Final Exam Flashcards
Brunisols
Less developed forest soils
Related to luvisols and podzols
Dependent on soil texture
Brunisol Great Groups
Melanic
Eutric
Sombric
Dystric
Basic Great Groups
Melanic
Eutric
Great Groups with Ah
Sombric
Melanic
Acidic Great Groups
Sombric
Dystric
Great Groups without Ah
Dystric
Eutric
Podzols
High precipitation
Highly acidic soils, enhanced weathering of primary minerals
Strong leaching = sandy
Podzolic Diagnostic Horizon
Illuvial Ae above B B >10cm thick 7.5 YR or redder Coarse texture Coastal forests and areas
Podzol Great Groups
Humic
Ferro-Humic
Humo-Ferric
Humic
Organic Matter forms Bh
A lot of organic matter production
Ferro-Humic
Bhf
Not as wet, not as dry, some organic matter, some Fe, not as dark, more red
Humo-Ferric
Bf
Dry
Less intense weathering
What soils do Eutric soils become?
Gray Luvisols
What soils do Melanic soils become?
Gray-Brown Luvisols
What soils do Dystric soils become?
Podozols
Types of space in soil
Pore Space
Solid Space
Pore Space
Gas or Liquid Void
Solid Space
Mineral particles Organic matter (disregard
Interactions of Solid Space and Pore Space
Open spaces called pores, pores fill with water (soil water), soil porosity influences soil water movement
Macropores
> 0.08mm
Water drainage
Habitat for arthropods
Gas exchange
Micropores
<0.1mm Water storage (where bacteria are)
Porosity
Doesn’t change
Volume of the pores divided by the bulk soil volume
Total percentage, doesn’t tell if micro or macro pores
Bulk Density
Soil Mass/Soil Volume Measured oven dry Changes as pore space changes - compaction increases bulk density Surface Soils = 1.1 - 1.4 Subsoils = 1.3 - 1.7
Factors on Bulk Density
Texture
Aggregation
Surface
Texture and Bulk Density
Finer textures = lower BD
Aggregation and Bulk Density
More Aggregates = lower BD
Particle Density
Mass of particles divided by the volume of particles Typically 2.65 g/cm3 Used with BD to caluculate porosity Porosity = 1-BD/2.65 x 100 Influenced by structure and texture BD increases, Porosity decreases
Adhesion Water
Water attracted to solid surfaces Held by strong electrical forces (low energy) Little movement - held tight by soil Exists as film, unavailable to plants Removed by drying in oven
Cohesion water
Water attracted to other water molecules
Held by H bonding
Major source of water for plants
Greater energy than adhesion water
Gravitational Water
Water under the influence of gravity
Moves freely due to gravitational forces
Greatest energy
Exists in macropores
Potential Energy
Systems tend to change from a state of high energy to states of low energy
Behaviour of an object within a system is dictated by potential energy
Water Potential
Way to measure current energy state of unit of water
Water Behaviour
How does water flow in soils?
Upward and downward
Drier to wetter
Low concentration to high concentration
Soil Water Potential Types
Matric Potential Gravitational Potential (usually 0) Osmotic Potential (usually 0)
Matric Potential
Major force
Adhesive forces
Cohesive forces
As soil dries, decreases (negative number)
Soil Water Classification
Unavailable to Plants
Plant Available
Unavailable to Plants
0 to -10 kPa
-1.5Mpa to -100Mpa
Available to Plants
-10 kPa (field capacity) to -1500 kPa (Wilting point)
Sandy Textured Soil and Water
Low available water
Large pores that cannot hold cohesive water, mostly gravitational
Clay Textured Soil and Water
Low available water
Small pores mostly under wilting point
Loam Textured Soils and Water
High available water
Even pore distribution
Lots of capillary water
Volumetric Water Content
Volume of water in a given water of soil
Amount of water
Gravimetric Water Content
Easiest, most used way
Mass of water in a given mass of soil
[wet soil (g) - drysoil (g)]/drysoil (g)
Infiltration
Water entering the soil from precipitation
Infiltration is affected by:
Structure
Texture
Existing Water Conditions
Infiltration Rate Behaviour
Highest when soil is very dry
Decreases as soil becomes wetter
Effects of Soil Structure on Infiltration
Well aggregated granular and single grain have rapid flow
Subsurface structure has moderate
Massive structure and Platy have slower infiltration
Preferential Flow
Deposits surface chemicals to deeper soil layer
What affects saturated flow?
Soil texture, structure, existence of preferential flow channels
Moisture status of the soil
Calculated Hydraulic Conductivity
Rate at which water moves through a material
Saturated flow
Pore size decreases, Kstat decreases
Unsaturated Flow
Matric forces at play
Moves from wet to dry
Aerobic Soil Respiration
Plant roots, soil bacteria and fungi
Conversion of O.M. create gradients of oxygen and carbon dioxide
Anaerobic Soil Respiration
Bacteria can use compounds other than oxygen for respiration
Preferable compounds are nitrate and ferric iron
Carbon Cycle
Conversion of soil carbon to carbon dioxide and methane
Loss of carbon from the soil
Nitrogen Cycle
Conversion of soil nitrate to nitrous oxide and nitrogen gas (anaerobic)
Loss of nitrogen from soil
Colloids
Particles less than 1 or 2 micrometers
Very large surface area
Very reactive chemically (cation exchange, ionic double layer)
Components of Colloidal Fraction
Crystalline silicate clays
Non-crystalline silicate clays
Iron and Aluminium oxides
Humus
Building Blocks for Crystalline Silicate Clay minerals
Silicon Tetrahedron
Aluminium octahedron
Crystalline Silicate Clay Minerals
Pure form have no charge, changes at sheet edges and has negative charge
Isomorphic Substitution
Tetrahedron - Al for Si
Octohedron - Mg for Al or Zn for Al
Kaolinite
Bonding between layers are hydrogen bonds
No interlayer swelling
Little isomorphous substitution => lower negative charge
Lower surace area
1:1 sheet
Bonding between layers is hydrogen bonds (Strong)
Montmorillonite
2:1 clay Extensive isomorphous substitution Cations and water exist between unit layers Swelling Bonding between layers in cations (weak)
Illite
Isomorphic substitution (Si replaced by Al in tetrahedral sheet, Al substituted by Mg or Fe in octahedral sheet) Charge deficiency is balanced by the potassium ion between layers
Cation Exchange Capacity
Colloids have large amount of negative charge, attract positive charge (cations)
Importance of CEC
Fertility issues Acidity & liming rates Pesticides Contaminants Base saturation Chemical behaviour in soils
Common Soil Cations
Ca, K, H, Na, Mg, Al
Origin of Cations
Parent Geological Material
Additions
Parent Geological Materal
Soil minerals
Released through weathering
Additions
Atmospheric deposition (wind erosion, ash particles, cosmic dust) Fertilization
Fate of cations
Added/released to the soil
Switches between soil solution and plant biomass before being leached out of the soil (only leached out of soil from soil solution)
Rules of Cation Exchange
Cation Selectivity
Cation Equivalence
Ratio Law
Complementary Cations
Cation Selectivity
Large cations are held more tightly than small cations
Cation Equivalence
High charge cations are held more tightly than low charge cations
Al>Ca>Mg>K>Na
Ratio Law
Any one cation can replace any other if its concentration is high enough (all are reversible)
Mass Action Rule (part of ratio law)
Al will always win when 1 to 1
H will win when up agains 1000
Complementary Cations
The combined influence of charge equivalencies ion selectivity and complementary ions drive the exchange at cations
Lower charge gets knocked off easier
Generally cation with largest ionic radius and lowest hydration energies that absorb more strongly on the permanent charge sites
Quantifying CEC
Measuring positive charges of cation, quantifying amount of positive charges supplied by soils
Measuring CEC
- Known volume/concentration of NH4
- Replace all cations in soil with NH4
- lush with K
- Measure NH4 in leachate, NH4 concentration = TCEC
CEC and Fertility
CEC measures the total ability of a soil to retain cations
Does not provide information about what types of cations are retained
Calculations using CEC
Base Saturation
Percentage affects uptake by plants
Base Saturation
Measure of base cations located on exchange sites
Sources of Acidity in Soils
Carbonic and other organic acids Accumulation of OM Oxidation Reactions Plant uptake of Cations Free Al Human Activities
Carbonic and Other organic Acides
Dessolved CO2 in rainwater
Accumulation of OM
Carboxyl group (COOH)
Oxidation Reactions
Microbial usage produces H
Plant Uptake of Cations
Removal of base cations
Free Al
Weathering
Human Activities
Acid rain is important one
Mineral Weathering and Aluminum
- Weathering of Aluminum releases it into soil
2. Reaction of Al with H2O creates excess H in soil
Acid Rain
Fossil Fuel combustion creates NOx and SOx
Dissolve in rainwater to produce nitric and sulfuric acids
Fertilization
Intentional
Unintentional
Intentional Fertilization
Adding acidifying agents to alkaline soils
Unintentional Fertilization
Oxidation of Ammonium to Nitrate
Removal of base cations by harvesting plants that took cations out of soil
Pools of Acidity in Soils
Active (Small/Reactive)
Exchangeable (Large/Reactive)
Residual (Largest/Unreactive)
Active Acidity
H in the soil solution
Determines solubility of many substances in soil
Exchangeable Acidity
H &Al associated with colloidal cation exchangesites
Residual Acidity
Associated with structural H and Al in physillicate structures
Slowly released by weathering
Base Cations
Ca, Mg, K, Na
How do base cations act as bases?
Exchange places with H in solution
Leaching Losses of Base Cations
Acidifying processes continually add H with cations lost to leachingB
Gradual increase in soil pH as H dominates
Buffering Actions
Carbonate Buffering
Aluminium Buffering
Carbonate Buffering
pH>8
Ca exchanges with H and Al
CO3 reacts with free H and Al
Aluminium Buffereing
pH<5
Al absorbs OH
Resists rise in pH
Soil Nutrients
Macronutrients
Micronutrients
Macronutrients
Inhibited by low pH
Micronutrients
Inhibited by high pH
pH effects on Plants and Soils
Excess H = leaching loss of soil nutrients
Direct tissue damage
Change in soil bacteria
ALuminium Toxicity
Blocks Ca from entering into plants
Binds with Phosphorus in ATP
Restricts cell wall expansion
