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SOIL ACIDITY HOW TO MEASURE SOIL ACIDITY - University of

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11/25/2010
Lecture 25: The Geography of Soils:
Chemical soil properties and Soil Classification
SOIL ACIDITY
Acid, neutral, Basic (Alkaline): all soil acids contain H +
Pure water: H2O = H+ + OH(1 hydrogen + 1 hydroxyl)
пѓ the H+ concentration of pure water = 10-7 mol/l
пѓ hence the OH- concentration is also 10-7 mol/l
Total for pure water at 25 C: [H+][OH-] = 10-14 (ionization
constant)
If an acid is added to water пѓ hydrogen concentration пѓ©
e.g. [H+]=10-4 пѓ then [OH-] = 10-10
Geog 1000 Introduction to Physical Geography Fall 2010 : Dr. Hester Jiskoot, University of Lethbridge
HOW TO MEASURE SOIL ACIDITY
http://www.anr.state.vt.us/dec/waterq/bass/pHscale2.gif
THE pH RANGE IN NATURE AND IN COMMON MATERIALS
Add a certain amount of soil to demineralised water (has pH 7)
and stick in a hydrogen electrode.
pH= way of expressing Hydrogen ion concentration
pH = -log [H+] = log 1
[H+]
Alkaline
neutral
Scale range 0-14 with 7=neutral
Acidic
Acidic
OPTIMUM pH RANGES FOR CROPS
Soils usually pH > 5
If there are components in a horizon that
take up H+ then the pH is higher for that
horizon:
Examples:
A horizon: Humus and Litter (organisms
and fungi)
C-horizon: Oxides/Feldspar/Micas
www.fieldtesting.co.uk
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11/25/2010
Global variation in soil pH.
Red = acidic soil.
Yellow = neutral soil.
Blue = alkaline soil.
Black = no data.
CATION EXCHANGE CAPACITY (CEC)
пЃ¶ CEC is a calculated value that is an estimate of the
soils ability to attract, retain, and exchange cation
elements (positively charged ; often useful nutrients).
пЃ¶ CEC is used as a measure of fertility, nutrient
retention capacity, and the capacity to protect
groundwater from cation contamination.
Cation-exchange capacity (CEC)
SCHEMATIC LOOK AT CEC
Cations and Anions are charged particles
Soil colloids
CEC: between soil
colloid and soil
solution
High CEC пѓ good soil fertility
CLAYS HAVE A LARGE SURFACE AREA
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11/25/2010
Combined P & N deficiency limits biomass and promotes
further erosion and soil degradation
WATER QUALITY DEGRADATION DUE TO EXCESS Phosphorous (P) & Nitrogen(N)
пѓ Eutrophication
Point sources
Sewage outflows (phosphates in soaps)
Industries
Non-point sources
Runoff water
Eroded sediment from soils in affected watershed
“Too much of a good thing”
FACTORS RELATED TO SOIL DEGRADATION
Have to consider the natural context.
Two main components:
1) Disturbance of plant communities.
Over-grazing, deforestation, inappropriate crop production methods, and
overexploitation.
2) Deterioration of Soil
Erosion, pollution, weakening of structure, large changes in pH, nutrients,
chemical composition
SOIL & TROUBLE
Regions of physical and chemical soil degradation
SOIL CLASSIFICATION
AND
SOIL TAXONOMY
"Soil and trouble." Science 304.5677 (June 11, 2004): 1614(2).
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11/25/2010
REASONS FOR SOIL CLASSIFICATION
BASIS OF SOIL CLASSIFICATION
1. Organize knowledge ALONG A HIERARCHY
2. Communicate knowledge to other people
3. Remember properties of the objects classified
4. Study relationships among individuals and classes of the
population being classified
5. Group objects into classes (with similar behaviour, use and
management, productivity, etc).
soil-forming factors
↓
soil-forming processes
↓
diagnostic horizons, properties, materials
↓
soil taxonomic system
Classification helps us deal with complexity
SOIL FORMING PROCESSES
(example)
Diagnostic horizons:
SOIL HORIZONS : DETAILS
пѓ relate horizon to soils forming process
A
B
C
Humus –rich
Eluviation (leaching)
Illuviation (deposition)
e.g. clay/lime/iron/humus
Parent material
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11/25/2010
THE SOIL PROFILE GROUPED INTO CLASSES
SOIL TAXONOMY
• A comprehensive soil classification system is
known as a Soil Taxonomy.
Soil profiles differ because of differences
in the soils forming factors
– Based on soil properties.
– Diagnostic soil horizons (define place in
taxonomy).
– Based on observable criteria today
Different soil profiles can be grouped into
different classes of soils
Different classes of soils have a specific
geographic distribution: both at a global
scale and at the landscape scale.
• May change through time.
SOIL TAXONOMY PRINCIPLES
ARE THE SAME AS ANY OTHER TAXONOMY
SOIL TAXONOMY SYSTEMS
пѓ From the general to the more specific (or from the regional to the local)
Plant Classification
Soil Taxonomy System
Phylum
Spermatophyta
Order
Mollisols
Class
Angiospermae
Subclass
Monocotyledonae
Great group
Chernozem
Order
Graminales
Subgroup
Brown
Chernozem
Family
Graminae
Family
Loamy Brown
Chernozem
Series
Rego Brown
Chernozem
Genus/Species Triticum aestivum
• Canadian system is based on the Russian system
(soil forming factorsпѓ soil forming processesпѓ different soils).
• Similar to systems in Europe.
• The system used in the text was developed by the USDA
and the FAO.
– Food and Agriculture Organization of the UN.
– Genetic world wide system.
CANADIAN SYSTEM OF SOIL CLASSIFICATION
Soils of Canada
Canadian soil scientists classify soils based on pedogenic processes in cool
climatic environments.
Ten Soil Orders
Differentiated on the basis of characteristics of the soils that reflect
1) the nature of the total soil environment
2) the effects of the dominant soil forming processes
Remember the 5 soils
forming factors:
climate, living matter,
parent material,
topography, and time
пѓ these are broadly
represented here
Brunisol
Chernozem
Cryosol
Gleysol
Luvisol
Organic
Podzol
Regosol
Solonetz
Vertisol
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11/25/2010
SOIL ZONES OF WESTERN CANADA
Chernozems
Soils that have developed under grasses
and forbs in cool to cold, subarid to
subhumid climates.
Alberta
Saskatchewan
Black
Dark Brown
Brown
Grey
Dark Grey
Manitoba
BLACK CHERNOZEM SITE
Black Chernozem
Brown Chernozem
These soils have a dark-coloured surface
(Ah, Ahe, Ap) horizon and a B or C
horizon or both
The order consists of the Brown, Dark
Brown, Black, and Dark Gray Great
Groups.
BROWN CHERNOZEM SITE
Brunisols
Soils whose horizons are developed
poorly.
Ah
Occur under a wide variety of climatic
and vegetative conditions.
All have brownish B.
Ah
Quite often in forested areas.
B
B
C
C
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11/25/2010
Brunisol site and soil
Podzol
•
Soils in which organic matter
and aluminum, with or without
iron, have eluviated and then
accumulated in B horizon.
Bmf
•
•
Grey E horizon
Black and Red B horizon
C
•
Podzols are acidic
Ae
PODZOL
Cryosolic
A
• Soils that have permafrost
affecting the soil
Eluviated horizon
E
• Freeze-thaw action in the
active layer �churns’ the soil
and is called
CRYOTURBATION
B
C
Soils close to Raymond (S Alberta)
ICE LENSES, FROST HEAVE AND CRYOTURBATION
Frost heave:
Ah
Present soil:
BROWN CHERNOZEM
C
Cy
Cryoturbation (frost churning):
Palaeosol:
CRYOSOL
mixing of materials from various horizons
of the soil (sometimes down to bedrock)
due to freezing and thawing.
Gelisols or Cryosols experience
cryoturbation
Frost Heave West Greenland 1991
Churned up by freeze-thaw action during early Holocene
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Reading for Monday
Chapter 16:
Ecosystems and Biomes
Pages 526-552
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