Soils exam 2
Calcic
(Bk) Illuvial, accumulation of calcium carbonate CaCO3
petrocalcic
(Bkm) Cemented calcic horizon
Reading soil colors optimum conditions
-Natural light -clear, sunny day -midday -light at right angles -soil moist -No Sunglasses!
1% silt =
1500cm
Salic Horizons
Accumulation of soluble salts Arid/semi-arid area
Major Forms of Iron and Effect on Soil Color
Form Chemical Formula Color Ferrous oxide FeO Gray Ferric oxide(Hematite) Fe2O3 Red Hydrated ferric oxide(Limonite) 2Fe2O3-3H20 Yellow
Sand
Gritty feel Can be seen with the naked eye Hand sampling: No residue left on hand or in pores
udic
Soil moisture is sufficiently high enough year round to meet plant needs
Determining the texture in the laboratory uses a basic principle of sedimentation called
Stokes law (Bigger particles settle more quickly Density of the water (due to suspended silt and clay) holds up hydrometer)
Value
The degree of light/dark of a color in a relation to a neutral gray scale.
Sulfuric horizons
Very acid horizons pH < 3.5
Melanic Epipedon
Very black > 6% organic C 30 cm thick, usually develops in volcanic ash - light weight and fluffy
Cambic horizon
Weakly developed horizon Some color change. Slight alteration
In which of the following epipedons is the organic matter level generally lowest?
ochric
Duripan
silica cemented
Information that can be obtained from soil color includes
-Relative organic matter content - Mineralogy - Depth to seasonal high water table - Geologic history - Genesis of diagnostic features in the soil
Factors that give soil color
-organic matter -weathered mineral material that composing the soil -quantity and condition of iron present in the soil
Sub-soil Color Determination
-quantity and condition of iron -red colors= usually associated with unhydrated iron oxides and indicate well drained soil. - yellow colors = largely due to hydrated iron oxides and generally indicate a more moist condition than red soil
silt
0.05 - 0.002mm
very fine sand
0.1 - 0.5mm
importance of soil texture
1. water retention 2. nutrient retention 3. weathering rates and release of nutrients 4. soil structure 5. Microorganisms - colonize particle surfaces 6. biochemical reactions
stage 6
10,000 years depending on climate/land use Organic matter in surface has decreased climate - more humid Eluviation/illuviation- Loss of iron and organic matter produces a more prominent E horizon BE horizon - has become E material Clays have altered - mainly kaolinites and iron/ Al oxides Northern areas - Bt is Argillic Southeast - Bt becomes Kandic Underlying Cr has become C horizon with Cr below Base saturation in horizon above Cr is < 35% Soil Order Ultisol
stage 6
15,000 years depending on climate/land use Tropic/subtropic climate, high rainfall Organic matter in surface has decreased significantly Less than 10% weatherable minerals remain Bt horizon - has Bo - Oxic horizon Mineralogy - some kaolinites, but mainly iron/ Al oxides - especially gibbsite Very low base saturation - low fertility Soil has a net positive charge - high anion exchange capacity Soil Order Oxisol
very coarse sand
2 - 1mm
Histic Epipedon
20-60 cm thick, composed of organic materials, usually black or brown, low density
1% clay =
3,000,000cm
1% sand =
30cm (
stage 5
5000-6000 years depending on climate/land use Organic matter in surface has reached equilibrium Change in vegetation - erosion - climate - more humid Eluviation/illuviation- most iron and organic matter has move down - a E horizon forms BE horizon - transitional horizon- mainly B material but E material is becoming evident Clays have continued to move an accumulate with 3 Bt horizons forming Mineralogy - mix of smectites, illites, kaolinites Underlying rock is Cr - Some C horizon material, but significant parent rock remains Base saturation in horizon above Cr is > 35% Soil Order Alfisol
clay
<0.002mm
The main difference between an Umbric epipedon and a Mollic epipedon is:
A Mollic has a base saturation > 50%, an Umbric has a base saturation < 50%
Agric horizon
A horizon in which clay, silt and humus derived from an overlying cultivated and fertilized layer have accumulated. The wormholes and illuvial clay, silt and humus, occupy at least 5% of the horizon by volume.
Argillic Horizons
Accumulations of silicate clays Illuvial or may have formed in place
aridisol
Arid/dry climates Organic matter low due to lack of vegetation Eluviation/illuviation slow - low precipitation Bw - structure formed Bk - Calcic or petrocalcic By-Gypsic or petrogypsic Bz - Salic Btn - natric Bqm - duripan Mineralogy - usually 2:1 clays High base saturation Soil Order Aridisol
Sombric horizon
Cool, high altitude of tropical areas High organic matter
vertisol
Developed in limestones, marls, basalts High shrink-swell Gilgai - wavy soil surface Slickensides - smooth pressure faces on peds Wet - sticky; dry - hard, large cracks Fertile soils - difficult for plants - wet seals - poor aeration dry - hard for roots/seedlings to break through Not good for building Soil Order Vertisol
Epipedons
Diagnostic horizons that occur at the soil surface
Diagnostic Subsurface Horizons
Diagnostic horizons that occur under the epipedon or surface horizon
clay
Dry: Hard feel Wet: Sticky, plastic feel Can be seen with an electron microscope Hand Sampling: Thick film residue
silt
Dry: Powdery smooth feel Wet: Creamy slick, slippery feel No sticky or plastic feel Can be seen with a hand lens or microscope Hand sampling: Coats hand, able to brush off Remains in pores
stage 4
Grassland vegetation Soil has been remained stable ~200 years Grasses have added high amounts of organic matter to A or Ap horizons Mollic epipedon has formed Eluviation/illuviation of Fe, Mn, carbonates, significant amount of clay - Bw has become a Bt horizon - Argillic Ustic or drier areas - may have: Bk - Calcic By - Gypsic g. Mineralogy -vermiculites,smectites, illites, h. Base saturation in all horizons is > 50% I, Soil Order Mollisol
Natric Horizons
High activity clays, clay skins present >15% exchangeable sodium Arid/semiarid regions Columnar or prismatic structure
Oxic Horizons
Highly weathered High content of Fe and Al oxides Low cation exchange capacity <10 % weatherable minerals Tropics and subtropics
Spodic Horizons
Illuvial horizon- acidic environment Accumulation of organic matter and Al oxides, may have Fe oxides Forest soils, humid climates Sandy parent materials
Kandic Horizons
Illuvial horizons Accumulation of low activity clays, Fe and Al oxides
Gypsic Horizons
Illuvial, Accumulation of Gypsum CaSO4 - 2H2O
Albic Horizons
Light colored horizon with some clay and Fe, Al removal Eluvial horizon
stage 1
Material deposited by flood waters - notice layers of stratified soil materials - C horizons Ab at bottom is a buried A horizon - this was the old surface
Pans
Materials cemented or densely packed Resist water movement and penetration of plant roots Duripan, Fragipan, Placic horizons
xeric
Mediterranean climate- cool, moist winters, dry summers with long periods of drought in summer
Plaggen Epipedon
Modified by humans due to repeated additions of manures
Anthropic Epipedon
Modified by humans, high P content
histisol
Organic parent material >12% C Cold and/or wet environments - rate of decomposition < rate of addition of new organic material. Weak to moderate development Histic epipedon Oi - little decomposition - Fibric Oe - moderate decomposition- Hemic Oa - strong decomposition - Sapric Low bulk density, - erosion problems High water retention To cultivate - drained and packed down High cation exchange capacity Soil Order Histosol
gelisol
Permafrost in upper 1 m soil -temperature must remain below 0oC for 2 years continuously in upper 2m if gelic materials are present Gelic materials- evidence of cryoturbation - frost churning freezing & thawing in parts of subsoil - heaves & churns soil materials. Low intensity management - fragile Soil Order Gelisol
Oxisol
Plinthite may be present - very hard Easily eroded when disturbed Phosphorus deficiencies
stage 2 soil development begins
Seeds begin to sprout - vegetative cover Development of an A horizon at the surface - increased organic matter - Ochric epipedon Only A and C horizons in the new materials (may have a small O horizon) Mineralogy - mixed fine-grained micas, smectites, illites, kaolinites, chlorites, vermiulites Soil Order Entisol f. Extremely variable due to parent material, time of development, environmental conditions
stage 3
Soil has been stable for a period of time - ~50 years Eluviation/illuviation has begun to alter underlying C material C material begins to form structure - some movement of illuvial clay Bw horizon forms -eventually becoming a Cambic horizon Mineralogy - mixed fine-grained micas, smectites, illites, kaolinites, chlorites, vermiulites Soil Order Inceptisol
andisol
Volcanic parent material Weak to moderate development Melanic epipedon Bw - structure formed - Cambic Low bulk density, - wind erosion problems Amorphous clays Rapid drainage Low soil strength when disturbed High base saturation Soil Order Andisol
Determining Soil Texture - Feel Method
Wet soil in hand Make ribbon Length of ribbon indicates clay content Grit or lack of grit indicates sand or silt Smoothness indicates silt
Which of the following diagnostic horizons would likely not restrict root growth in soils?
albic
A horizon designated as a Bt would likely have
an accumulation of clay
Which of the following describes a soil likely to contain a significant content of low activity clays?
an oxisol in central brazil
Which soil moisture regime has the highest soil moisture levels?
aquic
What property would the following diagnostic horizons have in common: Kandic horizon, Argillic horizon, Oxic horizon, and Natric horizon? Each may be characterized by a significant accumulation of
clay
Argillans or clay skins
clay coatings on the surface of peds or pore walls
materials larger than 2mm
coarse fragments (Round- gravel, cobbles, stones, boulders Flat - channers, flagstones, stones, boulders)
Mollic Epipedon
dark color due to > 0.6% organic C Color value and chroma 3.5 or less >25 cm thick base saturation > 50%
fragipan
dense brittle Prismatic structure
Mattrix
dominant (background) color of soil horizon
Hue
dominant spectral color
In which of the following soil orders would recent alluvium most likely be a common parent material
entisols
quantity of color contrasting areas
few-less than 2% (<2%) common-2 to 20% (2%-20%) many-more than 20% (>20%)
While investigating the soils of northern Canada in summer, you dig a soil pit easily through fairly uniform peat material until, at 75 cm deep, your shovel hits a layer that is frozen solid. Into which type of soil are you most likely digging?
gelisol
ustic
generally adequate available moisture for plants during growing season, but some periods of drought may occur
In which of the following epipedons is the organic matter level generally highest?
histic
If soils are to be used for crop production, for which soil order would land drainage be most critical?
histisols
The two soil orders with low bulk densities that would be prone to soil erosion when dry are the
histisols and andisols
What property would the following diagnostic horizons have in common: fragipan, petrocalcic horizon, and placic horizon? Each may be characterized by a significant accumulation of
inhibit water movement
Which of the following soil temperature regimes would provide the warmest and least variable soil temperatures?
isohyperthermic
yellow colors
largely due to hydrated iron oxides and generally indicate a more moist condition than red soil
Umbric Epipedon
like a mollic epipedon, but base saturation is < 50%; develops in areas with higher rainfall parent material has lower content of Ca and Mg
Bluish, grayish, and greenish or (gleying) subsoils indicates?
longer periods each year of waterlogged conditions and inadequate aeration
The two soil orders that are typical of the breadbaskets of the world are the
mollisols and afisols
What property would the following diagnostic horizons have in common: Histic epipedon, Sombric horizon, Mollic epipedon, and Spodic horizon? Each may be characterized by a significant accumulation of
organic matter
Which of the following subsurface diagnostic horizons would you expect to find in a highly weathered soil of the humid tropics?
oxic
The determination of soil texture is called
particle size analysis or mechanical analysis
Hue = dominant spectral or "rainbow" color
red, yellow, blue, green
What property would the following diagnostic horizons have in common: Calcic horizon, Petrogypsic horizon, Salic horizon, and Natric horizon? Each may be characterized by a significant accumulation of
salts
aridic
soil is dry for at least one half of the growing season and moist less than 90 consecutive days
Aquic
soil saturated for periods of time allowing for reduction of iron
redoximorphic (redox) Features
specific features formed from oxidation reduction reactions used to predict seasonal high water tables
Mottle
splotch of color opposite the matrix (Spots of different colors. Generally indicate that the soil has periods of inadequate aeration each year)
Soils in this order are commonly sandy in texture, quite acidic and develop primarily under coniferous trees in cool to cold climates.
spodosols
Chroma
strength of hue
Value-munsell color page
the amount of light reflected from a chip
dark color in the A horizon usually represents?
the presence of organic matter (is characteristic of A horizon)
Soil Texture
the relative proportion of soil separates i.e sand, silt, and clay, particle size fractions.
Pedon:
the smallest three dimensional unit that can be called a soil
Ochric Epipedon
too light, thin, or too low in organic C to be a mollic or umbric epipedon
Gley Charts
two supplemental charts containing grayish, bluish, and greenish colors often found in very wet mineral soils are contained on these charts. (charts also contain a neutral hue (No Chroma))
A soil has a thick black A horizon, a distinct B horizon, has reasonably stable soil structure, and was formed under grassland natural vegetation. Base saturation is > 50% in all horizons. In which suborder, is it most likely classed?
udolls
You have a soil on your farm with a base saturation of 25%. It has an Ochric epipedon and an argillic subsurface diagnostic horizon. Which of the following soil orders would best describe this soil?
ultisols
Munsell color book
use to document color in a standard notation
red colors
usually associated with unhydrated iron oxides and indicate well drained soil.
The strong shrink-swell capability of clay soils predominantly composed of smectite makes these soils troublesome sites on which to build a home. In which soil order, would these soils be classified
vertisol
Gilgai would be characteristic of
vertisols
Placic horizon
very hard, Fe, Mn cemented
Jarosite
yellow/orange mineral common Common in marsh / tidal areas