Principles of Soil Science - Modules 1, 2, and 3

Comprehensive practice flashcards covering fundamental soil concepts, soil formation and development, and physical properties of soils.

What are the two primary approaches used in the study of soil, and how do they differ?

The pedological approach considers soil as a natural body with emphasis on its origin, characterization, and classification. The edaphological approach considers soil in relation to practical uses, particularly how soil properties affect plant growth.

What are the volumetric proportions of the four major components in an ideal soil for plant growth?

An ideal soil consists of $45\%$ mineral matter, $5\%$ organic matter, $25\%$ water, and $25\%$ air by volume.

Which volumetric breakdown of major soil components is depicted in this diagram?

It shows an ideal soil composed of $50\%$ solid materials ($45\%$ mineral material and $5\%$ organic material) and $50\%$ pore space ($25\%$ air and $25\%$ water).

What are the typical concentrations of the main gases found in soil air?

Soil air is composed largely of elemental nitrogen ($78\%$), oxygen ($20\%$), carbon dioxide ($0.5\%$), and traces of other gases.

What are the 16 essential nutrient elements required for normal plant growth?

The 16 essential elements are carbon ($C$), hydrogen ($H$), oxygen ($O$), nitrogen ($N$), phosphorus ($P$), potassium ($K$), calcium ($Ca$), magnesium ($Mg$), sulfur ($S$), iron ($Fe$), copper ($Cu$), zinc ($Zn$), manganese ($Mn$), boron ($B$), molybdenum ($Mo$), and chlorine ($Cl$).

Which 9 essential elements are categorized as macronutrients?

The macronutrients are carbon ($C$), hydrogen ($H$), oxygen ($O$), nitrogen ($N$), phosphorus ($P$), potassium ($K$), calcium ($Ca$), magnesium ($Mg$), and sulfur ($S$).

What is Hans Jenny's (1941) mathematical equation representing the factors of soil formation?

The equation is $S = f(CL, LO, R, P, T)$, where $S$ represents soil properties, $CL$ represents climate, $LO$ represents living organisms, $R$ represents relief, $P$ represents parent material, and $T$ represents time.

What are the eight most abundant chemical elements in the Earth's crust by percentage weight?

They are oxygen ($46.6\%$), silicon ($27.7\%$), aluminum ($8.14\%$), iron ($5.0\%$), calcium ($3.63\%$), sodium ($2.83\%$), magnesium ($2.09\%$), and potassium ($8.14\%$).

What are the chemical formulas of the primary minerals Quartz, Orthoclase, Na-plagioclase, and Ca-plagioclase?

Quartz is $SiO_2$, Orthoclase is $KAlSi_3O_8$, Na-plagioclase is $NaAlSi_3O_8$, and Ca-plagioclase is $CaAl_2Si_3O_8$.

What are the chemical formulas of the primary minerals Muscovite, Biotite, Hornblende, Augite, and Apatite?

Muscovite is $KAl_3Si_3O_{10}(OH)_2$, Biotite is $K(Mg, Fe)AlSi_3O_{10}(OH)_2$, Hornblende is $Ca_2Al_2Mg_2Fe_3Si_6O_{22}(OH)_2$, Augite is $Ca_2(Al, Fe)_4(Mg, Fe)_4Si_6O_{24}$, and Apatite is $Ca_5(PO_4)_3(OH)\cdot(Cl, F)$.

What are the chemical formulas of the secondary minerals Calcite, Dolomite, Gypsum, Limonite, and Hematite?

Calcite is $CaCO_3$, Dolomite is $CaMg(CO_3)_2$, Gypsum is $CaSO_4 \cdot 2H_2O$, Limonite is $Fe_2SO_3 \cdot 3H_2O$, and Hematite is $Fe_2O_3$.

How do extrusive and intrusive igneous rock formations differ?

Extrusive (volcanic) formation occurs when magma is ejected onto the Earth's surface and cools rapidly, forming fine-grained rocks like basalt and andesite. Intrusive (plutonic) formation occurs when magma solidifies slowly inside the crust, forming coarse-grained rocks like granite, diorite, and gabbro.

What are the main chemical weathering processes affecting rocks and minerals?

1. Hydrolysis: Reaction with water forming acid and base. 2. Hydration: Rigid attachment of water molecules without structural destruction. 3. Oxidation: Transformation of iron from ferrous to ferric form. 4. Carbonation: Reaction with carbonic acid ($H_2CO_3$). 5. Solution: Dissolution of minerals into component ions.

What is the difference between residual and transported parent materials, and how are transported materials classified?

Residual (sedentary) materials develop in place from underlying rock. Transported materials are moved by agents: running water (alluvium), lakes (lacustrine), oceans (marine), glaciers (glacial till/moraine), wind (aeolian), or gravity (colluvium).

What do the soil development processes Melanization, Illuviation, Lessivage, Podzolization, and Laterization refer to?

Melanization is organic matter admixing that darkens mineral soil; Illuviation is material deposition into a lower layer; Lessivage is fine mineral particle washing from A to B horizon; Podzolization (silication) translocates Fe/Al/organic matter concentrating silica; Laterization (desilication) removes silica concentrating Fe/Al oxides (sesquioxides).

Which master soil horizons are shown in this soil profile diagram?

The diagram depicts horizon O (humus or organic), A (topsoil), E (eluviated horizon), B (subsoil), C (parent material), and R (bedrock).

What is the difference between Solum and Regolith?

Solum refers to the upper layers ($A$ and $B$ horizons) where soil formation is active. Regolith refers to the entire loose mantle of weathered rock and soil above bedrock ($A$, $B$, and $C$ horizons).

What are the particle size ranges for sand, silt, and clay separates defined by the International Soil Science Society (ISSS)?

Sand ranges from $2.0\,mm$ to $0.02\,mm$, silt ranges from $0.02\,mm$ to $0.002\,mm$, and clay is less than $0.002\,mm$.

What are the five USDA subgroups for sand particles based on size?

1. Very coarse sand ($2.0 - 1.0\,mm$) 2. Coarse sand ($1.0 - 0.5\,mm$) 3. Medium sand ($0.5 - 0.25\,mm$) 4. Fine sand ($0.25 - 0.10\,mm$) 5. Very fine sand ($0.10 - 0.05\,mm$)

What is Stoke's Law equation as applied to mechanical soil textural analysis?

The equation is $V = K D^2$, where $V$ is settling velocity ($cm/min$), $K$ is a constant ($6000$ at $25^\circ\text{C}$), and $D$ is particle diameter ($mm$).

Which diagram is used to determine soil textural classification based on percentages of sand, silt, and clay?

The Soil Textural Diagram, which plots Percent Clay, Percent Silt, and Percent Sand to define 12 textural soil classes.

How are loam, clay loam, and clay differentiated in the roll method based on ribbon length?

Types of loam form ribbons $\le 2.5\,cm$; types of clay loam form ribbons $2.5 - 5\,cm$; types of clay form ribbons $\ge 5\,cm$.

Why do calcium ions ($Ca^{2+}$) promote soil aggregation while sodium ions ($Na^+$) cause soil dispersion?

Calcium ions ($Ca^{2+}$) have a smaller hydrated size and double positive charge, allowing them to come close to clay surfaces, neutralize negative charges, and form aggregates (floccules). Sodium ions ($Na^+$) have a larger hydrated radius and single positive charge, failing to neutralize charges and causing clay particles to repel.

Which type of soil structure is illustrated in this diagram?

Granular structure, which consists of rounded, porous aggregates characteristic of surface soils with high organic matter.

Which type of soil structure is illustrated in this diagram?

Subangular blocky structure, consisting of cube-like aggregates with somewhat rounded edges.

Which type of soil structure is illustrated in this diagram?

Angular blocky structure, characterized by cube-like aggregates with sharp edges and distinct rectangular faces.

Which soil structural types are shown from left to right in this diagram?

Prismatic structure (pillar-like with level tops), Columnar structure (pillar-like with rounded tops), and Platy structure (disc-like horizontal aggregates).

What is the formula for calculating Soil Bulk Density ($BD$)?

The formula is $BD = \frac{W_s}{V_t}$, where $W_s$ is oven-dry weight of soil ($g$) and $V_t$ is total soil volume ($cm^3$), expressed in $g/cm^3$.

What is the formula for calculating Soil Particle Density ($PD$)?

The formula is $PD = \frac{W_s}{V_s}$, where $W_s$ is oven-dry weight of soil solids ($g$) and $V_s$ is volume of soil solids ($cm^3$), expressed in $g/cm^3$.

What is the formula to calculate percent soil porosity ($PS$) from bulk density ($BD$) and particle density ($PD$)?

The formula is $PS = \left(1 - \frac{BD}{PD}\right) \times 100$.

What molecular properties shown in this diagram explain why water molecules are dipolar?

Hydrogen atoms attach to the oxygen atom at an angle of $105^\circ$, making the hydrogen side electropositive ($+\text{pole}$) and the oxygen side electronegative ($-\text{pole}$).

What are the definitions of adhesion, cohesion, and osmosis in soil water dynamics?

Cohesion is the attraction between water molecules. Adhesion is the attraction between water molecules and solid surfaces. Osmosis is the attraction between water molecules and solutes.

What are the Soil Moisture Tension (SMT) values at Hygroscopic Coefficient, Permanent Wilting Point, and Field Capacity?

Hygroscopic coefficient is held at $31\,atm$ (or bars); Permanent Wilting Point ($PWP$) is held at $15\,bars$; Field Capacity ($FC$) is held at $\frac{1}{3}\,bar$.

How is plant available water ($AW$) in soil calculated?

Available water is calculated as $AW = FC - PWP$, where $FC$ is moisture content at field capacity and $PWP$ is moisture content at permanent wilting point.

What are the three components of the Munsell Soil Color Chart and what does each indicate?

1. Hue: Dominant spectral color (e.g., $10YR$). 2. Value: Lightness or darkness of color ranging from $1$ (dark) to $8$ (light). 3. Chroma: Purity or strength of color ranging from $1$ (pale) to $8$ (bright).