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