Lecture 3: Inventory and Analysis of the Biophysical Environment
Part IV: Soils

Stop treating our Soils like Dirt!
Important questions
What is soil?
How is it made?
Where (location) does it come from?
How is it changed?
For the better
For the worse

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But we often use two characteristics to describe it...
Texture
Composition

COMPOSITION
4 components
Mineral Particles - 50-80% volume -- skeletal structure and bearing capacity
Organic Matter - Low bearing capacity, high water storage
Air
Water


TEXTURE
Clay
Sand
Silt

Soil Texture Triangle
Loam = 40 % sand, 40% silt, 20% clay



How do you know?
Field hand test
Professional soils test


Two kinds of water
Water is also a key element in soils -- Two kinds of water
Capillary - which allows upward movement
Gravity - which usually allows downward transport

Drainage
Soil's ability to transfer Gravity Water downward
INFILTRATION CAPACITY
PERMEABILITY - Movement within
PERCOLATION - Absorption tests - key for wastewater

What makes soil erode?
Splash
Sheeting -- surface erosion

Universal Soil Loss Equation (USLE)
A = R x K x L x S x C x P
A Computed Soils loss over a unit area
R Rainfall (Average annual R factor - 150)
K Soil Erodibility ( .37)
L Slope Length (400')
S Slope Gradient (.25)
C Crop Management - land cover (1.0 - .05)
P Erosion Control Practice


Major environmental problems
Soils Loss - Wind and Water erosion
Some is lost forever - continental shelf
Compaction - driving, walking, plowing - roto-tiller
Sedimentation - A lot of the lost soils end up somewhere else - dams, roads and sidewalks, storm sewers, Atchafalaya delta