LCC- Soils MT

What is soil?

4 pt definition:

 

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1)a naturally occurring, unconsolidated material composed of mineral (inorganic) and living (organic) components

-naturally occurring means product of pedogenesis

-unconsolidated means it is not rock..

 

 

2)at least 10cm thick

-prefer at least 50cm of soil depth to be non-limiting to productivity

 

3)found at or near the earth’s surface

-soils are found where the natural pedogenic processes have formed them

-some soils may be ‘buried’ at loewr slopes of hills by mass wasting and erosion, but these are still not considered to be at ‘great depth’

;

4)which is capable of supporting life

-soil provides 5 of 6 factors essential for plant growth

The importance of soils and their function in the ecosystem

-soil is the foundational resource in providing for and regulating vegetative growth and productivity

;

-soil is the medium by which the sun’s energy; available moisture and the range of essential nutrients become concentrated and stored in plants (and ultimately converted to animal tissue)

 

-this stored energy is an end product of, and what drives, the nutrient balance of the ecosystem

 

 

SIX ESSENTIAL GROWTH FACTORS:

-light

-heat*

-nutrients**

-moisture**

-aeration**

-mechanical support**

There are two approaches to studying soils:

1) PEDOLOGICAL approach

-pedologists study soils as they occur and are found within the environent

-soils are mapped to accurately indicate where certain types of soils are located

 

-pedologists use a standardized system to reproducibly classify the soils according to type (establish soil taxa)

 

-there ris no attempt to interpret the productivity potential or value of the soil

 

-the end result are survey maps

 

2)EDAPHOLIGICAL approach

-this is the study of soils with the objective of determining their current and/or potential productivity

 

-land managers can use information provided by pedologists

Soil Horizons and properties

1)A horizon is an individual, more or less horizontal layer distinguishable from other layer(s) within the soil cross-section

 

2)Soil horizons are distinguishable (from one another) on the basis of:

-physical properties and/or

-chemical properties and/or

-biological properties

 

PHYSICAL

-includes color, texture, structure, consistence, pore volume (porosity), water holding capacity, tilth

 

CHEMICAL

-presence of carbonates, soil pH, presence of soluble salts, fertility/nutriend status, etc

 

BIOLOGICAL

-organic matter (humus) content, roots, microorganisms, etc

 

*Changes in a specific soil property often results in one or more other properties*

(ie. higher humus = darker, more nutrients)

Typical profile from Lethbridge area

Ah = 0-15cm

Bm = 15-50cm

Ck = 50+cm

Master Soil Horizons

Soil horizons are divided into 2 fundamental classes, with a miscellaneous 3rd class:

 

1)Master Mineral Horizons

-organic matter is less than 30% mass (or less than 17% organic carbon by mass)

-designated as A, B, and C

 

2)Master Organic Horizons

-in this case, the master OM content is greater than 30 (or OC>17%)

-designated as L,F or H for well drained sites

-may be used in combination (could be LF, FH, LFH, etc)

Of, OM, and Oh under poorly drained conditions

-organic material must be greater than 40cm thick overlying water to be classified as soil and may consist of several layers (horizons) with somewhat variable characteristics

 

 

3) Designations applied to various layers of surficial deposits include:

-those used to  distinguish surficial deposits as “soil” vs “non-soil”; the latter falls into a miscellaneous category; essentially labeled “non-soil”, including:

 

-a layer designated R (consiolidated rock, regolith) at or near surface

-(must be at least 10cm to be soil)

-soil covered by a veneer of fresh surficial deposit at least 50 cm thick is classified as a buried soil (a Paleosol)

-land fills and earth fills also considered “non-soil”

 

and also:

-a surface layer designated W

-indicates free water >60cm in depth overlying unconsolidated mineral parent material

-indicates organic material in layers  less than 40cm thick over free water

Designation of Mineral Horizons

-sand silt and clay is greater than 70%

 

A and B always require a lower case modifier suffix

-modifier suffixes indicate specifically what kind of master mineral horizon is present

-also how the horizon has been modified from PM

 

C may or may not use modifying

-since they show negligible change from original PM

 

organic:

-an organic horizon must have a minimum thickness of 5cm to be included in the profile description

-therefore, organic horizons are commonly found under forest stands (duff) and in poorly drained locations (bogs, muskegs, etc)

-though there is some leaf litter associated with grasslands these layers do NOT constitute organic horizons (not thick enough)

Examples of some common mineral horizons (9)

Ah

-h designates a zone of maximu accumulation of humus at the surface of the profile

-Ah are darker in color than the lower horizons

-usually have granular structure and friable (not hard) consistence

-typical of soils developed under grassland vegetation

 

Ae

-e indicates eluviation of clay or other minerals and/or humus

-generally lighter in color than the underlying horizons in the soil profile

-Ae horizons are characteristic of surface horizons in soils formed under forest vegetation

 

Bt

-t indicates the accumulation of clay in a B horiozn (and therefore eluviation from Ae above)

-logically a Bt horizon is usually found immediately below an Ae horiozn

-Bt horizons are common in forested soils of western Canada, even after the land has been cleared for agriculture or other uses

 

Bf

-f indicates the process of iron and aluminum oxides accumulation below a severely leached eluviated Ae horizon

-this is typical of B horizons in soils found uner well developed, extremely acidic deciduous and coniferous forest vegetation

-Bf horizons have a typical redish-orange color

 

Ck

-k denotes the presence of carbonate materials (free lime)

-this is indicated by characteristic efferevescence when treated with dilute acid

-the presence of carbonate minerals results in an alkaline pH

 

Cca

 -ca indicates the accumulation (ie. measurable increase, not just presence) of free lime in the C

-Ck and Cca horizons are common subsoils of western Canada; Cca horizons are more frequent in the driest zones of the region

 

Csa

-indicates the accumulation of soluble salts and salinity

 

Cg

-indicates gleying as a result of high water table

 

C

indicates the starting point or PM of the soil profile with no or littler modification from original

solum (pl. sola)
-refers to the A and B horizons taken collectively to depth; essentially all horizons above the C horizon within the soil profile
profile
-includes the A ad B horizons plus a thin slice of the C horizons (or parent material, PM); therefore the soil profile contains the solum plus a portion of the PM
Regolith
-Relates to all unconsolidated material over the bedrock. Includes A, B, C, and parent material above the bedrock. On the southern prairies of W Can  the regolith is relatively thick; common depths in teh Lethbridge area range from 5m to more than 30m thick although at some locations, thickness may be less than 1m.
Parent Material

-represents the starting material from which soil isformed (also referred to as IC)

can be either mineral or organic in origin

 

-Mineral PM refers to the geological material from which the soil has been generated (C horizon closely esembles the PM of mineral soils)

 

Mineral PM vs Organic PM

-PM is referred to as mineral if the OM content is less than 30%

-PM is referred to as organic if the OM content is greater than or equal to 30%

-organic PMis found on imperfectly ot poorly frained sites in central to northern locations in Can

-organic is the most common PM in West Can

-climate in these areas does not allow for agricultural production

Definitions of topsoil and subsoil

topsoil: refers to the uppermost zone of soil; generally considered to represent the A horizon

– a more technical term for the topsoil is Ah, Ahe, etc

-for soils formed under prairie sod conditions, topsoil is usually assumed to be enriched with organic matter/humus

 

subsoil:

-refers to the lower part of the active soil profile, including the B and at least the upper C

-less active, though roots can access moisture and nutrients here

Pedon

The soil pedon represents a sampling format for ail in the field that:

-is small enough in size to permit a high degree of uniformity plus the opportunity to verify the same/similar soil properties in detail

 

but

 

-is large enough to encompass and allow the observer to gauge real differences and variations in osil horizons

 

-characteristically 1 to 10m squared

-expected to extend downwards to the PM

 Extrapolating the Pedon to a 3D view of soil

-When properly established and classified in the field, the pedon represents a true classificationsoil type in real terms

-as such, the pedon represents the smallest unit of soil that can be mapped as a single entity in the field

 

polypedon: a grouping of continuous pedons

-radiates out from the central pedon until one or more pedogenic factors changes sufficiently in its effect to cause a significantly different soil pedon to form

 

-at this point the classficiation is changed, a line of delineation is drawn around all similar pedons (to form on polypedon unit) and a “new” polypedon unit continues

-this concept allows ALL soil pedons with similar characteristics to be grouped into a single (polypedon) unit

 

-since the polypedon units are usually irregular in shape and size, they are also referred to as soil polygons

 

these polypdon units become the individual map units (polygons) viewed on soil survey maps

Pedogenesis

Soils form due to the action and interaction of 5 distinct soil-forming factors**

1)Type of PM

2)Climate

3)Organisms

4)Topography

5)Time

Influence of PM in pedogenesis

PM is a soil forming factor which influences many properties of the soil that ultimately forms at a particular site

-when the type of PM varies, the end result is a wide variety of very different soil types, characteristics, and inherent (natural) productivity

***the PM ultimately determines the physical and chemical properties of the soil

 

PHYSICAL AFFECTED BY PM

texture

-in turn, texture affects:

1)water retention

2)erosion (wind severe with high S/Si, water severe when high Si or C)

3)rate of infiltration of watr

4)compaction hazard

 

CHEMICAL PROPERTIES AFFECTED BY PM

1)soil salinity (high salt in PM)

2)Reaction (pH)

3)Fertility (high C means more fertility)

4)susceptibility to leaching (coarse leached of ions

Leaching

The process whereby ions dissolved in soil water will move downward in solution

-presumably these ions, which includes available nutrients in the soil profile, can move below and be lost from the root zone over time

 

Coarse textured (sandy) soils are redily leached of ions

not all, but many of these are plant nutriends (ie. NH4-ammonium, and NO3-nitrate)

 

-high C decreases leaching

Residual PM

-occurs when the bedrock weathers in place (in situ) and the weathered products yield the unconsolidated (loose, non-rock) mineral material which in turn will eventually form the soil

 

-soils developed on residual PM inherit the general haracteristics of the weathered bedrock

 

ie. weathered sandstone yields sandy soils, weathered shale yields fine textured soils

 

Residual soils are not widely distributed in western canada because unconsolidated PM has been transported and deposited on top of the bedrock

Transported PM

-mostly deposited 20-25k years ago.. glaciation

 

1) Glacial till (or morainal)

-agent is ice

-small angular stones, coal flecks

-wave like landscape

 

2)Fluvial

-transport/depositional agent is moving water within drainage channels

-usually high in sand and gravel…rounded stones

-often low lying areas

 

3)Lacustrine PM

-also referred to as glacio-lacustrine

-depositional agent is stagnant water as it collected in drainage basins

-usually high clay, no stones/coal flecks

-very flat

 

4)Aeolian (or eolian)

-wind blown, inclued loess

-very fine, no stones, coarse stuff

-crescent form from above

 

5)Colluvial (colluvium)

-PM deposited by gravity, scree and talus are examples, may bury existing soils

-generally low productivity

-coulee bottoms, base of hills, mountainous areas

Effects of PM on soil development

1) Texture is affected by type of PM

-Till tends to give medium texture

-fluvial tends to give coarse

-lacustrine fine

-aeoliaan tends to give medium (very fine though- holds moisture well)

 

 

2)Topography

-till gives waves (hummocky)

-fluvial lower in elevation and meanders through landscape

-lacustrine usually fills in topo lows b/w tops of hills… generally flat

**although lacustrine and other types of PM may be relatively thick, in SAB glacial till is usually found somewhere below the unconsolidated material over bedrock

-aeolian PM may be seen as inactive or dormant sand dune

 

3)In southern AB and SK, there are two main general effects of siol PM with respect to the chemical proeprties of soils:

a)PM tends to be high in free lime

b)soils may be saline

Effects of Free Lime

-The source of most carbonate (CO32-) comes from calcium carbonate (CaCO3)

-chemically, calcium carbonate dissolves in water to form carbonate and calcium… in acidic conditions, (H+ available), these react to form CO2, H20, and calcium

 

POSITIVE EFFECTS

1)Carbonate neutralizes soil acidity

-too low pH damagaes vegetation

-alfalfa is very vulnerable (poor growht caused by acidity called alfalfa sickness)

-lime can be incorporated as “soil amendment”

-adding ilme called liming

-usually done when pH falls below 5.5

-liming is very expensive.. usually must be repeated every 3-5 years

-will be required on many agricultural soils in the future to counter acidification

 

-acidic soils can occur naturally (forest vegetation, PM, etc), or anthropogenically (acid rain, Sulfur from Sour gas plants, nitrogen fertilizers)

 

 

2) PM and Free Lime contribute essential nutrients

-calcium, magnesium, potassium

-west canada doesn’t need Ca fertilizer, which is applied more than N fertilizers on a world-wide basis

-also, potash (K) fertilizer is rarely recommended in W Canada…. only exceptions are regions of coarse texture, when certain vegetation has higher demand of potassium (potatoes, sugar beets)

;

;

Disadvantages

calcareous soils are higher than 8.5 pH

-in these soils, a portion of the soluble phosphate fertilizer added reacts with Ca at an alkaline pH to form a phosphate compound with extremely low solubility

-therefore some of the added phosphate becomes unavailable for plant uptake

;

-The practice of deep banding P-fertilizers can allow a substantial cut in application rate compared to broadcast applications on calcareous soils

-P-fertilizer is “banded” approx 2″ to the side and below the seed…

PM affects the potential for the development of soil salinity

-soil salinity can be the result of the presence of a high concentration of soluble salts in the PM

Examples include sodium sulfate, potassium sulfate, potassium chloride)

 

-The salts contributing to soil salinity are soluble salts, therefore the carbonate salts (free lime) are NOT considered to contribute to salinity because these have low solubility values

-high concentrations of soluble salts are not found in all PM sources, but where they do exist, the POTENTIAL to develop soil salinity exists

-NOT all soils with high soluble salt content will develop into saline soils. To form soil salinity, three conditions must exist simultaneously:

1)high concentration of soluble salts in PM

2)a high water table; depth to waer table must be less than 2m

3)a high rate of evapotranspiration which results from hot dry summers

 

**PM can significantly affect #1 and #2

Climate as a Pedogenic Factor

Two major components: Temperature and Moisture

 

Effects of Temperature

1)increase in the mean annual temperature causes the rate of soil formation increases

-10C increase, rate of soil formation increases by approx 2X

-warmer usually means deeper soil (when ppt is there)

 

Moisture

-semi-arid to arid conditions result in slower rate of osil formation

-dry regions usually not as deep profiles

 

-therefore very dry and cold means slow rate of formation (Arctic soils take thousands of years)

 

Soil Moisture:

a)indirectly affects soil formation by determining and modifying vegetative cover and other organisms.. (sep. ped. factor)

 

b)directly affects soil formation by causing translocations of ions of compounds in solution as well as extremely small (colloidal) particals of clay and humus downward in the soil profile (eluviation)

 

c)causes differential movemen of water through the soil profile

-cited as major reason for formation of different horizons within profile since these zones experiencedifferent degree of water percolation

Organisms as a Pedogenic Factor

Soils cannot form in the absence of biotic activity. Furthermore, the species distribution and productivity affect the very nature of soils formed.

 

General categories of organisms that have a direct effect on soil development include:

-vascular plants*

-mesofauna

-microorganisms**

-vertebrates/burrowing animals

-humans*

Vascular plants as a pedogenic factor

The major effects of vegetation include:

1)control of the quantity of the aerial portions and plant roots that regulates the effective additions of OM when OM stabilizes as humus

-directly controlled by the quantity and type of veg

 

2)the actual species composition and nature of vegetation is important

-grassland soils favor the accumulation of humus in the topsoil… forest vet results in a much less desirable soil humus content and type

 

-low quantities of OM incorporated into forested soils results in a thin Ah or non-existant Ah

-much greater quantity of the C and H in forest is lost as CO2 (more volatile)

-results in less than ideal physical properties and fertility

-results in low base saturation (this is related to soil acidity and poor fertility)

Microorganisms as a pedogenic factor

 

Main functions:

-decomposition and resynthesis of soil OM (formation of humus)

-the release of available nutrients and nutrient cycling in general… total vs available nutrient… microbes can make available

 

NUTRIENT CYCLING

-specific microbes are an essential vector in “fixing” N2 gas from the atmosphere into soil as NH4

-other microbial species convert ammonium in soils to nitrate, and others are also responsible for incorporating ammonium and nitrate into organic… blah blah… NITROGEN CYCLE

 

heterotrophic microbes: obtain body carbon and energy by oxidizing carbon from organic sources

(also called decomposers)

 

autotrophic microbes: obtain energy by inortanic (mineral) oxidation and reduction reactions and obtain body carbon from CO2 (inorganic)

 

1)and extremely important combination of autotrophic microbes are responsible for converting ammonium to nitrate in N-cycle

2)other autotrophic microbes are responsible for oxidation of elemental sulfur to sulfate which is a major factor in acid rain and soil aidification as well as the reduction of iron and other metal ions under anaerobic/anoxic conditions (ie. the  gleying process under saturated soil conditions)

 

The main families of soil microorganisms include bacteria and actinomycetes (unique to soils)

 

-some soil organisms cause disease in plants and vegetation

 

*nematodes and earthworms are classified as microfauna rather than microflora

*bacteria and actinomycetes have high live biomass in soil than algae, nematodes, and earthworms
-fungi is the highest

Other Biota that impact soils…

-one grouping of organisms include earthworms, burrowing insects, millipedes, etc (mesofauna)

-earthworms process soil and improve overall tilth

 

-humans can have positive and negative effects

Effects of Topography on Soil Formation

The two components are aspect and eleveation

 

Elevation

1)When the difference in elevation is significant, soils at higher elevations resemble those developd under cooler, moisture conditions

2)however, even when changes in elevation are relatively small, the effects on soil formation can still be significant

-the main effect is due to differential erosion and also changes in microclimate

 

*The variation in soil characteristics due to variations in elevation in a conined area is referred to as toposequence

-generally Ah gets deeper the lower you go

-same with OM, however, if you’re going below tree line OM may decrease

 

 

Aspect

-refers to the orientation of the slope and soil surface relative to the points of a compass

-In AB S+W facing slopes are generally drier, grassland, thick Ah, neutral pH, high fertility, better tilth

-In AB N+E aspect are high in effective moisture, forested, Ah degraded, low OM, solum pH is acidic, lower nutrient content, poor tilth

Time as a factor in Soil Formation

Time is often referred to as the passive or inactive pedogenic factor.

-Under drier and cooler climativ conditions, soil formation required more time to reachequilibrium

-the rate of soil building has been estimatd as 0.75mm/yr in central prairies

 

PRACTICAL APPLICATIONS IN INTERPRETING TIME AS A PEDOGENIC FACTOR

-Soil profile characteristics can also indicate the relatie period of time the PM at a particular site has been subjected to pedogenic factors. Over time, soil profiles will reach a terminal point (equilibrium) that can be used as reference point for the “typical” soil profile of the area.

 

Variations from the typcal soil profile, particularly in depth, may be indicative of soil disturbance and/or soil erosion. Following are a number of applied views on using time vs soil profile development in asessing history of soil development

 

1)free lime within the boundaries of the solum indicate insufficient time to have cleared and translocated carbonates to C

-indicates a young, developing soil profile yet to reach equilibrium.

 

CAUTION:

-carbonates in solum may also indicate slow or incomplete drainage of the soil due to an impermeable layer or a perched water table and saturated subsoil conditions that prevent translocation of carbonates in percolating water

 

2)”poorly developed” horizons compared to typical soil profiles in the area

-therefore the horizon characteristics are not as well expressed as compared to soils that hve reached equilibrium with pedgenic factors

 

3)a profile lacking a B horizon… as this requires time to form

Example of Pedogenic Factors Acting Independently….. Organisms

Organisms as a pedogenic factor…

 

1)A soil profile developped under grassland in an area with a subhumid climate is likely of the Chernozemic Order

2)A soil profile developed under forested vegetation with a similar subhumid climate will usually classify as Luvisolic ORder

 

3)These two orders represent soil profiles with significant differences in properties (physical, chemical, biological) and productivity potential, and best practices management requirements simply on the basis that one soil is formed on grassland and the other under a relatively closed forest canopy

Examples of the Interaction of Two or More Pedogenic Factors..

1)A vry common interaction in the foothills and the eastern slopes of teh Rockies, particularly in the south and central areas where teh climate is in a “tension zone”

-therefore even small changes in microclimate can have a direct impact on vegetation present

 

2)In this case, topography, whether in the form of aspect or slope affects Climate (microclimate)

-S and W facing slopes are drier

-lower slpes, concave valleys and swales collect more runoff and increases soil moisture

-in these moister locations, poplar clones and other woody species take hold (so organisms change) and this has a profound effect on the properties of the soils developed here

-therefore, changes in topography cause change in climate at different sites which in turn affects organisms present and ultimately the soils formed

 

 

-S + W facing slopes have a drier microclimae for the area and support grassspp; corresponds to Black Chernozemic soils

-Swales and concave valleys on S and W have higher moisture; support aspen and other woody spp; yielding dark grey chernozemic and Brunisolic soils

-N and E facing slopes have moister/mesic microclimate; support woody spp, predominantely aspen but also including some grass and white spruce; results in dark gray luvisolic and gray luvisolic

Four major physical/chemical properties controlled by PM

physical

1)moisture holding

2)drainage and airation

3)erosion potential

4)compaction hazard

 

chemical

1)plant nutrients/fertility

2)degree of leaching

3)soil reaction (pH)

4)salinity

 

Adv and Dis of Glacial Till

ADVANTAGES
-moderate sand/silt/clay- medium texture

-don’t need Ca fertilizers

-rare acidification

 

DISADVANTAGES

-degree of stoniness

-variable soil productivity

-soil salinity

Soil Zones

Black soil

Dark Brown

Brown

Grey (lowest OM)

Bulk Density/Particle Density/Porosity/Percent Water/Bulk Specific Gravity

Db = Dry Mass/Volume

Dp= Dry Mass/Volume Solids

Porosity= (1-Db/Dp)*100

 

*as Db increases, porosity increases

Pw= (moistmass-drymass/drymass)*100

Pv= Pw*Bsg

 

Bsg= Db/water density (1)

Identify 2 methods used to determine Db and list one advantage and one disadvantage for each

 

 

1)Cre Sampes

-quick

-require equipment

 

2)Dig a hole

-cheap

-not as accurate

Sampling types, and how to get a representative sample

Depth Priority= 0-15cm, 15-30cm, 30+cm

Horiozn Priority= Full range depth

 

Depth is quick and easy, though arbitrary depths are used

 

Horizon pit allows sampler to delineate and sample from specific horizons, though it is tedious and time consuming and requires a trained professional

 

REPRESENTATIVE SAMPLE

1)avoid unusual areas

2)size up each field

3)divide field into subsets

4)get many data points (at least 20)

5)know about area- fertilizers etc

6)space out subsamples