Soils 101 Finals Material

Why are soil resources shrinking?

-Catastrophic loss from climate change displaces soil

-Water pushes soil aside

6 Roles of Soil

-Plant growth

-Organic waste system

-Modifier of carbon cycle

-Habitat for organisms

-Building surface

-Water purification

Difference between limestone and sandstone

-Limestone is more neutral

-Sandstone is acidic

Difference between rock and mineral

-Mineral is a single substance

-Rock is made of 2/more minerals

Difference between primary and secondary mineral

-Primary: mineral present when rock formed

-Secondary: Mineral created through chemical weathering

Difference between chemical and physical weathering

-Physical: Done by external pressures

-Factors: (temp fluctuations, fire, freezing, salt crystals, root pressure, unloading/exfoliation, wind/water erosion)

-Chemical: Chemical reactions with water or biological activity

-Factors: hydration, hydrolysis, dissolution, redox, carbonation, complexation

Is quartz or calcite more resistant to weathering

Quartz is more resistant

What types of climate promotes weathering

Warmer=faster (reaction rates double every 10 degrees C)

Types of Chemical Weathering

-Hydration: yummy water

-Hydrolysis: water breaks shit up (dissolution + change composition)

-Carbonation: Carbonic acid dissolves shit (causes caves)

-Redox: oxidation and reduction that fluctuates redox features (red and black blotches)

-Dissolution: Limestone and salty rocks dissolving in water

-Complexation: shit combines into a larger molecule

What soil environments promote redox reactions

-Oxidation: aerobic

-Reduction: Anaerobic

What is the general progression of horizon development

Unweathered bedrock → parent material → soil

Difference between eluviation and illuviation

-Eluviation: remove nutrients and organic material from superficial horizons

-Illuviation: deposits that stuff

4 Basic processes of soil formation

-Transformation: Chemical/Physical alterations or destructions of soil to form other stuff

-Translocation: Movement of materials laterally or vertically by water/animals

-Additions: material input from outside sources

-Losses: material lost from soil

How does clay content change as soils become weathered

-Color: more distinct between horizons

-Gets darker and more compact

What are the 6 horizons

O: Organic material

A: Top horizon that has minerals. Has some organic material

E: Zone of maximum leaching, bleached almost white

B: Zone of illuviation, parent material cant be discerned

C: Unconsolidated material below A and B

Transition Horizons

Occur when boundaries between horizons are gradual

What types of structure for each horizon

O

A: Granular, platy if compacted

E: Granular

B: Subangular Blocky, occasionally prismatic

C: Structureless/Massive

How to read Munsell chart

-Sun behind you, place chart on top of soil

-Column is value, row is chroma, different pages is hue

Ex: 5 YR (hue) 6(value)/4(chroma)

Color results from Fe, Mn, Humus

Fe: yellow, red, brown

Mn: Black

Humus: Black

Field method for determining soil texture

Texture by feel, ribbon test for clay (10% per inch), ball to determine sand composition, texture pyramid for silt

Soil vs coarse fragment size difference

soil<2mm

Different types of redox features and how to identify them

-Redox Concentrations: Iron and manganese accumulations, mottled appearance

-Redox Depletions: Areas without iron and manganese, pale

-Redox matrices: low soil colors, results in lines

5 Soil Forming Factors (CLOPRT)

Climate

Organisms

Relief

Parent Material

Time

2 Most important parts of climate related to soil formation

Temperature and Precipitation

Soil Temperature Regime of Central PA

Mesic

Soil Moisture Regime of Central PA

Udic

Grasslands vs Forest Soils

-Grasslands: Less acidic, no O, deep A, less acidic leaching

-Forests: More acidic, o horizon, shallow A, more acid leaching

Floodplain vs Terrace Soil

-Floodplains: More soil, further from original rock formation, younger

-Terrace: Less soil, closer to original rock formation, older

Name the 6 Physiographic Regions of PA

Central Lowlands.

Appalachian Plateaus.

Ridge and Valley.

New England.

Piedmont.

Atlantic Coastal Plain.

How time affects soil development

Soil development can take many years, time it takes to develop is affected by the other factor

How to read map units

Codes

Soil series, soil phases, slope phases, dominant surface texture, second series

What info can be found in web soil survey

Soil characteristics, boundaries, soil classifications

What is soil taxonomy

A hierarchical system-groups soil individuals based on soil properties

Epipedon

-Surface pedons, mostly organic material overlying non organic material

-Mollic/Melanic/Histic

Subsurface

-Subsurface pedons, mostly mineral with chemical weathering

Argillic, Oxic, Spodic, Fragipan

Order for soil taxonomy from largest to smallest

Order →Suborder→Great Group→Subgroup→Family→Series

6 soil orders

Entisol, inceptisol, mollisol, ultisol, afisol, oxisol

Entisol

Has no horizons. Formed very recently, catch all

Inceptisol

Inception of soil development, Cambic B horizon maybe

Mollisol

Intermediate Weathering, grasslands, semi-arid to moist, mollic, epipedon

Afisol

Moist, mildly acidic, clay accumulation, intermediate weathering

Utisol

Wet tropical and subtropical, acid silicate, Fe and Al oxides, Strongly weathered

Oxisol

wet tropical forests, extreme weathering, low activity clays, Al and Fe oxides

PA State Soil

Hazelton

Summit

Top, residual material,easy to differentiate horizons

Shoulder

Residual Material, not deep, difficult to see horizons

Backslope

Colluvial Material, lots of rock fragments w/ distinguishable horizons

Terrace

Alluvium material, very flat w/ restricted soil, difficult to see horizons

Floodplain

Alluvial material, distinct layers, net to water and very moist

Residuum

Hasn't moved, residual underlying material

ID: no particle sorting, C horizon shows bedrock

Colluvium

Transported Downhill by gravity

ID: mix of rock types, no sorting or rounding, buried horizon, RE not in original position

Alluvium

Transported by water

Mix of rock types with rounding and sorting, buried horizons

Other Parent Material

Lacustrine, Coastal marine sediments, eolian, loess

EXAM 2 Material

Starts here if you go in order

What is the difference between sand, silt and clay?

Sand: Grains are very visible

Silt: can be seen, but is extremely small

Clay: Invisible to the naked eye

Size Range in mm for sand, silt, and clay?

Sand: 2-0.05 mm

Silt: 0.05-0.002 mm

Clay: <0.002 mm

What is a "soil sized" particle? Course/rock fragments?

Soil Sized: 0.002-2mm

Course Fragment/Rock: >2 mm

Use % sand, silt, clay to read soil triangle

I mean...just use your eyes

How to determine soil texture in field (% clay, %sand)

Ribbon test: 10% clay per inch of ribbon, 5% for high organic matter, 20% if bright red

Sand % estimation: Form 2 pea sized balls of soil, palm cupped to hold water, spray water, let drain, estimate % sand grains by comparing what's left to og size

How to determine soil texture in lab

Put soil in sieves of increasingly small sizes (4.75-2-0.6-0.25- 0.15-0.075-0.053mm), separates out sand and gravel, then weigh to find %

Hydrometer: Take 50g <2 mm soil, place in water w sodium hexametaphosphate, let settle for specific times, measure what remains for clay and silt %

Why add sodium hexametaphosphate?

Disperses clay particles

Stokes Law

Describes: Velocity of particle falling through fluid

General Idea: Combined with hydrometer, lets us figure out what time it will take for each size particle to settle

Do clayey or sandy soils have larger pores? Greater porosity?

Larger Pores: Sandy

Higher porosity: Clay

Volumetric Composition of a Loamy Soil:

50% soil, 20-30% air, 20-30% water, 0% organic

Why is soil structure also important in addition to soil texture?

Soils Structure aggregates come in different types that will impact permeability/infiltration.

Ex: more compaction (platy, blocky)=slower water movement

Units for Bulk Density

Mg/m3=g/cm3=t/m3

What is the common assumed particle density?

2.65 g/cm3

How is Bulk Density calculated?

Dry weight/volume

What is the common range for bulk density?

Undisturbed: 1-1.4 g/cm3

Does compaction increase or decrease Bulk Density?

Increase

Does compaction increase or decrease porosity?

Decrease

Root limiting bulk density for clayey soils.

1.39-1.49 g/cm3

Are soils more compactable when wet or dry?

Wet (unless too wet, which can cause difficulties due to pores being overfull of water. Dry has too much friction.)

What is a soil proctor test?

A test to determine the optimal moisture content that a soil can be most effectively compacted at

Effects of extensive tillage/plowing.

Bulk Density: Increases

Aggregate Size: Decreases

Crop Yield: Decreases

Porosity: Decreases

How can you improve soil tilth?

Minimize tillage

Stay off wet soil

Dedicated traffic lanes

Mulch

Add organic matter

Cover crops

Return crop residues to fields

tillage/ forage radishes alleviate compaction

How to calculate gravimetric moisture content?

Gravimetric Moisture= (Mw/Ms) x 100

Mw = mass of water, Ms = mass of soil (dry)

Lab method for measuring/calculating gravimetric moisture content

Time domain reflectometry and gravimetric method (gravimetric moisture equation)

Approximate soil potential at Saturation

0 kpa

Approximate soil potential at Field Capacity

-33 kpa

Approximate soil potential at wilting point

-1500 kpa

What potentials make up the total soil water potential? What forces do each of these account for?

Matric Potential: Cohesion + adhesion (connectivity of H2O to soil particles)

Osmotic Potential: Salt (negligible unless dry, fertilizers increase it thought)

Gravitational Potential: Force of gravity, only important in saturated soils (pulls water down rapidly)

What is capillary rise?

Water rising upwards from soil particles acting on its molecules

Is capillary rise higher in clayey or sandy soil?

Clayey

What is field capacity?

Amount of water held in soils after excess has drained away

What is wilting point?

Water content where plants wilt in the daytime

Do sandy, silty, or clayey soils hold the most water?

Clayey

Do sandy, silty, or clayey soils have the most plant available water?

Silty Clay

Does organic matter generally hold low or high amounts of water? Is that water plant available?

High

It is plant available due to the charge

Darcy's Law

Equation: (G x L)/(A x t x(Ѱ₁-Ѱ₂)

Describes: Saturated hydraulic conductivity

General Idea: The larger the macropores (>0.05 mm) the higher the potential pressure head driving water down, the faster the flow rate

Does water move faster through sandy or clayey soils?

Sandy

In addition to texture, what other soil properties affect the rate of water movement?

Soil structure (ex: Prismatic and platy will slow the movement of water, granular will not)

What is the perching effect and what does it cause?

It's where water gathers, usually at a point of abrupt texture change. Occurs due to unsaturated periods where capillary action is the driving force.

What are soil colloids?

Solid soil particles <2 um with extremely large surface areas. They are the most "active" chemical component.

What are the different types of soil colloids?

Phyllosilicate Clays (1:1, 2:1, 2:1:1)

Non Crystalline silicate clays

Fe and Al oxides

Humus

What is the centrally coordinated action in the tetrahedral layer of phyllosilicate clays? Octahedral?

Refer to the photo

What is the difference between a 1:1 and a 2:1 phyllosilicate?

1:1 Clay: 1 tetrahedral layer and 1 octahedral

2:1 Clay: 2 Tetrahedral layers and 1 octahedral

What is the isomorphic substitution?

-Substitution of one element for another of equal size

-Happens in formation of both sheet types

-Al2+ for Si4+ in tetra

-Fe2+, Mg 2+, Ni 2+, Zn2+, Cu 2+ for Al 3+ in octa

Are soils general + or - charged?

Negative

How is internal/external surface area, total surface area, and Caption Exchange Capacity related?

Caption exchange capacity (CEC) is the sum total of exchangeable cations a soil can absorb. More surface area=more stored nutrients=more exchange