Chapter 14
Soil Resources
Current events to share
Question of the day:
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What ecosystem services does soil provide
for us?
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Soil or dirt? What is the scientific term?
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What is the study of soil?
Overview of Chapter 14
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What is soil?
Soil Properties
Major Soil Orders
Soil Problems
Soil Conservation
Soil Reclamation
Soil
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Uppermost layer of earth’s crust that
supports plants, animals and microbes
Soil Forming Factors
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Parent Material
Time
Climate
Organisms
Topography
Soil formation- 1 m = 100-100,000 years
Soil formation
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Physical weathering- rock weathered by
wind, water, ice, temperature change
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Chemical weathering- Plant roots produce
carbonic acid that dissolves nutrients and
air and water react with minerals in the
exposed cracks. Organic matter (humus) is
partially decomposed dead organic matter
and their waste.
Soil Composition
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Mineral Particles (45%)
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Organic Material (5%)
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Weathered rock
Provides essential nutrients for plants
Litter, animal dung, dead remains of plants and
animals, humus (picture)
Water (25%)
Air (25%)
Soil Composition
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Pore space
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50% of soil
Soil air- good for
aeration
Soil waterprovides water to
roots
Soil HorizonsSoil cores
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O-horizon
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A-horizon
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Topsoil
B-horizon
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Rich in organic
material
Lighter colored subsoil
C-horizon
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Weathered parent
material
Soil Organisms
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There are millions of microorganisms in 1
tsp of fertile agricultural soil
Soil Organisms
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Soil organisms provide ecosystem services
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Def: Important environmental benefits that
ecosystems provide
Examples
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Decaying and cycling organic material
Breaking down toxic materials
Cleansing water
Soil aeration (especially done by earthworms)
Nutrient Cycling
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Nutrients are cycled
between plants,
organisms and soil
Example
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Bacteria and fungi
decompose plant and
animal wastes
They are
transformed into
CO2, soil nutrients
and water
Soil Properties
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Soil Texture
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Relative proportion of sand, silt and clay
Sand: 2mm-0.05mm
Silt: 0.05mm-0.002mm
Clay: >0.002mm
Soil Properties
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Soil texture affects soil properties
Coarse textured soil (sandy)
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Will not hold water well- flows through easily
Fine textured soil (high in clay)
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Poor drainage
Low oxygen levels in soil
Due to negatively charged surface, able to hold
onto important plant nutrients (K+, Ca2+, NO2-)
Soil Properties
Soil Properties
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Soil Texture
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Relative proportion of sand, silt and clay
Sand: 2mm-0.05mm
Silt: 0.05mm-0.002mm
Clay: >0.002mm
Soil Properties
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Soil texture affects soil properties
Coarse textured soil (sandy)
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Will not hold water well- flows through easily
Fine textured soil (high in clay)
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Poor drainage
Low oxygen levels in soil
Due to negatively charged surface, able to hold
onto important plant nutrients (K+, Ca2+, NO2-)
Questions of the day:
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What event occurred yesterday that
relates to class?
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What role does soil texture play in soil
nutrients amount?
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What is terra preta? Why is it so
valuable?
Soil Properties
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Soil Acidity
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Measured using pH scale
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0-7 = acidic
7 = neutral
7-14 = basic
pH of most soils range from 4-8
Affects solubility of certain plant nutrients
Optimum soil pH is 6-7
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This is the pH where plant nutrients are most
available to plants
Soil amendments (ex: lime) can be used to achieve this
pH
Major Soil Groups
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Variations in soil forming factors cause
variation in soils around globe
Soil Taxonomy
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Separates soils into 12 orders
Subdivided into more than 19,000 soil series
that vary by locality
Five common soil orders (just briefly going
over)
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Spodosols, alfisols, mollisols, aridosols, oxisols
Major Soil Groups
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Spodosols
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Form under coniferous
forests
O-horizon composed
of needles
E-horizon is ash-gray
under A-horizon
Not good farmlandtoo acidic
Major Soil Groups
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Alfisols
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Brown to gray-brown
A-horizon
Precipitation high
enough to leach most
organics and nutrients
out of O-, A- and Bhorizons
Soil fertility
maintained by leaf
litter
Major Soil Groups
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Mollisols
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Found in temperate,
semi-arid grassland
Very fertile soil
Thick, dark brown/
black A-horizon
Soluble nutrients stay
in A-horizon due to
low leaching
Major Soil Groups
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Aridosols
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Found in arid regions
of all continents
Low precipitation
preclude leaching and
growth of lush
vegetation
Development of salic
horizon possible
Major Soil Groups
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Oxisols
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Found in tropical and
subtropical areas with
high precipitation
Very little organic
material accumulation
due to fast decay rate
B-horizon is highly
leached and nutrient
poor
Soil Problems
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Soil Erosion
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Why a problem?
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Def: wearing away or removal of soil from the
land
Caused primarily by water and wind
Causes a loss in soil fertility as organic
material and nutrients are eroded
More fertilizers must be used to replace
nutrients lost to erosion
Accelerated by poor soil management
practices
Case in Point: American
Dust Bowl
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Great Plains have low
precipitation and subject
to drought
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1930-1937 severe drought
No natural vegetation roots
to hold soil in place
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Replaced by annual crops
Winds blew soil as far east
as NYC and DC.
Farmers went bankrupt
Ken Burns “American Dust Bowl”
documentary
Soil Problems
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Nutrient Mineral Depletion
Soil Problems
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Soil Salinization
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Often in arid and semiarid areas
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Def: gradual accumulation
of salt in the soil, usually
due to improper irrigation
techniques
The little precipitation that
falls is quickly evaporated
Leaves behind salts
Salt concentrations get to
levels toxic to plants
Soil Problems
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Desertification
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Def: degradation of oncefertile rangeland, agricultural
land, or tropical dry forest
into nonproductive desert
Typically a human-induced
condition
Change in vegetation
changes climate, further
decreasing precipitation
levels
Soil Conservation
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Conservation Tillage
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Residues from
previous year’s crops
are left in place to
prevent soil erosion
Includes no tillage
Crop Rotation
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Planting a series of different crops in the same
field over a period of years
Lessens pest and insect disease
Soil Conservation
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Contour Plowing
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Plowing around hill
instead of up-down
Decreases soil erosion
Strip Cropping
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Strip Cropping
Alternating strips of
different crops along
natural contours
Terracing
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Creating terraces on
steep slopes to prevent
erosion
Terracing
Preserving Soil Fertility
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Organic fertilizers
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Animal manure, crop residue, bone meal and
compost
Nutrient available to plants only as material
decomposes
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Slow acting and long lasting
Inorganic fertilizers
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Manufactured from chemical compounds
Soluble
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Fast acting, short lasting
Environmentally sound to limit use
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Mobile- easily leach and pollute groundwater
Soil Reclamation
Two steps
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1.
2.
Stabilize land to prevent
further erosion
Restoring soil to former
fertility
Best way to do this is
shelterbelts
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Row of trees planted to
reduce wind erosion of
soil
Soil Conservation Policies in US
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Soil Conservation Act 1935
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Authorized formation of Soil Conservation
Service, now called Natural Resource
Conservation Service (NRCS)
Assess soil damage and develop policies to
improve soil
Food Security Act (Farm Bill) 1985
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Required farmers with highly erodible soil had
to change their farming practices
Instituted Conservation Reserve Program
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Pays farmers to stop farming highly erodible land
Soils Pop Quiz
1. What is the study of soil?
2. What is the study of agriculture?
3. What three components make up soil texture?
4. What materials makes up soil? In what
percentages?
5. Name two elements that we may want to
examine to determine the soil’s health and
ability to grow plants.
Day 2 Pop Quiz
1.What is the study of soil = pedology
2. Study of agriculture = agronomy
3. Soil texture = sand, silt, clay
4. Minerals 45%(from parent material= bedrock),
humus 5% (organic matter), water 25%, air
25%
5. N, P, K, (main three) maybe Ca, Mg