regressive
pedogenesis steps backward Arguable in many
circumstances because it implies that the
processes are reversible In many instances they
are not e.g., clay mineral formation is a one
way street
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Steady State soils often achieve steady state
where they dont progress any further