Cal Poly SS 120 Final

Define soil and 6 components

3 dimensional

natural body

mineral + organic material

at Earth's surface

vertically differentiated

modified by soil forming factors

Why do we care about soil

medium for plant growth

regulation of water supply

recycle raw materials

habitat for soil organisms

engineering medium

carbon storage

Typical soil composition

45% minerals

5% organic material

25% water

25% air

Define humus

the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms.

What fills pore space?

air: CO2 and O2

water

soil atmosphere

more carbon dioxide found in soil than above ground: 3%

Where does CO2 come from in soils and how does it affect soils

Carbon sequestration

it stimulates plant growth and more carbon for microbes

difference between primary and secondary minerals

Primary: minerals present in starting rock

Secondary: weathered from primary minerals

plant essential nutrients

C. HOPKiNS CaFe

C, H, O, N, P, K, Ca, Mg, S, Fe, B, Cu, Cl, Mn, Mo, Zn, Co, Ni

Igneous rock

sedimentary rock

metamorphic rock

Igneous: magma rock

Sedimentary: underlie 2/3 of soil + weathering

Metamorphic: highly weathered igneous or sedimentary

Sandstone

Shale

Limestone

Sandstone: >50% sandd

Shale: clay/silt

Limestone: >50% carbonate

A

B

C

E

O

R

A: surface darkened by OM

B: Substrate horizon of alteration

C: Unaltered but not bedrock

E: eluviation, strongly leeched

O: organic horizon

R: bedrock

Residual parent material

transported parent material

organic parent material

Residual: breakdown of bedrock

Transported: parent material transported in some way

Organic: usually swamp, no gravel

Transported parent material ways:

alluvium

glacial

aeolian

colluvium

Alluvium: deposits of running water

Glacial: till/outwash

Aeolian: wind carried

Colluvium: gravity

loess deposits

sand dunes

Loess: wind carries clay/silt far

Sand Dunes: doesn't blow far

Chemical vs Physical Weathering

Physical: breaks rocks into pieces

Chemical: change chemical composition, form/destroy minerals, faster in hot climates, promoted by carbonic acid

Examples of physical weathering

temp, salt crystals, root pressure, release of overburden, increase in porosity

Dissolution

Carbonation

Oxidation

Reduction

Redox

Hydrolysis

Dissolution: carbonates/salt dissolves

Carbonation: rock minerals react with carbonic acid

Oxidation: electron loss in Fe, red soil

Reduction: electron gain in Fe, glayed soil

Redox: alternated oxidation + reduction from water table

Hydrolysis: splitting water, drastic modification

How physical and chemical weathering influence each other

positive feedback

physical increases surface area for chemical

chemical weakens rock for physical

Soil genesis

Soil profile

Soil horizon

Illuviation

Eluviation

Soil Genesis: additions, losses, transfers, transformations

Soi Profile: vertical sequence of soil layers

Soil Horizon: distinct layer within soil profile

Illuviation: deposit leached material into B horizon

Eluviation: washing out of fine soil components

Small Letters

p

t

k

h

m

n

o

g

z

w

r

p: plowed

t: clay accumulation

k: carbonate accumulation

h: illuvial organic accumulation

m: cemented

n: sodium accumulation

o: oxide accumulation

g: gleyed

z: soluble salt accumulation

w: weak development

r: soft weathered bedrock

What are the 5 factors of soil formation?

ClORPT

climate, organisms, relief, parent material, time

How does climate influence soil formation?

most influential factor

principle variables: temp, precipitation, effective precipitation, evapotranspiration

distribution: how spread-out rain is on per week basis

more precipitation = more clay

effective precipitation

The amount of precipitation that is actually added and stored in the soil.

factors that influence effective precipitation

soil slope, soil texture, slope face direction

define stokes law

describes velocity of particle falling through liquid

heavier particles fall faster

soil textures effect on:

total porosity

permeability

surface area

Total Porosity: smaller pores have more porosity

Permeability: bigger pores = better movement

Surface Area: smaller particle = larger SA

How soil color described?

Value: lightness or darkness

Chroma: strength or purity

Hue: dominant spectral color

Soil color meaning?

Red/yellow:

Black:

Brown:

White:

Gray:

Blue-green:

Red/yellow: oxidized iron

Black: organic matter

Brown: combination of red, yellow, black

White: salt accumulation or strong eluviation

Gray: reduced soil with leeching Fe

Blue-green: redox features, rare

define following soil structures:

Granular:

Blocky:

Prismatic:

Columnar:

Wedge:

Platy:

Massive:

Single Grained:

Granular: no cohesive strength, little clay

Blocky: square, high clay content

Prismatic: form small vertical columns

Columnar: salt on top cause large columns

Wedge: lots of clay, look like wedges

Platy: shale, slow water movement

Massive: no plains of weakness

Single Grained: like granular, fast water movement

How is soil produced?

From the breakdown of rocks, dead plants, and/or dead animals

define:

Bulk Density:

Particle Density:

Porosity:

Bulk Density: mass of particles / total volume

Particle Density: density of material that particles are composed of

Porosity: pore space

Typical values for bulk density and particle density

Bulk Density: 1 - 1.4

Particle Density: 2.65

soil tilth and impact on soil properties

the physical condition of the soil in relation to plant growth

Impacts: structure, water content, friability

Define:

Polarity:

Hydrogen bonding:

Cohesion:

Adhesion:

Surface Tension:

Polarity: positive and negative side of molecule

Hydrogen bonding: weak bond by polarity

Cohesion: attraction of like molecules

Adhesion: attraction of unlike molecules

Surface Tension: cohesive forces at surface

Define capillary action

movement of water due to cohesion, adhesion, and surface tension

Define:

Gravitational Water:

Hydroscopic Water:

Saturation:

Field Capacity:

PWP:

Plant Available Water:

Gravitational Water: water drained by gravity 0-.33 bar

Hydroscopic Water: water held very tightly

Saturation: 0 bar, too much water

Field Capacity: -.33 bar

PWP: -15 bar

Plant Available Water: -.33 - 15 bar, FC - PWP

Define soil water potential

water flows from high potential to low potential

components: gravity, matric (unsaturated), hydrostatic (saturated), and osmotic (across semi-permeable membrane)

Which soil holds most water at field capacity and why:

Sand

Silt Loam

Clay

Clay holds the most water because it has the most porosity and surface area for water to stay.

Which soil has the most plant available water and why:

Sand

Silt Loam

Clay

Sand does because it has less surface area for water molecules to hold onto, and it lets water move more freely

Define saturated hydraulic conductivity and what soil properties affect it.

described by Darcy's Law

How does unsaturated water flow differ from saturated.

saturated water flows by gravity while unsaturated water flows by matric potential

Define:

Pedon:

Polypedon:

Epipedon:

Endopedon:

Pedon: soil individual

Polypedon: parcel of continuous pedons

Epipedon: surface soil horizons

Endopedon: subsurface soil horizons

Define the following Epipedons:

Mollic:

Histic:

Ochric:

Mollic: thick, dard, carbon rich, grasslands

Histic: OM, saturated, wetlands

Ochric: fails to meet other requirements

Define the following Endopedons:

Argillic:

Calcic:

Natric:

Duripan:

Cambic:

Argillic: subsurface accumulation of illuvial clay

Calcic: subsurface accumulation of carbonates

Natric: like agrillic, accumulation of Na, columnar

Duripan: cemented with silica, doesn't slake in water

Cambic: weak development, doesn't fit into any other

12 orders of Soil Taxonomy:

Gelisols:

Histosols:

Spodosols:

Andisols:

Oxisols:

Vertisols:

Aridisols:

Ultisols:

Mollisols:

Alfisols:

Inceptisols:

Entisols:

Gelisols: cold, permafrost, high altitude

Histosols: mainly OM, wetlands, low bulk density

Spodosols: acidic cool forests, accumulation of humus

Andisols: volcanic ash

Oxisols: highly weathered, tropical, low fertility

Vertisols: clay-rich, swell/shrink, limitations for humans

Aridisols: arid regions, dry, limited leeching

Ultisols: strongly leeched, low native fertility, tropical, acidic, older landscapes

Mollisols: grasslands, thick A horizon, most productive ag in world

Alfisols: moderately leeched, some subsurface clay accumulation, basic, forest soil with high native fertility

Inceptisols: minimal horizon development, lack features, steep slopes, resistant PM

Entisols: recent origin, all other soils, steep/rocky or next to rivers

Characteristics of:

Bacteria:

Archea:

Fungi:

Bacteria: enormous diversity, rapid evolution

Archea: extremophiles, lots unknown

Fungi: filamentous, defining individuals, clones

Define rhizosphere.

region of roots where symbiotic relationships happen

Define symbiosis

relationship in which two species live closely together

ex. nitrogen fixation

broad functions carried out by soil microbes

capture energy

breakdown nutrients

enhance plant growth

aerobic and anarobic heterotrophs and autotrophs

look in notes to study

Soil food web

community of organisms living all or part of their lives in the soil

Rank the following electron acceptors in order of most to least energy released

Oh No My Feet So Cold

3 definitions of clay

<.002mm

textural class

2-degree minerals

Define:

Secondary Mineral:

Phyllosilicate:

Isomorphous Substitution:

Secondary Mineral: formed in soil (not PM)

Phyllosilicate: silica + oxygen combine to form backbone of mineral sheets

Isomorphous Substitution: replacement of one ion for another of similar size

Kaolinite, Mica, Vermiculite, Smectite, Chlorite

look in notes to study

Define:

Exchangeable Cations:

CEC:

Exchangeable Cations: ions that neutralize negative charge of soil particles

CEC: total number of positive charges from exchangeable ions

What soil properties affect CEC?

clay amount, clay type, OM content, solution pH, oxide type and amount

permanent charge vs pH dependent charge

permanent: isomorphic substitution

pH dependent: protonation/deprotonation

study chart in notes

How does the CEC of soil organic matter compare with that of clay minerals? How does it change with pH?

OM has a much higher CEC than all other clay minerals. The lower the pH, the higher the concentration of H+

Cations-

Base:

Acid:

Base: Ca, Mg, Na, K

Acid: H, Al

How to measure CEC

add up base and acid cations

How is CEC calculated?

CEC calculation

study notes

Define base saturation

portion of exchange sites filled by base cations

Define carbon cycle

the movement of carbon from the nonliving environment into living things and back

processes of the carbon cycle (also look at notes)

photosynthesis: convert light to chemical energy

Immobilization: consumption of plant material

Carbon : Nitrogen Ratio

For every 10 carbon, microbes use one nitrogen

if high ratio, microbes fine another source of N (>30:1)

Define

Humus:

Fresh Organic Residue:

SOM Active Fraction:

Stabilized OM:

Humus: stable OM, mix of organic structures

Fresh Organic Residue: Rapid (1-2yrs), nutrient release, feed microbes

SOM Active Fraction: slow (5-100yrs), feed microbes

Stabilized OM: (500-1000yrs), hold water + nutrients, maintain soil structure, slow nutrient release

How does organic matter influence plant growth and soil properties?

supplies nutrients, high CEC, add soil structure, store water

What role do soils play in the global C cycle?

stores 3 times the amount of carbon in the atmosphere at CO2, puts it in stable forms

Why is N important to plants? What forms of N are plant-available?

enzymes use it, Chlorophyll, vegetative + root growth

N2 is available to plants

Nitrogen Cycle (study diagram)

N2 fixation: symbiotic

Mineralization: organic N to NH4, decompose proteins, 2-5% of nitrogen each year

Nitrification: aerobic autotrophic bacteria, NH4 to NO3, very leachable and subject to denitrification

Immobilization: uptake of inorganic N by plants + bacteria

Denitrification: respiration process by anaerobic bacteria, require organic C

Nitrification vs Denitrification

nitrification is when N is dissolved into soil

denitrifiction is when N is leeched, similar to volatilization lab with fertilizer

Why is P important to plants? In what forms is P taken up by plants?

nucleic acids, ATP, cell membranes

it is taken up as organic P, biomass P, and soluble P

describe P cycle

look at notes

How does pH affect P availability?

In high or low pH there is phosphate fixation. Due to the presence of less aluminum at higher pH there is more phosphorus. Phosphorus prefers the 6 -7 ½ range in pH because aluminum is below and calcium is above. Those two can cause fixation.

Why is K important to plants?

Potassium is in enzyme control, salt/water balance, and transports compounds in cells.

Describe the K cycle and each of its components.

Study diagram in notes

What are visual deficiency symptoms for N, P, and K?

N: stunted growth, yellowing

P: stunted growth, dark green/purpling

K: yellowing, tissue death, white spots

What is soil health? Name several components of soil health.

organisms, OM, fertility, pH, salinity, erosion

How do warm/humid regions compare to dry regions in terms of soil acidification?

Humid Regions: more acidic, leeching of base cations, more carbonic acid

Arid Regions: more basic, retain base cations, less carbonic acid formation

What problems are associated with acidification of soils?

Al, Mn, Fe toxicity

Ca, Mg, Mo deficiency

slower microbial activity

At what pH does Al toxicity begin to be an issue for plants? What are the negative effects of Al?

<5 pH

inhibits root formation, inhibits microbes (N cycle)

How does adding lime to an acidic soil raise the pH?

precipitates Al, Mn, Fe

supplies Ca and Mg

Define a calcareous soil?

High in calcium carbonate

What is considered a salt in salt-affected soils?

ionic bonds

Common Ions:

Cations: K, Na, Ca, Mg

Anions: SO4, Cl, HCO3, CO3

Compare/contrast: saline vs. sodic

Saline: lots of cations

Sodic: lots of sodium

Most common source of salt

climate

parent material

topography

ocean

humans

What do we measure to estimate salinity/sodicity in soils?

electrical conductivity (EC)

exchangeable sodium percentage (ESP): Na/CEC

What steps can be taken to reclaim saline soils? What would be done differently for sodic/saline-sodic soils?

Saline: add good quality water, provide drainage

Sodic: Replace Na with Ca by adding gypsum, add good quality water, drainage

If drainage is not an option, what are some methods to manage salt-affected soils?

plant tolerant crops

keep root zones wet during sensitive crop stages

use mulch/conservation tillage/surface water

manage irrigation method/ plant placement

How does geologic erosion differ from accelerated erosion?

geologic: happens naturally, raindrops have kinetic energy

Accelerated: humans speed it up

What are the two phases of soil erosion?

(1) The detachment of particles from the surface

(2) The transport of particles by erosive agents

Describe the following forms of erosion:

Sheet:

Rill:

Gully:

Wind:

Sheet: invisible, most dangerous

Rill: creates small channels

Gully: makes large gully/channels, hinders equipment

Wind: jumping/spinning motion, surface creep

What are the two general principles of erosion control? For each, describe one conservation practice that applies the principle.

add drainage, add mulch