Quiz 3 - Answers1.) T F Conservation tillage refers to methods of preparing the soil for planting that are more likely to

disturb or move soil than conventional tillage.

2.) T F One thing soil color helps to identify is the moisture regime of a soil.

3.) a. What textural class is a soil with 10% clay and 60% sand?

sandy loamb. What % silt would this soil have?

30% siltc. Can you change a soil’s textural class by adding organic matter?

Nod. Why or why not?

Soil texture is a property referring only to the mineral particles; therefore organic matter plays no part in determining a soil’s textural class.

4.) What is the % pore space of a typical mineral soil having a Db of 1.05 Mg/m3?

60.4% pore space5.) What did you learn about bulk density from the Sharratt article?

Some possible answers: In areas of compaction, bulk density can be higher. Bulk density did not account for a thinner A horizon. The effects of compaction causing greater bulk density can last for 100 yrs.

(1)(1)

(4)

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• http://nature.berkeley.edu/classes/espm-120/

Photo of Soil ProfileClassification = Typic Haplohumult

REVIEW:Processes of Soil Formation

•Additions–Organic C–Dust

•Removals–CO2

–Weathering products•Transfers

–Clay–Organic matter–Carbonate

•Transformations–Plants to SOM–Primary silicates to secondary silicates, carbonates

OM additions, OM transformations, weathering

CO2 flux

Clay transfers

Clay and carbonate transfers

Leaching

Soil Horizon Nomenclature

•Based on interpretation of dominant soil forming processes affecting that horizons

–Names based on presumed changes relative to parent material (t=0)

•Universal with some variance

•Originated by Russians in 19th Century

Master Horizon NomenclatureMaster Horizons Definition and Examples of Lower Case ModifiersO Layers dominated by organic matter. State of decomposition

determines type: highly (Oa), moderately (Oe), or slightly (Oi)1

decomposed.A Mineral horizons that have formed at the surface of the mineral

portion of the soil or below an O horizon. Show one of the following:(1) an accumulation of humified organic matter closely mixed withminerals or (2)properties resulting from cultivation, pasturing, orother human-caused disturbance (Ap)

E Mineral horizons in which the main feature is loss of silicate clay,iron, aluminum, or some combination of these, leaving aconcentration of sand and silt particles

B Horizons formed below A,E, or O horizons. Show one or more of thefollowing: (1) illuvial2 concentration of silicate clay (Bt), iron (Bs),humus (Bh), carbonates (Bk), gypsum (By), or silica (Bq) alone or incombination; (2) removal of carbonates (Bw); (3) residualconcentration of oxides (Bo); (4) coatings of sesquioxides3 that makehorizon higher in chroma or redder in hue (Bw); (5) brittleness (Bx);or (6) gleying4 (Bg).

C Horizons little affected by pedogenic processes. May include softsedimentary material (C) or partially weathered bedrock (Cr)

R Strongly indurated5 bedrockW Water layers within or underlying soil(1) The symbols in parentheses illustrate the appropriate lower case modifiers used todescribe specific features of master horizons.(2) The term illuvial refers to material transported into a horizon from layers above it.(3) The term sesquioxide refers to accumulations of secondary iron and/or aluminumoxides.(4) Gleying is a process of reduction (caused by prolonged high water content and lowoxygen concentrations) that result in soil colors characterized by low chromas andgray or blueish chromas.(5) The term indurated means strongly consolidated and impenetrable to plant roots

Example

A

Bt

Btqm

BC

Master Horizon Subdivisions

Lower CaseModifiers ofMasterHorizons

Definitions (relative to soil parent material)

a Highly decomposed organic matter (O horizon).b Buried soil horizonc Concretions or nodules of rion, aluminum, manganese or titanium.d Non-cemented, root restricting natural or human made (plow layers,

etc.) root restrictive layers.e Intermediate decomposition of organic matter (O horizon).f Indication of presence of permafrostg Strong gleying present in form of reduction or loss of Fe and resulting

color changes.h Accumulation of illuvial complexes of organic matter which coat sand

and silt particles.i Slightly decomposed organic matter (O horizon).j Presence of jarosite (iron sulfate mineral) due to oxidation of pyrite in

previously reduced soils.k Accumulation of calcium carbonate due to pedogenic processes.m Nearly continously cemented horizons (by various pedogenic

minerals)n Accumulation of exchangeable sodiumo Residual accumulation of oxides due to long-term chemical

weathering.p Horizon altered by human related activitiesq Accumulation of silica (as opal)r Partially weathered bedrocks Illuvial accumulation of sesquioxidesss Presence of features (called slickensides) caused by expansion and

contraction of high clay soilst Accumulation of silicate clay by weathering and/or illuviationv Presence of plinthite (iron rich, reddish soil material)w Indicates initial development of oxidized (or other) colors and/or soil

structurex Indicates horizon of high firmness and brittlenessy Accumulation of gypsumz Accumulation of salts more soluble than gypsum (e.g. Na2CO3, etc.)

Chapter 3:Soil Classification

“It is embarrassing not to be able to agree on what soil is. In this the pedologists are not alone. Biologists

cannot agree on a definition of life and philosophers on philosophy.”

-Hans Jenny from The Soil Resource: Origin and Behavior

Classification

• Pedon: the smallest volume that can be called “a soil”

• Polypedon: two or more contiguous pedons, also called “soil individual”

• Landscape: region, tract of land

Figure 3.1

Classification

• Genetic horizon: soil layers resulting from soil-forming processes (pg. 73)– presence or absence help classify soil

• Diagnostic horizon: soil layers having specific soil characteristics indicative of certain classes of soils– at surface: “epipedon”– below surface: “diagnostic subsurface horizon”

Figure 3.4