What is Soil

Conceptual Aspects:HabitatMicro-organisms Bacteria, Fungi both good and badVirusesMacro-organisms Worms, Arthropods, Detrivores and PredatorsPlantsSmall MammalsBirds

What is Soil?Conceptual Aspects:Provider to plant lifeRooting substrateWater holding and releaseNutrient supply and reserveHeat sink and releaseSoil gasesSymbiontsBacterial and fungalInsects

What is Soil?Physical Aspects:Minerals (from rocks)SandSilt Clay and ColloidsOrganic MatterPlants and RootsDetritus (decaying organic matter)Animal waste (including microbes)Pore SpaceAirWater

What is Soil?

pH Buffer creates resistance to pH change in a systemOrganic matter and clay are most significant buffers

Organic matter hydroxyl functional groups buffer pH

Clays buffer pH by adsorbing and releasing H+

Soil Chemistry - pHWe 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:FoodWaterAirShelterCover cropsMulchLivingDeadSnowTender loving care

What is Soil?

Click me

Short commercial breakMineral ComponentsSandSilt Clay

Physical Attributes of Soil

SandLargest soil mineral particles (.02 2 mm)Formed greatly from physical processesSpherical/erratic in shapeSand = little rocksLarger pore spacesGood 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 structureRelationship of Si-tetrahedral and Al-octahedral sheets2:1; 1:1; 4:1; 5:2

Physical Attributes of Soil2:1 ClayShrink and swell

1:1 ClayNo changePhysical Attributes of Soil

Shrink and Swell of ClayInterlayer space expandswith increasing watercontent in soilSpace contracts as wateris removedClay can crack when it shrinks

Physical Attributes of Soil

Mineral ratios determine soil texturePhysical Attributes of SoilAttributes of Different Soil TexturesPhysical Attributes of SoilPropertySand SiltClayWater HoldingPoorMedium to highHighNutrient HoldingPoorMedium to HighHighAerationGoodMediumPoorWhy 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 SoilClick meAnd now a short breakSoil 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 MatterOrganic matters role in soil:Holds soil particles together; stabilizes soilReduces erosion riskIncreases soils water holding and transmitting abilityStores and supplies nutrients to plants and microbesMinimizes soil compactionCarbon sinkAmeliorates the effect of environmental pollutantsImmobilizes them; reduces leaching

Usually 5-8% of soil; 30% or more in org. soilsOrganic MatterSoil 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/m3Bulk density: 180-200 kg/m3 (peat) or 130 kg/m3 (forest)Holds water better than mineral soils

Organic MatterTwo 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 MatterTwo 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

Organic MatterCarboxyl and Hydroxyl Groups

Organic Matter

Slide 78Go over CEC and stuff later; see lecture 17 for link to pH and CEC also talk about DDL and diffusion

27Organic MatterLiving MaterialDies onto soilHumicNon-Humic This process is driven by biological decomposition mostly from soil bacteria and fungiWhat role does OM play in texture?Organic Matter and Texture

Click me, damnitAnd another breakSoil ColloidsMicroscopic soil particles (w/electron microscope)Made up mostly of clays and organic materialsVery large surface areaCarry many exchange sites/chargesMostly negative except in acid soilsHold soil cations (positively charged)Holds water to cationsMajor contributor to soil nutrient holding capacity

Soil ColloidsThere might be a diagram here somedaySoil Colloids

Click MeAnd now another break Where does the mineral component come from?

From the weathering of rocks.

Rocks are made up of mineralsSoil FormationPrimary 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 FormationWeathering of Rocks

PhysicalChemical 1 Chemical 2(note: base-forming cations)Chemical 3 Biological

Soil FormationParent Material

Climate

Biota

Topography

Time

Five Soil Formation FactorsTiny little Video hereGleysol SoilWrite down what you recognize following under these 5 categories from the video

38You know what to doNot another oneParent MaterialResidualIn situ; long periods of weatheringCumuloseDue to plant life and anaerobic conditionsHigh water tablePeat and muck soils TransportedGravity - ColluviumWind - EolianWater - AlluviumIce - GlacialFive Soil Formation FactorsClimateTemperature and rainfall are major factorsAffect 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 FactorsTopographySlope influences soil developmentWater infiltration rateSurface runoffVegetation

AspectNorth and South slopes develop differently

ElevationClimate changes with altitude

Five Soil Formation FactorsTimeOften noted as most important soil formation factorOur soils in Lower Mainland are relatively youngSince last ice age 10,000 years ago

Five Soil Formation FactorsGreat Soil Formation Videos Here

Five Soil Formation FactorsAdditionsLossesTransformationsTranslocations

Soil Formation Processes

Video herePodzol Soil

Soil HorizonsOrganic (O) HorizonHigh in organic residue from plant dropA HorizonMineral component mixed with OMMost fertile part of soil; location of much root activityExhibits Eluviation in soil solutionB HorizonSubsoilExhibits Illuviation of clay, OM, oxidesC HorizonLittle influence by soil-forming processes

Soil HorizonsWater (W) HorizonDue to high water tableFound in Gleysols

BedrockUnderlying consolidated material (solid rock)

LFH HorizonsUsually found in forest soils with high surface residueSoil HorizonsClick MeAnd now another break Soil Structure: How the soil fits togetherPrimary particles are arranged into secondary particles called aggregates (or peds)Soil Structure

Why is Structure Important?Pore spaceAir and water movementRooting spaceNutrient storage and releaseContributes to soil resilienceCultivationErosion resistance

Soil StructureHow 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; OxidesSoil Structure

Soil StructureSoil 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 StructureSoil structure is particularly important in providing adequate pore space for:Root growthWater movementGas exchangeMicrobial activityMacrobial activitySoil StructureRelated 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 piecesDe-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 soilSoil Consistency

Cultivating soil when too wet

The wetter the soil - the more it acts like waterSoil Consistency

Soil Consistency

Particle density: Density of individual particles

Density = Mass/Volume (M/V)particle = Msolids /Vsolids

Some particle densities:Water: 1000 kg/m3Organic Matter: 900-1300 kg/m3Minerals: 2650 kg/m3

Soil Particle and Bulk DensityBulk density: Density of particles and pore space

bulk = Msolids /Vsoil

Some bulk densities:Mineral or organic soil: 1300 kg/m3Clay Soil: 1100 - 1300 kg/m3Sandy 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 valueFill graduated cylinder with waterRecord exact water levelDrop particles into cylinder of waterRecord new water levelNew 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 = r2hWeigh sample then dry in ovenRemoves water from sampleWeigh dried sampleThis is your soil MassMass/Volume = Bulk Density

Soil Particle and Bulk DensityWhy is density important?

Particle density: not as important as bulk density

Bulk density is indicator of pore spaceChanges in bulk density = changes in pore spaceSoil Particle and Bulk DensityAgricultural Capability Classes

Class 1Class 1 land is capable of producing the very widest range of crops. Soil and climate conditions are optimum, resulting in easy management.Class 2Class 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 3Class 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 4Class 4 land is capable of a restricted range of crops. Soil and climate conditions require special management considerations.Class 5Class 5 land is capable of production of cultivated perennial forage crops and specially adapted crops. Soil and/or climate conditions severely limit capability.Class 6Class 6 land is important in its natural state as grazing land. These lands cannot be cultivated due to soil and/or climate limitations.Class 7Class 7 land has no capability for soil bound agriculture.pH = - log [H+]Measure of soil acidity/alkalinityScale of 0-14Acid: 0 - 6.9Alkaline: 7.1 - 14Neutral: 7Typical range of soil pH = 5 to 9Ideal range: 6 7 for most annual vegetable crops

Soil Chemistry - pH

Soil Chemistry - pHRole of Al3+ in soil acidity

Al3+ + H2O AlOH2+ + H+

AlOH2+ becomes site for P adsorption

Soil Chemistry - pHTypes/Pools of pH:

Residual acidity is associated with H+ and Al3+ ions that are bound (non-exchangeable) on soil particle

Exchangeable acidity is associated with H + and Al3+ ions that are easily exchanged by other cations in the soil solution

Active acidity is due to H+ and Al ions in the soil solution

Soil Chemistry - pHSoil Chemistry - pH

Positively charges cations are attracted and held to (adsorbed to) negatively charged soil particles

Mass Ion effect: Introducing a large number of cations to the soil results in these cations replacing adsorbed cations on soil particles

Exchangeable cations are those cations which are readily displaced, by mass ion effect, from negatively charged colloids on which they are adsorbed

Cation exchange capacity (CEC) - number of exchangeable cations which soil solids can adsorbSoil Chemistry Adsorption and CECMass Ion Effect and Diffusion alter the number and type of cations that are adsorbed to soil particles

Soil Chemistry Adsorption and CEC

CEC Video 1CEC Video 2

The exchange of cations between soil particles and solution is a dynamic process, always in flux, yet alsways striving for equilibrium

More soil lecturesSoil Chemistry Adsorption and CEC

Soil Air and Water (Pore Space)Soil Water

Soil Air and Water (Pore Space)

Gardner Soil Water VideoSoil Air and Water (Pore Space)