SCSC 301

What is the mass of 1 ha of soil to 15cm depth ?

(1ha=10,000m2, density of water=1000kg/m3=1g/cm3, soil bulk density=1.5Mg/m3) 2,250,000kg

Clay vs Sand, which has the lower bulk density?

-Clay due to micropore space within aggregates; sand doesn't aggregate, only macropores -AFS with 1.5g/cm3 bulk density ~2,000,000 lbs. -HFS with 1.5g/cm3 bulk density ~2,000,000 kg

Particle density

-Dry mass/ particle (only) volume -2.5 g/cm3 (mineral particles)

Bulk density

-Dry mass/total (bulk) volume -Ranges from 1-2, <1.6g/cm3 is best for plants

Micropores ( and mesopores) (<0.08mm)

-Smal pores that are last to dry out because water is held so tightly. Common in fine-textured soils like clay -Slow conductor of water and air -Water moves by capillary movement (wicking effect) against the flow of gravity

Mottles

-Spots in soil where Fe has different redox environment -Indicates changing moisture conditions

Macropores (porosity) (>0.08)

-Super highway for water & air -Water drains out via gravity -Filled with water only when saturated

% Pore space

-Uses 2.65g/cm3 for PD -Just need BD to determine 100-(BD/PDX100)=% PORE SPACE

A soil sample occupies 30cm3 and weighs 50g when wet. When dry, the soil occupies 20cm3 and weighs 42g. What is the gravimetric water content of this soil sample?

.19

The range in bulk density for typical mineral soils that are suitable for growth is____g/cm3

1.2 to 1.6

Which of the following describes a composite sample?

10 samples of soil were collected across a field, mixed together, then used as the final single soil sample representing the field submitted for analysis

Which value is most likely represent the particle density of soil?

2.6

A typical moist surface soil ideally contains ____% water on a volume basis

25%

The porosity of the soil with a bulk density of 1.7g/cm3 and a particle density of 2.5g/cm3 is ______%

32 % Porosity = (1- 1.7/2.5) x100=32%

A soil has a color of 10YR 4/1, the value is _____, which indicates that the soil is relatively dark in color

4

A silty clay loam will have no more than ______% clay.

40%

Organic matter in soil typically accounts for ____% or less of the soils total volume.

5%

Density

= DRY mass/ Volume

Which horizon is most affected by the soil forming factors?

A

Which horizons in a soil containing A,B,C and R horizons are included in its solumn?

A,B

Physical processes (weathering)

Abrasion by wind, water, ice, gravity

Pore space in soil may contain either _____ or _____

Air Water

NOT essential for plants

Al, Si, Na

Soils that have parent materials affected by the movement of water include _____ soils, which are formed from deposition of sediments from streams and rivers into deltas and floodplains, and _____ soils, which are formed from deposition of sediment by lakes.

Alluvial Lacustrine

A soil typically contains a higher percentage of ____ than the rocks from which is it derived.

Aluminum

Soil organic matter forms from the decomposition of _____

Animal residue Manure Microorganism residue Plant residue

Weathering

Biological, chemical and physical processes that destroy or decompose rock to eventually form soil particles.

Which size aggregates are better, big or small?

Both are needed. Want a mix. Typically larger particles are more fragile and are easily lost via management

Regolith

C

Which horizon is not part of the soil solum?

C

Which of the following contains only PLANT ESSENTIAL elements that are common in rocks and soils?

Ca, Mg, K, Fe

As a primary mineral weather to form secondary minerals, elements can sometimes be lost. Which of the following are most likely to be lost to leaching?

Calcium (Ca) Potassium (K) Sodium (Na)

Though plants depend on soil for growth, which of the items below is found in soil, but not required for plant growth?

Carbon dioxide

Organic matter is made of carbon compounds. When it decomposes, what gas forms?

Carbon dioxide (C02)

Factors affecting aggregation

Cation type (Ca improves aggregation, Na does not) Natural causes of soil movement -Wetting/drying -Freezing/thawing -Expanding (heat)/ contracting (cool) Organisms -Plants, microbes, animals -Humans Substances that cement or stabilize aggregates -Microbial gums -Iron oxides -Carbon -Clay

Chroma

Chroma= how much color (none to all, 0-10) -6 or more (and with R or YR hue) is likely to be red or orange

Soils are the result of ______ and biota acting on parent material over time as modified by ______

Climate Topography

Soil is a dynamic natural body having properties due to combine effects of ______ as modified by topography acting on parent material over time

Climate and biota

What practices are used to reduce impact of tillage?

Conservation tillage (minimize silage, conserve residues on surface)

The behavior of a soil in response to manipulation at a specified moisture content is....?

Consistence

Soil profile

Contains 5 master horizons potentially founding a soil A->E->B->C

The color of soil organic matter is ____, which also influences the color of surface soils.

Dark brown to black

The parent material transported by wind is _____

Eolian

Soil is typically higher in

Fe/Al oxides and lower in basic cations than the parent material

Primary minerals that may weather to form secondary clay minerals in soils include

Feldspar, Hornsblende and mica

Which of the following parent materials has a very low degree of sorted materials?

Glacial till

The most probable sequence of aggregate types from the surface downward in a soil is...?

Granular, subangular, block, massive

Polypedon

Group of smaller pedons

Rocks

Groups of minerals that form from earth processes Igneous, sedimentary and metamorphic

Which of the following mineral is the most soluble? The high solubility causes it to easily weather and be lost from soil profiles.

Gypsum

Intensive weathering typically results in soils with high concentrations of_____ because these are secondary minerals that are resistant to further weather

Hematite and gibbsite

Which of the following weathers to form silicate clay minerals in soils

Hornblende and feldspar

The dominant wavelength of light (color) reflected by a soil is called ________

Hue

Hue value/chroma

Hue=color -Reds= oxidized and dry (hematite Fe compounds present) -Yellows= Oxidized and moderately wet (goethite Fe compounds present) -Grey/green/blue= Reduced and very wet (reduced Fe compounds present)

Another word for soil organic matter is _____

Humus

Chemical processes (weathering)

Hydration, hydrolysis, redox, dissolution, complexation

The transformation of a primary mineral to a secondary mineral to a secondary mineral could occur though which process?

Hydrolysis

Aggregation helps fine-textured soils become more suitable for plant growth because it _____

Increases microporosity

Sand particles

Largest, low affinity for water, nutrients and each other

When there is a dominant influence of one particular soil forming factor

Lithosequence= parent material Climosequence=Climate Biosequence=Biota Toposequence=Topography Chronosequence=Time

The chemical composition of minerals in a residual soil usually has a ____ from that of the parent rock.

Lower percentage of basic cations (Ca,Na,Mg, K)

From a plant's perspective, the most important role of soil structure in fine-textured soils is to increase_____

Macroporosity

The structure of a soil horizon is reported as "strong, medium, crumb". Which is the structural size?

Medium

Silt particles

Medium sized, moderate affinity for water, nutrients and each other, low affinity for nutrients

Which of the following are primary minerals?

Mica Quartz Olivine Hornblende Feldspar

By volume, soil is made up of which of the following?

Mineral matter Air Water Organic matter

Surface soils are ____ than subsoils

More porous

Soil Solum

O,A,E,B

Horizons

O,A,E,B,C

Aggregation of soil particles is related to the content of...?

Organic matter and clay

Which soil forming factor can be transported before it affects soil formation?

Parent material

Reactivity of materials in soils is primarily a function of _________

Particle size

Bulk density is the oven dry mass of soil divided by _____

Particle+ Pore volume

A major assumption made in applying Stoke's Law to sedimentation of soil particles in cylinder is...

Particles will settle in order of decreasing size and density (large dense particles settle first)

Biological processes (weathering)

Plants and microbes can do both physical and chemical processes Over time results in -Increasingly smaller particles -Increasingly more stable minerals (less stable minerals weather away) -Release of soluble components ( loss of elements from the less stable minerals Ca2+, Mg 2+, K+, Na+, SO4 2-) Decreases in most primary minerals and increases in secondary minerals Usually accumulation of Fe and Al oxides (most stable minerals; they are secondary)

A mineral, such as quartz, that has not been altered since its formation from magma is a _____ mineral.

Primary

A two dimensional vertical cross sectional view of a soil referred to as a soil _________

Profile

A primary silicate mineral that is resistant to weathering is?

Quartz

Which primary mineral is relatively resistant to weathering and does not weather into another mineral?

Quartz

Soil that forms in place is called _____?

Residual

Parent Material Types

Residual= Gravity Colluvial= Flowing water Alluvial= Flowing water Marine= Ocean Lacustrine= Lake Glacial= Glacier Eolian= Wind Organic= organic residuals

Topsoil vs. subsoil

SUB- Less affect from soil forming factors (lighter in color, fewer organism) & usually less porous ( more compacted) larger aggregates, more clay

Particle sizes arranged in order from least to most adsorption are ____

Sand, silt, clay

A soil containing 30% clay, 50% sand and 20% silt is in which textural class?

Sandy clay loam

The most portable sequence of soil textures surface to subsoil is...?

Sandy loam, clay loam, clay

How does tillage affect BD and porosity?

Short-term: May decrease BD and increase porosity Long-term: Increases BD and decreases porosity, especially macroporosity. Why? -Weakens soil -Depletes organic matter that might cement aggregates together

Minerals

Silicates -Primary: Quartz, feldspar, amphiboles, pyroxenes, micas (these all can form clays) -Secondary: Kaolinite, smectite, vermiculite, chlorite Other secondary minerals Carbonates (somewhat soluble) -Calcite & dolomite Sulfates (relatively soluble) -Gypsum Hallides (very soluble) -Halite, sylvite Phosphates (very soluble) -Apatite

Clay particles

Smallest (largest surface area) High affinity for water, nutrients and each other Tends to aggregate Can act as a colloid

Pedon

Smallest 3D unit of soil with all the soil characteristics

Soil compaction has no effect on ________

Soil texture

Which physical soil property is an inherent property of the soil that cannot be changed in our lifetime?

Soil texture

4 major soil components

Solids- Mineral matter (~45%) Organic matter (~5%) Pore space- Air (25%) Water (25%)

Shapes

Spheroidal= granular & crumb Blocky= angular and sub angular blocky Prism-like= columnar and prismatic Platy Structureless= massive and single grain

Grades

Strong, moderate, weak, structureless

Given the scenarios below, which is most likely?

Surface soils are more porous, less dense, and typically of coarser texture than subsoils

Texture vs Structure

TEXTURE= size distribution of sand, silt, clay -inherent property that doesn't change over our lifetimes -What is texture of 10% clay, 70% sand, 20% silt Structure= how the particles are aggregated -Dynamic property that can be changed by managaement

Topsoil vs. subsoil

TOP- More affect from soil forming factors (darker, more organisms) & usually more porous, smaller aggregates, less clay and more sand/silt

Compare a humid tropical rainforest to a cool and dry mountain plain and elect the most correct answer.

The humid tropical rainforest will weather faster and the soil will develop more rapidly due to intense weathering climate

Which of the following soil forming factors is passive?

Time

Which of the following are soil forming factors?

Time Parent material Topography Biota Climate

Medium to high sorting=

Transported by water or wind

Value

Value=darkness to lightness 1-10 -4 or less= organic matter is most likely to be present

Sizes

Very fine, fine, medium, coarse, very coarse

A soil that supports plant life provide each of the following, EXCEPT

Water

Alluvial is parent material that is transported by ______

Water

Soil horizons exhibiting a high chroma are probably ________

Well drained