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Conceptual Aspects:Habitat
Micro-organisms Bacteria, Fungi – both good and badViruses
Macro-organisms Worms, Arthropods, Detrivores and Predators
PlantsSmall MammalsBirds
What is Soil?
Conceptual Aspects:Provider to plant life
Rooting substrateWater holding and releaseNutrient supply and reserveHeat sink and releaseSoil gasesSymbionts
Bacterial and fungalInsects
What is Soil?
Physical Aspects:Minerals (from rocks)
SandSilt Clay and Colloids
Organic MatterPlants and RootsDetritus (decaying organic matter)Animal waste (including microbes)
Pore SpaceAirWater
What is Soil?
Carbon SinkWater filterIndicator of ecosystem health
What is Soil?
We need to keep all these things in mind in our management practices
How does this change how we treat the soil?
What is Soil?
HabitatWhat happens when we disturb this habitat?
At micro and macro level?What happens when we make additions to, or
removals from, this habitat?Carbon:Nitrogen ratio?How do soil organisms and plants respond?Nutrient loss or gain?
Providing for plant lifeWhat are the short-term and long-term results?Are we providing for the soil as well as the plants?
What is the difference?
What is Soil?
As a habitat we need to treat soil like a living organism, which requires:FoodWaterAirShelter
Cover cropsMulch
LivingDeadSnow
Tender loving care…
What is Soil?
Mineral ComponentsSandSilt Clay
Physical Attributes of Soil
SandLargest soil mineral particles (.02 – 2 mm)Formed greatly from physical processesSpherical/erratic in shape
Sand = little rocksLarger pore spaces
Good drainageDoes not hold a chargeDifficult to compact
Physical Attributes of Soil
SiltSize between sand and clay (.002 - .02 mm)Usually physically formed out of sandHold and releases water wellFlat or round in shapeHolds very little chargeFeels soapyCarried in moving water
Physical Attributes of Soil
ClaySmallest soil mineral particle (< .002 mm)Holds water very wellHolds strong negative charge for mineral
adsorptionSusceptible to compactionPlaty-/flat-shaped particlesVarious lattice structures
Physical Attributes of Soil
ClayUnderstanding structure of clay is
important for:CompactionWater holdingCation adsorptionSoil cultivation
Clays are categorized by their layer structure
Relationship of Si-tetrahedral and Al-octahedral sheets
2:1; 1:1; 4:1; 5:2
Physical Attributes of Soil
2:1 ClayShrink and swell
1:1 ClayNo change
Physical Attributes of Soil
Shrink and Swell of ClayInterlayer space expands
with increasing watercontent in soil
Space contracts as wateris removed
Clay can crack when it shrinks
Physical Attributes of Soil
Mineral ratios determine soil texture
Physical Attributes of Soil
Attributes of Different Soil Textures
Physical Attributes of Soil
Property Sand Silt ClayWater
HoldingPoor Medium to
highHigh
Nutrient Holding
Poor Medium to High
High
Aeration Good Medium Poor
Why is Texture Important?Water InfiltrationWater StorageFertility AerationTrafficability
Soil texture knowledge is the key to developing an overall soil maintenance and improvement plan
Physical Attributes of Soil
Soil organic materials are made up of:Dead and decaying plants or animalsAnimal manuresMicrobial by products
Materials decomposed to different stages exist simultaneously
Manure and compost are common OM additions to soil
Organic Matter
Organic matter’s role in soil:Holds soil particles together; stabilizes soil
Reduces erosion riskIncreases soil’s water holding and transmitting abilityStores and supplies nutrients to plants and microbesMinimizes soil compactionCarbon sinkAmeliorates the effect of environmental pollutants
Immobilizes them; reduces leaching
Usually 5-8% of soil; 30% or more in org. soils
Organic Matter
Soil Organic Matter CharacteristicsHigh Cation Exchange Capacity (CEC)High in Carbon (C) C:N ratio- indicator of Nitrogen (N) availability
to plantsNutrient concentration and ratios variableParticle density: 900-1300 kg/m3
Bulk density: 180-200 kg/m3 (peat) or 130 kg/m3 (forest)
Holds water better than mineral soils
Organic Matter
Two Types of Organic Matter
Non-humicPrimary components from fresh animal and plant
wasteEasily decomposed by microbes (when present)Comprise 20-30% of Soil OMDecompose to:
Carbohydrates (several types)Amino AcidsLipidsLignin
Very resistant to decayOther compounds
Organic Matter
Two Types of Organic Matter
HumicBiochemical decomposition of non-humic materialsResistant to further decompositionAccumulate in soilDark in colour – give soil dark characteristic60-80% of soil OM3 types:
Humins: larger particles; low number of carboxyl groups; inactive.
Humic acids: smaller than humins (approximately colloid-sized); more carboxyl groups than humins.
Fulvic acids: smallest humic substances; large number of carboxyl groups; most active among humic substances.
Organic Matter
Carboxyl and Hydroxyl Groups
Organic Matter
Organic Matter
Living Material
Dies onto soil
HumicNon-
Humic
This process is driven by biological decomposition – mostly from soil bacteria
and fungi
What role does OM play in texture?
Organic Matter and Texture
Click me, damnit
And another break…
Soil ColloidsMicroscopic soil particles (w/electron
microscope)Made up mostly of clays and organic materialsVery large surface areaCarry many exchange sites/charges
Mostly negative except in acid soilsHold soil cations (positively charged)
Holds water to cationsMajor contributor to soil nutrient holding
capacity
Soil Colloids
There might be a diagram here someday…
Soil Colloids
Where does the mineral component come from?
From the weathering of rocks.
Rocks are made up of minerals
Soil Formation
Primary Minerals Sand and SiltFormed at high T and P (at depth); anaerobic
conditionsPhysically and chemically formed
Secondary Minerals ClayCome from primary mineralsFormed at low T and P (at surface) with
Oxygen presentMostly chemically formed
Soil Formation
Weathering of Rocks
PhysicalChemical 1 Chemical 2
(note: base-forming cations)Chemical 3 Biological
Soil Formation
Parent Material
Climate
Biota
Topography
Time
Five Soil Formation Factors
Tiny little Video here
Gleysol Soil
Parent MaterialResidual
In situ; long periods of weatheringCumulose
Due to plant life and anaerobic conditionsHigh water table
Peat and muck soils Transported
Gravity - ColluviumWind - EolianWater - AlluviumIce - Glacial
Five Soil Formation Factors
ClimateTemperature and rainfall are major factors
Affect intensity of weatheringIncreased T and precipitation accelerate
weathering
BiotaPlants influence organic matterArthropods and worms mix soil; add to OMSmall mammals also mix soil
Five Soil Formation Factors
TopographySlope influences soil development
Water infiltration rateSurface runoffVegetation
AspectNorth and South slopes develop differently
ElevationClimate changes with altitude
Five Soil Formation Factors
TimeOften noted as most important soil
formation factorOur soils in Lower Mainland are relatively
youngSince last ice age 10,000 years ago
Five Soil Formation Factors
Great Soil Formation Videos Here
Five Soil Formation Factors
AdditionsLossesTransformationsTranslocations
Soil Formation Processes
Video here
Podzol Soil
Organic (O) HorizonHigh in organic residue from plant drop
A HorizonMineral component mixed with OMMost fertile part of soil; location of much root
activityExhibits Eluviation in soil solution
B HorizonSubsoilExhibits Illuviation of clay, OM, oxides
C HorizonLittle influence by soil-forming processes
Soil Horizons
Water (W) HorizonDue to high water tableFound in Gleysols
BedrockUnderlying consolidated material (solid rock)
LFH HorizonsUsually found in forest soils with high surface
residue
Soil Horizons
Soil Structure: How the soil fits togetherPrimary particles are arranged into
secondary particles called aggregates (or peds)
Soil Structure
Why is Structure Important?Pore space
Air and water movementRooting space
Nutrient storage and releaseContributes to soil resilience
CultivationErosion resistance
Soil Structure
How does aggregate formation occur?
Flocculation + Cementation = Aggregation
Flocculation: Primary pulled close together (into flocs) by
attractive forces (electrostatic forces, H bonding)
CementationPrimary particles held together by cementing
agentsCarbonates; clays; OM; Oxides
Soil Structure
Soil Structure
Soil Aggregates are classified by their shape
Soil Structure
SpheroidalTypical in A HorizonRounded; loose Granular (porous) or Crumb (very porous)Greatly affected by soil
management/mismanagementImproved with OM additions
Soil Structure
Soil structure is particularly important in providing adequate pore space for:Root growthWater movementGas exchangeMicrobial activityMacrobial activity
Soil Structure
Related to textureVery important when considering soil
cultivation
Dependant on Texture/clay contentClay typeSoil water content
Soil Consistency
Soil Consistency
Cultivating soil when too dryBreaks aggregates into small pieces
De-aggregatesCan result in dust
Very damaging to soil structure
The drier the soil – the more it acts like powder
Soil Consistency
Cultivating soil when too wetWhere to start?!
CompactionRisk and depth of compaction increases in
wet soil
Soil Consistency
Cultivating soil when too wet
The wetter the soil - the more it acts like water
Soil Consistency
Soil Consistency
Particle density: Density of individual particles
Density = Mass/Volume (M/V)ρparticle = Msolids /Vsolids
Some particle densities:Water: 1000 kg/m3
Organic Matter: 900-1300 kg/m3
Minerals: 2650 kg/m3
Soil Particle and Bulk Density
Bulk density: Density of particles and pore space
ρbulk = Msolids /Vsoil
Some bulk densities:Mineral or organic soil: 1300 kg/m3
Clay Soil: 1100 - 1300 kg/m3
Sandy Soil: 1500 – 1700 kg/m3
Soil Particle and Bulk Density
Measuring Particle Density:
Weight out a dry sample of particle type (e.g., sand)This is your Mass value
Fill graduated cylinder with waterRecord exact water level
Drop particles into cylinder of waterRecord new water level
New Reading – Old Reading = VolumeMass/Volume = Particle Density
Soil Particle and Bulk Density
Measuring Bulk Density:
Collect known sample (Volume) size of soilUse soil core; Volume = πr2h
Weigh sample then dry in ovenRemoves water from sample
Weigh dried sampleThis is your soil Mass
Mass/Volume = Bulk Density
Soil Particle and Bulk Density
Why is density important?
Particle density: not as important as bulk density
Bulk density is indicator of pore spaceChanges in bulk density = changes in pore
space
Soil Particle and Bulk Density
Soil Air and Water (Pore Space)
Soil Water
Soil Air and Water (Pore Space)
For future lecture…
Soil Air and Water (Pore Space)
Agricultural Capability Classes Class 1
Class 1 land is capable of producing the very widest range of crops. Soil and climate conditions are optimum, resulting in easy management.
Class 2 Class 2 land is capable of producing a wide range of crops. Minor restrictions of soil or
climate may reduce capability but pose no major difficulties in management. Class 3
Class 3 land is capable of producing a fairly wide range of crops under good management practices. Soil and/or climate limitations are somewhat restrictive.
Class 4 Class 4 land is capable of a restricted range of crops. Soil and climate conditions require
special management considerations. Class 5
Class 5 land is capable of production of cultivated perennial forage crops and specially adapted crops. Soil and/or climate conditions severely limit capability.
Class 6 Class 6 land is important in its natural state as grazing land. These lands cannot be
cultivated due to soil and/or climate limitations. Class 7
Class 7 land has no capability for soil bound agriculture.
