APBI 200 Final - copied

Order

differentiated based on dominant soil-forming processes

Great Group

based on the strength of soil-forming processes

Subgroups

differentiated based on kind and arrangement of horizons

Families

differentiated based on the basis of the parent material characteristics

Series

differentiated on the basis of detailed features of the pedon

Regosolic Order

-diagnostic feature: no B horizon

-associated with landforms where the land surface is unstable

-soil has little time to develop

Brunisolic Order

-diagnostic horizon: Bm**, Bfj, Btj that are at least 5cm thick, or Bf<10cm thick

-forest soil, not well developed

Luvisolic Order

-diagnostic horizon: Bt

-forest soil in areas with parent material from sedimentary rocks

-eluviation of clay from Ae horizon and deposition into Bt horizon

Gleysolic Order

-diagnostic horizon: Bg (or Cg ≥ 10cm thick within 50cm of soil surface)

-prolonged periods of intermittent or continuous saturation with water

Organic Order

-diagnostic horizons: Of, Om, and Oh must extend to a depth ≥ 40cm

-include peat, bog, and fen soils

-dominant wetland soils in forested regions of Canada, but also occur in non-wetlands in upland sites where leaf litter accumulates

-boreal forest soils

Chernozemic Order

-diagnostic horizon: chernozemic Ah > 10cm thick, Ahe

-grassland soil with high level of organic matter

Solonetzic Order

-diagnostic horizon: Bn or Bnt

-grassland ecosystem

-stinky

-low Ca/Mg ratio

-high levels of Sodium in B horizon

-clay-rich B horizon and saline C horizon

Podzolic Order

-diagnostic horizon: Bf, Bhf, Bh ≥ 10cm thick

-forested soil associated with coniferous vegetation on igneous-rock derived parent materials

-high acidity in A horizon results in Ae horizon with deposits of iron and aluminum in B horizon

Cryosolic Order

-diagnostic horizon: By, Cy, Cz (permafrost)

-arctic and tundra regions

-hard to build on, sensitive soils

Vertisolic Order

-diagnostic horizon: Bss, or Css and Cv

-high clay glacio-lacustrine landscapes

-shrinking and swelling of clays

-poor soil for building and plant growth

A horizon

-mineral horizon near the soil surface

-characterized by eluviation of materials in solution and/or accumulation of organic matter

-most fertile part of the soil profile

Ah

enrichment with organic matter

Ae

eluvial horizon with losses of clay, organic matter, Fe and Al oxides

Ahe

enriched with organic matter but eluviated

B horizon

mineral horizon characterized by illuviation of clay, organic mater, and iron and aluminum oxides, or by in situ weathering

Bm

modified horizon only slightly developed by hydrolysis, oxidation, or solution that is different from adjacent horizons in color, structure, or both

Bt

enriched with silicate clay, usually from Ae horizon above

Bf

enriched with Fe and Al oxides

Bh

enriched with organic matter

Bn

presence of high % of Na ions, with distinct prismatic or columnar structure

Bnt

Na ions and illuvial silicate clay

Bg

gleyed horizon with grey color, mottling, or both as a result of permanent or periodic intense anaerobic conditions

AB

transition between A and B, where A dominates

BA

transition between B and A, where B dominates

C horizon

mineral horizon characterized by little or no alteration through the soil-forming processes operating in the A and B horizons

-usually represents the parent material from which the A and B horizons have formed

Cg

gleyed horizon

Cy

horizon affected by cryoturbation (frost action)

Cz

perennially frozen layer

BC

transition between B and C where C dominates

b

buried horizon

c

cemented irreversibly

ss

presence of several (>2) slickensides

v

affected by agrillipedoturbation (disruption and mixing of soil as a result of shrinking as swelling of clays)

R

rock

W

water

Mor

-matted F horizon

-abrupt boundary between mineral and organic layer

-yes/no H, yes/no Ah

-no clay-humus complex

Moder

-loosely structured F horizon

-more gradual boundary between mineral and organic layer

-yes/no H, yes Ah

-clay-humus complex

-arthropods present in Ah

Mull

-F and H horizons thin or absent

-yes Ah

-no H

-clay-humus complex

-worms and other animals present in Ah

Well-drained conditions

L: litter, well preserved organic structure

F: partly decomposed organic matter, original structures can be hard to recognize

H: accumulation of decomposed organic matter

Poorly-drained conditions

Of: least decomposed, large amounts of well-preserved fibers

Om: intermediate decomposition, mesic

Oh: most decomposed, humic

Heat transfer is due to...

-conduction (through molecular collision)

-convection (by mass movement of molecules)

-radiation (by electromagnetic waves)

Thermal conductivity

describes heat flow in response to a temperature gradient

-higher in mineral layer

-increases as water content increases

Soil heat capacity

represents the amount of heat needed to cause a 1° C change in temperature of a unit volume of soil

-increases with water content

-higher in mineral layer than organic

-water has high heat capacity, air has low heat capacity

Thermal admittance

represents the ability of soil to accept and release heat

-higher in mineral layer than organic

-increases as water content increases

Thermal diffusivity

indication of subsurface temperature response to surface temperature change

Practices that increase admittance and diffusivity...

-adding sand to organic soil

-cultivation

-adding water to dry soil

-removal of organic surface layers

Oxygen flux

the amount of O2 which crosses a plane per unit of time

Diffusive Double Layer (DDL)

occurs where counter ions are attracted to the charged surface of a particle and form a layer

-ions are held by Coulombic forces

-DDL forms under dry conditions

-particles with a thick DDL tend to disperse (high pH)

-particles with a thin DDL tend to flocculate (low pH)

-thickness of DDL depends on concentration of soil solution, valence of attracted ions, and cation size

Neutral soil

pH = 7

H+ and OH- are equally abundant

Acidic soil

pH < 7

more H+ than OH- ions present

Alkaline (basic) soil

pH > 7

more OH- than H+ ions present

Residual acidity

refers to bound H+ and Al3+ that cannot be replaced by unbuffered salt solution

Exchangeable acidity

portion of H+ and Al3+ ions that are absorbed by soil colloids that can be replaced by an unbuffered salt solution such as KCl or NaCl

Active acidity

refers to H+ and Al3+ ions in the salt solution

Consequences of soil salinity

-detrimental effects on plant growth (osmotic potential)

-reduction of water quality

-soil erosion

-damage to infrastructure

-sodic soils --> dispersion, surface sealing, decrease infiltration

Sources of soil acidity

comes from H+ and Al3+ ions in the soil solution and adsorbed to soil colloidal surfaces

Sources of soil basicity

basic soils have a high saturation of base cations (K+, Ca2+, Mg2+, Na+)

Mass ion effect

if many Na+ ions are added, they will likely replace nearly all K+ ions

-as the amount of Na+ ions increases, the probability that Na+ will replace K+ increases

Exchangeable cations

readily displaced by mass ion effect from negatively charged colloids on which they are adsorbed

Cation Exchange Capacity (CEC)

the number of exchangeable cations that soil solids can adsorb

Significance of CEC

-contributes to soil buffering

-contributes to nutrient retention in available forms

-contributes to retention of various contaminants

Base saturation (BS)

fractions of cations on the cation exchange sites occupied by base cations (Ca2+, Mg2+,K+, Na+) rather than H+ and Al3+

Mineralization

the overall process of conversion of an organic form of an element to an inorganic state as a result of microbial decomposition

Immobilization

the conversion of an element from the inorganic to organic form in microbial tissues, thus rendering the element unavailable to plants

Significance of C/N ratio

-residues with a high C/N ratio added to soils --> creates intense competition among microbes and higher plants for available N

-C/N ratio indicates the rate of a residue's decay and the rate at which N is made available to plants

-C/N ratio > 25:1 leads to N deficiency for higher plants

-decay of organic matter is delayed if there's not enough N to support microbial growth

Chelates

organo-mineral complexes in which a metallic ion is bonded to an organic molecule by means of multiple bonds (at least 2), thus forming a ring structure

Organic substances that chelate metals include...

-substances that are synthesized by roots

-various humic substances that have multiple carboxyl groups

-synthetic substances

Dispersed chelates...

contribute to nutrient (metal) availability

Flocculated humic substances...

contribute to nutrient (metal) deficiency

SOM effects on soil physical properties

-dark soil colour

-increases aggregation

-increases water retention

-reduces plasticity and stickiness of clay soils

-improves aeration and drainage

SOM effects on soil chemical properties

-increases CEC

-improves buffering capacity

-provides nutrients (N, S, P)

-chelating agent which can improve nutrient availability (Fe, Zn, Cu, Mn)

Macroorganisms

>2mm in width

Mesoorganisms

0.2-2mm in width

Microorganisms

<0.2mm in width

Rhizosphere

zone of soil influenced by living roots and associated microorganisms

-microorganisms usually feed on the plants and sugars released by roots and sloughed off by cells

-usually extends 1-2mm out of the root surface

Fungi

Kingdom composed of heterotrophs; many obtain energy and nutrients from dead organic matter

Functions:

-aid in decomposition of organic matter

-colonization of plant roots

-killing plants

-biocontrol

Hyphae

The branching, threadlike tubes that make up the bodies of multicellular fungi

Mycelium

network of hyphae

Bacteria

single-celled organisms that lack a nucleus; prokaryotes

Functions:

-N-fixing bacteria make N available to plants

-decompose organic matter and release nutrients in plant-available forms

-convert soil N to gaseous forms

Actinobacteria

filamentous bacteria that:

-decompose soil organic compounds (chitin and cellulose)

-produce antibodies

Archea

single celled prokaryotes, microorganisms

-seen in harsh environments, as well as a broad range of habitats

Protozoa

"primitive animals"

-feed on fungi and bacteria, or fragments of organic matter

-help suppress disease by competing with or feeding on pathogens

-food source for other soil organisms

Nematodes

threadworms

-bacteria feeders --> after consuming bacteria, they excrete much if the excess N as inorganic N (ammonia), which increases nutrient cycling

-predators (biocontrol of insect pests)

-plant parasites (root feeders)

Biological N fixation (transformation of N)

biological conversion of N2 gas to ammonia (NH3) by some bacteria, cyanobacteria, and actinobacteria

-symbiotic N fixers with legumes

Mineralization (transformation of N)

aminization (by heterotrophs)

-ammonification (by heterotrophs)

-nitrification (by chemo-autotrophic bacteria and archea)

Ammonification (transformation of N)

-amines and amino acids are released from the decomposition of proteins, further decomposed by heterotrophic microorganisms

-NH4+ released into the soil is either converted to nitrites or nitrates by nitrification, absorbed by plants, used by heterotrophic microorganisms, absorbed by clay minerals, or released into the atmosphere as elemental N

-R-NH2 + HOH ---> NH3 (ammonia) + R-OH + energy

Sources of Nitrogen

-biological fixation on N

-deposition on N compounds from atmosphere by precipitation

-fertilizers

-organic amendments

-plant residues

Losses of N

-plant removal

-leaching

-wind and water

-ammonium fixation

-gaseous losses (denitrification and NH3 volatilization)

S importance for plants

-protein synthesis

-photosynthesis

-strengthening cell walls

S issues

-atmospheric S deposition

-organic S compounds are not available to plants, microbes need to help

-air, water, and soil pollution with S compounds

P importance for plants

-photosynthesis

-crop maturation

-root development

-strengthening cell walls in grasses

P issues

-total soil P content is low

-solubility of P-containing minerals is low

-soluble P forms (fertilizer) are quickly turned to unavailable forms

Non-humic substances (primary components)

easily decomposed by microorganisms, persist in the soil for a brief time

-carbohydrates, lignin, amino acids, lipids, other compounds

Humic substances (secondary components)

1) fulvic acids

2) humic acids

3) humin

-humic substances possess carboxyl groups, which help buffer pH

-overall change on SOM is negative

Algae

autotrophic, microflora, most active and abundant in wet soils

-make symbiotic associations with fungi, forming lichen

-certain algae secrete polysaccharides, improving soil aggregates